Longevity of posterior composite restorations: not only a matter of materials

dentalmaterials 28 (2012)87–101

Available

online

at

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j our na l h o me p ag e:w w w . i n t l . e l s e v i e r h e a l t h . c o m / j o u r n a l s / d e m a

Longevity

of

posterior

composite

restorations:

Not

only

a

matter

of

materials

Flávio

F.

Demarco

,

Marcos

B.

Corrêa

_,

_Maximiliano

_S.

_Cenci

_,

Rafael

R.

Moraes

_,

_Niek

_J.M.

_Opdam

a_{GraduatePrograminDentistry,SchoolofDentistry,FederalUniversityofPelotas,RS,Brazil}

b_{DepartmentofRestorativeandPreventiveDentistry,RadboudUniversityNijmegenMedicalCentre,Nijmegen,TheNetherlands}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received5August2011 Receivedinrevisedform 12September2011 Accepted13September2011 Keywords: Clinicaltrials Failure Long-termevaluations Longevity Posteriorrestorations Resincomposites Survival

a

b

s

t

r

a

c

t

Resincompositeshavebecomethefirstchoicefordirectposteriorrestorationsandare increasinglypopularamongcliniciansandpatients.Meanwhile,anumberofclinicalreports intheliteraturehavediscussedthedurabilityoftheserestorationsoverlongperiods.Inthis review,wehavesearchedthedentalliteraturelookingforclinicaltrialsinvestigating poste-riorcompositerestorationsoverperiodsofatleast5yearsoffollow-uppublishedbetween 1996and2011.Thesearchresultedin34selectedstudies.90%oftheclinicalstudiesindicated thatannualfailureratesbetween1%and3%canbeachievedwithClassIandIIposterior compositerestorationsdependingonseveralfactorssuchastoothtypeandlocation, oper-ator,andsocioeconomic,demographic,andbehavioralelements.Thematerialproperties showedaminoreffectonlongevity.Themainreasonsforfailureinthelongtermare sec-ondarycaries,relatedtotheindividualcariesrisk,andfracture,relatedtothepresenceof aliningorthestrengthofthematerialusedaswellaspatientfactorssuchasbruxism. Repairisaviablealternativetoreplacement,anditcanincreasesignificantlythelifetimeof restorations.Asobservedintheliteraturereviewed,alongsurvivalrateforposterior com-positerestorationscanbeexpectedprovidedthatpatient,operatorandmaterialsfactors aretakenintoaccountwhentherestorationsareperformed.

©2011AcademyofDentalMaterials.PublishedbyElsevierLtd.Allrightsreserved.

1.

Introduction

Directrestorationshavebeenlargelyemployedtorestore pos-teriorteethduetotheirlowcostandlessneedfortheremoval ofsoundtoothsubstancewhencomparedtoindirect restora-tions,aswellastotheiracceptableclinicalperformance[1–4]. Despite the fact that both amalgam and composite resin are considered suitable materialsfor restoringClass I and Class II cavities, some advantages can be related to com-positerestorations suchas better esthetics;their adhesive

∗ _{Correspondingauthorat:GraduatePrograminDentistry,FederalUniversityofPelotas,RuaGonc¸alvesChaves457,96015-560Pelotas,RS,} Brazil.Tel.:+555332226690x135;fax:+555332226690x135.

E-mailaddresses:fl[email protected],[email protected](F.F.Demarco).

properties,resultinginreducedpreparationsize[5];and rein-forcement ofthe remaining dental structure [6]. A clinical studyhasshownthatpainfulvitalteethwithincomplete frac-turescanbetreatedsuccessfullybyreplacingtheamalgam fillingswithbondedcompositerestorations[7].Ontheother hand,posteriorcompositerestorationshavebeenshownto produce higher failure rates due to secondary caries[8,9]. However,althoughusedinmanypracticesaroundtheworld, amalgamisfacingitsdemise,leavingresincompositeasthe mostlikelymaterialforposteriorrestorationsforwidespread useinthenearfuture.

0109-5641/$–seefrontmatter©2011AcademyofDentalMaterials.PublishedbyElsevierLtd.Allrightsreserved. doi:10.1016/j.dental.2011.09.003

88

Eventhoughacceptablesurvivalratesare achievedwith ClassIandIIrestorationsindentalhealthcare,the replace-mentoffailingrestorationsisstillarelevantissue.Dentists stillspendasignificantamountoftimereplacingrestorations, contributingtotherepetitiverestorativecycle described by Elderton[10].Factorsrelatedtothepatient,operator,tooth, cavitysize,andmaterialshavebeenreportedintheliterature as potentially relevant forrestoration failures [2,3,8,11–13], althoughevidenceofthisisstilllimited.

Despitetheconsiderabledifferencesinpropertiesamong commercial composites as found in laboratory analysis [14–20],invitrotestsarelimitedinpredictingtheclinical sur-vivalofcompositerestorations.Duetotheconstantinfluxof newposterior restorativematerialson themarket and the needformanufacturerstoprovetheclinicalsafety oftheir newmaterials,therehasbeenanemphasisonrelatively short-termclinicalstudieswithalimitednumberofrestorations, mostlyplacedinlow-risk patients.In thosestudies, differ-encesinperformanceareseldomfound,asmostmaterials performwell on ashort-termbasis, withafew exceptions [21,22].

