University of Groningen

Effects of dental implants on hard and soft tissuesTymstra, Nynke

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32

Chapter 3

Anteriormaxillaryresidualridgeresorptionandposteriorresidual ridge resorption in patients with an implant-retained mandibular overdenture compared to patients with a conventionalmandibulardenture;a10-yearprospectivestudy

This chapter is an edited version of the manuscript:

TymstraN,RaghoebarGM,VissinkA,MeijerHJA.

Anteriormaxillaryresidualridgeresorptionandposteriorresidualridgeresorptioninpatients

with an implant-retained mandibular overdenture compared to patients with a conventional

mandibulardenture.A10-yearprospectivestudy.

Submitted

33

Abstract

AimThepurposeofthisstudywastocomparetheeffectofanimplant-retainedmandibular

overdenture on 2 or 4 dental implants with the effect of a conventional denture on resorption

oftheresidualridgeoftheanteriormaxillaandposteriormandibleoveraperiodof10years.

Material and methods In total 120 patients, 30 patients treated with an overdenture on 2

implants (two-implantgroup),30patientswithanoverdentureon4 implants (four-implant

group) and 60 patients treated with a conventional full denture (conventional group),

participatedinthisstudy.Allpatientshadaconventionalmaxillarydenture.Onpanoramic

radiographs,madebeforeand10yearsaftertreatment,proportionalareameasurementswere

applied to determine changes in bone height.

Results After 10years, a statistically significant amount of bone resorptionhad occurred

intheanteriormaxillainthetwo-implantgroupandinthefour-implantgroup(p=0.003and

p=0.004respectively).Asignificantamountofboneresorptionhadoccurredintheposterior

mandible in all three groups (two-implant group: p<0.001, four-implant group: p=0.006,

conventionalgroup:p=0.011).Therewerenostatisticallysignificantdifferencesbetweenthe

groups in both areas. Patients presented large individual differences. No correlation was found

betweenresorptionoftheresidualridgeoftheanteriormaxillaandposteriormandible.

Conclusions Patients rehabilitated with implant-retained mandibular overdentures are

not subjected tomore residual ridge resorption in the anteriormaxilla when compared to

patients wearing a conventional full denture. Regarding the mandibular posterior residual

ridge, resorption was irrespective of wearing an implant-retained mandibular overdenture or a

conventional mandibular denture.

3434

Introduction

Edentulouspatientsoftenexperienceproblemswiththeirdentures.Maincomplaintsarelack

ofstabilityand retentionof theirdentures, togetherwithadecreasedchewingability (Van

Waas,1990).Animplant-retainedoverdentureisatreatmentpossibilitywhichimprovesoral

function, chewing force and comfort for edentulous patients and eliminates a substantial part

oftheproblemswhichedentulouspatientsexperience(Boerrigteretal.,1995;Fontijn-Tekamp

etal.,1998).Althoughimplant-retainedmandibularoverdenturesastreatmentpossibilityhave

beenexaminedthoroughlybyseveralstudygroups,mostarticlespredominantlyfocusonthe

effectoftreatmentonthemandibleandonlyafewarticlesfocusontheeffectoftreatment

ontheresorptionpatternsinthemaxilla(Barberetal.,1990;Jacobsetal.,1993;Lechner&

Mammen,1996;Narhietal.,2000;Kreisleretal.,2003).

In previous studies it was suggested that the chance of developing the so-called combination

syndrome,asobserved inpatientswithanedentulousmaxillaopposingashorteneddental

arch in combination with a prosthetic device in the mandible, increases in persons wearing

mandibular implant-retainedoverdentures (Barber etal., 1990; Jacobsetal., 1992; Lechner

