The Mandibuiar Speech Envelopein Subjects with and without

Incisai Tooth WearC. Andrew Burnett, BDS, FDS RCPS, PhDThomas J. Clifford, BDS, FDS RCPS,

Purpose: The purpose of ihis study was to describe a mandibular envelope of motionduring speech for 2 subject groups. One subject group had experienced no tooth wear andthe other had incisai tooth wear. The speech envelope was to be described with regard toits maximal dimensions in the vertical, anteroposterior, and lateral directions, and its mostsuperior and anterior positions in relation to intercuspal position. Materials and Methods;An electromagnetic method of jaw tracking was employed to record mandibular speechmovements for 60 subjects whose teeth exhibited no tooth wear and 30 subjects withincisai dental attrition. The test speech exercise contained all of the word sounds thatoccur in the Engiish language. The test was recorded 3 times, and mean values forparameters were reported. Results: The speech envelope of the tooth wear group wassignificantly smaller (Student's (test, P < 0.01) in all 3 dimensions than that of the normalgroup. The tooth wear group speech envelope was also located closer to the intercuspalposition in the vertical dimension {P< O.OI) and was not as anteriorly placed [P< 0.01). Inthe normal group, correlations were found between the vertical incisor overlap and themosL superior speech position {r- 0.48, P< 0.0001), and between the horizontal incisoroverlapand the most anterior mandibular speaking position ( r= 0.63, P< 0.0001).Conclusion: The envelope of mandibular movement during speech differed in dimensionand position between the 2 groups investigated. Int J Prosthodont 1999;'!2:514-518.

In the management of dentate and edentulous pa-tients, valuable clinical information such as anterior

tooth position, incisai guidance, and occlusal verticaldimension may be rendered by an assessment of

'Clinical Lecturer, Division of Restorative Dentistry, School ofClinical Dentistry, The Queen's University of Beifast, NorthernIreland.''Senior Lecturer and Consultant, Division of Restorative Dentistry,School of Clinicai Dentistry, The Queen's University of Belfast,Beifast, Northern Ireland.

Reprint requests: Dr C. A. Burnett, Division of RestorativeDentistry, School of Clinical Dentistry, The Queen's University ofBelfast, The Royai Croup of Hospitais, Grosvenor Road, BelfastBTU 68P, Northern ireland. Fax: + 44-1232-438861. e-mail:c.burnett@quh.ac.uk

mandibular positions assumed during speech.'^ Toothwear, the noncarious loss of tooth tissue, often neces-sitates restorative intervention, and although it seemsto be commonly accepted that the condition is on theincrease, data on its prevalence are limited. It hasbeen suggested that more than 5% of tootb surfaces,rising to nearly 9% in tbe oldest age group, are unac-ceptably worn.^ When this is considered with the in-crease in longevity and tooth retention, concerns areraised regarding future restorative needs. Tooth wearbas a multifactorial etiology in which attrition, a phys-ical process whereby tootb substance is removedthrough the movement of teetb against one another,has been shown to be contributory to pathologic wearin 27% of referred cases. Attrition usually occurs overa sufficient period of time to allow physiologic mech-anisms to operate in compensation for loss of occlusal

The international lournai or Proiiliodoolics 5 1 4 • 12, Number 6,1°

Burnett/Clilíord Mandibular Speecii Envelope witii and wlihout incisai We

vertical dimension,^-^ This can greatly complicatedental management with regard to providing space forrestorative materials.

Mandibular movement during oral functions in-volving occlusal contact is influenced by the form ofthe occlusion and may be affected by changes of it,'"Investigations have also shown that age and changesin dental condition may affect oral motor func-tion.' '-' ^ Speech movements, although not reliant onocclusal contact, are nonetheless affected by anom-alous ¡aw and occlusal relations.'-"^

The purpose of this study was to describe the 3-di-mensional limits of the mandibular envelope of mo-tion during speech and its most superior and anteriorpositions. Two subject groups were investigated, agroup without tooth wear and a group with incisaitooth wear caused by attrition.