To estimate how long posterior composite restorations last,long-termstudiesareneededtoidentifymodesof fail-ureandpossiblereasonsforthesefailures.Inacomparative amalgam–composite study after5 years, no differences in performancewere found;after12years,however,the com-positeshowedsignificantlybetterperformance[12].Giventhe considerabledifferencesbetween(non-bonded)amalgamand compositeandthefactthat,after5years,nodifferencesin performancewereobserved,itisnotlikelythatthemajority ofcompositerestorationswillshowdifferentlongevitywhen investigatedbeforeatleast5yearsofclinicalservice.Because oflimitedobservationtimesofmostclinicalstudies[4], lim-itedinformationisavailableontheperformancedeterminants andreasonsforthefailureofposteriorcompositerestorations inthelongterm.Althoughtherapidevolutionofcomposites makesitdifficultforlong-termevaluationstobeconducted usingmaterialsstillavailableinthemarket,thegoodresults shown with previous and presently available materials in clinicalstudies [3,4,12]foster thequestion ofwhether new materialsare actuallyimprovements,and theauthors tend toconcludethatthisisnotlikely.Thismeansthat,basedon theavailablelong-termstudies,especiallystudieswith obser-vationtimesexceeding5years,anexpectationregardingthe long-termbehaviorofposteriorcompositerestorationscanbe made.Inthepresentarticle,weaimtoreviewanddiscuss, withanemphasisontheavailablelong-termliterature,the longevityofposteriorcompositerestorations,andthemain factorsassociatedwithrestorationfailures.

2.

Methods

and

results

2.1. Selectionofpapers

To investigate the longevity of composite restorations as reportedinclinicalstudiesinthedentalliterature,aPubMed searchforarticlesthatevaluatedlongitudinaldatafor pos-teriorresin compositerestorationspublishedbetween1996 and2011wasperformed.Thetermsusedinthesearchwere

‘posteriorcompositerestorations’and‘survival’or‘longevity’ or ‘failure’. After selecting only papers reporting clinical longevity studiesofcompositerestorationswithevaluation periodsofatleast5years,atotalof34papersreportingon variedmaterials,techniques,andmethodsofevaluationwas found. Theselected papersincluded prospectiveand retro-spective clinicalstudies,aswell aslongevitystudies based onsecondarydata.Excludedforlongevityassessmentwere cross-sectionalstudiesastheseareconsideredtodeliver unre-liabledatawithrespecttolongevity[23].Theselectedpapers weresearchedforthereportedlongevityoutcome,expressed in annualfailure rates (AFRs)or mediansurvival, and fac-torsassociatedwithcompositefailureasmentionedbythe respectiveauthors.

2.2. Longevityofposteriorcompositerestorations

From Table 1, the following conclusions regarding the

longevityofposteriorcompositerestorationscanbemade:on average,theAFRsofClassIandIIposteriorcomposite restora-tionsplacedinvitalteethvarybetween1%and3%.Thisisin accordancewiththeresultsreportedinthemostrecentreview published byManhart et al.[4]. For endodonticallytreated teeth,theAFRsvaryfrom2%to12.4%.

3.

Aspects

that

influence

longevity

3.1. Clinical

Clinicalrelatedfactorsplayanimportantroleinrestoration longevity and causes of failure. Several studies have indi-catedthatthepositionofthetoothinthemouthorthetooth typedirectlyaffectsrestorationlongevity,withrestorationsin premolarsshowingbetterperformancethanthoseinmolars [2,3,24–26]. One paperreported arisk ofrestorationfailure twice ashigh formolars comparedto premolars[24]. One studywitha22-yearobservationtimefoundtheriskoffailure ofrestorationsplacedinlowermolarstobe3timeshigherthan theriskoffailureinupperpremolars[3].However,astudyon largerestorationsof3ormoresurfacesdidnotfinddifferences betweenthelongevityinmolarsandpremolars[12].

Thefindingsmentionedaboveareexplainedbythe knowl-edgethatrestorationsplacedinmolarteetharesubjectedto highermasticatorystressesthanrestorationsplacedin pre-molars.Similarly,cavitysize,cavitytype,andthenumberof restored surfacesarerelatedtothefailurerisk.Inthis con-text,multi-surfacerestorations,extensivecavities,andClass IIrestorations,aremorelikelytofailthansingle-surfaceand ClassIrestorations[2,3,9,13,24,26–29].Onestudyshowedthat ClassIIrestorationshavearelativeriskoffailureof2.8 com-paredtoClassIrestorations,andthatrestorationswith3or moresurfaceshavearelativeriskoffailureof3.3inrelationto single-surfacerestorations[2].Anotherstudycalculatedthat everysurfacemoreresultedinanincreasedriskoffailureof 40%[24].

Two papers reportedan increasedrisk offailure witha higher number of restored teeth per patient [9,13]. These patients maybeconsideredtohaveahigherriskofcaries,

d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 87–101

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Table1–Resultsfromtheliteraturesearch:clinicaltrialswithfollow-upperiodsofatleast5yearspublishedbetween1996and2011.

Author,year Evaluation

period/studydesigna

Materialstested Evaluated

restorations

AFRb_{/outcome/survival} rateofcomposite

Factorsassociatedwith compositefailure

DaRosaRodolphoetal.,2011[3] 22years,RL Composite ClassIandII AFR:between1.5%and

2.2%

Toothtype,cavitysize, material

Opdametal.,2010[12] 12years,RL Compositevs.amalgam LargeClassII AFR:1.68% Cariesrisk

Fokkingaetal.,2008[104] 17years,PL Composite Endodonticallytreated

teethwithorwithouta prefabricatedmetalpost

AFR:2.8%(restoration level)and1.2%(tooth level)

Nofactorsassociated

Bernardoetal.,2007[8] 7years,PL Compositevs.amalgam ClassIandII AFR:2.1% Secondarycaries

Opdametal.,2007[24] 9years,RL Composite ClassIIwithatotal-etch

techniqueorwith glass-ionomerlining

AFR:1.3%(total-etch) and3.3%(glass-ionomer lining)

Presenceofalining,caries risk

Opdametal.,2007[13] 5and10years,RL Compositevs.amalgam ClassIandII AFR:1.7%(5years)and

1.8%(10years)

Amountofrestored surfaces

Soncinietal.,2007[9] 5years,PL Amalgamvs.