&Mammen,1996).Thefive symptoms that commonlyoccur in the combinationsyndrome

are(1)lossofbonefromtheanteriorpartofthemaxillaryridge,(2)developmentoffibrous

or bony enlargements of the tuberosities, (3) papillary hyperplasia of the hard palate, (4)

extrusionof themandibularanterior teethand (5) reductionofmandibularbonebeneatha

mandibulardistalextensionofaremovablepartialdenture.Saundersetal.(1979)haveposed

thatthecombinationsyndromestartswithresorptionoftheposteriormandibularresidual

ridge.Consequently,thisresorptionisthoughttograduallyresultinalossofposteriorocclusal

loadandanincreaseinanteriorocclusal load.Thisincreasedanteriorloadingmayresultin

resorption of the anteriormaxillary residual ridge. Similar oral changes alsomay occur in

patientswearinganimplant-retainedmandibularoverdenture.Asaresultofabuilt-inpossibility

of rotation in the implant-retained mandibular overdenture a similar unfavourable distribution

ofocclusal loadof theposteriormandibleandanteriormaxillamightexist.Kordatzisetal.

(2003) refuted this hypothesis in their study investigating the degree of resorption of the

posterior mandibular residual ridge under conventional dentures and mandibular overdentures

supportedby2 implants.Their resultsshowedthat theyobserved less resorptionunderan

overdenturethanunderaconventionaloverdenture.Similarly,Wrightetal. (2002)reported

Chapter 3

35

low rates of posterior mandibular ridge resorption for patients rehabilitated with a stabilised

removable prosthesis and even bone apposition in the posterior mandibular area in patients

withafixedprosthesis.

Studiesfocusingonthemaxillashowcontradictingresults.Nährietal.(2000)concludedthat

thedecreaseinthewidthofthemaxillaryresidualridgeissmallandindependentofthetype

of mandibular denture, being an implant-supported overdenture on 5 implants, an implant-

mucosa-supported overdenture and a conventional denture. Other studies demonstrated a

higherannualmaxillaryresidualridgeresorptioninpatientswearingaconventionaldenture

thaninpatientswearinganimplant-retainedmandibularoverdenture(Jacobsetal.,1993;Abd

El-Dayemetal., 2007), or reportedon significant vertical bone loss in theanteriormaxilla

inpatientswearinganimplant-retainedmandibularoverdenture(Barberetal.,1990;Kreisler

etal.,2003).Finally,fromasystematicreviewitwasconcludedthat,althoughtheliterature

isvery limited, therewasnoevidence thatmaxillary ridge resorptionwasacceleratedwith

implant-retainedmandibularoverdentureon2implants(Rutkunasetal.,2008).

There are no studies to date, however, comparing resorption of the residual ridge of the

anterior maxilla and posterior mandible in patients treated with either implant-retained

mandibular overdentures on two or four dental implants, or conventional mandibular dentures.

Therefore,thepurposeofthisstudywastoassesstheeffectofanimplant-retainedmandibular

overdenture on two or four dental implants and a conventional denture on resorption of the

residualridgeoftheanteriormaxillaandposteriormandibleoveraperiodof10years.

Materials and Methods

Patient selection

Forthisstudy,panoramicradiographs(Orthopos,Siemens,Bensheim,Germany)thathadbeen

madeaccordingtoprotocolbeforeand10yearsafterprosthodontictreatmentwereavailable

of 3 groups of patients that were enrolled from 2 previous prospective studies. The studies had

beenperformedbythedepartmentofOralandMaxillofacialSurgeryattheUniversityMedical

Center Groningen and encompassed 30 patients treated with a mandibular overdenture on

2 IMZ implants (Friedrichsfeld,Mannheim,Germany) and amaxillary denture (two-implant

group)(Batenburgetal.,1998);30patientstreatedwithamandibularoverdentureon4IMZ

implants(Friedrichsfeld,Mannheim,Germany)andamaxillarydenture(four-implantgroup)

3636

(Batenburgetal.,1998),and60patientstreatedwithconventionalmaxillaryandmandibular

dentures (conventional group) (Meijer et al., 1999). The patients in both studies had been

selectedonthebasisofthefollowinginclusioncriteria:edentulousmaxillaandmandiblefor

atleast1year,problemswithretentionandstabilityofthemandibulardenture,amandibular

boneheightbetween8and25mmasmeasuredat themandibular symphysis regionona

lateral cephahalometric radiograph and no history of former preprosthetic surgery or

contraindications for a surgical procedure.

