Oumlrebro universitet

Institutionen foumlr haumllsovetenskap och medicin

Enheten klinisk medicin

Kurs Medicin avancerad nivaring Examensarbete

Datum 2015-06-07

30-year (1983-2013) trends in saliva flow rate

and saliva buffer capacity Analyses from 10-

year repeated cross-sectional population

samples in the Joumlnkoumlping area

Foumlrfattare Martin Aringgren

Handledare Ingegerd Johansson

Professor

Umearing Universitet

ABSTRACT

OBJECTIVE To determine trends in saliva flow rate and saliva buffer capacity and to evaluate

associations between saliva flow rate and buffer capacity with potential explanatory factors including

chewing ability medication and other health variables including oral health

MATERIALS AND METHODS The study group consisted of 2509 individuals (1204 men and 1305

women) randomly selected from the town of Joumlnkoumlping Sweden All participants underwent an oral

examination as well as completed a questionnaire

RESULTS The highest mean saliva flow rate in men and women was seen at age 50 and 40 years

respectively Sex and age standardized means for saliva flow rates for all subjects differed significantly

between the screening years but they did not follow a linear trend over time Through PLS analysis

low buffer capacity (pH lt55) being a woman xerostomia less occlusal support zones (Eichner index)

and having more daily meals of food or having less teeth were identified to have a significant

correlation to lower saliva flow rate The analytic method of buffer capacity evaluation changed

between the study years thus differences between screening years are not taken into consideration

In 8 out of 14 strata mean flow rate was significantly higher in those with buffer pH gt55 than those

with a buffer pHlt55 Univariate analysis from variables indicated in the PLS analysis revealed that

low saliva flow rate moderate degree of periodontal disease smokers and those with the poorest

Eichner index have low buffer capacity

CONCLUSIONS The stimulated salivation is dependent on gender number of teeth Eichner index

subjective xerostomia and buffer capacity Different normal salivation distribution scales could be

needed for men and women

KEYWORDS Saliva trends oral health

REGISTER

Introduction 1 The Joumlnkoumlping study 4 Aim 4 Subjects and method 4 Study cohort 4 Questionnaire 5 Outcome variables 5 Saliva collection and buffer capacity analyses 5 Potential explanatory or confounding variables 5 Statistical analyses 6 Ethical aspects 6 Results 7

Participants 7 Identification of potential confounders 7 Thirty year time trends in saliva flow rate 8 Identification of factors associated with saliva flow rate 9 Thirty years time trends in buffer capacity 11 Identification of factors associated with buffer capacity 12

Discussion 14 Conclusion 16 Acknowledgements 16 References 17

1

30-YEAR (1983-2013) TRENDS IN SALIVA FLOW RATE AND SALIVA BUFFER CAPACITY ANALYSES

FROM 10-YEAR REPEATED CROSS-SECTIONAL POPULATION SAMPLES IN THE JOumlNKOumlPING AREA

Author Aringgren Martin

INTRODUCTION

Saliva plays a crucial role in protection of the oral cavity (Edgar et al 2004) Thus flushing (clearance

and exposure) of the soft and hard tissues and biological effects of saliva constituents such as pH-

regulatory components inorganic components participating in the de- and remineralisation of tooth

tissues and proteins peptides lipids and carbohydrates affecting microbial growth and colonization

are of importance Saliva flow and oral muscle activities are the key determinants for flushing Lack of

proper amount of saliva may lead to discomfort for the individual such as a burning sensation

dysphagia speech impairment taste disturbances and increase risk for dental caries (Bergdahl 2000

Naumlrhi 1994)

Knowledge of population based reference values are important for identification of conditions

which need to be observed or treated For saliva flow rate the cut off values 07 mLmin to 10

mLmin and 01 mLmin for stimulated and unstimlated saliva respectively are applied for

hyposalivation (Fujibayashi et al 2004 Bergdahl 2000) Values above are considered normal If the

flow rate has drifted in the population such as indicated in Bergdahl (2000) these cut-offs may be

misleading and should eventually be questioned For buffer capacity the cut off for low capacity is a

final pH lt55 after addition of a standardized amount of acid This is a reflection of the pKa value and

buffer range of the bicarbonate ion The buffer capacity is crucial for dental erosion caries and

microbiota ecology as a pH below 55 creates an environment of demineralisation and supports a

bacteria dysbiosis characterized by acidophilic and aciduric bacteria (Schuurs 2013 Marsh 2010)

Saliva is produced by the three paired major salivary glands the parotid submandibular and

sublingual glands and numerous minor salivary glands distributed in the oral mucosa In an

unstimulated state the submandibular glands account for two thirds of the secreted saliva When

stimulated secretion from the parotid glands increases proportionally the most and accounts for up

to 60 of the secretion (Carpenter 2013) The parotid glands are comprised of serous and the

submandibular glands of both mucous and serous acinar cells with a majority of the latter In

comparison to the parotid saliva saliva from the submandibular glands is more viscous and mucin-rich

The smallest of the major salivary glands are the sublingual glands which produce highly viscous

mucous saliva that accounts for a few per cent of the total amount of saliva The minor glands

2

contribute for le10 of the secreted saliva They produce mainly mucous saliva rich in secretory IgA

(Dawes and Wood 1973)

Secretion of saliva is regulated by the parasympathetic and the sympathetic systems Secretion is

initiated by afferent signals from three cranial nerves the trigeminal (V) facial (VII) and

glossopharyngeal (IX) nerves The afferent innervation stems from mechanoreceptors in the

periodontal ligament and chemoreceptors in the taste buds The stimulated salivation is increased by

frequency of chewing cycles force of chewing and number of teeth occluding on the object chewed

upon The increase in salivation from the parotid glands is higher on the ipsilateral side but the

contralateral side also shows an increase in salivation (Jensen Kjeilen et al 1987 Samnieng et al

2012) The masticatory-salivary reflex is initiated not only by the periodontal ligament as it has been

shown that edentulous subjects also have an increase in parotid salivation when chewing (Scott et al

1998) The salivation is also dependent on conditioned reflexes controlled through the autonomic

nervous system This central control inhibits unstimulated salivation during sleep fear and mental

depression and excites salivation during fight The classical parasympathetic and sympathetic

transmitters ie acetylcholine and either noradrenaline (norepinephrine) or adrenaline (epinephrine)

respectively are the main activators of salivation (Ekstroumlm 1989) The parasympathetic system mainly

regulates water secretion and the sympathetic protein secretion The complex regulation of the

secretory cells makes secretion sensitive to numerous external and intrinsic factors Examples of such

factors are medications diseases stress water balance starvation and lack of chewing stimulation

(Bardow et al 2008)

Water secretion from the acinar cells is driven by intracellular loss of potassium to the

insterstitium and chloride to the lumen The loss of potassium to the extracellular fluid forces sodium

into the lumen causing a salty environment which drives water through osmosis into the lumen of

the salivary gland During its way through the duct of the salivary gland the primary saliva is modified

in a flow rate related fashion by selective reabsorptionsecretion of electrolytes Among the

electrolytes that are affected during secretion are sodium and bicarbonate (Bardow et al 2008)

One important aspect of saliva action is its contribution to remineralisation of the teeth as well as

preventing demineralisation by buffering (Selwitz et al 2007) After each intake of food the pH in

dental plaque drops and remains at that state until soluble carbohydrates are cleared from the oral

cavity and the acids produced from bacteria are neutralized (buffered)

The magnitude and the time period below the tooth tissue critical pH are determined by the

amount of acid produced by bacteria by the buffer capacity of the saliva and saliva flushing There are

three systems in saliva that contribute in buffering the pH after an acid attack and striving it above the

3

critical pH for caries development in tooth enamel (around 55) or dentin (around 62) as well as

erosion

Fig 1 Schematic drawing of the complex interactions and interplays in the caries process The figure is redrawn from Selwitz RH Ismail AI Pitts NB 2007 Dental caries Lancet 36951ndash59

The phosphate buffer system - In stimulated saliva phosphate is mainly in the form of hydrogen

phosphate compared to in unstimulated saliva where it is mainly dihydrogen phosphate Thus

stimulated saliva is a bit more alkaline than unstimulated saliva The acid dissociation constant or pK

for the equilibrium between these two phosphate forms is around pH 7 At this neutral pH the

phosphate buffer system is most efficient with a buffer span of about plusmn 1 pH unit around the pK As

the phosphate concentration in saliva decreases with the flow rate of saliva the contribution from the

phosphate buffer system to the overall buffer capacity ranges from around 50 in unstimulated saliva

to 10 in highly stimulated saliva (Bardow et al 2008)

The bicarbonate buffer system - As opposed to the phosphate buffer system the contribution of

the bicarbonate buffer system to the buffering effect increases when saliva flow rate increases In

unstimulated saliva this system contributes to less than 50 and in stimulated saliva more than 90

of the buffering effect The pK value for the bicarbonate buffer system lies around pH 6 with a

buffering effect up to pH 7 (Bardow et al 2008) The lower limit of a pure bicarbonate buffer system is

at pH 55 under that the effect of this system is minimal (Garbacz et al 2013) In addition CO2 in gas

form is undersaturated versus the ambient air leading to loss of CO2 and a so called phase buffering

(Bardow et al 2008 Birkhed and Heintze 1989)

The protein buffer system - Saliva proteins and peptides can act as buffers if the pH exceeds (both

positively and negatively) their isoelectric points leading to the proteins accepting or releasing

protons Many of the saliva proteins have their isoelectric points at pH 5 and pH 9 making them

effective as buffers at alkaline environments as well as when the pH drops below the critical value for

4

demineralisation Although generally less effective than the two first buffer system the local

concentration of proteinspeptides may render local significant buffer effect (Bardow et al 2008)

The Joumlnkoumlping study

Joumlnkoumlping is a middle sized Swedish town with 130000 inhabitants in in 2013 It is the Capital of the

Joumlnkoumlping County and is situated on the main transport roads between the three biggest cities in

Sweden namely Stockholm Gothenburg and Malmouml The Public Dental Service of Joumlnkoumlping County

also manages the Institute for Postgraduate Dental Education in Joumlnkoumlping The Joumlnkoumlping study

(Hugoson et al 2005 ab) with its 10-year repeated oral screenings with for the most part

standardized methods is one of few studies worldwide offering the capacity to do a ldquolongitudinalrdquo

evaluation of trends in saliva flow and buffer capacity in repeated cross-sectional population based

samples over a long time

AIM

The primary aim of the present study was to evaluate time trends for saliva flow rate and saliva buffer

capacity using the 10-year screenings in the Joumlnkoumlping study A second aim is to evaluate the

associations between saliva flow ratebuffer capacity and potential explanatory factors including

number of teeth chewing ability diet intake and medication

SUBJECTS AND METHODS

Study cohort

In the Joumlnkoumlping study independent cross-sectional selections of individuals in the age groups 3 5 10

15 20 30 40 50 60 70 and 80 years have been randomly selected from individuals residing in

Kristine Ljungarum Sofia and Jaumlrstorp parishes as defined in 1973 (by 2006 the two first parishes

merged into one and so did the two last in 2010) The examinations are done on a decennial basis

since 1973 saliva flow rate and buffer capacity was not measured in 1973 though The selected

individuals have been invited and in those who agreed to participate about a 100 in each age group

an extensive oral examination was performed under good clinical conditions (Hugoson et al 1986