Materials and Methods

A total of 90 individuals participated in tbe study. Nosubject suffered any speech defect or exhibited anysigns or symptoms of dysfunction of the masticatorysystem. The first subject group, the so-called normalgroup, comprised 30 female and 30 male dental stu-dents. Their mean age was 22 ± 1 years, ranging from20 to 25 years. All had intact dentitions, and althoughsome subjects in this group had evidence of loss ofenamel surface characteristics, such as on tbe caninecusps, for the purposes ofthis investigation this groupwas assumed not to have suffered tooth wear. The in-cisor relationship of each subject was recorded andclassified''^ on the basis of contact of the mandibularincisors, or a continuation of their axial plane, with thepalatal surface of tbe maxillary incisors when oc-cluding in the intercuspal position (ICP). The compo-sition of this subject group, with regard to relativenumbers ofthe 4 different incisor relationship classes,was determined to closely reflect an average ofthatreported for a young British population,'^"'^ whichwas taken as tbe accepted standard for the study.Random allocation, from a total sampling frame of 80subjects, to each ofthe 4 incisor subgroups suppliedthe makeup of the final subject group, with 26 ClassI, 17 Class II division 1,12 Class II division 2, and 5Class III subjects. There was no statistically significantproportional difference (Chi-squared) in relation to in-cisal classification between the subject group and theaccepted standard. The magnitude of incisor overlapin ICP, in the vertical and horizontal dimensions, wasrecorded using a millimeter rule.

The second study group, the so-called tooth weargroup, comprised 30 consecutive consenting sub-jects who fulfilled tbe selection criteria and were re-ferred for dental management by their general

dental practitioner to a hospital tooth wear clinic. Thecriteria for selection to the tooth wear group was thateach subject retained all of their incisor teeth and thatthese teeth had tooth wear, of approximately at least'/i of the crown height, for which attrition was diag-nosed as the major etiologic factor. The group wasmade up of 23 men and 7 women, a ratio that re-flected the overall attendance pattern at this clinic.Their mean age was 49 ± 9 years, ranging from 34 to63 years. All 30 subjects had an edge-to-edge incisairelationship in ICP.

Jaw movements were recorded using a Sirognatho-graph (SCG, Siemens!. The SGC was connected to acomputerized system (Bio-Pak, ßio-Research Asso-ciates) that recorded and displayed, to the nearest 0.1mm, spatial coordinates in 2 planes: frontal (verticaland lateral dimensions! and sagittal (anteroposteriorand vertical dimensions!. The system has beenshown-" to have linear output for up to about 40 mmof vertical displacement when lateral movement isless than 10 mm, and these conditions were fulfilledin this study.

Mandibular movement was recorded as subjectsread a 106-word test passage of text closely modeledon that suggested by Kestenberg,^' The passage con-tains all ofthe phonemes that occur in the English lan-guage, and the frequency of their occurrence in theparagraph is approximately the same as their relativefrequency in conversational English.

How are you Tom Dope? and no oranges are growing inMexico and it is nice to see my grandfather swim abouthere and George dependí on Ruth to bake a big lemoncake and roses are red and violets are blue and three lash-ings won't hurt poor old Dick and Tim show Harry whereto wash your clothes tub and Wednesday will be a laughfor all otusand the sixty five fast trucks leave the zoo eachyear and perhaps you need to fire the man in England tooandsweet Peggy Nun caught that fur hat and the childrenweren't catching anything.

The speech test was verbally demonstrated for pro-nunciation and rate and volume of speech. The latter2 parameters were described as being of normal con-versational speech and subjects were given a fewminutes to rehearse the tests. The SCG headset wasmounted and aligned with the subject seated uprighton a plastic chair with the head firmly supportedagainst the rear chair support. Subjects were instructedto keep their head as steady as possible during record-ing. Recording artifacts caused by head movement ordisplacement ofthe antenna device may occur whenusing the SCG. - ^ For this reason, movements oftheheadset were checked for by inspection and by hav-ing subjects start and finish each test at the referencepoint, ICP as identified onscreen; discrepancies were

^ Volume 12, Number 6,1999 5 1 5 The Internatiorüil íournsl oí Proslhodonlics

MandibuisrSpeecii Envelope with and wilhout incisai Wear Bumett/Clifford

Table 1 Dimensions ot the Speech Envelope and Its Most Superior and AnteriorPositions for the Normal and Tooth Wear Groups (mm)

Normal group (n = 60) Tooth waar group (n = 30)

Speech envelope di

AnteioposleriOfLaterai

Speech position

Anterior

Mean

imensions10,9'5.2'3 , r

2,2*1.9'

SD

2,61 61,0

1.31,9

Range

5,8-16,02.4-9.81,3-S.6

0-7.0-2.8-11 1

Mean

9,r4,r2,1-

1,0'0.5'

SD

1.3

0,91.7

Range

0.1-3,6-2.3-5.2

•Significant aifterence between groups (Student's (test. P i 0,01).SD = star a ara deviation.