The patients treated within these studies had been informed about the different treatment

options, possible risks and themethod employed for assignment to the treatment groups.

Patients in the conventional group were given the option to change to an implant-retained

overdentureafter1yeariftheywerenotsatisfiedwiththeirconventionaldenture.Informed

consentwasobtainedfromallparticipants.Bothstudieswereapprovedbythemedicalethical

committeeoftheuniversitymedicalcenter.Baselinecharacteristicsofthethreegroupsare

listed in Table 1.

Table 1. Characteristics of the groups at baseline.

Group two-implant four-implant conventional

Number of participants 30 30 60

Gender(m/f) 9/21 6/24 19/41

Age(years;mean/SD/range) 54.0/8.7/38-77 55.7/12.3/35-79 56.9/11.6/34-84

Edentulousperiodmandibularjaw(years;mean(SD))

21.0(9.0) 21.8(10.5) 22.7(9.6)

Mandibular bone height (mm;mean(SD))

15.8(2.3) 15.7(2.7) 17.0(4.8)

Surgical and prosthetic procedures

All patients were treated in the same department (Department of Oral and Maxillofacial

Surgery, University Medical Center Groningen, Groningen, the Netherlands) by two

experienced oral-maxillofacial surgeons and/or two experienced prosthodontists. In the

two-implant group, two implants were placed in the canine region of the mandible, about

Chapter 3

37

1 cm left and right from the midline. In the four-implant group, there was an equal distance

betweenthefourimplantsandthemostlateralimplantswereplacedatleast5mmmedially

of the mental foramen. Standard postoperative treatment was composed of analgesics and

chlorhexidine 0.2% mouth rinses (Corsodyl, GlaxoSmithKline Consumer Healthcare BV,

Utrecht,TheNetherlands),butnoantibiotics.

Threemonthsaftertheimplantplacement,secondstagesurgery(thinningoftheperi-implant

mucosa and placement of the abutment) was performed. Two weeks thereafter standard

prosthetictreatmentwasprovidedbeinganewmaxillarycompletedentureandamandibular

overdenture supported by an individually made round bar with a clip attachment system

(Ackermann,PreatCorporation,SantaYnez,CA).Nodistalbarextensionswereused.Noneof

the overdentures were reinforced with a pre-cast metal construction.

The conventional group was treated with a new conventional denture in the maxilla and

mandible jaw. A uniform prosthetic procedure for all patients was performed. A balanced

occlusion and monoplane articulation was used in all three groups.

Radiographic analysis

Anterior maxillary ridge resorption

Maxillary bone resorption was evaluated using a previously described method based on

proportional areameasurements (Kreisler et al., 2000). The radiographs were digitised by

scanning.IncooperationwiththedepartmentBiomaterialsoftheUniversityMedicalCenter

Groningen a computer program was developed. With this software the sizes of the anatomic

andreferenceareasweredeterminedbyoutliningreferencepointsandlines(describedbelow)

withacursor.The followingreferencepointswereused for the investigation (Figure1).The

anterior nasal spine Sandthetwo lowermostbonymarginsof theorbitOrightandOleft form

the‘centraltriangle’.ThelineojoinsOrightandOleft. The intersection between o and p, a line

perpendicular to o through S, is point P. the point R divides the distance [PO] into two thirds

andonethird.Thisvaluewasdeterminedexperimentallysoastodividethemaxillainanterior

and posterior regions. r is a line perpendicular to o through R. u is a line parallel to o through S.

u and r meet at the point U. P’wasmarkedbymeasuringthedistance[UR] starting from S. R’

wasmarkedbymeasuringthedistance[UR] starting from U the line iconnectsR’rightandR’left.

1 is the intersection of the alveolar crest with p, 2 is the intersection of the alveolar crest with r.

