Loss of natural abutment teeth with cast copings retaining overdentures: a systematic review and meta-analysis

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Article

Reference

Loss of natural abutment teeth with cast copings retaining overdentures: a systematic review and meta-analysis

MERCOURIADIS-HOWALD, Alexander, et al.

Abstract

To analyze the available evidence in the English, German and Japanese literature on the survival and complications of natural teeth with cast copings used to retain overdentures (ROD).

MERCOURIADIS-HOWALD, Alexander, et al . Loss of natural abutment teeth with cast copings retaining overdentures: a systematic review and meta-analysis. Journal of Prosthodontic Research , 2018, vol. 62, no. 4, p. 407-415

DOI : 10.1016/j.jpor.2018.05.002 PMID : 29891420

Available at:

http://archive-ouverte.unige.ch/unige:120138

Disclaimer: layout of this document may differ from the published version.

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Loss of natural abutment teeth with cast copings retaining overdentures: a systematic review and meta-analysis

Alexander Mercouriadis-Howald

^a

, Noemie Rollier

^a

, Sayaka Tada

^b

, Gerald McKenna

^c

, Kensuke Igarashi

^a,d

, Martin Schimmel

^a,e,

*

aDivisionofGerodontology,UniversityofBern,Bern,Switzerland

bDisciplineofEndodontics,OperativeDentistryandProsthodontics,FacultyofDentistry,NationalUniversityofSingapore,LowerKentRidgeRoad,Singapore

cCentreforPublicHealth,Queen’sUniversityBelfastInstituteofClinicalSciences,Belfast,UnitedKingdom

dDepartmentofLifeScienceDentistry,TheNipponDentalUniversity,Niigata,Japan

eDivisionofGerodontologyandRemovableProsthodontics,UniversityofGeneva,Geneva,Switzerland

ARTICLE INFO Articlehistory:

Received25October2017

Receivedinrevisedform27April2018 Accepted3May2018

Availableonline8June2018 Keywords:

Overdenture Abutmentteeth Coping

Weightedaverageloss Systematicreview Meta-analysis

ABSTRACT

Purpose:ToanalyzetheavailableevidenceintheEnglish,GermanandJapaneseliteratureonthesurvival andcomplicationsofnaturalteethwithcastcopingsusedtoretainoverdentures(ROD).

Studyselection:AsystematicsearchstrategywasconductedusingMeSHtermsandpre-deﬁnedcriteria.

Two groups of researchers searched Pubmed, CENTRAL, Embase (English, German), Ichushi-web (Japanese)as wellas handsearching. Datawereextracted independently bythetwo groups.The estimatedfrequencyofabutmenttoothlosswascalculatedfromdataonthenumberoflostteethand exposuretime.Ameta-analysiswasconductedtoestimatetheannualfrequencyofabutmenttoothloss acrossallincludedstudies.

Results:Atotalof4791eligiblestudiesfromPubMed,Embase,andCENTRAL.Anadditional316articles wereidentiﬁedfromtheIchushi-Webplusanother131articlesfromadditionalsources.Fromthose manuscripts, 19reportedrelevantoutcomedatathatwasthenextracted.Thepooleddataincludedatotal of1954abutmentteethwithacombinedtotalexposuretimeof9098years.Theestimatedlinearrateof losswas1.76%/year(95%CI1.13;2.72).Cariesandperiodontalinfectionswereidentiﬁedasthemost commonreasonsforabutmenttoothloss.

Conclusions:Naturaltoothretainedoverdenturesoftenconstitutethelastresortbeforeedentulismand mightaidinthistransition,especiallyinveryoldpatientswithreducedadaptivecapacities.Givencorrect design,preparationandaftercare,RODswithcastcopings,stillareavalidtreatmentoptioninpartially edentulouspatients.

ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by- nc-nd/4.0/).

1.Introduction

Inmostofthewesternworld,toothlossisincreasinglydelayed intooldageandtheprevalenceofedentulismisdeclining[1–3].

This can lead to challenging clinical situations where elderly patientsstruggle toperformoralhygienemeasuresbutretaina numberof natural teeth[4].In thesecircumstancesone of the prosthodontic treatment options available is theuseof natural root-supported overdentures (RODs), as the shortening of the abutmentteethmightincreasetheirsurvival[5].Accordingtothe

AcademyofProsthodontics,thetermoverdenture(OD)isdeﬁned as“anyremovabledentalprosthesisthatcoversandrestsononeor moreremainingnaturalteeth,therootsofnaturalteeth,and/ordental implants;adentalprosthesisthatcoversandispartiallysupportedby naturalteeth,naturaltoothroots,and/ordentalimplants”[6](Fig.1).