1995 2005 ab) The age groups of 3 5 10 and 15 are not included in the present evaluation (Koch et

al 2009) At all screening occasions 130 randomly selected adult in each of the 10-year age group

were invited to participate (Huguson et al 2005) Due to a low participation rate in 2013 additionally

40 40 and 50 subjects were invited in the age groups of 30 40 and 50 years

5

Questionnaire

All participants answered a questionnaire in immediate connection to the examination In the

questionnaire the participants answered questions on the number of meals and snacks per day

medication and graded their subjective experience of xerostomia health tobacco use and ease of

chewing

Outcome variables

The outcome variables in the present study are flow rates of stimulated whole saliva and buffer

capacity of the same saliva from the screenings in 1983 1993 2003 and 2013

Saliva collection and buffer capacity analyses

Whole saliva stimulated by chewing on a 1 gram piece of paraffin was collected into graded test

tubes for 3 minutes Flow rates were calculated and buffer capacity analysed The analysis method of

the buffer capacity changed over the years In 1983 and 1993 it was done according to Ericssonrsquos

laboratory buffer capacity test (Ericsson 1959) In 2003 and 2013 chair-side simplified methods

(Dentobuff Strip Orion Diagnostica Espoo Finland GC Saliva Check GC Europe NV Leuven Belgium)

was used A study showed best agreement among results provided by strip-type systems in patients

with high buffering capacity all compared to Ericssonrsquos laboratory buffer capacity test (Cheaib et al

2012) Therefore buffer capacity measures were dichotomized into low and normal capacity ie ltpH

55 and ge pH 55 respectively

Fig 2 Correspondence between Ericssonrsquos laboratory buffer capacity test Dentobuff Strip and GC Saliva-Check The figure is drawn from Cheaib et al 2012

Potential explanatory or confounding variables

The following variables were evaluated for a potential explanatory effect or included as confounders in

statistical models Sex age number of teeth Eichner index subjective reported chewing capacity

dietary variables medication and periodontal health The Eichner index describes the number of

occlusal support zones in the mouth that is where occlusion (chewing) is supported with a maximum

of four support zones These are the molar support zone (left and right) and the premolar support

zone (left and right) If occlusion exists in all four support zones the occlusion is categorised as class A

and sub grouped if the support zones lacks teeth in either one or both of the jaws if there exists an

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

ABSTRACT

OBJECTIVE To determine trends in saliva flow rate and saliva buffer capacity and to evaluate

associations between saliva flow rate and buffer capacity with potential explanatory factors including

chewing ability medication and other health variables including oral health

MATERIALS AND METHODS The study group consisted of 2509 individuals (1204 men and 1305

women) randomly selected from the town of Joumlnkoumlping Sweden All participants underwent an oral

examination as well as completed a questionnaire

RESULTS The highest mean saliva flow rate in men and women was seen at age 50 and 40 years

respectively Sex and age standardized means for saliva flow rates for all subjects differed significantly

between the screening years but they did not follow a linear trend over time Through PLS analysis

low buffer capacity (pH lt55) being a woman xerostomia less occlusal support zones (Eichner index)

and having more daily meals of food or having less teeth were identified to have a significant

correlation to lower saliva flow rate The analytic method of buffer capacity evaluation changed

between the study years thus differences between screening years are not taken into consideration

In 8 out of 14 strata mean flow rate was significantly higher in those with buffer pH gt55 than those

with a buffer pHlt55 Univariate analysis from variables indicated in the PLS analysis revealed that

low saliva flow rate moderate degree of periodontal disease smokers and those with the poorest

Eichner index have low buffer capacity

CONCLUSIONS The stimulated salivation is dependent on gender number of teeth Eichner index

subjective xerostomia and buffer capacity Different normal salivation distribution scales could be

needed for men and women

KEYWORDS Saliva trends oral health

REGISTER

Introduction 1 The Joumlnkoumlping study 4 Aim 4 Subjects and method 4 Study cohort 4 Questionnaire 5 Outcome variables 5 Saliva collection and buffer capacity analyses 5 Potential explanatory or confounding variables 5 Statistical analyses 6 Ethical aspects 6 Results 7

Participants 7 Identification of potential confounders 7 Thirty year time trends in saliva flow rate 8 Identification of factors associated with saliva flow rate 9 Thirty years time trends in buffer capacity 11 Identification of factors associated with buffer capacity 12

Discussion 14 Conclusion 16 Acknowledgements 16 References 17

1

30-YEAR (1983-2013) TRENDS IN SALIVA FLOW RATE AND SALIVA BUFFER CAPACITY ANALYSES

FROM 10-YEAR REPEATED CROSS-SECTIONAL POPULATION SAMPLES IN THE JOumlNKOumlPING AREA

Author Aringgren Martin

INTRODUCTION

Saliva plays a crucial role in protection of the oral cavity (Edgar et al 2004) Thus flushing (clearance

and exposure) of the soft and hard tissues and biological effects of saliva constituents such as pH-

regulatory components inorganic components participating in the de- and remineralisation of tooth

tissues and proteins peptides lipids and carbohydrates affecting microbial growth and colonization

are of importance Saliva flow and oral muscle activities are the key determinants for flushing Lack of

proper amount of saliva may lead to discomfort for the individual such as a burning sensation

dysphagia speech impairment taste disturbances and increase risk for dental caries (Bergdahl 2000

Naumlrhi 1994)

Knowledge of population based reference values are important for identification of conditions

which need to be observed or treated For saliva flow rate the cut off values 07 mLmin to 10

mLmin and 01 mLmin for stimulated and unstimlated saliva respectively are applied for

hyposalivation (Fujibayashi et al 2004 Bergdahl 2000) Values above are considered normal If the

flow rate has drifted in the population such as indicated in Bergdahl (2000) these cut-offs may be

misleading and should eventually be questioned For buffer capacity the cut off for low capacity is a

final pH lt55 after addition of a standardized amount of acid This is a reflection of the pKa value and

buffer range of the bicarbonate ion The buffer capacity is crucial for dental erosion caries and

microbiota ecology as a pH below 55 creates an environment of demineralisation and supports a

bacteria dysbiosis characterized by acidophilic and aciduric bacteria (Schuurs 2013 Marsh 2010)

Saliva is produced by the three paired major salivary glands the parotid submandibular and

sublingual glands and numerous minor salivary glands distributed in the oral mucosa In an

unstimulated state the submandibular glands account for two thirds of the secreted saliva When

stimulated secretion from the parotid glands increases proportionally the most and accounts for up

to 60 of the secretion (Carpenter 2013) The parotid glands are comprised of serous and the

submandibular glands of both mucous and serous acinar cells with a majority of the latter In

comparison to the parotid saliva saliva from the submandibular glands is more viscous and mucin-rich

The smallest of the major salivary glands are the sublingual glands which produce highly viscous

mucous saliva that accounts for a few per cent of the total amount of saliva The minor glands

2

contribute for le10 of the secreted saliva They produce mainly mucous saliva rich in secretory IgA

(Dawes and Wood 1973)

Secretion of saliva is regulated by the parasympathetic and the sympathetic systems Secretion is

initiated by afferent signals from three cranial nerves the trigeminal (V) facial (VII) and

glossopharyngeal (IX) nerves The afferent innervation stems from mechanoreceptors in the

periodontal ligament and chemoreceptors in the taste buds The stimulated salivation is increased by

frequency of chewing cycles force of chewing and number of teeth occluding on the object chewed

upon The increase in salivation from the parotid glands is higher on the ipsilateral side but the

contralateral side also shows an increase in salivation (Jensen Kjeilen et al 1987 Samnieng et al

2012) The masticatory-salivary reflex is initiated not only by the periodontal ligament as it has been

shown that edentulous subjects also have an increase in parotid salivation when chewing (Scott et al

1998) The salivation is also dependent on conditioned reflexes controlled through the autonomic

nervous system This central control inhibits unstimulated salivation during sleep fear and mental

depression and excites salivation during fight The classical parasympathetic and sympathetic

transmitters ie acetylcholine and either noradrenaline (norepinephrine) or adrenaline (epinephrine)

respectively are the main activators of salivation (Ekstroumlm 1989) The parasympathetic system mainly

regulates water secretion and the sympathetic protein secretion The complex regulation of the

secretory cells makes secretion sensitive to numerous external and intrinsic factors Examples of such

factors are medications diseases stress water balance starvation and lack of chewing stimulation

(Bardow et al 2008)

Water secretion from the acinar cells is driven by intracellular loss of potassium to the

insterstitium and chloride to the lumen The loss of potassium to the extracellular fluid forces sodium

into the lumen causing a salty environment which drives water through osmosis into the lumen of

the salivary gland During its way through the duct of the salivary gland the primary saliva is modified

in a flow rate related fashion by selective reabsorptionsecretion of electrolytes Among the

electrolytes that are affected during secretion are sodium and bicarbonate (Bardow et al 2008)

One important aspect of saliva action is its contribution to remineralisation of the teeth as well as

preventing demineralisation by buffering (Selwitz et al 2007) After each intake of food the pH in

dental plaque drops and remains at that state until soluble carbohydrates are cleared from the oral

cavity and the acids produced from bacteria are neutralized (buffered)

The magnitude and the time period below the tooth tissue critical pH are determined by the

amount of acid produced by bacteria by the buffer capacity of the saliva and saliva flushing There are

three systems in saliva that contribute in buffering the pH after an acid attack and striving it above the

3

critical pH for caries development in tooth enamel (around 55) or dentin (around 62) as well as

erosion

Fig 1 Schematic drawing of the complex interactions and interplays in the caries process The figure is redrawn from Selwitz RH Ismail AI Pitts NB 2007 Dental caries Lancet 36951ndash59

The phosphate buffer system - In stimulated saliva phosphate is mainly in the form of hydrogen

phosphate compared to in unstimulated saliva where it is mainly dihydrogen phosphate Thus

stimulated saliva is a bit more alkaline than unstimulated saliva The acid dissociation constant or pK

for the equilibrium between these two phosphate forms is around pH 7 At this neutral pH the

phosphate buffer system is most efficient with a buffer span of about plusmn 1 pH unit around the pK As

the phosphate concentration in saliva decreases with the flow rate of saliva the contribution from the

phosphate buffer system to the overall buffer capacity ranges from around 50 in unstimulated saliva

to 10 in highly stimulated saliva (Bardow et al 2008)

The bicarbonate buffer system - As opposed to the phosphate buffer system the contribution of

the bicarbonate buffer system to the buffering effect increases when saliva flow rate increases In

unstimulated saliva this system contributes to less than 50 and in stimulated saliva more than 90

of the buffering effect The pK value for the bicarbonate buffer system lies around pH 6 with a

buffering effect up to pH 7 (Bardow et al 2008) The lower limit of a pure bicarbonate buffer system is

at pH 55 under that the effect of this system is minimal (Garbacz et al 2013) In addition CO2 in gas

form is undersaturated versus the ambient air leading to loss of CO2 and a so called phase buffering

(Bardow et al 2008 Birkhed and Heintze 1989)

The protein buffer system - Saliva proteins and peptides can act as buffers if the pH exceeds (both

positively and negatively) their isoelectric points leading to the proteins accepting or releasing

protons Many of the saliva proteins have their isoelectric points at pH 5 and pH 9 making them

effective as buffers at alkaline environments as well as when the pH drops below the critical value for

4

demineralisation Although generally less effective than the two first buffer system the local

concentration of proteinspeptides may render local significant buffer effect (Bardow et al 2008)

The Joumlnkoumlping study

Joumlnkoumlping is a middle sized Swedish town with 130000 inhabitants in in 2013 It is the Capital of the