3838

IntheanteriorregiontheexperimentalareaisoutlinedbytheareaS12U and the reference area

bytheareaSP’R’U. Anatomic and reference areas on the right and left sides were averaged, and

aratio(AnteriorMaxillaryRidgeRatio)fortheanteriormaxillaryboneareawascalculatedby

dividingtheanatomicboneareabythereferencearea.ThechangeinAnteriorMaxillaryRidge

Ratio(AMaxRR)wascalculatedbysubtractingtheratioat0yearsfromtheratioat10years.

Posterior mandibular residual ridge resorption

The method consisted of proportional area measurements of the posterior mandible, similar to

thatusedbyWrightetal(2002)Usingproportionsminimiseserrorsrelatedtomagnification

anddistortion.Foreveryradiographatracingwasmadeonthemandible.Figures2and3show

the areas that were traced. The anatomical landmarks M(lowerborderofmentalforamen),S

(sigmoidnotch)andG(gonion)wereusedtoconstructthetrianglesontheright (M-S-G) and

left (M’-S’-G’) side of the mandible with centre N(Figure2).Boundarieswereconstructedbythe

Figure 1.

Geometricdesignusedformeasuringthebonegainorlossintheanteriormaxillaryridge.Boneareasareshown on the left, reference areas on the right (see materials and methods for the definition of reference points).

Chapter 3

39

Figure 2.

The anatomical landmarks M, M’ (lower borderof mental foramen); S, S’ (Sigmoid notch); G, G’(gonion)wereusedtoconstructthetrianglesM-S-Gand M’-S’-G’ with centres N and N’ respectively.Boundary lineswereconstructedas follows:M-GandM’-G’,A-LandA’-L’(crestofresidualridgetolower border of mandible perpendicular to M-G and M’-G’),M-NandM’-N’,andG-PandG’-P’(G-NandG’-N’extendedtothecrestoftheresidualridgeatPandP’).

Figure 3.

The areas were defined as follows: posterior bone arearight and posterior bone arealeftbythecrestoftheresidualridgeP-AandP’-A’andtheboundarylinesA-MandA’-M’,M-G andM’-G’, andG-P andG’-P’, respectively; and the posterior referencearearight and posterior reference arealeft by thetriangles M-G-N and M’-G’-N’, respectively. ThePosterior Mandibular Ridge Ratio was calculated from(bone arearight / reference arearight + bone arealeft/referencearealeft)/2.

followinglines:theboundarylineM-G,theboundarylineA-L;alinefromthecrestofresidual

ridge (point A)tothelowerborder(pointL)throughM perpendicular to M-G,theboundaryline

M-NandboundarylineG-P;the lineG-Nextendedtothecrestoftheresidualridgethrough

point P. The experimental bone area was eventually outlined by the area PAMG and the

referenceareaby the triangleMGN (Figure3). ThePosteriorRidgeRatiowas calculatedby

dividingtheboneareabythereferencearea.Theratiosfortherightenleftpartinonepatient

wereaveraged.ThechangeinPosteriorMandibularRidgeratio(PMandRR)wascalculatedby

subtractingtheratioat0yearsfromtheratioat10years.

Reproducibility of measurements.

Before starting the study, a pilot studywas performed to determine the reproducibility of

measurementsandifthequalityoftheradiographwasofanyinfluence.Sixradiographswere

selectedwithvaryingqualityofvisibilityofthetracingpoints.Allradiographsweremeasured

10timesbyoneexaminerusingthemethodplannedforthemainstudy.Thestandarddeviation

and the coefficient of variation were calculated for each set of measurements. The coefficient

ofvariationrangedbetween0.88%and2.72%wherethelowestvariationwasassociatedwith

bone area

reference area

4040

clear visibility of the tracingpoints. Therefore, only radiographswith clear visibility of the

tracingpointswereincludedinthemainstudy.

Panoramic radiographs selection

Panoramicradiographswereobtainedfromallpatientsimmediatelybeforeand10yearsafter

treatment.Radiographswereonlyincludedifthereferencepointsusedforbothmethodswere

distinct and if there were no gross distortion of the images. Patients were included if both the

preoperativeradiographandthe10yearsradiographsatisfiedthetwoselectioncriteria.