Iffurther toothlossoccurs, RODscaneasilybetransformed intocompletedentures.Thiscanprovideasmoothtransitionto edentulousnesswithoutoverstretchingpatients’adaptivecapac- ity.RODsareindicatedwhentheremainingnaturalteethcannot adequatelyserveas abutmentteethfor ﬁxedor clasp-retained partialdenturesduetoanunfavorabledistributioninthearch, lossofperiodontalattachment,complexfunctionaloraesthetic needs or severe attrition. They may also be indicated when provisionofendosseusimplantstosupportoverdentures(IODs) isnotpossible[7,8].

* Correspondingauthorat:DivisionofGerodontologyandRemovableProstho- dontics,UniversityofGeneva,RueBarthlemy-Menn19,1205Geneva,Switzerland.

E-mailaddress:[email protected](M.Schimmel).

https://doi.org/10.1016/j.jpor.2018.05.002

by-nc-nd/4.0/).

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RODsaretypicallydesignedascompletedenturesandcover the remaining naturalabutments. In most cases, theseabut- mentsneedtoundergoelectivedevitalisationastheteethare significantly shortened toprovide sufficient restorativespace for the prostheses. The abutments can either be covered by plastic filling materials, such as glass ionomer cement, amalgam or composite [9,10], or restored with cast copings, commonly constructed from gold alloy [11]. The abutment teeth will then serve to transmit masticatory forces thus protectingtheunderlyingmucosaandalveolarbone[12].They also serve to maintain a degree of proprioception as the periodontal ligament receptors remain intact [13]. Fontijn- Tekampetal.hasdemonstratedthatpatientswithRODsshow a chewing efficacy similar to those with a shortened dental archandbetterthan implant-ODsor completedentures [14].

Newtonetal.alsodemonstratedthatthelossofmusclemass of the jaw-closing muscles could be delayed if natural roots supportedan overdenture[15].

Wherecastcopings areusedonthenaturalabutmentteeth thesecanalsobeutilizedtoprovideprecisionattachmentswhich add extra retention to the overdenture [16]. The precision attachmentsconsist of twoelements:a male castrootcap,on whichtheretentiveelementis soldered(e.g.,sphericalattach- ment, cylinder, magnet) [16,17] and a corresponding female matrix which is incorporated into the ﬁtting surface of the prostheses.Retentionwithinthematricescan bemodiﬁed and thecomponentscanbechangediftheybecomewornout.RODs areexpensiveremovableprosthesesbecauseofthecomplexityof treatmentandthelaboratorycomponentsusedintheirproduc- tion.Unfortunatelyanumberofstudieshavedemonstratedthat thenaturalteethusedtosupportRODsaresusceptibletocaries andperiodontaldisease[11,18–20](Fig.2).Theneedtoprevent such complications and the high maintenance burden can generateadditionalexpenses.

Theaimofthissystematicreviewwastocollectandanalyze alltheavailableevidenceintheEnglish,GermanandJapanese literatureonthesurvivalandcomplicationsofrootswithcast copingsandprecisionattachmentsusedtoretainaROD.Ameta- analysis was conducted to calculate the estimated annual frequencyof loss of the naturalabutment teeth.The focused questionforthereviewwas:“Inpartiallyedentulouspatients withRODs,whatistheestimatedannuallossofabutmentteeth and complications of the abutment teeth in clinical studies publishedinEnglish,GermanandJapaneseliterature?” 2.Materialsandmethods

Thissystematicreviewwasconductedinaccordancewiththe PRISMA(PreferredReporting Items for SystematicReviews and Meta-Analyses)guidelines[21].

2.1.Informationsources

A systematic literature search was conducted using the combinedMeSHterms“overdenture”or“dentalprosthesis”and

“rootsupportedoverdenture”or“denturebases”or“toothroot” and“anchorsystem”or“dentureretention”or“dentalabutment” or “root cap” or “attachment” or “abutment” and limited by

“German” and “English” and “Japanese” in the databases. The electronic databases PubMed, CENTRAL and EMBASE were searched for relevant scientiﬁcreports publishedin English or GermanaswellastheJapanesedatabasesIchushi-Webforarticles publishedin Japanese with thetranslatedterms (Table 1). The electronicsearchbycombinedMeSHtermwasfurtheraugmented in the Web of Science (96 titles) and then by hand searched throughthefollowingjournals:BritishDentalJournal,International JournalofProsthodontics,QuintessenceInternational,JournalofOral Rehabilitation, Dental Update, The Journalof Prosthetic Dentistry, JournalofDentalRestoration,InternationalJournalofPeriodontics&

Restorative Dentistry, InternationalJournal of Prosthetic Dentistry, Journalof ClinicalPeriodontology, JournalofDental Research,and JournalofPeriodontology.Theaimwastoidentifyallpublications Fig.1.Clinicalexampleofacastcopingwithsphericalattachmentfortheretentionandsupportofanoverdenture.