Joumlnkoumlping County and is situated on the main transport roads between the three biggest cities in

Sweden namely Stockholm Gothenburg and Malmouml The Public Dental Service of Joumlnkoumlping County

also manages the Institute for Postgraduate Dental Education in Joumlnkoumlping The Joumlnkoumlping study

(Hugoson et al 2005 ab) with its 10-year repeated oral screenings with for the most part

standardized methods is one of few studies worldwide offering the capacity to do a ldquolongitudinalrdquo

evaluation of trends in saliva flow and buffer capacity in repeated cross-sectional population based

samples over a long time

AIM

The primary aim of the present study was to evaluate time trends for saliva flow rate and saliva buffer

capacity using the 10-year screenings in the Joumlnkoumlping study A second aim is to evaluate the

associations between saliva flow ratebuffer capacity and potential explanatory factors including

number of teeth chewing ability diet intake and medication

SUBJECTS AND METHODS

Study cohort

In the Joumlnkoumlping study independent cross-sectional selections of individuals in the age groups 3 5 10

15 20 30 40 50 60 70 and 80 years have been randomly selected from individuals residing in

Kristine Ljungarum Sofia and Jaumlrstorp parishes as defined in 1973 (by 2006 the two first parishes

merged into one and so did the two last in 2010) The examinations are done on a decennial basis

since 1973 saliva flow rate and buffer capacity was not measured in 1973 though The selected

individuals have been invited and in those who agreed to participate about a 100 in each age group

an extensive oral examination was performed under good clinical conditions (Hugoson et al 1986

1995 2005 ab) The age groups of 3 5 10 and 15 are not included in the present evaluation (Koch et

al 2009) At all screening occasions 130 randomly selected adult in each of the 10-year age group

were invited to participate (Huguson et al 2005) Due to a low participation rate in 2013 additionally

40 40 and 50 subjects were invited in the age groups of 30 40 and 50 years

5

Questionnaire

All participants answered a questionnaire in immediate connection to the examination In the

questionnaire the participants answered questions on the number of meals and snacks per day

medication and graded their subjective experience of xerostomia health tobacco use and ease of

chewing

Outcome variables

The outcome variables in the present study are flow rates of stimulated whole saliva and buffer

capacity of the same saliva from the screenings in 1983 1993 2003 and 2013

Saliva collection and buffer capacity analyses

Whole saliva stimulated by chewing on a 1 gram piece of paraffin was collected into graded test

tubes for 3 minutes Flow rates were calculated and buffer capacity analysed The analysis method of

the buffer capacity changed over the years In 1983 and 1993 it was done according to Ericssonrsquos

laboratory buffer capacity test (Ericsson 1959) In 2003 and 2013 chair-side simplified methods

(Dentobuff Strip Orion Diagnostica Espoo Finland GC Saliva Check GC Europe NV Leuven Belgium)

was used A study showed best agreement among results provided by strip-type systems in patients

with high buffering capacity all compared to Ericssonrsquos laboratory buffer capacity test (Cheaib et al

2012) Therefore buffer capacity measures were dichotomized into low and normal capacity ie ltpH

55 and ge pH 55 respectively

Fig 2 Correspondence between Ericssonrsquos laboratory buffer capacity test Dentobuff Strip and GC Saliva-Check The figure is drawn from Cheaib et al 2012

Potential explanatory or confounding variables

The following variables were evaluated for a potential explanatory effect or included as confounders in

statistical models Sex age number of teeth Eichner index subjective reported chewing capacity

dietary variables medication and periodontal health The Eichner index describes the number of

occlusal support zones in the mouth that is where occlusion (chewing) is supported with a maximum

of four support zones These are the molar support zone (left and right) and the premolar support

zone (left and right) If occlusion exists in all four support zones the occlusion is categorised as class A

and sub grouped if the support zones lacks teeth in either one or both of the jaws if there exists an

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

REGISTER

Introduction 1 The Joumlnkoumlping study 4 Aim 4 Subjects and method 4 Study cohort 4 Questionnaire 5 Outcome variables 5 Saliva collection and buffer capacity analyses 5 Potential explanatory or confounding variables 5 Statistical analyses 6 Ethical aspects 6 Results 7

Participants 7 Identification of potential confounders 7 Thirty year time trends in saliva flow rate 8 Identification of factors associated with saliva flow rate 9 Thirty years time trends in buffer capacity 11 Identification of factors associated with buffer capacity 12

Discussion 14 Conclusion 16 Acknowledgements 16 References 17

1

30-YEAR (1983-2013) TRENDS IN SALIVA FLOW RATE AND SALIVA BUFFER CAPACITY ANALYSES

FROM 10-YEAR REPEATED CROSS-SECTIONAL POPULATION SAMPLES IN THE JOumlNKOumlPING AREA

Author Aringgren Martin

INTRODUCTION

Saliva plays a crucial role in protection of the oral cavity (Edgar et al 2004) Thus flushing (clearance

and exposure) of the soft and hard tissues and biological effects of saliva constituents such as pH-

regulatory components inorganic components participating in the de- and remineralisation of tooth

tissues and proteins peptides lipids and carbohydrates affecting microbial growth and colonization

are of importance Saliva flow and oral muscle activities are the key determinants for flushing Lack of

proper amount of saliva may lead to discomfort for the individual such as a burning sensation

dysphagia speech impairment taste disturbances and increase risk for dental caries (Bergdahl 2000

Naumlrhi 1994)

Knowledge of population based reference values are important for identification of conditions

which need to be observed or treated For saliva flow rate the cut off values 07 mLmin to 10

mLmin and 01 mLmin for stimulated and unstimlated saliva respectively are applied for

hyposalivation (Fujibayashi et al 2004 Bergdahl 2000) Values above are considered normal If the

flow rate has drifted in the population such as indicated in Bergdahl (2000) these cut-offs may be

misleading and should eventually be questioned For buffer capacity the cut off for low capacity is a

final pH lt55 after addition of a standardized amount of acid This is a reflection of the pKa value and

buffer range of the bicarbonate ion The buffer capacity is crucial for dental erosion caries and

microbiota ecology as a pH below 55 creates an environment of demineralisation and supports a

bacteria dysbiosis characterized by acidophilic and aciduric bacteria (Schuurs 2013 Marsh 2010)

Saliva is produced by the three paired major salivary glands the parotid submandibular and

sublingual glands and numerous minor salivary glands distributed in the oral mucosa In an

unstimulated state the submandibular glands account for two thirds of the secreted saliva When

stimulated secretion from the parotid glands increases proportionally the most and accounts for up

to 60 of the secretion (Carpenter 2013) The parotid glands are comprised of serous and the

submandibular glands of both mucous and serous acinar cells with a majority of the latter In

comparison to the parotid saliva saliva from the submandibular glands is more viscous and mucin-rich

The smallest of the major salivary glands are the sublingual glands which produce highly viscous

mucous saliva that accounts for a few per cent of the total amount of saliva The minor glands

2

contribute for le10 of the secreted saliva They produce mainly mucous saliva rich in secretory IgA

(Dawes and Wood 1973)

Secretion of saliva is regulated by the parasympathetic and the sympathetic systems Secretion is

initiated by afferent signals from three cranial nerves the trigeminal (V) facial (VII) and

glossopharyngeal (IX) nerves The afferent innervation stems from mechanoreceptors in the

periodontal ligament and chemoreceptors in the taste buds The stimulated salivation is increased by

frequency of chewing cycles force of chewing and number of teeth occluding on the object chewed

upon The increase in salivation from the parotid glands is higher on the ipsilateral side but the

contralateral side also shows an increase in salivation (Jensen Kjeilen et al 1987 Samnieng et al

2012) The masticatory-salivary reflex is initiated not only by the periodontal ligament as it has been

shown that edentulous subjects also have an increase in parotid salivation when chewing (Scott et al

1998) The salivation is also dependent on conditioned reflexes controlled through the autonomic

nervous system This central control inhibits unstimulated salivation during sleep fear and mental

depression and excites salivation during fight The classical parasympathetic and sympathetic

transmitters ie acetylcholine and either noradrenaline (norepinephrine) or adrenaline (epinephrine)

respectively are the main activators of salivation (Ekstroumlm 1989) The parasympathetic system mainly

regulates water secretion and the sympathetic protein secretion The complex regulation of the

secretory cells makes secretion sensitive to numerous external and intrinsic factors Examples of such

factors are medications diseases stress water balance starvation and lack of chewing stimulation

(Bardow et al 2008)

Water secretion from the acinar cells is driven by intracellular loss of potassium to the

insterstitium and chloride to the lumen The loss of potassium to the extracellular fluid forces sodium

into the lumen causing a salty environment which drives water through osmosis into the lumen of

the salivary gland During its way through the duct of the salivary gland the primary saliva is modified

in a flow rate related fashion by selective reabsorptionsecretion of electrolytes Among the

electrolytes that are affected during secretion are sodium and bicarbonate (Bardow et al 2008)

One important aspect of saliva action is its contribution to remineralisation of the teeth as well as

preventing demineralisation by buffering (Selwitz et al 2007) After each intake of food the pH in

dental plaque drops and remains at that state until soluble carbohydrates are cleared from the oral

cavity and the acids produced from bacteria are neutralized (buffered)

The magnitude and the time period below the tooth tissue critical pH are determined by the

amount of acid produced by bacteria by the buffer capacity of the saliva and saliva flushing There are

three systems in saliva that contribute in buffering the pH after an acid attack and striving it above the

3

critical pH for caries development in tooth enamel (around 55) or dentin (around 62) as well as

erosion

Fig 1 Schematic drawing of the complex interactions and interplays in the caries process The figure is redrawn from Selwitz RH Ismail AI Pitts NB 2007 Dental caries Lancet 36951ndash59

The phosphate buffer system - In stimulated saliva phosphate is mainly in the form of hydrogen

phosphate compared to in unstimulated saliva where it is mainly dihydrogen phosphate Thus

stimulated saliva is a bit more alkaline than unstimulated saliva The acid dissociation constant or pK

for the equilibrium between these two phosphate forms is around pH 7 At this neutral pH the

phosphate buffer system is most efficient with a buffer span of about plusmn 1 pH unit around the pK As

the phosphate concentration in saliva decreases with the flow rate of saliva the contribution from the

phosphate buffer system to the overall buffer capacity ranges from around 50 in unstimulated saliva

to 10 in highly stimulated saliva (Bardow et al 2008)

The bicarbonate buffer system - As opposed to the phosphate buffer system the contribution of

the bicarbonate buffer system to the buffering effect increases when saliva flow rate increases In

unstimulated saliva this system contributes to less than 50 and in stimulated saliva more than 90

of the buffering effect The pK value for the bicarbonate buffer system lies around pH 6 with a

buffering effect up to pH 7 (Bardow et al 2008) The lower limit of a pure bicarbonate buffer system is

at pH 55 under that the effect of this system is minimal (Garbacz et al 2013) In addition CO2 in gas

form is undersaturated versus the ambient air leading to loss of CO2 and a so called phase buffering

(Bardow et al 2008 Birkhed and Heintze 1989)

The protein buffer system - Saliva proteins and peptides can act as buffers if the pH exceeds (both

positively and negatively) their isoelectric points leading to the proteins accepting or releasing

protons Many of the saliva proteins have their isoelectric points at pH 5 and pH 9 making them

effective as buffers at alkaline environments as well as when the pH drops below the critical value for