composite/compomer

Childrenaged6–10with morethanoneposterior restoration

AFR:2.98% Numberofrestorations,

cavitysize

Lindbergetal.,2007[105] 9years,PL Composite/composite–

compomeropen sandwich

ClassII AFR:1.1% Nofactorsassociated

Gordanetal.,2007[55] 8years,PL Composite ClassIandII AFR:0% Notinvestigated

DaRosaRodolphoetal.,2006[2] 17years,RL Composite ClassIandII AFR:2.4% Tooth,cavitytype,cavity

size Burkeetal.andLucarottietal.,2005

[27–29,37]

Upto10years,RS Amalgam,composite andglass-ionomer

ClassIandII AFR:8.4%(5years)and 5.7%(10years)

Operator:age,countryof qualification,employment status;Clinical:cavitysize, rootfilling;Patient:age, charge-payingstatus, practiceassiduity

Nagasirietal.,2005[106] 5years,RL Composite,amalgam

andOZE

Endodonticallytreated molars

AFR:12.4% Remainingcoronaltooth

structure

Mannoccietal.,2005[107] 5years,PL Amalgam/composite

withpost,

endodonticallytreated tooth

ClassII AFR:2% Morerootfracturewith

amalgam,moresecondary carieswithcomposite

Opdametal.,2004[40] 5years,RL Composite ClassIandIIplacedby

dentalstudents

AFR:2.6% Operator:yearof

graduation;Clinical: proximalcontactstatus Andersson-Wenckertetal.2004[30] 9years,PL Compositeand

glass-ionomer,open sandwich

ClassII AFR3.2% Notinvestigated

Coppolaetal.,2003[39] 5years,RS Compositevs.amalgam Posteriorrestorations

with2surfacesatleast

Averagelongevity:42 months

Dentistexperience

HayashiandWilson,2003[108] 5years,PL Composite ClassIandII AFR:3.76% Marginaldeterioration,

90

Author,year Evaluation

period/studydesigna

Materialstested Evaluated

restorations

AFRb_{/outcome/survival} rateofcomposite

Factorsassociatedwith compositefailure

PallesenandQvist,2003[25] 11years,PL Composite,directvs. indirect

MediumtolargeClassII AFR:1.45% Toothtype

Turkunetal.,2003[76] 7years,PL Composite ClassIandII AFR:0.82% Nofactorsassociated

vanNieuwenhuysenetal.,2003[26] 5–22years,RL Amalgam,composite andcrowns

Posteriorextensive restorations

Averagesurvivaltime: 7.8years

Clinical:toothtype, extensionofrestoration, pulpalvitality,useofbase material;Patient:age, 3-yearperiodoftreatment

Busatoetal.,2001[109] 6years,PL Composite ClassIandII AFR:2.5% Notinvestigated

Gaengleretal.,2001[31] 10years,PL Compositewithglass

ionomercement

ClassIandII AFR:2.6% Notinvestigated

Kohleretal.,2000[51] 5years,PL Composite ClassII AFR:5.5% Cariesrisk

vanDijken,2000[110] 11years,PL Composite,direct

inlays/onlaysand restorations ClassII AFR:1.6% (inlays/onlays)and2.5% (directrestorations) Toothtype

Wasseletal.,2000[111] 5years,PL Composite,directvs.

inlay

ClassIandII AFR:1.5% Notinvestigated

LundinandKoch,1999[112] 5and10years,PL Composite ClassIandII AFR:2%(5years)and

2.1%(10years)

Notinvestigated

Raskinetal.,1999[41] 10years,PL Composite ClassIandII AFR:8.6% Notinvestigated

Wilderetal.,1999[113] 17years,PL Composite ClassIandII AFR:1.4% Notinvestigated

Collinsetal.,1998[73] 8years,PL Composite ClassIandII AFR:1.71% Notinvestigated

Mair,1998[74] 10years,PL Compositevs.amalgam ClassII 100%ofsuccess Notinvestigated

Nordboetal.,1998[75] 10years,PL Composite Saucer-shapedClassII AFR:3.0% Notinvestigated

Studiesusingsecondarydataarehighlightedingray.

a _{R:retrospective;P:prospective;L:longitudinal;S:secondarydataacquisition.} b _{AFR:annualfailurerate.}

dental materials 28 (2012)87–101

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whichwouldexplainthehigherratesofrestorationfailures observedinthesepatients.

The type of the substrate on which the composite is placedcould alsoaffect the restorationlongevity. The use ofaglass-ionomerbaseunderanadhesiverestorationwas showntodecreaserestorationsurvivalcomparedwith total-etchrestorations[24],withfracture asthemainreasonfor failure. Itisnotyet clear, however,whether thickness and typeofglass-ionomercementsplayaroleinthefailure behav-ior.Other clinicalstudies inwhich abaseofglass-ionomer wasusedalsoshowedincreasedfailurebyfractureovertime [2,3,26,30,31],buttheabsenceofarestorativecontrolgroup placedusingtotal-etchbondingprocedureinthosestudiesor alackofspecificationsfortheappliedlinermakesit impossi-bletodrawmoredefinitiveconclusions.Itisalsopossiblethat extensivelayersofcalciumhydroxideliningsandtheamount ofsoftcarioustissueleftbehindmightaffectthestrengthand longevityofcompositerestorations.Althoughthereis clin-icalevidencethattheremovalofsoftdecayedtissueisnot necessarytostopacariesprocessonceawell-sealed restora-tionisplaced[32,33],itremainsquestionablewhetherthiswill reducethestrengthoftherestorativecomplexandincrease theamountoffailureinthelongterm[34,35].

FromTable1,itcanalsobeconcludedthatposterior com-positerestorationsplacedinendodonticallytreatedteethhave areducedsurvivalrate,whichisexplainedbytheextensive lossoftoothsubstancethattheseteethsuffer.