Fig.2.Cariesisafrequentlyobservedcomplicationinabutmentteethwithcast copings.

408 A.Mercouriadis-Howaldetal./journalofprosthodonticresearch62(2018)407–415

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reporting these on attachment systems for root coping — supportedoverdenturesuptoJuly1stof2017.

2.2.Searchstrategyandstudyselection

Allclinicalstudies,excludingcasereports,reportingonpartially edentatepatientswithoverdenturesretainedbynaturalrootswith castcopingsandprecisionattachmentsincludingballattachments, Gerberattachmentsormagnetsthatsatisﬁedthelistedpredeﬁned inclusioncriteriawereincludedinthissystematicreview.

The included studies had to report at least: number of participants, type of cast coping and attachment, number of abutmentteethatthebeginningandendoftheobservationperiod and the mean observation period. Excluded studies included overdenturesretainedonrootsrestoredwithplasticrestorations, casereportsortechnicalreportswithoutstatisticalcomparisons.

Thefollowinginformationwasextracted:nameofauthor/sand yearof publication, sample size,patient age, mean observation periodinmonths,genderofparticipants,numberofcastrootcaps, numberof overdentures,survivalrates, overdenture attachment type,prostheticandbiologicalcomplications.Thenumberofnatural abutment teeth with biological complications such as caries, periodontaldisease,endodonticfailure,fractureandmobility,as wellas prostheticcomplication suchas copingremake, denture repair,chipping, matrix repairs and change of activations were noted.

Twogroupsofinvestigatorsworkedindependentlyinorderto analyzetheEnglishandGerman(AMandNR)literatureandthe Japaneseliterature(KIandST).Eachinvestigatorcreatedalistof studiesforfulltextanalysis.Thelistswerecomparedwithinthe languagegroupsandstudiescommontobothlistswereshortlisted.

Mutualagreementonanyincludedstudywasnecessarytoproceed with further analysis. Data extraction for the two groups was performed independently and the researchers were blinded.

Disagreements were solved bya consensus discussionpresided overbytheseniorauthor(MS).Asensitivityanalysiswasperformed atthelevelofthedataextraction.Therefore,theinter-investigator reliabilitywascalculatedusingkappa(

k

⁾^statistics^[22].^In^cases^of

identiﬁedstudiesreportingonthesamecohortatdifferenttime points,onlythemostrecentpublicationwasincludedinthereview.

Furthermore,asubgroupanalysisthatcomparedcastcopingswith orwithorwithoutprecisionattachmentswasperformed.

2.3.Riskofbiasandqualityassessmentoftheincludedstudies TheNewcastle–Ottawascale(NOS)wasusedfortheassessment of the risk of bias and quality assessment of the included prospectivecohort/case-controlstudies[23,24].

2.3.1.Primaryoutcomemeasure

Theprimaryoutcomemeasurewastheestimatedlossofabutment teethwithcastcopingsinoverdenturepatients,i.e.,frequencyofloss per100years.Therefore,thenumberofabutmentteeth, thetotal exposuretime(meanobservationperiod),thefrequencyofabutment toothlossandtheannualrateoflosswerecalculated.

2.3.2.Secondaryoutcomemeasures

Informationonthebiologicaland technicalcomplications in abutmentteethandoverdentureswerealsoextracted;thisdata hasbeenreportedqualitatively duetotheheterogeneityofthe informationprovided.

2.4.Statisticalanalysis

The total exposure time was calculated as the number of abutmentteethmultipliedbythereportedmeanfollow-upperiod ofthestudy.Forexample,Ratanenetal.[25]thiswas156years,as theproductof52abutmentteethobservedover36months(=1872 months=156years). Thefrequency of abutment tooth losswas calculated as the differencebetween the number of abutment teethatthebeginningofthestudyandtheendofthestudy.The estimated frequencyof abutment toothlossper 100 yearswas calculated as a percentage from the 100x number of losses/

exposuretime.Forexample,arateof3.21wouldmeanthatfor100 abutmentteeth,alossof3.21%couldbeexpectedafteraperiodof oneyear[25].Additionallythe95%conﬁdenceintervals(CI)forthe frequency are reported on the assumption that the frequency showsaPoissondistribution.Thecumulatedestimatedfrequency overallstudieswasweightedaccordingtotheratio(percentage)of thefollow-upofagivenstudyinrespecttothecumulatedoverall exposure time. The heterogeneity of the included studies was analyzedbyplottingafunnelplot.

Theanalysiswasperformedbya seniorbio-statisticianusing Stata/IC14.2forWindows.

3.Results

3.1.Studyselection

Thesearchstrategyidentiﬁeda totalof4791eligiblestudies fromPubMed,Embase,and CENTRAL,another131articlesfrom additionalsourcesaswellas316articlesfromtheIchushi-Web.