4

demineralisation Although generally less effective than the two first buffer system the local

concentration of proteinspeptides may render local significant buffer effect (Bardow et al 2008)

The Joumlnkoumlping study

Joumlnkoumlping is a middle sized Swedish town with 130000 inhabitants in in 2013 It is the Capital of the

Joumlnkoumlping County and is situated on the main transport roads between the three biggest cities in

Sweden namely Stockholm Gothenburg and Malmouml The Public Dental Service of Joumlnkoumlping County

also manages the Institute for Postgraduate Dental Education in Joumlnkoumlping The Joumlnkoumlping study

(Hugoson et al 2005 ab) with its 10-year repeated oral screenings with for the most part

standardized methods is one of few studies worldwide offering the capacity to do a ldquolongitudinalrdquo

evaluation of trends in saliva flow and buffer capacity in repeated cross-sectional population based

samples over a long time

AIM

The primary aim of the present study was to evaluate time trends for saliva flow rate and saliva buffer

capacity using the 10-year screenings in the Joumlnkoumlping study A second aim is to evaluate the

associations between saliva flow ratebuffer capacity and potential explanatory factors including

number of teeth chewing ability diet intake and medication

SUBJECTS AND METHODS

Study cohort

In the Joumlnkoumlping study independent cross-sectional selections of individuals in the age groups 3 5 10

15 20 30 40 50 60 70 and 80 years have been randomly selected from individuals residing in

Kristine Ljungarum Sofia and Jaumlrstorp parishes as defined in 1973 (by 2006 the two first parishes

merged into one and so did the two last in 2010) The examinations are done on a decennial basis

since 1973 saliva flow rate and buffer capacity was not measured in 1973 though The selected

individuals have been invited and in those who agreed to participate about a 100 in each age group

an extensive oral examination was performed under good clinical conditions (Hugoson et al 1986

1995 2005 ab) The age groups of 3 5 10 and 15 are not included in the present evaluation (Koch et

al 2009) At all screening occasions 130 randomly selected adult in each of the 10-year age group

were invited to participate (Huguson et al 2005) Due to a low participation rate in 2013 additionally

40 40 and 50 subjects were invited in the age groups of 30 40 and 50 years

5

Questionnaire

All participants answered a questionnaire in immediate connection to the examination In the

questionnaire the participants answered questions on the number of meals and snacks per day

medication and graded their subjective experience of xerostomia health tobacco use and ease of

chewing

Outcome variables

The outcome variables in the present study are flow rates of stimulated whole saliva and buffer

capacity of the same saliva from the screenings in 1983 1993 2003 and 2013

Saliva collection and buffer capacity analyses

Whole saliva stimulated by chewing on a 1 gram piece of paraffin was collected into graded test

tubes for 3 minutes Flow rates were calculated and buffer capacity analysed The analysis method of

the buffer capacity changed over the years In 1983 and 1993 it was done according to Ericssonrsquos

laboratory buffer capacity test (Ericsson 1959) In 2003 and 2013 chair-side simplified methods

(Dentobuff Strip Orion Diagnostica Espoo Finland GC Saliva Check GC Europe NV Leuven Belgium)

was used A study showed best agreement among results provided by strip-type systems in patients

with high buffering capacity all compared to Ericssonrsquos laboratory buffer capacity test (Cheaib et al

2012) Therefore buffer capacity measures were dichotomized into low and normal capacity ie ltpH

55 and ge pH 55 respectively

Fig 2 Correspondence between Ericssonrsquos laboratory buffer capacity test Dentobuff Strip and GC Saliva-Check The figure is drawn from Cheaib et al 2012

Potential explanatory or confounding variables

The following variables were evaluated for a potential explanatory effect or included as confounders in

statistical models Sex age number of teeth Eichner index subjective reported chewing capacity

dietary variables medication and periodontal health The Eichner index describes the number of

occlusal support zones in the mouth that is where occlusion (chewing) is supported with a maximum

of four support zones These are the molar support zone (left and right) and the premolar support

zone (left and right) If occlusion exists in all four support zones the occlusion is categorised as class A

and sub grouped if the support zones lacks teeth in either one or both of the jaws if there exists an

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

1

30-YEAR (1983-2013) TRENDS IN SALIVA FLOW RATE AND SALIVA BUFFER CAPACITY ANALYSES

FROM 10-YEAR REPEATED CROSS-SECTIONAL POPULATION SAMPLES IN THE JOumlNKOumlPING AREA

Author Aringgren Martin

INTRODUCTION

Saliva plays a crucial role in protection of the oral cavity (Edgar et al 2004) Thus flushing (clearance

and exposure) of the soft and hard tissues and biological effects of saliva constituents such as pH-

regulatory components inorganic components participating in the de- and remineralisation of tooth

tissues and proteins peptides lipids and carbohydrates affecting microbial growth and colonization

are of importance Saliva flow and oral muscle activities are the key determinants for flushing Lack of

proper amount of saliva may lead to discomfort for the individual such as a burning sensation

dysphagia speech impairment taste disturbances and increase risk for dental caries (Bergdahl 2000

Naumlrhi 1994)

Knowledge of population based reference values are important for identification of conditions

which need to be observed or treated For saliva flow rate the cut off values 07 mLmin to 10

mLmin and 01 mLmin for stimulated and unstimlated saliva respectively are applied for

hyposalivation (Fujibayashi et al 2004 Bergdahl 2000) Values above are considered normal If the

flow rate has drifted in the population such as indicated in Bergdahl (2000) these cut-offs may be

misleading and should eventually be questioned For buffer capacity the cut off for low capacity is a

final pH lt55 after addition of a standardized amount of acid This is a reflection of the pKa value and

buffer range of the bicarbonate ion The buffer capacity is crucial for dental erosion caries and

microbiota ecology as a pH below 55 creates an environment of demineralisation and supports a

bacteria dysbiosis characterized by acidophilic and aciduric bacteria (Schuurs 2013 Marsh 2010)

Saliva is produced by the three paired major salivary glands the parotid submandibular and

sublingual glands and numerous minor salivary glands distributed in the oral mucosa In an

unstimulated state the submandibular glands account for two thirds of the secreted saliva When

stimulated secretion from the parotid glands increases proportionally the most and accounts for up

to 60 of the secretion (Carpenter 2013) The parotid glands are comprised of serous and the

submandibular glands of both mucous and serous acinar cells with a majority of the latter In

comparison to the parotid saliva saliva from the submandibular glands is more viscous and mucin-rich

The smallest of the major salivary glands are the sublingual glands which produce highly viscous

mucous saliva that accounts for a few per cent of the total amount of saliva The minor glands

2

contribute for le10 of the secreted saliva They produce mainly mucous saliva rich in secretory IgA

(Dawes and Wood 1973)

Secretion of saliva is regulated by the parasympathetic and the sympathetic systems Secretion is

initiated by afferent signals from three cranial nerves the trigeminal (V) facial (VII) and

glossopharyngeal (IX) nerves The afferent innervation stems from mechanoreceptors in the

periodontal ligament and chemoreceptors in the taste buds The stimulated salivation is increased by

frequency of chewing cycles force of chewing and number of teeth occluding on the object chewed

upon The increase in salivation from the parotid glands is higher on the ipsilateral side but the

contralateral side also shows an increase in salivation (Jensen Kjeilen et al 1987 Samnieng et al

2012) The masticatory-salivary reflex is initiated not only by the periodontal ligament as it has been

shown that edentulous subjects also have an increase in parotid salivation when chewing (Scott et al

1998) The salivation is also dependent on conditioned reflexes controlled through the autonomic

nervous system This central control inhibits unstimulated salivation during sleep fear and mental

depression and excites salivation during fight The classical parasympathetic and sympathetic

transmitters ie acetylcholine and either noradrenaline (norepinephrine) or adrenaline (epinephrine)

respectively are the main activators of salivation (Ekstroumlm 1989) The parasympathetic system mainly

regulates water secretion and the sympathetic protein secretion The complex regulation of the

secretory cells makes secretion sensitive to numerous external and intrinsic factors Examples of such

factors are medications diseases stress water balance starvation and lack of chewing stimulation

(Bardow et al 2008)

Water secretion from the acinar cells is driven by intracellular loss of potassium to the

insterstitium and chloride to the lumen The loss of potassium to the extracellular fluid forces sodium

into the lumen causing a salty environment which drives water through osmosis into the lumen of

the salivary gland During its way through the duct of the salivary gland the primary saliva is modified

in a flow rate related fashion by selective reabsorptionsecretion of electrolytes Among the

electrolytes that are affected during secretion are sodium and bicarbonate (Bardow et al 2008)

One important aspect of saliva action is its contribution to remineralisation of the teeth as well as

preventing demineralisation by buffering (Selwitz et al 2007) After each intake of food the pH in

dental plaque drops and remains at that state until soluble carbohydrates are cleared from the oral

cavity and the acids produced from bacteria are neutralized (buffered)

The magnitude and the time period below the tooth tissue critical pH are determined by the

amount of acid produced by bacteria by the buffer capacity of the saliva and saliva flushing There are

three systems in saliva that contribute in buffering the pH after an acid attack and striving it above the

3

critical pH for caries development in tooth enamel (around 55) or dentin (around 62) as well as

erosion

Fig 1 Schematic drawing of the complex interactions and interplays in the caries process The figure is redrawn from Selwitz RH Ismail AI Pitts NB 2007 Dental caries Lancet 36951ndash59

The phosphate buffer system - In stimulated saliva phosphate is mainly in the form of hydrogen

phosphate compared to in unstimulated saliva where it is mainly dihydrogen phosphate Thus

stimulated saliva is a bit more alkaline than unstimulated saliva The acid dissociation constant or pK

for the equilibrium between these two phosphate forms is around pH 7 At this neutral pH the

phosphate buffer system is most efficient with a buffer span of about plusmn 1 pH unit around the pK As

the phosphate concentration in saliva decreases with the flow rate of saliva the contribution from the

phosphate buffer system to the overall buffer capacity ranges from around 50 in unstimulated saliva

to 10 in highly stimulated saliva (Bardow et al 2008)

The bicarbonate buffer system - As opposed to the phosphate buffer system the contribution of

the bicarbonate buffer system to the buffering effect increases when saliva flow rate increases In

unstimulated saliva this system contributes to less than 50 and in stimulated saliva more than 90

of the buffering effect The pK value for the bicarbonate buffer system lies around pH 6 with a

buffering effect up to pH 7 (Bardow et al 2008) The lower limit of a pure bicarbonate buffer system is

at pH 55 under that the effect of this system is minimal (Garbacz et al 2013) In addition CO2 in gas

form is undersaturated versus the ambient air leading to loss of CO2 and a so called phase buffering

(Bardow et al 2008 Birkhed and Heintze 1989)

The protein buffer system - Saliva proteins and peptides can act as buffers if the pH exceeds (both

positively and negatively) their isoelectric points leading to the proteins accepting or releasing

protons Many of the saliva proteins have their isoelectric points at pH 5 and pH 9 making them

effective as buffers at alkaline environments as well as when the pH drops below the critical value for

4

demineralisation Although generally less effective than the two first buffer system the local

concentration of proteinspeptides may render local significant buffer effect (Bardow et al 2008)

The Joumlnkoumlping study

Joumlnkoumlping is a middle sized Swedish town with 130000 inhabitants in in 2013 It is the Capital of the

Joumlnkoumlping County and is situated on the main transport roads between the three biggest cities in