3.2. Operator

Itisgenerallyacknowledgedthattheoperatorisprobablythe mostimportantfactorin thelongevity ofa dental restora-tion.However,evidencefromclinicalstudiesdoesnotsupport thisassumption.Clinicalstudiesonposteriorrestorationsand clinical procedures in which more than one operator was involved,donotrevealdifferencesinstudyoutcomeamong theoperators[13,36].Itislikelythateverydentistwhoisaware thathisworkisinvolvedinaclinicaltrialwillworkas accu-ratelyas possible,resulting in fewer operatorfailures that couldinfluencethestudyoutcome.

However,secondarydatastudiessuggestthatthe opera-torsignificantlyinfluencesthelongevityofarestorationand mentionrelevantfactorssuchasage,countryofqualification andemploymentstatus[27–29,37].Moreover,itisthedentist whodecideswhetherarestorationneedstobereplaced.From thosesecondarydatastudies,itisknownthatpatients chang-ingdentisthaveanincreasedchancethattheirrestorations willbereplaced[27–29,37].Reducedlifetimeforcompositeand amalgamrestorationshasbeenreportedforpatients chang-ingdentists[38],beingthiseffectaccountedtothehighlevel ofvariabilityindiagnosticdecisionsamongclinicians.Amore conservativeapproachtowardrestorationreplacementwould, therefore,leadtoincreasedrestorationlongevity.

Technique-relatedaspectsofaposteriorrestorationrely on the knowledge and sufficient skills of the operator. A studyconductedbyCoppolaetal.[39]revealedthatefficient workingdentistsproducerestorationswithahighersurvival rate than inefficientworking providers. In that study [39], a decision-making approachwas used to measure relative efficienciesofoperatorsbyconsideringmultipleinputsand

outputs regarding clinical decisions in order to identify the most efficient providers. Other study has shown that inexperienced undergraduate students were more closely associated with certain types of restoration failures than moreexperiencedstudents[40].

In the past, dentists complained about difficulties in achievingadequateproximalcontactwhenplacinga poste-riorcomposite,andthiswasalsofoundinaclinicalstudy[41]. Nowadays,techniqueshaveevolvedinthatrespect,andthe operatorcannowuseseveraltypesofmatricesand separa-tionringsthatresultineventightercontactthanbeforethe treatment[36,42,43].

Theoften-mentionedproblemsofpost-operative sensitiv-ityrelatedtoposteriorcompositerestorationsmayberelated toadhesiveprocedureshavingnotbeendoneproperlydueto the inappropriateselectionofadhesivematerialsand tech-niquesortheapplicationofmaterialsnotinaccordancewith the manufacturers’ instructions. It has been foundin sev-eral studiesthatself-etch adhesivesleadtolesssensitivity [44–47], though,inrecentliterature,thesensitivityproblem seemstobelessprominent,whichmightberelatedtogreater experience amongdentists withincreased knowledge con-cerningtheproperapplicationofstate-of-artadhesiveagents andincreaseduseofself-etchmaterials.Arelativelyrecent studyonpost-operativesensitivityfoundthatthiswasmainly relatedtothecavitysizeandconcludedthatmostsensitivity haddisappearedovertime[48].

Some clinicians tend tomake restorationsof very high qualitywhenitcomestothecolorandanatomyofthe restora-tion[49,50].However,theserestorationsareneversubjectedto longevityevaluation,anditisunlikelythattheseesthetic qual-ityaspectshaveanyinfluenceonposteriorrestorationsurvival ingeneral.Moreover,thesetypesofcompositerestorations,as inspiringtheycanbeforthecolleaguedentist,arenotfeasible toplaceineverydaypractice.

3.3. Patients

Althoughevidenceislimited,itislikelythatthetypeofpatient andtheoralenvironmentplayanimportantroleinthe sur-vivalofdental restorations.Thecariesrisk ofpatientshas beenshowntosignificantlyinfluencethelongevityof restora-tions. Amongtheselected studies,several investigatedthe cariesriskandfoundincreasedriskoffailureofrestorations placedinpatientswithcariesrisk[12,24,51].Restorationsin ahigh-cariesriskgrouphadafailureratemorethantwice ashighcomparedtolow-riskpatients[12].Inthatstudy,the cariesriskwasestablishedbythetreatingdentistbasedon thedental historyandtheexpectedriskofnewlesion[52]. Anotherstudythatusedacariesriskassessmentalsoshowed thathigh-cariesriskpatientshaveincreasedriskoffailureof posteriorcompositerestorations[53].Inastudyondirect pos-teriorrestorationsinchildren,thosewithahighDMFTindex hadanincreasedriskofrestorationfailure[35].

In investigating the prevalence ofsatisfactory posterior compositerestorationsinabirthcohort,ahigherprevalence ofunsatisfactoryrestorationsattheageof24wasobserved inpatients exhibitingahigher levelofdental cariesatthe ageof15[54].Clinicalprospectivestudiesperformedin uni-versityclinicsthatevaluatethelongevityofrestorationsof

92

newmaterialsarelikelytoincludeonlymotivatedpatients with good oral health and, consequently, low caries risk. Thiswould explainwhy,insomeprospectiveclinicaltrials, a high survival rate is found in the absence ofsecondary caries,orwithveryfewrestorationsfailingduetosecondary caries[41,55],whilecross-sectionalstudieshaveshownthat cariesare the most importantreason forthe replacement ofcompositeandamalgamrestorations[56–59].Also,when restorationsareperformedinpatientswithahighereconomic statusinaprivateclinic,secondarycariesdonotseemtobea mainreasonforthefailureofposteriorcompositerestorations [2,3].