After the ﬁrst screening and removal of duplicates 154 titles remained. Inclusion and exclusion criteria wereapplied which produced77articlesfromtheEnglishandGermanliteratureplus 14articlesfromtheJapaneseliteratureforfull-text analysis. Of combination

Electronic PubMed,Embase,TheCochraneCentralRegisterofControlledTrials(CENTRAL)andIchushi-Web(Japanese) Database

search

Journals AllpeerrevieweddentaljournalsavailableinPubMed,EmbaseandCENTRAL.Japanesepeerrevieweddentaljournalsavailablein Ichushi-Web.

Inclusioncriteria Rootsupportedoverdentures.Mustspecifythestudydesign,numberofpatients,survivalrateandcomplications.

Selection criteria

Exclusioncriteria Casereports.Implant-supportedoverdentureprostheses.Studieswithoutabstracts

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thosemanuscripts,19reportedonthedeﬁned outcomeparam- etersfromwhichinformationcouldbeextracted(Fig.3,[21]).The inter-rater agreement for study selection was substantial (

k

⁼^0.6576)^and ^ranged^for ^the^data^extraction^fromsubstantial toalmostperfect(0.6269<

k

<1).

3.2.Frequencyoflossofabutmentteethwithcastcopings

The19studiesprovidedpooledinformationonatotalof1954 abutmentteethwithacombinedtotalexposuretimeof9098years.

Theestimatedlinearrateoflossper100yearswascalculatedas 1.76(95%CI1.13;2.72),i.e.,1.76%oftheabutmentteethwerelost everyyearassumingthatthelossoccurslinearly(Table2,Fig.4).

3.3.Biologicalcomplications 3.3.1.Caries

Eleven studies [4,11,17,25–32] with an observation period rangingfrom2to16yearsreporteddataoncariesinabutment teethwithcastcopings.Theprevalenceofcariesvariedconsider- ablybetweenstudies,rangingfrom0.5%to83%(Table3).

3.3.2.Periodontaldisease

Thirteen studies [11,25,27–37] reportedonperiodontal outcomes for abutment teeth during observation periods ranging from 2 to 15 years. The outcomes of these studies vary signiﬁcantly, out of the19studies,13 reported onperiodontal diseasewithreportedprevalencerangingfrom4%to86%.The largest retrospective study by Angermeider and Stadelmann showeda10%increaseinpocketdepthsaroundabutmentteeth afterupto16yearsofobservation[35].

3.3.3.Toothmobility

Sevenstudies[17,25,28,29,32,33,37]withafollow-upperiod rangingfrom2to12yearspresenteddataonthemobilityofthe abutmentteeth. Five of the articles stated a slight increasein mobility(Table3).Along-termstudybyCocaetal.[29]showed, that after 12 years 73.7 % of the abutment teeth showed no mobility.

3.3.4.Toothfracture

Fivestudies[11,20,28,30,35]presenteddataonfractureofthe abutmentteethduringanobservationperiodrangingfrom2to16 years.Therateoffracturesreportedwassmall,witharangefrom 1.0 to 1.7 %. The long-term study from by Angermeider and Stadelmannshoweda1.1%rateofabutmentfractureafterupto16 yearsofobservation[35].

3.4.Technicalcomplications

Prosthetic complications such as coping remakes, denture repairs, activation or repair of matrices, overdenture fracture, decementation, reline and remakes of the overdentures were recorded. Reports of technical complications varied widely amongsttheincludedstudies(Table4).Studiesreportedfrequent prosthetic maintenance was required, mainly for overdentures withexclusiverootsupport[20].

Sevenstudiespresenteddataaboutthedecementationofthecast copings which occurred in 6–32 % of all abutments [20,25,27,30,32,34,35].Gondaetal.reportedthatafter5yearsonly 9%ofthecastcopingsontheabutmentteethhaddecemented.Their data suggests that cast copings cemented/bonded with a resin cementshowedfewerepisodesofdecementation[35].

Fig.3.Flowchartofthesearchstrategy,accordingtothePRISMAguidelines.

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Therateofchippingoftheoverdenturewasreportedinthree studiesandrangedfrom9to17%[20,25,27].Therateoffracture oftheoverdenturewasrecordedinsevenstudiesandrangedfrom 2 to 27 % [17,20,25,28,32–34]. Gonda et al. reported that

complicationssuchasdecementationandoverdenturefractures couldbepreventedwiththeuseofanadhesiveresinprimeron thematrixatinsertionandtheappropriatedenturedesignwitha reinforcedframework[32].

Two studies reported data on the number of overdenture relines required and ranged from 28 to 35.2 % [17,38]. Shaw reportedthatreliningisindicatedassoonasthematrixcontacts theﬁttingsurfaceoftheprosthesistoensurethattheoverdenture remainsmucosasupportedandattachmentiswellretained[38].