Sweden namely Stockholm Gothenburg and Malmouml The Public Dental Service of Joumlnkoumlping County

also manages the Institute for Postgraduate Dental Education in Joumlnkoumlping The Joumlnkoumlping study

(Hugoson et al 2005 ab) with its 10-year repeated oral screenings with for the most part

standardized methods is one of few studies worldwide offering the capacity to do a ldquolongitudinalrdquo

evaluation of trends in saliva flow and buffer capacity in repeated cross-sectional population based

samples over a long time

AIM

The primary aim of the present study was to evaluate time trends for saliva flow rate and saliva buffer

capacity using the 10-year screenings in the Joumlnkoumlping study A second aim is to evaluate the

associations between saliva flow ratebuffer capacity and potential explanatory factors including

number of teeth chewing ability diet intake and medication

SUBJECTS AND METHODS

Study cohort

In the Joumlnkoumlping study independent cross-sectional selections of individuals in the age groups 3 5 10

15 20 30 40 50 60 70 and 80 years have been randomly selected from individuals residing in

Kristine Ljungarum Sofia and Jaumlrstorp parishes as defined in 1973 (by 2006 the two first parishes

merged into one and so did the two last in 2010) The examinations are done on a decennial basis

since 1973 saliva flow rate and buffer capacity was not measured in 1973 though The selected

individuals have been invited and in those who agreed to participate about a 100 in each age group

an extensive oral examination was performed under good clinical conditions (Hugoson et al 1986

1995 2005 ab) The age groups of 3 5 10 and 15 are not included in the present evaluation (Koch et

al 2009) At all screening occasions 130 randomly selected adult in each of the 10-year age group

were invited to participate (Huguson et al 2005) Due to a low participation rate in 2013 additionally

40 40 and 50 subjects were invited in the age groups of 30 40 and 50 years

5

Questionnaire

All participants answered a questionnaire in immediate connection to the examination In the

questionnaire the participants answered questions on the number of meals and snacks per day

medication and graded their subjective experience of xerostomia health tobacco use and ease of

chewing

Outcome variables

The outcome variables in the present study are flow rates of stimulated whole saliva and buffer

capacity of the same saliva from the screenings in 1983 1993 2003 and 2013

Saliva collection and buffer capacity analyses

Whole saliva stimulated by chewing on a 1 gram piece of paraffin was collected into graded test

tubes for 3 minutes Flow rates were calculated and buffer capacity analysed The analysis method of

the buffer capacity changed over the years In 1983 and 1993 it was done according to Ericssonrsquos

laboratory buffer capacity test (Ericsson 1959) In 2003 and 2013 chair-side simplified methods

(Dentobuff Strip Orion Diagnostica Espoo Finland GC Saliva Check GC Europe NV Leuven Belgium)

was used A study showed best agreement among results provided by strip-type systems in patients

with high buffering capacity all compared to Ericssonrsquos laboratory buffer capacity test (Cheaib et al

2012) Therefore buffer capacity measures were dichotomized into low and normal capacity ie ltpH

55 and ge pH 55 respectively

Fig 2 Correspondence between Ericssonrsquos laboratory buffer capacity test Dentobuff Strip and GC Saliva-Check The figure is drawn from Cheaib et al 2012

Potential explanatory or confounding variables

The following variables were evaluated for a potential explanatory effect or included as confounders in

statistical models Sex age number of teeth Eichner index subjective reported chewing capacity

dietary variables medication and periodontal health The Eichner index describes the number of

occlusal support zones in the mouth that is where occlusion (chewing) is supported with a maximum

of four support zones These are the molar support zone (left and right) and the premolar support

zone (left and right) If occlusion exists in all four support zones the occlusion is categorised as class A

and sub grouped if the support zones lacks teeth in either one or both of the jaws if there exists an

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

2

contribute for le10 of the secreted saliva They produce mainly mucous saliva rich in secretory IgA

(Dawes and Wood 1973)

Secretion of saliva is regulated by the parasympathetic and the sympathetic systems Secretion is

initiated by afferent signals from three cranial nerves the trigeminal (V) facial (VII) and

glossopharyngeal (IX) nerves The afferent innervation stems from mechanoreceptors in the

periodontal ligament and chemoreceptors in the taste buds The stimulated salivation is increased by

frequency of chewing cycles force of chewing and number of teeth occluding on the object chewed

upon The increase in salivation from the parotid glands is higher on the ipsilateral side but the

contralateral side also shows an increase in salivation (Jensen Kjeilen et al 1987 Samnieng et al

2012) The masticatory-salivary reflex is initiated not only by the periodontal ligament as it has been

shown that edentulous subjects also have an increase in parotid salivation when chewing (Scott et al

1998) The salivation is also dependent on conditioned reflexes controlled through the autonomic

nervous system This central control inhibits unstimulated salivation during sleep fear and mental

depression and excites salivation during fight The classical parasympathetic and sympathetic

transmitters ie acetylcholine and either noradrenaline (norepinephrine) or adrenaline (epinephrine)

respectively are the main activators of salivation (Ekstroumlm 1989) The parasympathetic system mainly

regulates water secretion and the sympathetic protein secretion The complex regulation of the

secretory cells makes secretion sensitive to numerous external and intrinsic factors Examples of such

factors are medications diseases stress water balance starvation and lack of chewing stimulation

(Bardow et al 2008)

Water secretion from the acinar cells is driven by intracellular loss of potassium to the

insterstitium and chloride to the lumen The loss of potassium to the extracellular fluid forces sodium

into the lumen causing a salty environment which drives water through osmosis into the lumen of

the salivary gland During its way through the duct of the salivary gland the primary saliva is modified

in a flow rate related fashion by selective reabsorptionsecretion of electrolytes Among the

electrolytes that are affected during secretion are sodium and bicarbonate (Bardow et al 2008)

One important aspect of saliva action is its contribution to remineralisation of the teeth as well as

preventing demineralisation by buffering (Selwitz et al 2007) After each intake of food the pH in

dental plaque drops and remains at that state until soluble carbohydrates are cleared from the oral

cavity and the acids produced from bacteria are neutralized (buffered)

The magnitude and the time period below the tooth tissue critical pH are determined by the

amount of acid produced by bacteria by the buffer capacity of the saliva and saliva flushing There are

three systems in saliva that contribute in buffering the pH after an acid attack and striving it above the

3

critical pH for caries development in tooth enamel (around 55) or dentin (around 62) as well as

erosion

Fig 1 Schematic drawing of the complex interactions and interplays in the caries process The figure is redrawn from Selwitz RH Ismail AI Pitts NB 2007 Dental caries Lancet 36951ndash59

The phosphate buffer system - In stimulated saliva phosphate is mainly in the form of hydrogen

phosphate compared to in unstimulated saliva where it is mainly dihydrogen phosphate Thus

stimulated saliva is a bit more alkaline than unstimulated saliva The acid dissociation constant or pK

for the equilibrium between these two phosphate forms is around pH 7 At this neutral pH the

phosphate buffer system is most efficient with a buffer span of about plusmn 1 pH unit around the pK As

the phosphate concentration in saliva decreases with the flow rate of saliva the contribution from the

phosphate buffer system to the overall buffer capacity ranges from around 50 in unstimulated saliva

to 10 in highly stimulated saliva (Bardow et al 2008)

The bicarbonate buffer system - As opposed to the phosphate buffer system the contribution of

the bicarbonate buffer system to the buffering effect increases when saliva flow rate increases In

unstimulated saliva this system contributes to less than 50 and in stimulated saliva more than 90

of the buffering effect The pK value for the bicarbonate buffer system lies around pH 6 with a

buffering effect up to pH 7 (Bardow et al 2008) The lower limit of a pure bicarbonate buffer system is

at pH 55 under that the effect of this system is minimal (Garbacz et al 2013) In addition CO2 in gas

form is undersaturated versus the ambient air leading to loss of CO2 and a so called phase buffering

(Bardow et al 2008 Birkhed and Heintze 1989)

The protein buffer system - Saliva proteins and peptides can act as buffers if the pH exceeds (both

positively and negatively) their isoelectric points leading to the proteins accepting or releasing

protons Many of the saliva proteins have their isoelectric points at pH 5 and pH 9 making them

effective as buffers at alkaline environments as well as when the pH drops below the critical value for

4

demineralisation Although generally less effective than the two first buffer system the local

concentration of proteinspeptides may render local significant buffer effect (Bardow et al 2008)

The Joumlnkoumlping study

Joumlnkoumlping is a middle sized Swedish town with 130000 inhabitants in in 2013 It is the Capital of the

Joumlnkoumlping County and is situated on the main transport roads between the three biggest cities in

Sweden namely Stockholm Gothenburg and Malmouml The Public Dental Service of Joumlnkoumlping County

also manages the Institute for Postgraduate Dental Education in Joumlnkoumlping The Joumlnkoumlping study

(Hugoson et al 2005 ab) with its 10-year repeated oral screenings with for the most part

standardized methods is one of few studies worldwide offering the capacity to do a ldquolongitudinalrdquo

evaluation of trends in saliva flow and buffer capacity in repeated cross-sectional population based

samples over a long time

AIM

The primary aim of the present study was to evaluate time trends for saliva flow rate and saliva buffer

capacity using the 10-year screenings in the Joumlnkoumlping study A second aim is to evaluate the

associations between saliva flow ratebuffer capacity and potential explanatory factors including

number of teeth chewing ability diet intake and medication

SUBJECTS AND METHODS

Study cohort

In the Joumlnkoumlping study independent cross-sectional selections of individuals in the age groups 3 5 10

15 20 30 40 50 60 70 and 80 years have been randomly selected from individuals residing in

Kristine Ljungarum Sofia and Jaumlrstorp parishes as defined in 1973 (by 2006 the two first parishes

merged into one and so did the two last in 2010) The examinations are done on a decennial basis

since 1973 saliva flow rate and buffer capacity was not measured in 1973 though The selected

individuals have been invited and in those who agreed to participate about a 100 in each age group

an extensive oral examination was performed under good clinical conditions (Hugoson et al 1986

1995 2005 ab) The age groups of 3 5 10 and 15 are not included in the present evaluation (Koch et

al 2009) At all screening occasions 130 randomly selected adult in each of the 10-year age group

were invited to participate (Huguson et al 2005) Due to a low participation rate in 2013 additionally

40 40 and 50 subjects were invited in the age groups of 30 40 and 50 years

5

Questionnaire

All participants answered a questionnaire in immediate connection to the examination In the

questionnaire the participants answered questions on the number of meals and snacks per day

medication and graded their subjective experience of xerostomia health tobacco use and ease of

chewing

Outcome variables

The outcome variables in the present study are flow rates of stimulated whole saliva and buffer

capacity of the same saliva from the screenings in 1983 1993 2003 and 2013

Saliva collection and buffer capacity analyses

Whole saliva stimulated by chewing on a 1 gram piece of paraffin was collected into graded test

tubes for 3 minutes Flow rates were calculated and buffer capacity analysed The analysis method of

the buffer capacity changed over the years In 1983 and 1993 it was done according to Ericssonrsquos

laboratory buffer capacity test (Ericsson 1959) In 2003 and 2013 chair-side simplified methods

(Dentobuff Strip Orion Diagnostica Espoo Finland GC Saliva Check GC Europe NV Leuven Belgium)

was used A study showed best agreement among results provided by strip-type systems in patients

with high buffering capacity all compared to Ericssonrsquos laboratory buffer capacity test (Cheaib et al

2012) Therefore buffer capacity measures were dichotomized into low and normal capacity ie ltpH

