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University of Groningen
Effects of dental implants on hard and soft tissuesTymstra, Nynke
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Publication date:2010
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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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