Fivearticlesreportedonoverdenturerepairsillustratingarange from 21 to88 % of the prostheses [20,27,29,34,38]. Coca et al.

reportedafter12years,halfoftheoverdenturesneededrepairs.All the denture repairsinvolved a puncturefracture of theacrylic coveringthematrix[29].

Two studiesreportedtherate ofremakeofthecastcopings.

Shawdescribedafterupto7years,11%oftherootcapsrequiredto beremadecomparedto5%inthestudybyCoca[29,38].

Concerning complications with the matrices; four studies reportedrepairratesof22–30%furtheractivationwasrequiredin 36–21%ofcasesandachangeinretentionlevelwasrequiredin9% [20,25,35,38].

The subgroup analyses of abutment teeth with cast coping without precision attachments [17,30,39] versus copings with precision attachments [11,17,20,25,27–29,31–35,37,38,40,41] did not showa differencein the frequencyof abutment toothloss betweenthem(p=0.538,Table5).

3.5.Riskofbiasandheterogeneity

Theriskofbiasofmostoftheincludedstudieswas ashigh, mostlybecauseoftheretrospectivestudydesignsandtheabsence ofcontrol-groups(Table6).Theanalysisofheterogeneity,i.e.,the riskofapublicationbiaswasanalyzedwithafunnelplot(Fig.5).

4.Discussion

4.1.Principalﬁndings

This systematic review and meta-analysis of the English, German and Japanese literaturereveals a relatively low rate of linear loss of abutment teeth with cast copings retaining an overdentureoflessthan2%peryear.Theprevalenceofcariesand Fig.4. Graphicalrepresentationofthemeta-analysisforthelosseswiththeir95%

conﬁdenceintervals(95%CI).

Coca 2002 99 495 8 1.62 0.70 3.18 5.44

Hug 2006 88 264 1 0.38 0.01 2.11 2.90

OtaniRyuichiro 2006 31 140 10 7.17 3.44 13.18 1.53

Brkovic-Popovic10y 2007 17 170 5 2.94 0.95 6.86 1.87

Brkovic-Popovic6y 2007 33 198 5 2.53 0.82 5.89 2.18

Monfrin 2007 60 135 5 3.70 1.20 8.64 1.48

Meriscke 2008 419 1816 27 1.49 0.98 2.16 19.96

Yang 2012 70 484 0 0 – – 5.32

Gonda 2013 211 1055 8 0.76 0.33 1.49 11.60

YaoXi 2013 60 130 0 0 – – 1.43

Yang 2014 22 68 1 1.47 0.04 8.21 0.75

Estimationassumingpoisson-distributedloss-rate.

aCalculationoftherateandtheconﬁdenceintervalwithaPoissonregressionwithrandomeffectstudy.

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periodontaldiseaseishighandthoseconditionscontributetothe majorityoflostabutmentteeth.Technicalcomplicationsaremost frequentlyseenintheﬁrstyearofserviceandoftencompriseof issuesaroundactivationofmatricesanddecementationofthecast copings.

4.2.Strengthsandweaknessesofthereview

ProspectiveclinicalstudiesthatinvestigateRODsarescarceand rarelycomprisecontrol-groups.Theindicationtoprovideapatient withaRODisoftenanultima-ratiodecision,andaimstodelaythe Table3

Attachmenttypeandbiologicalcomplications.

Study(ﬁrst author)

Year Observation period(months)

Mean age

Participants WSK (start)

WSK (end)

Overdentures Attachment type

Caries (%)

Root fracture (%)

Periodontal disease(%)

Mobility (%)

Lost (%)