Table 2 Dimensions of the Speech Envelope and Its Most Superior and AnteriorPositions for the 4 Incisai Subgroups of ttie Normal Group (mm)

Class I(n - 26)

Class II div 1(n = 17)

Ciass li div2(n = 12)

Class III(n = 5)

Mean

Speech envelope dimensionsV ártica iAnteroposteriorLaterai

Speech positionSuperiorAnterior

11,35 23.4

2,21,8

SD

2.51.51,0

1,10,8

Mean

11 75 73,4

2,33,3'

SD

2,31,70,9

0,72,5

Mean

9,94.82.6

2,30,7

SD

2,82.00,8

1.31.6

Mean

8,84,52,5

0.9-0.5

SD

2,11,00,9

0,7C.7

'Signiticant diftererice among groups (ANOVA, P< (),0t¡,SD = standard deviation.

seldom found, bul when they were, the recordingwas repealed. The influence of recording and subjectvariability has been previously investigated-"'with re-gard to speech movements, and these were shown tobe reproducible after a &-month time intervai. Thesame method was employed in this investigation. Foreach subject, 3 recordings of jaw movement weremade and mean values were calculated for each pa-rameter. The mandibular envelope of motion duringspeech was described as the maximum range of move-ment in the vertical, anteroposterior, and lateral di-mensions recorded during recitation ofthe test. It wasfurther described in relation to its most superior andanterior positions. The mandibular position that cameclosest to ICP in the vertical dimension during the ex-ercise was taken to represent the superior speaking po-sition. The most anterior mandibular position assumedin relation to ICP was taken to represent the anteriorspeaking position. Those positions in the anteropos-terior dimension that were posterior to ICP were la-beled with a negative value.

Statistical anaiysis was performed by 2 group un-paired Student's itests and analysis of variance(ANOVA) multiple comparison tests using the Scheffécriterion, with Pvalues less than 0.01 interpreted asstatistically significant.

Results

There was a difference in the size of the speech en-velope between tbe normal and the tooth wear groups(Table 1), with that of the latter being significantlysmaller in all 3 dimensions (P < 0,01), The toothwear group also demonstrated a smaller superiorspeaking position and anterior speaking position thanthe normal group (P< 0,01) (Table 1), with theirspeech envelope located closer to ICP in the verticaldimension and being more posteriorly placed.

Of the 4 incisai subgroups of the normal group,there was a trend for the dimensions of the recordedparameters ofthe Class III incisai group to be smaller,although this was only supported statistically forsuperior speaking position (P< 0,01) (Table 2), Theanterior speaking position of the Class II division 1subgroup was found to be significantly more anteriorthan the other incisai subgroups (P< 0,01),

The correlation ofthe normal group's vertical in-cisal overlap in ICP with their superior speaking po-sition was significant (r - 0,48, P < 0,0001 ) (Fig 1 ),There was also a significant linear relationshipdemonstrable between this group's horizontal incisaioverlap and their anterior speaking position (r= 0,63,P<0,0001)(Fig2),

The Inlernationai i of Prosthodontics 516 Volume 12, Number 6,

Burnett/Clifford

E

i

king

srio

r sp

ea

dng

8

6

4

2

0 2

•

1

•

t

>1

f -0 .48

•

4 6 S 10 12

Vertical incisor overlap (mm)

Mandibular Speech Envelope willi and without Incisai Wear

E

ositi

orak

ing

p

Q.

c

12

10

8

6

4

2

-2

— 1 -0 2 4

Horizontal incisor

r = 0

6 8

oveFlap [m m)

3

fO

Fig 1 Superior speaking position correlated with verfioal incisoroveriap

Fig Z Anterior speaking posifion correlated with horizontai in-cisor o ierlap

The norfnal group results were analyzed with re-spect to gender regarding speech envelope dimen-sion5, superior speaking position, anterior speakingposition, and incisai classification. No statistically sig-nificant difference for any of these variables wasfound between the male and female subjects.