Statistical analysis

Fordescriptionof thedata themeanvalues,standarddeviations,minimumandmaximum

were calculated for the change in residual ridge resorption. Since the data for the change in

anteriormaxillaryresidualridgeratio(AMaxRR)andtheposteriormandibularresidualridge

ratio(PMandRR)bothviolatedtheassumptionsofanormaldistribution,differencesbetween

thethreegroupswereanalysedusingtheKruskal-Wallistest.Differencesbetweenthe0year

dataandthe10yeardatawithinthegroupswereanalysedusingtheWilcoxonmatched-pairs

test.Correlationbetweenposteriormandibularresidualridgeratioandtheanteriormaxillary

residual ridge ratio within the groups and for the patients altogether was calculated with the

Spearman correlation test. For all tests, a significance level of 0.05 was chosen.

Results

Patients

Ofthe30patientsinthetwo-implantgroupatbaseline,therewasadropoutofsixpatients

at the 10-years evaluation: 2 patients had died, 3 patients did not attend the 10-years

evaluationand1patientdidn’twanta10-yearsradiographtobetaken.Of the24patients

left,8radiographshadtobeexcludedbecauseofunclearreferencepointsorgrossdistortion.

Leavingpanoramicradiographs(0and10years)of16patientsavailableforfurtheranalysis

in the two-implant group. The four-implant group had a drop out of 10 patients: 6 patients had

diedand4patientsdidnotattendthe10-yearsevaluation.Another6radiographshadtobe

excludedbecauseofunclearreferencepoints.Leavingpanoramicradiographsof14patients

available for furtheranalysis in the four-implantgroup.Theconventionalgrouphadadrop

Chapter 3

41

out of 42 patients: 22 patients had meanwhile chosen for an implant-supported overdenture

becausetheywerenotsatisfiedwiththeirconventionaldenture,10patientshaddiedand10

patientsdidnotattendthe10-yearsevaluation.Ofthe18patientsleft,3radiographshadto

beexcludedbecauseofunclearreferencepoints.Leavingpanoramicradiographsavailablefor

furtheranalysisof15patientsintheconventionalgroup(Table2).

Table2.Characteristicsofthegroupsatthetenyearsevaluation.

Group two-implant four-implant conventional

Number of participants 16 14 15

Gender(m/f) 3/13 4/10 3/12

Age(years;mean/SD/range) 54.2/8.0/38-70 52.1/8.7/38-69 58.0/7.6/47-70

Edentulous period mandibular jaw (years;mean(SD))

20.2(8.9) 19.8(8.3) 22.7(10.3)

Mandibularboneheight(mm;mean(SD)) 15.7(2.9) 15.0(2.3) 16.8(4.0)

Reasonsfornotattendingtheevaluationsweremainlysickness,oldageandnotbeingableto

trace a patient because he or she had moved without leaving a new address. The assumption

wasmadethatdrop-outofpatientswasnotrelatedtoresorptionofthemandibularormaxillary

ridge.Moreover,beforethestudyandateachannualcheck-uppatientswereaskedabouttheir

medical condition. No particular diseases occurred that could be linked to bone resorption, also

notinthepatientsthathaddroppedoutduringthe10yearsevaluationperiod(norelevant

issues in their medical condition had occurred until their last recall visit.

Assessment of resorption

ThechangeinAMaxRRandPMandRRwascalculatedforeachpatientbysubtractingtheratio

valueat0yearsfromtheratiovalueat10years.Therefore,anegativedifferenceindicated

resorption, and a positive difference indicated an increase in area or apposition of bone. Table 3

indicatesthatonaverageboneresorptionhadoccurredintheanteriormaxillainpatientsfrom

allthreegroupsatthe10yearsevaluation.Thisbonelossintheanteriorresidualridgebetween

0and10yearswasstatisticallydifferentforthetwo-implantgroupandthefour-implantgroup,

4242

but not for the conventional group. There were no significant differences between the groups.

Regarding the posterior mandibular residual ridge resorption, in all groups significant resorption

hadoccurredbetween0and10years(Table4),buttheextentofresorption(PMandRR)wasnot

different between the groups. Moreover, there was no correlation between the PMandRR and

AMaxRR.