55 and ge pH 55 respectively

Fig 2 Correspondence between Ericssonrsquos laboratory buffer capacity test Dentobuff Strip and GC Saliva-Check The figure is drawn from Cheaib et al 2012

Potential explanatory or confounding variables

The following variables were evaluated for a potential explanatory effect or included as confounders in

statistical models Sex age number of teeth Eichner index subjective reported chewing capacity

dietary variables medication and periodontal health The Eichner index describes the number of

occlusal support zones in the mouth that is where occlusion (chewing) is supported with a maximum

of four support zones These are the molar support zone (left and right) and the premolar support

zone (left and right) If occlusion exists in all four support zones the occlusion is categorised as class A

and sub grouped if the support zones lacks teeth in either one or both of the jaws if there exists an

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

3

critical pH for caries development in tooth enamel (around 55) or dentin (around 62) as well as

erosion

Fig 1 Schematic drawing of the complex interactions and interplays in the caries process The figure is redrawn from Selwitz RH Ismail AI Pitts NB 2007 Dental caries Lancet 36951ndash59

The phosphate buffer system - In stimulated saliva phosphate is mainly in the form of hydrogen

phosphate compared to in unstimulated saliva where it is mainly dihydrogen phosphate Thus

stimulated saliva is a bit more alkaline than unstimulated saliva The acid dissociation constant or pK

for the equilibrium between these two phosphate forms is around pH 7 At this neutral pH the

phosphate buffer system is most efficient with a buffer span of about plusmn 1 pH unit around the pK As

the phosphate concentration in saliva decreases with the flow rate of saliva the contribution from the

phosphate buffer system to the overall buffer capacity ranges from around 50 in unstimulated saliva

to 10 in highly stimulated saliva (Bardow et al 2008)

The bicarbonate buffer system - As opposed to the phosphate buffer system the contribution of

the bicarbonate buffer system to the buffering effect increases when saliva flow rate increases In

unstimulated saliva this system contributes to less than 50 and in stimulated saliva more than 90

of the buffering effect The pK value for the bicarbonate buffer system lies around pH 6 with a

buffering effect up to pH 7 (Bardow et al 2008) The lower limit of a pure bicarbonate buffer system is

at pH 55 under that the effect of this system is minimal (Garbacz et al 2013) In addition CO2 in gas

form is undersaturated versus the ambient air leading to loss of CO2 and a so called phase buffering

(Bardow et al 2008 Birkhed and Heintze 1989)

The protein buffer system - Saliva proteins and peptides can act as buffers if the pH exceeds (both

positively and negatively) their isoelectric points leading to the proteins accepting or releasing

protons Many of the saliva proteins have their isoelectric points at pH 5 and pH 9 making them

effective as buffers at alkaline environments as well as when the pH drops below the critical value for

4

demineralisation Although generally less effective than the two first buffer system the local

concentration of proteinspeptides may render local significant buffer effect (Bardow et al 2008)

The Joumlnkoumlping study

Joumlnkoumlping is a middle sized Swedish town with 130000 inhabitants in in 2013 It is the Capital of the

Joumlnkoumlping County and is situated on the main transport roads between the three biggest cities in

Sweden namely Stockholm Gothenburg and Malmouml The Public Dental Service of Joumlnkoumlping County

also manages the Institute for Postgraduate Dental Education in Joumlnkoumlping The Joumlnkoumlping study

(Hugoson et al 2005 ab) with its 10-year repeated oral screenings with for the most part

standardized methods is one of few studies worldwide offering the capacity to do a ldquolongitudinalrdquo

evaluation of trends in saliva flow and buffer capacity in repeated cross-sectional population based

samples over a long time

AIM

The primary aim of the present study was to evaluate time trends for saliva flow rate and saliva buffer

capacity using the 10-year screenings in the Joumlnkoumlping study A second aim is to evaluate the

associations between saliva flow ratebuffer capacity and potential explanatory factors including

number of teeth chewing ability diet intake and medication

SUBJECTS AND METHODS

Study cohort

In the Joumlnkoumlping study independent cross-sectional selections of individuals in the age groups 3 5 10

15 20 30 40 50 60 70 and 80 years have been randomly selected from individuals residing in

Kristine Ljungarum Sofia and Jaumlrstorp parishes as defined in 1973 (by 2006 the two first parishes

merged into one and so did the two last in 2010) The examinations are done on a decennial basis

since 1973 saliva flow rate and buffer capacity was not measured in 1973 though The selected

individuals have been invited and in those who agreed to participate about a 100 in each age group

an extensive oral examination was performed under good clinical conditions (Hugoson et al 1986

1995 2005 ab) The age groups of 3 5 10 and 15 are not included in the present evaluation (Koch et

al 2009) At all screening occasions 130 randomly selected adult in each of the 10-year age group

were invited to participate (Huguson et al 2005) Due to a low participation rate in 2013 additionally

40 40 and 50 subjects were invited in the age groups of 30 40 and 50 years

5

Questionnaire

All participants answered a questionnaire in immediate connection to the examination In the

questionnaire the participants answered questions on the number of meals and snacks per day

medication and graded their subjective experience of xerostomia health tobacco use and ease of

chewing

Outcome variables

The outcome variables in the present study are flow rates of stimulated whole saliva and buffer

capacity of the same saliva from the screenings in 1983 1993 2003 and 2013

Saliva collection and buffer capacity analyses

Whole saliva stimulated by chewing on a 1 gram piece of paraffin was collected into graded test

tubes for 3 minutes Flow rates were calculated and buffer capacity analysed The analysis method of

the buffer capacity changed over the years In 1983 and 1993 it was done according to Ericssonrsquos

laboratory buffer capacity test (Ericsson 1959) In 2003 and 2013 chair-side simplified methods

(Dentobuff Strip Orion Diagnostica Espoo Finland GC Saliva Check GC Europe NV Leuven Belgium)

was used A study showed best agreement among results provided by strip-type systems in patients

with high buffering capacity all compared to Ericssonrsquos laboratory buffer capacity test (Cheaib et al

2012) Therefore buffer capacity measures were dichotomized into low and normal capacity ie ltpH

55 and ge pH 55 respectively

Fig 2 Correspondence between Ericssonrsquos laboratory buffer capacity test Dentobuff Strip and GC Saliva-Check The figure is drawn from Cheaib et al 2012

Potential explanatory or confounding variables

The following variables were evaluated for a potential explanatory effect or included as confounders in

statistical models Sex age number of teeth Eichner index subjective reported chewing capacity

dietary variables medication and periodontal health The Eichner index describes the number of

occlusal support zones in the mouth that is where occlusion (chewing) is supported with a maximum

of four support zones These are the molar support zone (left and right) and the premolar support

zone (left and right) If occlusion exists in all four support zones the occlusion is categorised as class A

and sub grouped if the support zones lacks teeth in either one or both of the jaws if there exists an

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

4

demineralisation Although generally less effective than the two first buffer system the local

concentration of proteinspeptides may render local significant buffer effect (Bardow et al 2008)

The Joumlnkoumlping study

Joumlnkoumlping is a middle sized Swedish town with 130000 inhabitants in in 2013 It is the Capital of the

Joumlnkoumlping County and is situated on the main transport roads between the three biggest cities in

Sweden namely Stockholm Gothenburg and Malmouml The Public Dental Service of Joumlnkoumlping County

also manages the Institute for Postgraduate Dental Education in Joumlnkoumlping The Joumlnkoumlping study

(Hugoson et al 2005 ab) with its 10-year repeated oral screenings with for the most part

standardized methods is one of few studies worldwide offering the capacity to do a ldquolongitudinalrdquo

evaluation of trends in saliva flow and buffer capacity in repeated cross-sectional population based

samples over a long time

AIM

The primary aim of the present study was to evaluate time trends for saliva flow rate and saliva buffer

capacity using the 10-year screenings in the Joumlnkoumlping study A second aim is to evaluate the

associations between saliva flow ratebuffer capacity and potential explanatory factors including

number of teeth chewing ability diet intake and medication

SUBJECTS AND METHODS

Study cohort

In the Joumlnkoumlping study independent cross-sectional selections of individuals in the age groups 3 5 10

15 20 30 40 50 60 70 and 80 years have been randomly selected from individuals residing in

Kristine Ljungarum Sofia and Jaumlrstorp parishes as defined in 1973 (by 2006 the two first parishes

merged into one and so did the two last in 2010) The examinations are done on a decennial basis

since 1973 saliva flow rate and buffer capacity was not measured in 1973 though The selected

individuals have been invited and in those who agreed to participate about a 100 in each age group

an extensive oral examination was performed under good clinical conditions (Hugoson et al 1986

1995 2005 ab) The age groups of 3 5 10 and 15 are not included in the present evaluation (Koch et

al 2009) At all screening occasions 130 randomly selected adult in each of the 10-year age group

were invited to participate (Huguson et al 2005) Due to a low participation rate in 2013 additionally

40 40 and 50 subjects were invited in the age groups of 30 40 and 50 years

5

Questionnaire

All participants answered a questionnaire in immediate connection to the examination In the

questionnaire the participants answered questions on the number of meals and snacks per day

medication and graded their subjective experience of xerostomia health tobacco use and ease of

chewing

Outcome variables

The outcome variables in the present study are flow rates of stimulated whole saliva and buffer

capacity of the same saliva from the screenings in 1983 1993 2003 and 2013

Saliva collection and buffer capacity analyses

Whole saliva stimulated by chewing on a 1 gram piece of paraffin was collected into graded test

tubes for 3 minutes Flow rates were calculated and buffer capacity analysed The analysis method of

the buffer capacity changed over the years In 1983 and 1993 it was done according to Ericssonrsquos

laboratory buffer capacity test (Ericsson 1959) In 2003 and 2013 chair-side simplified methods

(Dentobuff Strip Orion Diagnostica Espoo Finland GC Saliva Check GC Europe NV Leuven Belgium)

was used A study showed best agreement among results provided by strip-type systems in patients

with high buffering capacity all compared to Ericssonrsquos laboratory buffer capacity test (Cheaib et al

2012) Therefore buffer capacity measures were dichotomized into low and normal capacity ie ltpH

55 and ge pH 55 respectively

Fig 2 Correspondence between Ericssonrsquos laboratory buffer capacity test Dentobuff Strip and GC Saliva-Check The figure is drawn from Cheaib et al 2012

Potential explanatory or confounding variables

The following variables were evaluated for a potential explanatory effect or included as confounders in

statistical models Sex age number of teeth Eichner index subjective reported chewing capacity

dietary variables medication and periodontal health The Eichner index describes the number of

occlusal support zones in the mouth that is where occlusion (chewing) is supported with a maximum

of four support zones These are the molar support zone (left and right) and the premolar support

zone (left and right) If occlusion exists in all four support zones the occlusion is categorised as class A

and sub grouped if the support zones lacks teeth in either one or both of the jaws if there exists an

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

5

Questionnaire

All participants answered a questionnaire in immediate connection to the examination In the

questionnaire the participants answered questions on the number of meals and snacks per day

medication and graded their subjective experience of xerostomia health tobacco use and ease of

chewing

Outcome variables

The outcome variables in the present study are flow rates of stimulated whole saliva and buffer

capacity of the same saliva from the screenings in 1983 1993 2003 and 2013

Saliva collection and buffer capacity analyses

Whole saliva stimulated by chewing on a 1 gram piece of paraffin was collected into graded test

tubes for 3 minutes Flow rates were calculated and buffer capacity analysed The analysis method of

the buffer capacity changed over the years In 1983 and 1993 it was done according to Ericssonrsquos

laboratory buffer capacity test (Ericsson 1959) In 2003 and 2013 chair-side simplified methods