Rantanen 1971 48 48 31 52 47 33 Bar 39 – 35 35

stable 5

Manabe 1976 42 – 47 128 128 71 Bar – – 86 0.7 –

Nagaoka 1982 30 – 16 32 32 18 Ball 15 – – – –

Shaw 1984 84 62 23 52 47 33 Bar – – – – –

Murakami 1985 60 62 5 12 11 7 Dome 83 – 83 36 8

Mericske 1993 120 74.1 109 359 335 125 Gerber 5 0.1 4 – 2

Kido 1994 14 – 40 57 57 42 Magnet – – 10 10 –

Schriber 1999 24 70 38 151 137 40 Gerber 20.4 1.7 8.3 less 9.2

Coca 2002 144 65 66 99 79 – Caps/

magnets

9 – 53 73,7

stable 8

Hug 2006 24 67 14 88 87 59 Gerber/ball – 1.1 – – –

Ryuichiro 2006 54 69.4 16 31 21 – Magnet – – 32 – 32

Brkovic- Popovic

2008 72 71.4 15 33 28 – Copings – – – – 15.2

Brkovic- Popovic

2008 120 75.4 7 17 12 – Copings – – – – 29.4

Monfrin 2007 48 62 29 60 55 – Copings 1 1 5 – 8.3

Angermeider 2008 192 66.3 159 419 392 183 Gerber/ball 14.7 1 11.2 – 6.4

Yang 2012 84 65.2 35 70 70 – Copings 12.8 – 25.7 – –

Gonda 2013 60 67.5 131 211 203 133 Magnets 0.5 – 52

increase 27 increase

3.8

Yaoxi 2013 36 68 45 60 60 – Magnet/

ball/clasp

– – – Magnet –

Yang 2014 37 66.8 16 22 21 17 Magnet 16.5 – 29.3 No

change –

Table4

Attachmenttypeandprostheticcomplications.

Study (ﬁrst author)

Year Observation period (months)

Participants Overdentures Attachment type

Refabricate (%)

Decementation (%)

Overdenture fracture(%)

Repairs matrices (%)

Chipping (%)

Reline (%)

Remake coping (%)

Repair denture (%)

Rantanen 1971 48 31 33 Bar – 6 27 9 9 – – –

Manabe 1976 42 47 71 Bar 5.6 – 5.6 – – – – –

Nagaoka 1982 30 16 18 Ball – – – – – – – –

Shaw 1984 84 23 33 Bar – – – 22.2 – 28 11 88

Murakami 1985 60 5 7 Coping – 16.7 – – 14.3 – – 42.9

Meriscke 1993 120 109 125 Gerber – – – – – – – –

Kido 1994 14 40 42 Magnet – – – – – – – –

Schriber 1999 24 38 40 – – – 5 – – – – –

Coca 2002 144 66 – Cap/magnet – – – – – – 5 50

Hug 2006 24 14 59 Gerber/ball – 5.7 1.7 36 16.9 – – 22

Ryuichiro 2006 54 16 – Magnet – 32 21 – – – – 21

Brkovic- Popovic

2008 72 15 – Coping – – – – – – – –

Brkovic- Popovic

2008 120 6 – Coping – – – – – – – –

Monfrin 2007 48 29 – Coping – 11 – – – – – –

Angermeider 2008 192 159 183 Coping – 26 – 30 – – – –

Yang 2012 84 35 – Coping – – – – – – – –

Gonda 2013 60 131 133 Magnet – 9 14 – – – – –

Yaoxi 2013 36 45 – Magnet/

ball/clasp

– – – – – – – –

Yang 2014 37 16 17 Magnet – – 11.7 – – 35.2 – –

Table5

Frequencyofabutmenttoothlossinthetwosubgroupswith95%CIandthep-valueforcomparison.Thecalculationoftherates,95%CIandthep-valueisdonewithaPoisson regressionwithrandomeffectstudy.

Attachmenttype Numberofrootcaps Totalexposuretime(years) Losses Calculatedloss/100years95%-CI p-Value

Castcoping/noattachment 1774 8111 113 1.65 0.97 2.82

Castcoping/withattachment 180 978 115 2.16 1.11 4.21 0.538

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time until a complete denture must be provided. Thus, the introduction of appropriate control-groups may be almost impossible.AsRODsareusuallyprovidedforelderlyorgeriatric patients, prospective study designs and the introduction of comparable parameters are especially challenging, due to a numberof logisticaland ethicalchallenges.Onecouldargue to compareRODstoIODs,butthiscomparisoncannotbejustiﬁed,as teeth should only be replaced by implants as a last resort of treatment.Therefore,mostoftheincludedstudiesshowahighrisk ofbias,duetotheirretrospectivedesignandtheabsenceofvalid controls.Unlikeimplants,abutmentteethareveryheterogeneous inregardtoendodonticanatomy,structuraldeﬁcitsorperiodontal condition. Furthermore, different clinicians may judge the prognosisofabutmentteethonvaryingparameters,resultingin afurtherincreaseofheterogeneitybetweenindividualsubjects, datasetsandpublications.

In order to reduce, but also reﬂect this heterogeneity, the authorsofthecurrentsystematicreviewincludedstudiesfroma largegeographicalbase.Therefore,andcontrarytootherreviews, thelanguagerestrictionsthatconstituteamajorinclusionbiasin othersystematicreviewswerewidened,asGermanandJapanese articlesandtheseswereincluded.

The analysisof heterogeneity withthe funnelplot method further strengthens the impression, that different clinicians judge the prognosis of abutment teeth differently and that differenttreatmentconceptsresultinvaryingsurvivalratesof theabutments.Ifthereisneitherapublicationbiasnorastrong heterogeneity of the studies, then most of the points in the funnel plot are expected to be within the 95 % conﬁdence interval. The points in the plot should roughly describe a triangularform.Thereshouldbenoareaofthey-axiswherethe dotsclusterononesideoftheverticallines(pooledrate).Ifall studies with a low exposuretime have a lossrate below the pooledrate,thismayindicateapublicationbias.Theincluded studies are therefore more heterogeneous than one would expect. In particular, there are unexpectedly many studies reportingonlowfrequenciesofabutmenttoothloss,whichare outsidetheconﬁdenceinterval.