Table3.Changeinanteriormaxillaryresidualridgeresorption(AMaxRR)overtenyears.

Group two-implant* four-implant* conventional*

Number of participants 16 14 15

Mean(SD)AMaxRR -0.12(0.14) -0.11(0.10) -0.04(0.11)

MinimumAMaxRR -0.51 -0.29 -0.30

MaximumAMaxRR 0.12 0.05 0.11

* Negativevaluesindicatedresorptionandpositivevaluesindicatedanincreaseintheareaofanteriormaxillaryresidual ridge or bone apposition. KruskalWallistestshowednosignificantdifferencesinresidualridgereductionbetweenthegroups. Wilcoxonmatched-pairstestshowedsignificantdifferencesbetween0and10yearsofthetwo-implantgroup (p=0.003)andthefour-implantgroup(p=0.004).

Table4.Changeinposteriormandibularresidualridgeresorption(PMandRR)overtenyears.

Group two-implant* four-implant* conventional*

Number of participants 16 14 15

Mean(SD)PMandRR -0.11(0.07) -0.07(0.08) -0.08(0.11)

Minimum PMandRR - 0.33 - 0.20 - 0.36

MaximumPMandRR - 0.02 0.03 0.10

* Negative values indicated resorption and positive values indicated an increase in the area of posterior mandibular residual ridge or bone apposition. Wilcoxonmatched-pairstestshowedsignificantdifferencesbetween0and10yearsofthetwo-implantgroup (p<0.001),thefour-implantgroup(p=0.006)andtheconventionalgroup(p=0.011). KruskalWallistestshowednosignificantdifferencesinresidualridgereductionbetweenthegroups.

Chapter 3

43

Discussion

Meanreductionofthemeasuredproportionalareasintheanteriormaxillawas0.12inthetwo-

implant group, 0.11 in the four-implant group and 0.04 in the conventional group. These results

revealedthatinthemandibularoverdenturegroups,ongoingresorptionoftheanteriormaxilla

hadoccurredduringthe10yearsevaluationperiod,whichwassignificantforboththetwo-

implant and four-implant groups. However, patients presented large individual differences.

These observations are in line with the findings of other authors who showed gradual

maxillaryridgeresorptioninpatientswearingimplant-retainedoverdentures(Saundersetal.,

1979;Lechner&Mammen,1996;Kreisleretal.,2003).Incontrasttothepresentstudy,these

studies did not include a control group, which can be considered an omission as the present

studyshowedthatresorptionpatternswererathersimilarbetweenpatientstreatedwithan

implant-retained overdenture and patients treated with a conventional denture. Although

thedifferencesbetween thegroupswerenot significant, there seemed tobea tendencyof

slightlymoremaxillaryresidualridgeresorptioninpatientstreatedwithatwo-implantand

four-implantmandibular overdenture.On the other hand, some studies concluded that the

maxillaryridgeresorptionwasmorepronouncedinpatientswearingaconventionaldenture

incomparisonwithpatientswearinganoverdentureorafixedprosthesis(Jacobsetal.,1993;

AbdEl-Dayemetal.,2007).Theseauthorsattributedthesefindingstotheinstabilityofthe

complete dentures, which contributed to an unfavourable stress distribution among the

denture-bearingareas.Thepatientsincludedinthepresentstudyreceivedspecialattention

regardingtheprostheticaftercare,includingroutinerecallvisitseveryyearcheckingdenture

fitandtheocclusion.Ifnecessary,thedentureswererelinedastoaccomplishoptimalfitand

therefore amore balanced stress distribution (Meijer et al., 1999; Visser et al., 2009). The

minimalchangeinresorptionfortheconventionalfulldenturewearersofthisstudycouldbe

theresultoflesschewingforces(Fontijn-Tekampetal.,1998).Theresultsinthepresentstudy

seemtocorrespondwiththefindingsofNährietal(2000)whofoundsignificantreductionof

themaxillary residual ridge.Their changesweresmallandnotassociatedwith the typeof

prostheticrestorationinthemandible(conventionaldentureoroverdenture).