Discussion

A speech envelope has been previously docu-mented,-^ with mean dimensions for 95 subjects re-ported as 8,3 mm vertical, 4.2 mm anteroposterior, and1,6 mm lateral. These values are slightly smaller thanthose found in the current study. The proportion oftheincisai Class III group in the previous study^^ was20%, compared to 8% in the current study, and as thisgroup displayed a trend to have a smaller speech en-velope, this may be reflected in the former result, A lim-itation of the current work, however, is the small num-ber of subjects in the Class III group. In completedenture design it has been advocated'"" that posi-tioning the anterior teeth when pronouncing closespeech sounds, such as the /S/ sound, with a verticalor "closest speaking" space hetween them of 1 to 2 mmwill achieve a satisfactory functional occlusal verticaldimension. This technique is based on the assumptionthat it reflects the anterior tooth relationship ofthe nat-ural dentition during pronunciation ofthe close speechsounds. The/S/sound has heen shown to clinically

produce the most superior incisai speaking position,^^However, the presence of a natural vertical incisai sep-aration greater than the vertical overlap ofthe anteriorteeth during/S/production is not supported by the lackof a strong correlation between these parameters foundin the current or previous studies,'"*- ' ® The implica-tion for prosthodontics is that by using commonly em-ployed speech techniques^"* in designing the physio-logic rest interocclu.sal distance, an excessive spacemay be produced. Therefore, we suggest that it isprobably sufficient to ensure only that the anteriorteeth do not contact during speech function.

Comparisons between the 2 subject groups are con-tentious because of their disparity, and the observedsignificant differences hetween them cannot be said tobe solely a result of tooth wear. Some of the factors thatmay have had an effect are age, gender, original or ha-bitual dental relationships, dental condition, andrecording variability. The latter parameter was dis-cussed above. Only a few studies have recorded pa-rameters of jaw movement as a measure of oral motorfunction specifically in relation to age."''^ These stud-ies, comparing elderly subjects (mean age 8f] y) toyounger subjects (mean age 26 y), concluded that agerather than the state of the dentition is related to areduction in some aspects of oral motor function. Inthe current study, the age difference between the 2 sub-ject groups, mean 49 versus 22 years, was not somarked as in these previous studies, but the effect of

Volume 12, t^umber 5,1999 5 ^ 7 The International fournal of Prosthodontics

Mandibuiar Speech Envelope with and without Incisai Wear 3urnetl/Clif!ord

an age-related diminution of speech movements can-not be dismissed. There were no apparent gender dif-ferences with respect to the dimensions and positionofthe speech envelope within the 2 study groups, andthis is ¡n agreement with a previous study.^^ Althoughthere was a preponderance of male subjects in thetooth wear group, which reflects the patient presenta-tion pattern in the hospital clinic from which theywere selected, the reduction in the size of the speechdimensions of the tooth wear group wai thought notto be caused by the gender distribution. Although aneffort was made in the method of the investigation tomake the normal group representative with regard toincisai relationships, this was not possible with thetooth wear group. An asse^ment of the original incisaiclassification could not be made because of the ante-rior tooth destruction, and all subjects in the toothwear group showed a habitual edge-to-edge anteriortooth relationship ¡n ICP. This was reflected in the di-mensions and position ofthe speech envelope, whichresembled that of the Class III normal group. Eachspeech sound requires a particular articulator formatthat is the result of a specific learned neuromuscularpattern. However, as the form of a speech sound ar-ticulator changes, such as with wear of the anteriorteeth, so compensatory changes in the structural for-mat of other articulators, such as the tongue andmandibular position, may occur. It is intended that fur-ther studies be carried out to compare speech move-ments in older, age-matched cohorts with heaithy andworn teeth, and in subjects before and after oral reha-bilitation.

Conclusion

Within the limitations ofthe study design, it was con-cluded that; (1) the envelope of mandibular move-ment during speech differed in dimension betweenthe 2 groups investigated, with that ofthe tooth weargroup being smaller; and ('2Jthe most superior and an-terior speech positions of the tooth wear group werecloser to ICP than those of the normal group.

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The Inter rial i on 31 journal of Prosthodontii 518