Forthemeta-analysisstudieswereweightedaccordingtothe proportion(percentage)oftheobservationtimeofastudyonthe sumoftheobservationtimesofallstudies.Theweightingofthe studieswillgivepreferencetolargestudiesandnotnecessarily well conducted ones.For example, the largest weight has the study ofMericskeandMericske-Stern (2118years) [11],which had a retrospective design and is thus prone tobe at risk for numerous forms of inclusion bias. Studies with a prospective design; those which are more difﬁcult to conduct and more expensive like the study by Brkovic-Popovic et al. [39] or Ryuichiro et al. [34] have a small weight, but might provide morereliableresults.Thiscouldhaveintroducedariskofbiasinto theresultsofthemeta-analysis.

4.3.Frequencyoflossofabutmentteethretaininganoverdenture Duetotheretrospectivedesignofmostoftheincludedstudies and the varying expose times of the abutment teeth, the cumulativelosshadtobeestimated.Themeanobservationperiod wasmultipliedbythenumbersoflostabutmentteeth;however thiscalculationisbasedontheassumptionthatthelossoccursata linear rate. In reality it is more likely that the frequency will

Hug 2006 Prospective ** * * High

Ryuichiro 2006 Prospective **** ** ** Low

Brkovic-Popovic 2008 Prospective ** ** * High

Monfrin 2007 Case-control ** * * High

Angermeider 2008 Retrospective ** ** * High

Yang 2012 Retrospective * * * High

Gonda 2013 Retrospective * * * Unclear

Yaoxi 2013 Retrospective ** ** * High

Yang 2014 Prospective ** ** * High

Fig.5.Inthecurrentmeta-analysis,thefrequencyofabutmentteethlosswas relatedtotheexposuretime.Theweightofthestudywasthereforetheexposure time.Italsodeterminestheaccuracyofthelossrate,sincethewidthofthe95% conﬁdence intervalsofthelossrateoftheindividualstudiesdependsonthe exposuretime(thesmallerthetime,thebroaderthe95%CI).Inthedepicted graphy,theexposuretimeofthe19studieswasplottedagainstthelossesper100 years.Theblackverticallineisthepooledlossrate(1.76/100years).Thegraylines describetheintervalinwhichthelossrateof95%ofthestudieswouldbeexpected ifthe‘true’loss ratecorrespondstothepooled rateandif thereisneithera publication bias nor heterogeneity. Because of the assumption of poisson- distributedlosses,theintervalisnotdistributedsymmetricalaroundthepooled rate.

(9)

augmentexponentiallywithtime,butthisbehaviorcouldnotbe calculated without the source data of each study. Thus, the calculatedannuallossof1.76teethper100maybeunrealisticfor shorterobservationperiods,butislikelytobeagoodindicatorfor long-termobservations—andwouldthereforepredictalossof8.8

%ofabutmentteethafter5years,or17.6%ofabutmentteethafter tenyears.

Again,oneshouldnotdirectlycomparetheseﬁgurestoimplant survival. The considerations to provide a patient with one treatment modality or the other vary considerably. Also, if maintained well, teeth will last a lifetime that is longer than implants [42]. However, this may not apply to endodontically treatedteeth that experience highmechanical stresses as they retaintheoverdenture.Retaininganoverdenturebynaturalroots or implants are complementary, and not competing, options.

Reportedimplantsurvivalvariesbetween73.0–95.5%depending ontheexperienceofthesurgeon,whereastoothsurvivalratesafter endodontictreatmentisreportedas89.7%or98.1%forgeneral practitionersorspecialists,respectively[43].

4.4.Biologicalcomplications 4.4.1.Caries

Cariesrepresentsonethemainconditionsthatcouldresultin the extraction of abutment teeth. Therefore effective caries prevention measures will increase the prognosis of both the abutmentteethandtheprostheses.Thisisdescribedinthestudy byToolsonandSmith[9],whoadvocatedtheuseoffluorideto prevent caries in abutment teeth without cast copings. The plaquescores of the groupof patients whocontinued using a fluoride gel were superior when compared to the group of patientswho electednot to usethe fluoride gel[9]. Over the courseofthestudy16patientswhousedthefluoridehadatotal of36teeth,35ofwhichhadnocariespresent.Incomparisonthe groupofpatientswhowerenotusingfluoridehadatotalof94 teeth, of which 20 showed clinical signs of caries. The use of fluoridegelwasshowntobeaneffectivemeanstopreventcaries on the retained overdenture abutments [9]. It has also been reported that caries development in overdenture abutments could be inhibited with a daily application of chlorhexidine– fluoridegel[44].