Mean reduction of the measured proportional areas in the posterior mandible was 0.11 in the

two-implant group, 0.07 in the four-implant group and 0.08 in the conventional group.

Regarding posterior residual ridge resorption of the mandible, minimal resorption was observed

4444

for all three groups. Although the differences between the groups were not significant, there

seemedtobeatendencyofslightlymoreposteriorresidualridgeresorptioninpatientstreated

with two implants in comparison to patients treated with four implants or a conventional

denture.

Jacobsetal.(1992)reportedhigherposteriormandibularresidualridgeresorptioninpatients

wearing a two-implant mandibular overdenture in comparison with patients wearing a

conventional denture or a fixed prosthesis. Importantly, the latter authors also reported

in their study thatwhenpatientswere edentulous formore then tenyears the differences

betweenthegroupsdisappeared,whichisinagreementwithourresults.Inthepresentstudy,

thepatientshadbeenedentulousfor,onaverage,20years(Table1).

Theinterindividualvariabilityoftheresorptionratiosforboththemaxillaandthemandible

were high, but comparable to earlier studies and could be related to the multifactorial

aetiologyofboneresorption(Tallgren,1972;Jacobsetal.,1993;Kordatzisetal.,2003;Kreisler

et al., 2003). In several studies it was suggested that the chance of developing conditions

of the combination syndrome increases in persons wearing mandibular implant-retained

overdentures. The anteriormaxillary ridge resorption was suggested to be a result of the

posteriormandibularridgeresorption,bothconditionsbeingsymptomsofthecombination

syndrome.However,thepresentstudyfoundnocorrelationbetweentheposteriormandibular

residual ridge resorption and the anterior maxillary residual ridge resorption. There was

indeed posterior mandibular residual ridge resorption in all groups but this resorption was

slight and there was not significant more posterior mandibular bone loss in patients wearing

mandibular implant overdentures. Furthermore, there were no significant differences in the

maxillary residual ridge resorption. The results of the present study couldnot confirm the

suggestionthatthecombinationsyndromealsomayoccurinconventionalmaxillarydentures

opposedbyanimplant-retainedmandibularoverdenture.Severalfactorscouldcontributeto

thesefindings.Firstly,allpatientsinthepresentstudyweretreatedwithabalancedocclusion

and monoplane articulation concept to avoid too much anterior pressure. This concept with

no anterior teeth contact has also been recommended for implant-retained mandibular

overdenturestopreserveanteriormaxillarybone(Lang&Razzoog,1992;Narhietal.,2000).

Secondly,optimaldenturefitandthereforeamorebalancedstressdistributionofthedenture

Chapter 3

45

wasachievedbygivingspecialattentionwithregardtotheprostheticaftercare(Meijeretal.,

2003;Visseretal.,2009).Finally,itcouldbethatthelongedentulousperiod(onaverage20

years)ofthedescribedpatientsaffectstheresidualridgeresorption.Possibly,mostresorption

takesplaceinanearlierstageaftertoothextractionandresorptionbecomeslesspronounced

in years. Although treatment with implant-retained mandibular overdentures resulted in

higherchewingforcesandimprovedmasticatoryfunction(Fontijn-Tekampetal.,1998),this

improvedoralfunctiondidapparentlynotresultinincreasedresorptionoftheresidualridgein

theposteriormandibleandanteriormaxilla.

Conclusions

Withinthelimitationsofthepresentstudy,itcanbeconcludedthattherewasnodifferencein

anteriormaxillaryresidualridgeresorptionbetweenpatientsrehabilitatedwithanimplant-

retained mandibular overdenture when compared to patients wearing a conventional full

denture. Regarding the mandibular posterior residual ridge, resorption was irrespective of

wearing an implant-retained mandibular overdenture or a conventional mandibular denture.

Acknwoledgements

TheinvestigatorsexpresstheirgratitudetoMr.J.deVries(BiomedicalEngineering,University

MedicalCenterGroningen)forhisvaluablehelpindevelopingthesoftwarefortheradiographic

measurements.

4646

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