(Dentobuff Strip Orion Diagnostica Espoo Finland GC Saliva Check GC Europe NV Leuven Belgium)

was used A study showed best agreement among results provided by strip-type systems in patients

with high buffering capacity all compared to Ericssonrsquos laboratory buffer capacity test (Cheaib et al

2012) Therefore buffer capacity measures were dichotomized into low and normal capacity ie ltpH

55 and ge pH 55 respectively

Fig 2 Correspondence between Ericssonrsquos laboratory buffer capacity test Dentobuff Strip and GC Saliva-Check The figure is drawn from Cheaib et al 2012

Potential explanatory or confounding variables

The following variables were evaluated for a potential explanatory effect or included as confounders in

statistical models Sex age number of teeth Eichner index subjective reported chewing capacity

dietary variables medication and periodontal health The Eichner index describes the number of

occlusal support zones in the mouth that is where occlusion (chewing) is supported with a maximum

of four support zones These are the molar support zone (left and right) and the premolar support

zone (left and right) If occlusion exists in all four support zones the occlusion is categorised as class A

and sub grouped if the support zones lacks teeth in either one or both of the jaws if there exists an

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

6

occlusion but at least one of the four support zones does not participate in the occlusion it is

categorised as class B which is sub grouped according to how many of the support zones that are

lacking if there are no occlusion or the individual is edentulous it is a class C sub grouped to whether

the individual is edentulous or have non-occluding teeth in either one or both jaws Tooth or implant

supported fixed dentures are considered to participate in the occlusion but removable dentures are

not (Eichner 1955) The number of teeth and the Eichner index does not include the wisdom teeth

ie maximum number is 28 teeth

Statistical analyses

Statistical analyses were performed for all subjects together and separately for men and women in 10-

year age strata using IBM SPSS version 22 (IBM Armonk NY USA) Statistical tests were two-sided and

p-values lt005 considered statistically significant Descriptive statistics include frequencies

proportions and means with measures of variation Differences in mean values for normally

distributed variables were tested with Studentacutes unpaired t-test or ANOVA followed by Bonferroni

post hoc tests where applicable Standardization for age andor sex was done by general linear

regression (glm) Non-normally distributed variables were tested by Chi2 ndashtest

Multivariate partial least square regression (PLS SIMCA 14 version 140 Umetrics AB Umearing

Sweden) was used to search for hidden structures in the data In contrast to traditional regression PLS

is suitable for data where the x variables co-vary and the group number is limited Variables were

autoscaled to unit variance and cross-validated prediction of Y calculated (Staringhle and Wold 1988)

Cross validation is done by a systematic prediction of 17th of the data by the remaining 67th of the

data The importance of each x variable in explaining the variation in y is displayed in a PLS loading plot

and the correlation coefficients in a bar plot with means and 95 CI Variables for which the 95 CI

does not include zero are statistically significant

Ethical aspects

The Joumlnkoumlping study is approved by the Linkoumlping Regional Ethical Review Board

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

7

RESULTS

Participants

The total number of participants in the four study years were 2509 (1204 men and 1305 women)

with a virtually equal distribution on sex and 10-year age groups at each screening occasions (Table 1)

The attendance rate was 772 in 1983 754 in 1993 690 in 2003 and 564 in 2013

Table 1 Numbers () of participants per study year in sex and 10-year age strata by study year

Agea

1983 1993 2003 2013

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

Men n ()

Women n ()

20 years 45 (45) 55 (55) 50 (50) 50 (50) 46 (55) 38 (45) 22 (29) 54 (71)

30 years 50 (51) 48 (49) 63 (62) 39 (38) 42 (46) 50 (54) 46 (50) 46 (50)

40 years 47 (47) 52 (53) 54 (58) 39 (42) 47 (57) 36 (43) 48 (52) 45 (48)

50 years 43 (41) 60 (59) 45 (46) 52 (54) 41 (45) 50 (55) 43 (43) 58 (58)

60 years 51 (52) 47 (48) 50 (54) 42 (56) 45 (50) 45 (50) 42 (51) 40 (49)

70 years 48 (48) 51 (52) 36 (36) 64 (64) 41 (46) 48 (54) 38 (41) 54 (59)

80 years 30 (38) 50 (62) 34 (48) 37 (52) 21 (35) 39 (65) 36 (51) 35 (49)

Total 314 (47) 363 (53) 332 (51) 323 (49) 283 (48) 306 (52) 275 (47) 312 (53)

a) Participants turning the age during the study year

Identification of potential confounders

As a first step the associations between saliva flow rate and buffer capacity on the one hand and sex

and age on the other were analysed Univariate comparisons revealed that the mean saliva flow rate

was systematically higher in men than women in all age groups (Table 2 Fig 3) and that it differed

among the age groups (Table 2 Fig 3) The highest mean saliva flow rate in men and women was seen

at age 50 and 40 years respectively and thereafter flow rate decreased continuously in both sexes (Fig

3) The proportion with low saliva buffer capacity differed by age in men but not women (Table 2 Fig

4) Hence measures for screening year comparisons should be standardized for age or sex

Table 2 Saliva flow rate and buffer capacity by sex and 10-year age groups Unstandardized means and 95 CI for flow rate and proportions with a low saliva buffer capacity ie a final buffer pH lt55

N

Saliva flow rate mLmin (mean (95 CI)

Proportion with saliva buffer pH lt55

Age Men

n=1178 Women n=1271

p-value

(sex)a N

Men n=1149

Women n=1229

p-value

(sex)b

20 years 358 17 (16-18) 15 (14-17) 0009 356 589 606 0412

30 years 376 17 (16-18) 16 (14-17) 0299 363 411 543 0008

40 years 355 19 (18-20) 17 (15-18) 0014 338 440 532 0057

50 years 388 19 (18-21) 16 (15-17) 0002 373 476 536 0147

60 years 351 17 (15-18) 15 (13-16) 0027 346 508 521 0445

70 years 359 17 (15-18) 14 (13-15) 0010 349 553 619 0126

80 years 262 15 (14-17) 11 (09-12) lt0001 253 566 593 0383

p-value (age) - 0002a lt0001

a - 0006

b 0309

b

a) Differences between means were tested with unpaired t-test (sex) or ANOVA (age) b) Differences in distributions were tested with a Chi

2-test

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

8

Fig 3 Unstandardized mean saliva flow rate with 95 CI in (A) men and (B) women)

Age

20 30 40 50 60 70 80

mL

min

00

05

10

15

20

Age

20 30 40 50 60 70 80

mLm

in

00

05

10

15

20

for p-005 and for plt001 for plt0001 when compared to all other age groups

Fig 4 Percentage of study subjects with low buffer capacity pH lt55 for (A) men (B) women)

for p-005 and for plt001 for plt0001 when compared with 1983

Thirty year time trends in saliva flow rate

Sex and age standardized means for saliva flow rates for all subjects differed significantly between the

screening years but they did not follow a linear trend over time (Fig 5A) The same pattern was seen

when men and women were analyzed separately with standardization for age (Fig 5B) and in sex and

age strata (data not shown) Thus mean flow rates in 1993 were significantly higher than in 1983 and

then again lower in 2003 and 2013 compared to 1993 Standardization for sex and age had very limited

effect on the mean values ie only the second decimal was affected compared to the means from the

univariate analyses

A B

A B

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

9

Fig 5 Mean (95 CI) of saliva flow rate by study year for (A) all subject and with standardization for age and sex and (B) for men and women standardized for age

Screening year

mLm

in

00

12

14

16

18

20

22

1983 1993 2003 2013

A

Screening year

mL

min

00

12

14

16

18

20

22Men

Women

1983 1993 2003 2013

B

for plt0001 compared to all other screening years

Identification of factors associated with saliva flow rate

As a final step all variables were included in multivariate PLS modeling to identify variables that were

associated with the saliva flow rate The PLS analysis identified that having a low buffer capacity being

a woman experiencing a feeling of dryness in the mouth having less occlusal support zones (Eichner

index) and having more daily meals of food was significantly associated with having a low saliva flow

rate whereas having more teeth was associated with higher saliva flow rate (Figs 6 7)

Variables indicated to be influential for flow rate by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 3) It was confirmed that

women had significantly lower flow rate than men as did subjects with low buffer capacity (pH lt55)

versus those with ldquonormalrdquo (pH ge55) capacity In addition mean flow rate decreased by increasing

experience of dry mouth and decreasing Eichner index but only those who had the highest number of

meals per day had had a significantly lower flow rate than others (Table 3)

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

10

Fig 6 Scatter plot of the relation between saliva secretion and the other variables of the study population

Fig 7 Coefficient plot of the correlation of stimulated salivation and other variables Where the error bars do not pass through the zero the correlation is significant (p lt005)

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

11

Table 3 Sex andor age standardized measures for variables identified as influential for saliva flow rate in the multivariate PLS model all screening years

Stimulated salivation mLmin mean (95 CI)

p-value between groups

Gender lt0001

Men (n=1178) 173 (168 ndash 179)

Women (n=1271) 148 (142 ndash 153)

Buffer capacitya lt0001

pH 55 and above (n=1108) 179 (174 ndash 185)

Below pH 55 (n=1267) 145 (140 ndash 150)

Subjective xerostomia lt0001

Never (n=904) 172 (167 ndash 178)

Occasionally (n=1215) 155 (150 ndash 161)

Often (n=200) 145 (132 ndash 158)

Always (n=31) 125 (092 ndash 158)

Number of teeth lt0001

0 to 4 (n=157) 128 (112 ndash 144)

5 to 9 (n=81) 122 (101 ndash 143)

10 to 14 (n=77) 124 (102 ndash 145)

15 to 19 (n=172) 130 (115 ndash 144)

20 to 24 (n=446) 150 (141 ndash 159)

25 to 28 (n=1516) 174 (168 ndash 179)

Eichner index lt0001

Class A (n=1777) 171 (166 ndash 175)

Class B (n=438) 133 (123 ndash 143)

Class C (n=227) 130 (116 ndash 143)

Daily meals 0013

One (n=142) 163 (147 ndash 178)

Two (n=711) 157 (150 ndash 164)

Three (n=1060) 164 (158 ndash 169)

Four (n=369) 159 (149 ndash 169)

Five or more (n=53) 120 (095 ndash 145) aThe analysis method changed between study years (see Method section)

Thirty years time trends in buffer capacity

Due to the shift in analysis method for buffer capacity estimation only measures from 1983 and 1993

could be compared and those from 2003 and 2013 As seen in Table 4 the proportion of individuals

with a low buffer capacity (pHlt55) was significantly higher in 1983 than 1993 and were lower in 2003

compared to 2013 To evaluate if the lower proportion of subjects in 1993 versus 1983 was associated

with saliva flow rate the saliva flow rate was compared in 10-year age groups of men and women with

a buffer pH lt55 and those with a buffer pHgt55 (Fig 8 AB) In 8 out of 14 strata mean flow rate was

significantly higher in those with buffer pH gt55 than those with a buffer pH lt55 For some of the age

groups a significant difference between buffer capacity and years are observed (Fig 4)