4.4.2.Periodontaldisease

Themaintenanceofperiodontalhealthappearstobeanother majorchallengeinoverdenturewearersasperiodontalcomplica- tionshavebeenshowntobeamajorcauseofabutmentloss[45– 47]. The majorityof thestudies showed an increase in pocket depthsaroundtheabutmentteethovertheobservationperiods.In general, after ﬁve years moderately deep pockets around the abutment teeth decreased; but the deeper pockets tended to remain[44].

Furtherstudiesshowednosigniﬁcantperiodontalbreakdown in despite of severely reduced periodontal support of many abutmentteeth[11].Inmanystudiestheperiodontalhealth,while not optimal, was not responsible for the loss of a signiﬁcant numberofabutmentteeth[9].

InthestudybyYaoetal.in2013[37]after3years,thegingival healthinthemagneticattachmentgroupwasbetterthantheball- capattachmentgroup.However,theamountof attachedtissue presentdecreased signiﬁcantlybetween the2nd and 5th year- recallexaminations.

Itmustbestatedhowimportantmechanicalcleaningandthe use of ﬂuoride is to prevent abutment tooth loss due to periodontalbreakdown with RODs. Inthe study by Yao et al.

[37],oralhealthmaintenanceandperiodicchecksafterprovision oftheoverdentureswasshowntomaintainabutmenthealthand

sustainlong-termtreatmenteffects.Fluoride-releasingmaterials suchas glass ionomer cement couldalso beincorporated into copingmaterialstofurtherdecreasesecondarycariesandpocket depths. In a study by Toolson et al. with conventional overdentures[9],theplaquescoresofthegroupofpatientswhowere motivated to continue using ﬂuoride gel were superior when comparedtothe groupof patientswho electednot tousethe ﬂuoridesolution.

4.4.3.Toothmobility

Cocaetal.[29]alsoshowed,thatafter12years,73.7%ofthe teeth had no mobility. Tooth mobility showed an interesting pattern especially after the reduction of theteeth for the cast coping.Itwasreported,alsoforabutmentteethwithoutcopings that after reducing the height of the abutment teeth to approximately 2mm above the gingival margin there was a markedreductioninmobility[44].

ThestudybyYaoetal.in2013[37]showed,thatthemobilityin abutmentteethrestoredwithmagneticattachmentswaslessthan thosewithballs.

4.4.4.Toothfracture

Fractureofabutmentteethwasfrequentlyreported. Reasons forthiscouldbeverywideorlongcastposts[48],inadequatetooth preparation or overloading [49]. However, fracture of the abutment teeth was reportedas a reason for tooth loss much less frequently than caries or periodontal breakdown. Monfrin etal.establishedthatperiodontaldiseaseproblemswerethecause of3extractions,subgingivaldecaycausedoneandrootfracture alsooneextraction[30].Intheretrospectivestudywiththelongest observation period by Angermeider and Stadelmann, 4 of 54 abutmentteethfailureswerereportedasrootfractureswithcaries and periodontal disease more frequent causes [35]. Schriber reported3outof14lostabutmentteethoriginatedfromfractures [28].

Thetypeofattachmentswastooheterogeneousbetweenthe studiestoperform a comparisonbetweenthem. It would have been interesting to compare more rigid attachments like the GerbercylinderortheFaeattachmenttothosethatallowmore degrees of freedom like the ball attachments or the magnets.

However,weperformedasubgroupanalysisofcementedrootcaps with or without attachment and did not find a significant difference.Webelievethat thedesign of theoverdenture,with an open or closed flange, might have a much more important influence; however there is rarely information on the specific denture designs marked in the available articles. Airoldi et al.

described the “perio-overdenture” that is successfully used to providepartiallyedentatepatientswithrootcap-retainedremov- able prostheses. The root caps in this perio-overdenture are designed to support prostheses with an open design, thus facilitatingoralhygieneandpromotingperiodontalhealth.[50].

Thegoodresultsoftheperio-overdentureaccordingtotheZurich school with regard to the survival rate of the prostheses, the survivalrateoftheabutmentteeth,thelowcariesincidenceand theextremelylow-inﬂammatoryconditionofthegingiva,suggest thattheincreasedconstructiveeffortformanufacturingtheperio- overdenturecomparedtotheconventionaloverdentureisworthit inlong-term[28].

5.Conclusion

RODsoftenconstitutethelastresortbeforerenderingpatients completelyedentate.Theymayaidinthistransition,especiallyin veryoldpatientswithreducedadaptivecapacities.Withcorrect design,preparationandaftercare,RODswithcastcopingstillarea validtreatmentoptioninpartiallyedentulouspatients.