Toothandrestorationfracturealsoareimportantreasons forrestorationfailure.Itis,therefore,likelythatbruxinghabits such as grinding and clenching play an important role in fatiguedevelopmentinthetooth-restorationcomplex, result-inginfractureinthelongterm.Thediagnosisofbruxismis noteasy,anddiagnostictoolsforthisarenotalwaysreliable [60].Sometimes,itismentionedintheinclusioncriteriafora clinicalstudythat“bruxingpatientswereexcludedfromthe sample”,withnomentionofthecriteriausedforsucha diag-nosis.Aclinical3-yearstudyonthelongevityofcomposite restorationsplacedinpatientswithseveretoothwearshowed unfavorableresultscomparedto‘normalpatients’,indicating thatthedestructive mouthhabits ofthesepatients (proba-blywithbruxism)resultedinmorefailures[61].Inastudyon crackedteeth[7],itwasspeculatedthatclenchinghabitsmight playaroleintheetiologyofcrackedandfracturedteeth,an importantreasonforthefailureofamalgamrestorationsin particular[12].Currently,novalidatedcriteriaareavailableto assessbruxinghabits,eitherforgrindingnorclenching;thus, conclusionsregardingadirectrelationshipbetweenbruxism andrestorationfailure,althoughsucharelationshipisvery likely,arestillnotpossible.

Post-operativesensitivityisapatient-relatedfactor,such aspainexperienceandamountofdiscomfort,thatcanvary betweenpatients.Inthepast,post-operativesensitivitywas acknowledgedasanimportantproblemfordentistsworking withcompositerestorations.However,as mentioned previ-ously,post-operativesensitivityismorecloselyrelatedtothe adhesivesystem[46]or restorativetechniqueapproach[62] andisalessprominentprobleminrecentliterature.

Esthetic demand from the patient is a further factor determiningrestorationlongevity.Highdemandforesthetic perfectionismis likelytoresult inmorerestorationsbeing replacedforestheticreasons.However,inaretrospective clin-icalstudy lessthan 1%oflargeamalgamrestorationswere replacedduetoestheticreasons[12],andnoposterior com-posite restorations were replaced due to esthetic reasons. Therefore,withrespecttothelongevityofposteriorcomposite restorations,failureduetoestheticreasonsseemstobevery rare.

3.4. Socioeconomic

Inadditiontoclinicalvariables,patientdemographic, socioe-conomicandbehavioralvariablesmayalsoaffectthelongevity of posterior restorations. Very few studies have investi-gated the association between these variables, but the findings suggest that such factors can play an important

role inthe longevityof restorations. Burke et al. [11] ana-lyzed data from General Dental Services in England and Wales between 1991and 2002, involving a total of503,965 restorations. While survival analysis showed no difference between genders, the age of the patients was significant, with older patients having a shorter interval before re-intervention.

Asdentalcariesarestronglyassociatedwithsocial deter-minants experienced during the life course [63–65], it is possible that social determinants can also influence the longevityofrestorationsbythesamepathway.However,this remains to be established,because most investigations on restoration longevity have focused on materialsand tech-niques or cavity preparation features [2–4,66]. In addition, most ofthe clinicaltrials reporting the longevityof poste-riorrestorationsarecarriedoutinuniversityclinicalsettings [67] and population-based studies are very rare [11]. How-ever, several retrospective studies have been conductedin general practices including at least some at-risk patients [2,3,9,12,13,24,51,68].Moreover,manyofthestudiesthat ana-lyzedpatientfactorsusedastatisticalapproachconsidering thetoothrestorationastheuniqueunitofanalysis.To ana-lyze the influence of socioeconomic factors on restoration longevity,oneshouldconsiderthefactthatvariationbetween subjects is great, and it is also important to consider the existing variationbetweentheteethofthesamepatient.A recentstudyin24-year-oldsubjectsfromabirthcohort[54] used amultilevel statisticalapproachto consider variables atboththepatientandtoothlevels.Thisstudyshowedthat thesocioeconomictrajectoryfrombirthtoage15was associ-atedwithposteriorrestorationfailure,evenafteradjustment bytooth-levelvariables.Peoplewhohadalwayslivedinthe pooreststratusofthepopulationhadmorerestoration fail-uresthanthosewholivedintherichestlayer(oddsratio:3.14; CI95%1.6–3.84)[54].

Otherfindingsshownbyaseriesofstudies[27–29,37]have corroboratedtheideathatsocioeconomicandbehavioral vari-ablesactdirectlyonthe longevityofposteriorrestorations. Thecharge-payingstatusofthepatienthad anassociation withsurvivalforcharge-payersbeingslightlyhigherover11 yearsthanfornon-payers.Also,astrongrelationshipbetween attendancefrequencyandsurvivaltimewasobserved,with restorationsofmorefrequentattendersperforminglesswell thanthoseoflessfrequentattenders.

3.5. Material

In vitro studies on the properties of resin composites for the restorationofposterior teethhaveshown considerable differences amongcommerciallyavailablematerials. Differ-encesinflexuralandcompressivestrength[15–18,69],elastic modulus[14,16–18],fracturestrengthandtoughness[19,70], hardness [15,16,69,71], and wear resistance [15,20,70,72], among others, have been shown to be significantly differ-entamongmaterialswhenlaboratorytechniqueswereused tocomparetherestoratives.Despitetheseconsiderable dif-ferences, which were usually considered to be a result of differences inorganicmatrix components, fillerloading,or particlemorphology/size,onlyminordifferencesinthe clini-calbehaviorofcompositerestorationsplacedwithdifferent

dental materials 28 (2012)87–101

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compositematerials are oftendescribed inclinical studies [22,25,73–76].

Arestrictioninclinicaltrialsisthatlongobservationtimes arehardlyfeasible.Asaresult,mostprospectiveclinical stud-ies comparing different composites report short follow-up periods,showingnodifferencesamongthematerialsunder investigation. A recent retrospective study, however, has shownthat,after22years,differencesinfillercharacteristics betweencompositesaffectedtheirclinicalperformance[3],as superiorlongevitywasobservedforahigherfiller-loaded com-posite(midfilled)comparedwithaminifilledmaterialwhen restorationswereevaluatedinthelongterm.Thisstudywas thefirsttoindicatethatthephysicalpropertiesofthe compos-itemayhavesomeimpactonrestorationlongevity.Fracture beingthemainreasonforfailureindicatesthatthemidfilled composite,whichhashigherelasticmodulusand hardness thantheminifilledmaterial,waslesssensitivetolong-term fatigue.