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

12

Table 4 Proportion () with a saliva buffer capacity pH lt55

Study year 1983 Study year 1993 p-value

1983 vs 1993

Study year 2003 Study year 2013 p-value

2003 vs 2013

Analysis method

Ericssonrsquos laboratory test

Ericssonrsquos laboratory test Dentobuff strip

GC Saliva Check Dentobuff strip

Men 593 783 lt0001 254 288 0218

Women 667 881 lt0001 320 353 0228

Differences in proportions are tested with a Chi2-test Significances are tested by t-test

Fig 8 Mean (95 CI) of saliva flow rate in (A) men (n=1149) and (B) women (n=1229) with buffer pH lt55 or

ge55 all screening years

for p-005 and for plt001 for plt0001

Identification of factors associated with buffer capacity

When all measured variables were included in a multivariate PLS model with low or ldquonormalrdquo saliva

buffer capacity as the dependent variables study year periodontal health a higher saliva flow rate

not being a smoker and number of teeth were significantly associated with having a normal buffer pH

(Fig 9) whereas less occlusal support zones (Eichner index) was associated with low buffer capacity

Variables indicated to be influential for buffer capacity by PLS were followed up in univariate

comparisons with standardization for age and sex as appropriate (Table 5) Thus more subjects had

low buffer capacity among those with low saliva flow rate among those with the moderate degree of

periodontal disease among smokers and those with the poorest Eichner index (Table 5)

A B

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

13

Fig 9 Coefficient plot of the correlation of buffer pH Negative numbers equals to higher buffer pH Where the error bars do not pass through the zero the correlation is significant (p lt005)

Table 5 Sex andor age standardized measures for variables identified as influential for saliva buffer pH in the multivariate PLS model Proportion of subjects with

buffer pH ge55 p-value between

groups

Saliva secretion lt0001

ge 10 mLmin (n=1818) 844

lt 10 mLmin (n=557) 697

Periodontal health classification lt0001

Healthy (n=441) 444

Gingivitis (n=508) 411

Periodontitis levis (n=589) 430

Periodontitis gravis (n=228) 417

Periodontitis complicata (n=93) 495

Smoking lt0001

Smoker (n=1852) 391

Non-smoker (n=445) 494

Number of teeth lt0001

0 to 4 (n=152) 309

5 to 9 (n=80) 288

10 to 14 (n=75) 347

15 to 19 (n=170) 388

20 to 24 (n=438) 418

25 to 28 (n=1463) 522

Eichner index 0013

Class A (n=1719) 518

Class B (n=430) 349

Class C (n=223) 296

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

14

DISCUSSION

The present study evaluated if saliva flow rate and saliva buffer capacity has changed in the

population from 1983 to 2013 and searched for factors associated with saliva flow rate and having a

poor or acceptable saliva buffer capacity respectively The main findings were that the present data

do not support the hypothesis that saliva flow rate has changed over the 30-year period but the

proportion with poor saliva buffer capacity tended to have increased between 1983 and 1993 where

the same analytic method was used

The strengths of the present study include that (i) all clinical assessments and samplings were

performed by experienced and calibrated dentists in well-equipped dental offices at all screening

rounds (ii) that the method for saliva collection was identical at each screening occasion and (iii) that

participants were randomly selected from population registers and represented a wide age range

Besides the weaknesses of a change in the buffer analysis method it is a weakness that stratification

for sex and age resulted in small groups in relation to the variation in the population This is especially

true for the higher age groups Further it cannot be excluded that the decreasing attendance rate ie

772 754 69 and 564 has resulted in an increasing selection bias The examination was free

for the participants but even with free screenings the attendance by those having a low socio-

economical background is lower compared to others (Zarrouk et al 2013) Another group that is likely

to not have attended for time reasons are busy healthy people which in fact is supported by that

extra subjects had to be invited in 2013 to get an acceptably sized group in middle-aged individuals

For the present study it can only be speculated on the potential selection bias but it may be

anticipated that health concerned subjects and those with an oral health related problem (including

dry mouth) are overrepresented in later years compared to in 1983 and 1993 when gt75 attended the

screening but that subjects with a socioeconomically weak background and worse dental status (but

not necessarily impaired saliva flow rate and buffer capacity) might be underrepresented (Wamala et

al 2006)

The incitement for the present longitudinal evaluation of saliva flow rate was that mean saliva

flow rates of 25 and 20 mLmin were reported for men and women respectively in a screening

performed in 1995 (Bergdahl 2000) The screening was based on approximately 1400 Swedish adults

Those flow rates were considerably higher than values reported in studies from the 1970ies (Heintze et

al 1983) It was plausible to hypothesize that the mean flow rate had increased in the population

given that the number of teeth had increased people were on average taller (an overall larger

anatomy and physiology thus larger glands) and many medications inhibiting saliva secretion were

over the years substituted for non-inhibitory alternatives Notably the flow rate in 1993 was higher

than in 1983 and approached the levels reported by Bergdahl (2000) It was therefore surprising to

find that the mean flow rates were again close to the 1983 levels in 2003 and 2013 Collection of

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

15

chewing stimulated saliva is a very well standardized and easy-to-perform measure which makes the

variations in flow rate hard to explain with anything but a selection bias in later screening years or

regression towards the mean Still it seems unlikely that two independent screenings performed in

the same time window (early 1990ies) and giving a very similar result would be influenced by the same

bias or systematic error However at present the conclusion is that the present data do not support

that the saliva flow rate has increased in the population over time but future large scale population-

based studies have to follow up on this The implication of an increased salivation paired with a lower

buffer capacity of the same saliva might confer the need of adjusted cut off values when it comes to

normal or sub-normal saliva flow rate or a completely new way of measuring the properties of saliva

as this would imply that even though the saliva flow rate increased its buffering capacity would have

decreased

A common finding in medical studies is that different measures are not independent ie body

weight is correlated with height saliva flow rate is correlated with buffer capacity number of teeth is

correlated with Eichner index etc This is an obstacle in traditional linear or logistic regression In the

present study the multivariate projection method PLS was selected The rational for choosing that

method is that it is insensitive to covariation among variables and it works well also in smaller samples

The drawback is that it does not report standardized central measures and variation Therefore PLS

was followed up with separate analyses where standardization for age andor sex was applied

As described the method for saliva buffer capacity was changed in 2003 The rational for this was

to save manpower since the Ericsson method need laboratory personal and logistics when it comes to

transporting the saliva When comparing the proportions with low buffer capacity in 1993 with 2003

and 2013 it is evident that the two methods did not perform as well as claimed by Cheaib et al (2012)

The comparisons for this factor were therefore done with greatest restriction ie dichotomized to

poor or good

The factors associated with saliva flow rate ie sex age in women subjective xerostomia

number of teeth occlusal support zones and buffer capacity are in accordance with what has been

reported in previous studies (Ikebe et al 2012 Heintze et al 1983) Thus though the results in the

present study are mainly confirmatory they are of significant clinical importance Subjective

xerostomia is not an explanatory factor but rather a symptom of possible hyposalivation Notably

both number of teeth and Eichner index correlated with stimulated saliva secretion a finding that

should be remembered when choosing between the options of extracting a tooth or save it Thus

quality of life and medicalbiological aspects must be considered and likely more so in patients with

impaired saliva secretion those taking medicine causing hyposalivation those that have short dental

arches or previous extractions or tooth aplasia One may speculate if fixed prosthodontics should be

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

16

encouraged in patients with lost teeth to improve the occlusal support zones and hence saliva

secretion Further studies are needed to evaluate this

CONCLUSION

The present study found chewing stimulated saliva secretion to be associated with sex number of

teeth Eichner index subjective dry mouth and buffer capacity but it does not support that saliva

secretion has increased over time in the population Saliva secretion and its buffer components is of

outmost importance for the oral environment Hyposalivation and an associated low buffer capacity

puts a person at risk for both dental diseases and oral infection including candida infections and

overall health problems as acute respiratory infection (Iwabuchi et al 2012) and an increase over time

might reduce the risk Given that several factors associated with improved saliva flow rate has taken

place in the population future studies should follow up on the results to confirm or reject that the

present results are not due to a selection bias

ACKNOWLEDGEMENTS

Prof Ingegerd Johansson DDS PhD without whom this essay could not have been written

The personal support of Dr Elisabeth Waumlrnberg Gerdin DDS PhD

The board of the Joumlnkoumlping Studies especially the chairman Dr Ola Norderyd DDS PhD

The County Council of Vaumlsterbotten who allowed me to take time to write this essay

17

REFERENCES

Bardow A Lagerloumlf F Nauntofte B Tenovuo J The role of saliva In Fejerskov O Kidd E (eds) Dental

Caries The Disease and Its Clinical Management 2nd

ed Oxford Wiley-Blackwell 2008 189-208

Bergdahl M Salivary flow and oral complaints in adult dental patients Community Dent Oral Epidemiol

20002859-66

Birkhed D Heintze U Salivary secretion rate buffer capacity and pH In Tenovuo J (ed) Human

Saliva Clinical Chemistry and Microbiology Vol I Boca Raton (FL) CRC Press 1989 25-73

Carpenter GH The secretion components and properties of saliva Annu Rev Food Sci Technol

20134267-276

Cheaib Z Ganss C Lamanda A Turgut MD Lussi A Comparison of three strip-type tests and two

laboratory methods for salivary buffering analysis Odontology 201210067-75

Dawes C Wood CM The contribution of oral minor mucous gland secretions to the volume of whole

saliva in man Arch Oral Biol 197318337-342

Edgar M Dawes C OrsquoMullane D (eds) Saliva and Oral Health 3rd

ed London British Dental

Association 2004

Eichner K Uumlber eine gruppeneinteilung der luumlckengebisse fuumlr der prothetik Dtsch Zahnaumlrztl Z 1955

101831-1834

Ekstroumlm J Autonomic control of salivary secretion Proc Finn Dent Soc 198985323-331 361-363

Ericsson Y Clinical investigations of the salivary buffering action Acta Odontol Scand 195917131ndash

165

Fujibayashi T Sugai S Miyasaka N Hayashi Y Tsubota K Revised Japanese criteria for Sjoumlgrens

syndrome (1999) availability and validity Mod Rheumatol 200414425-434

Garbacz G Kołodziej B Koziolek M Weitchies W Klein S An automated system for minitoring and

regulating the pH of bicarbonate buffers AAPS PharmSciTech 201314517-522

Heintze U Birkhed D Bjoumlrn H Secretion rate and buffer effect of resting and stimulated whole saliva as

a function of age and sex Swed Dent J 19837227ndash238

Hugoson A Koch G Bergendal T Hallonsten AL Laurell L Lundgren D et al Oral health of individuals

aged 3-80 years in Jonkoping Sweden in 1973 and 1983 I A review of findings on dental care

habits and knowledge of oral health Swed Dent J 198610103-117

Hugoson A Koch G Bergendal T Hallonsten AL Slotte C Thorstensson B et al Oral health of

individuals aged 3-80 years in Jonkoping Sweden in 1973 1983 and 1993 I Review of findings on

dental care habits and knowledge of oral health Swed Dent J 199519225-241

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O Sjoumldin B Sondell K Oral health

of individuals aged 3-80 years in Joumlnkoumlping Sweden during 30 years (1973-2003) I Review of

findings on dental care habits and knowledge of oral health Swed Dent J 2005a29125-138

Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

aged 3ndash80 years in Jonkoping Sweden during 30 years (1973ndash2003) II Review of clinical and

radiographic findings Swed Dent J 2005b29139ndash155

17

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Hugoson A Koch G Goumlthberg C Helkimo AN Lundin SA Norderyd O et al Oral health of individuals

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