However,whenthesamepopulationgroupwasassessed aftera17-yearfollow-up[2],nosignificantdifferencesamong thematerialscouldbeobserved,indicatingthatdifferencesin clinicalperformancebetweencompositematerialswith dif-ferentpropertiesmaybesignificantonlywhenthelatefailing behaviorofcompositerestorationsistaken into considera-tion.Atthesametime,it remainstobediscussedwhether thesesignificantdifferencesfoundafter22yearsarerelevant fromtheperspectiveofdentalhealthcare.Giventhefinding that,inmostclinicalstudies,AFRsbetween1%and3%have beenfoundforthecompositesused,onecanspeculateasto whetheranyrelevantimprovementinmaterialpropertiescan bemadethatwouldhaveaclinicalimpact.Inotherwords,the resincompositematerialsforuseinposteriorteethmarketed inthelasttwodecadesmayhaveaqualitystandardthatis sufficienttofulfilltheclinicalrequirementsinmostcases.

Nevertheless,numerousresin-basedmaterialstorestore posterior teeth are introduced into the market each year, claimingimprovedpropertiesandpresentinginnovationsin organic and inorganic components. A significant concern regardingclinical trialstocompare different restorativesis thatwhileagivencomposite isbeingassessedafterafew yearsofclinicalservice,thematerialmightnotbeavailablein themarketanymore.Themajorchangeintheinorganic for-mulationofcompositesforposteriorrestorationsinthepast decade wasthe introduction ofnanofilledcomposites, cre-atedinanendeavortoprovideamaterialwithsuperiorpolish andglossretentionfortheanteriorandposteriorareas. Clini-calevaluationsofnanocompositescomparedwithtraditional hybridsareincreasinglyavailableintheliterature[77–84],but theevaluationperiodsarestillshort(upto5years)todrawany significantconclusions.Todate,nomajorclinicaldifferences havebeen reported betweennanofilled and hybrid materi-als,exceptforperceivedbettersurfaceappearance/polishfor nanofills[81,82].Itisnotlikelythatthesenanofilled materi-alswould showsuperiorperformancecomparedtohybrids whenusedineverydaysituationsincludingpatientsatall lev-elsofrisk.Themainquestionwillbewhethertheseinnovative materialswillmeetthestandardsthatare,inthemeantime, setbytheavailable,mainlyhybridcomposites,showingthat anAFRof1–3%isfeasiblefortheaverageClassIIposterior compositerestoration.

Microfilledcomposites,incontrasttohybrids,are gener-allynotrecommendedforuseinposteriorrestorationsdue totheirlowerfracturestrength.Microfilledresincomposites usean‘organicfiller’approach,wherebyinorganicparticles andresinarecured,crushedandaddedtoresintoproduce thefinalcompositematerial.Theoverallamountoffillerthat canbeincorporatedintothesecompositesislimited, result-ing in higher coefficients of thermal expansion and lower elastic modulicomparedwithconventional hybrids[85,86]. Eventhoughaclinicalstudyinvestigatingposterior restora-tionslimitedinsizeshowedfavorableresultsforamicrofilled composite[73],thesamematerialshowedpoorclinical per-formancewhenusedinlargerestorationsandpatientswith toothwear[61].

Oneofthemostcomprehensivestudiesontheimpactof theformulationofrestorativecompositesontheirclinical per-formance waspublished in2001[87].Theeffect oforganic matrixcomponents,fillercompositionandfillersilanization werealladdressedbyclinicallyusingexperimental compos-ites. The authors found that the resin formulation was a significantfactoraffectingwear,withaUDMA/TEGDMA-based formulation showing significantly higher wear resistance, while the silane and filler were not significant factors. However, the paperconcentrated onlyon the wear of the restoratives, and the wear of current posterior composite restorationsisnotaclinicalproblem(seethefollowing sec-tionofthepaper).Nowadays,wearmaybeaproblemmainly for patients withbruxing and clenching habits [88]. These patientsmaybeservedbestwithawear-resistantcomposite when their lost tooth substances are tobe replaced. How-ever,resultsindicatingtheclinicalperformanceofcomposite restorationsplacedinpatientswithseveretoothwearare lim-ited.

Currentchangesintheorganicphaseofdental compos-ites focus on reducing the polymerization shrinkage and stressassociatedwithmethacrylate-basedmaterials[89,90]. Alow-shrinkage,silorane-basedresincompositewasrecently introduced, but clinical trials with this material are too recentandscarcetoindicateanyimprovementinrestoration longevity[68].Likewise,aswiththenanofilledcomposites,it canhardlybeimaginedthatthesematerialswillshow supe-riorperformancecomparedtothecurrenthybridcomposites intermsofsurvivalconsideringthemainreasonsforfailure reportedinthefollowingsectionofthepaper.Recent devel-opments incariology indicate that marginalleakage,often consideredanimportantphenomenonnegativelyinfluencing restorationperformance,isnotrelevantforsecondarycaries development[91,92].However,thereisalwaysroomfor inno-vation[93],andnovelmaterialsmightleadtoclinicalbenefits eveniftheydonotextendthesurvivalofrestorations, espe-ciallyifnewmaterialsare designedtomaketheplacement ofresin-basedcompositerestorationsalessstressfulandless technique-sensitiveexperience[94].

Thematerialpropertiesoftherestorativecompositeforthe posteriorarea,therefore,seemtohaveaminoreffectonthe longevityofrestorations,providedthathybridmaterialsare used, asthesematerialshavebeen showntoperform well toexcellentlywhenusedinposteriorcompositerestorations. Negativeexceptionsincludesomenovelmaterialsthatturned outtobeunacceptableshortlyafterbeingmarketed[21,22],

94

whichisareasonthatshort-termclinicaltrialsofaminimum of3yearsarestillneededbeforeadentistcanuseamaterial inaposteriorrestorationinaresponsible way.Meanwhile, cliniciansare advisedtostick withhybridmaterials,which canbeconsideredthe‘goldstandard’forposteriorcomposite restorations.

Other factors related to the restorative complex might influence the clinical behavior of composite fillings. The useofaliningmaterial,aspreviouslymentioned,hasbeen shown to significantly affect the longevity of restorations [24,26]. Due tothe possibleincreasedriskoffatigueinthe longterm,abaseorliningofglass-ionomercementshould not be applied when possible. The selection ofan appro-priate bonding agent, although significantly affecting the survival of Class V restorations [95], is usually described as having marginal to no [62,96–98] or a relatively low

[44–46] impact on the clinical performance of posterior

restorations.However,awell-performingdentaladhesivemay aid in reducing post-operative sensitivity. It is, therefore, advised that, when placing a posterior composite restora-tion,clinicians should use a‘gold standard’adhesive such asthree-step,etch-and-rinse,ortwo-step,self-etchbonding agents.

4.

Main

reasons

for

failure

Table 2 shows the maincauses of failure reported by the

studies included in this review (Table 1). The two main causes of failure identified were fracture (restoration or tooth) and secondary caries. In a previous review, it was shownthatearlyfailureswere morecloselyrelatedto frac-tures,whilestudieswithlongperiodsofobservationshowed a trend to find more caries-related failures [1]. However, according tothe present review,the same conclusion can-not be drawn since most long-term studies (more than 10 years of follow-up) showed a higher incidence of fail-ure due to fracture than to caries [2,3,25]. Similarly, some of the 5–7-year follow-up studies showed higher propor-tions of failure due to secondary caries [8,9,51] than to fracture. Therefore, factors suchas patient cariesrisk, the clinical setting of the study, and the socioeconomic char-acteristics of the population under study would be more determinantforthereasonsforfailurethantheclinicalage ofthe evaluatedrestorations[3,12,54]. Regardingsecondary caries, a recurrent problemin the literatureis the lack of standardized criteria for diagnosis among studies, which coulddirectlyaffecttheiroutcomes[92,99].Fewstudieshave addressedthespecificcriteriausedforsecondarycaries diag-nosis.

Other reported failure causes, such as failure due to endodontic reasons, pain, post-operative sensitivity, and estheticreasonscouldbeconsideredminorreasonsfor fail-ure sincethey are individually related to less than 5% of theobservationsinthedifferentstudiesshowninthetables. Also,somestudies,especiallyreportspublishedbefore2000, pointedoutmarginaldiscolorationandmarginaldefectsas cause of failure, responsible for1–10% ofthe observations dependingonthereport.ThestudyconductedbyRaskinetal. [41]evaluatingposteriorcompositerestorationsafter10years

ofclinicalserviceisremarkableinthatrespect,asitfound anAFRof8.6%,whichisveryhighcomparedtoother stud-ies.Moreover,themajorityoftherestorationswereconsidered tohavefailedduetothelossofanatomicform,alsoseldom foundasareasonforfailureinotherstudies.Itis remark-ablethatfracturewasnotfoundandthatonlytwocasesof secondary carieswere found.Thisindicates thateitherthe investigatedmaterialwasextremelysensitivetowearorthe appliedcriteriafortheevaluationofrestorationsweremainly used forproducing resultsinresearch ratherthan indicat-ingthatarestorationwasreallyclinicallyunacceptableand neededtobereplacedintheshortterm.However,wearand loss ofanatomic formare seldomconsidered tobe causes offailure inmorerecent studies.Sincetherevised studies haddistinctpurposesanduseddifferentevaluationtoolsand criteriaforrestorationassessment,certainvariationsinthe attributed failure causes listed in Table 2 are not surpris-ing.

5.

Repair

as

an

alternative

to

replacement

Failedrestorationsorrestorationspresentingsmalldefectsare routinelytreatedbyreplacementbymostclinicians.Because ofthis,formanyyears,thereplacementofdefective restora-tions hasbeenreportedasthemostcommontreatmentin generaldentalpractice,anditrepresentsamajorpartoforal healthcareinadults[100].When arestorationisreplaced, a significant amount ofsound tooth structure is removed andthepreparationisenlarged[100,101].Moreover,the gen-eral cost ofareplacementmay behigher than the costof alternative treatments, suchastherepairor resurfacingof restorations. These alternative treatments are reported to increasethelongevityofamalgamandcompositerestorations [26,100–102].Despitethepromisingresultsofthesemore con-servativetreatments,veryfewlongitudinalstudieshavebeen publishedassessingrepairsasanalternativetothe replace-mentofrestorations,andtherearenostudieswithfollow-ups longer than7years.Also,arecentpublicationshowedthat thereisstillroomforimprovementinteachingontherepair ofrestorations,especiallycomposites,duringundergraduate training[103].

Ourgrouphasrecentlypublishedanevaluationofupto 22yearsofposteriorcompositerestorationsplacedwithtwo composites [3]. In that study, 61 of110 failed restorations wererepairedasanalternativetocompletesubstitution.For statisticalpurposesinthatpublication,weconsideredboth repaired and replaced restorations to be failures, and the AFRwas1.9%over22years(Fig.1).However,whenrepaired restorationswereconsideredsuccessesinsteadoffailures,the AFRdecreasedto0.7%.Thesedatacorroboratetheexpressive impactofchoosingmoreconservativetreatmentswhen deal-ingwithrestorationdefectstopreventprematurefailuresand improverestorationlongevity.Fig.2showsrepresentative pic-turesofarestorationevaluatedonthe22-yearfollow-upstudy thatwasstillclinicallyacceptable(Fig.2A)orthathavebeen repairedduringthefollow-upperiod(Fig.2B).Inthelattercase, repairwasconsideredanalternativetoreplacement,andthe restorationwasstillclinicallyserviceable7yearsafterbeing repaired.

d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 87–101

95

Table2–Causesoffailureofposteriorcompositesaccordingtotheselectedstudies,showninTable1recordingclinicalfailures.

Author,year Periodof evaluation

Typeofrestoration Percentageoffailurecauses(inrelationtothetotalnumberof evaluatedrestorations) Restoration fracture Secondary/ primary caries Tooth fracture Endodontic treatment/ pain Esthetics Extraction

DaRosaRodolphoetal.,2011[3] 22years 14.1 7.5 5.3 1.9 0.83 0.83

Opdametal.,2010[12] 12years 0.9 8.2 1.4 3.5

Bernardoetal.,2007[8] 7years 1.8 12.7

Lindbergetal.,2007[105] 9years 2.3 5.9 0.7 2.2

Opdametal.,2007[24] 9years Total-etch 1 7

Sandwich 22 13

Opdametal.,2007[13] 5and10years 0.61 5 1.3 1.4 1.1

Soncinietal.,2007[9] 5years 0.27 12.6

daRosaRodolphoetal.,2006[2] 17years 18.8 7.8 1.8 1.8 3.9

Opdametal.,2004[40] 5years 2.6 2.7 0.57 1.3 0.85

PallesenandQvist,2003[25] 11years Indirectcomposite 8.9 5.4 3.6

Directcomposite 4.8 2.4

Turkunetal.,2003[76] 7years 5.7

Gaengleretal.,2001[31] 10years 1.5 2.6

Kohleretal.,2000[51] 5years 1.6 9.5 1.6

VanDijken,2000[110] 11years Directinlays/onlays 6.3 4.2 1.0

Directcomposite 12.2 9.1

Wasseletal.,2000[111] 5years Indirectcomposite 1.6 1.6 3.1

Directcomposite 3.1 1.6 4.7 1.6

Raskinetal.,1999[41] 10years 3.3

Wilderetal.,1999[113] 17years 2.3 3.5

96

Author,year Periodof evaluation

Typeof restoration

Percentageoffailurecauses(inrelationtothetotalnumberofevaluatedrestorations)

Proximal contact Restoration loss Marginal defects Post-operative sensitivity Marginal discoloration Anatomic form/wear Other/ unknown

DaRosaRodolphoetal.,2011[3] 22years

Opdametal.,2010[12] 12years 1.2

Bernardoetal.,2007[8] 7years Lindbergetal.,2007[105] 9years

Opdametal.,2007[24] 9years Total-etch 3

Sandwich 6

Opdametal.,2007[13] 5and10years 0.31 0.46 3.1

Soncinietal.,2007[9] 5years 0.14 1.7

daRosaRodolphoetal.,2006[2] 17years 0.71

Opdametal.,2004[40] 5years 1.3 1.1 0.43 0.14 2.4

PallesenandQvist,2003

[25] 11years

Indirectcomposite 1.8

Directcomposite 2.4 Turkunetal.,2003[76] 7years

Gaengleretal.,2001[31] 10years 4.1 8.2

Kohleretal.,2000[51] 5years 6.4 1.6 3.2

VanDijken,2000[110] 11years Directinlays/onlays 4.2 4.2

Directcomposite 6.1

Wasseletal.,2000[111] 5years Indirectcomposite 1.6

Directcomposite 6.3 1.6

Raskinetal.,1999[41] 10years 1.7 11.7 11.7 20

Wilderetal.,1999[113] 17years 2.3 3.5 11.7

dental materials 28 (2012)87–101

97

Fig.1–Kaplan–Meiersurvivalcurvesfortwocompositesevaluatedoveranupto22-yearobservationperiod.Whenboth repairedandreplacedrestorationswereconsideredtobefailures(lefthandsidegraph),theAFRwas1.9%.Ontheother hand,whenrepairedrestorationswereconsideredtobesuccesses(righthandsidegraph),theAFRdecreasedto0.7%.

Fig.2–Representativepicturesofarestorationevaluatedonthe22-yearfollow-upstudy[3]thatwasstillclinically acceptable(A)orthathavebeenrepairedduringthefollow-upperiod(B).In(B),repairwasconsideredanalternativeto replacementandtherestorationwasstillclinicallyserviceable7yearsafterbeingrepaired.

6.

Overall

considerations

Due to their esthetic properties and good clinical service, composites have become the preferred material for direct posteriorrestorations.When‘goldstandard’hybrid compos-itesare used,anAFRbetween1%and 3%can beexpected dependingmainlyuponfactors otherthanmaterial proper-ties.Themainreasonsforthefailureofposteriorcomposite restorationsaresecondarycariesandfracture.Thefailureof restorationsrelatedtothewearofthesematerialsinthe pos-terior region seems,nowadays, almost absentand may be restrictedtobruxingandclenchingpatients.Areviewofthe literatureonlong-termclinicaltrialsofposteriorcomposite restorationsshowedthatthelongevityoftheserestorations are influenced mainly by clinical variables (type,size, and locationoftherestoration),thequalityandtechniqueofthe operator, socioeconomic factors such as income and type ofdentalservice,demographicfactors(ageofpatients)and behavioralaspects(cariesprevalence).

Thereislittleevidencethatthematerialpropertiesofthe compositeusedarearelevantfactorinrestorationlongevity, asitisonlyafterextendedperiodsofobservationorinthe presenceofglass-ionomercementbasethatsignificant differ-encesinAFRscouldbeobserved.Recentreportshaveshown satisfactory survival rates for posterior composite restora-tions,includinghybridmaterialsthatarenolongeravailable inthemarket.Improvementsinclinicalperformanceshould address themainreasons forfailure.Themainreasonsfor failureobservedinclinicaltrialsarestillsecondarycariesand fracture (tooth orrestoration),and neithermayactuallybe afailureofthematerialsthemselves. Secondarycariesisa continuumofprimarycaries,beingafailureofcliniciansand patientstoacteffectivelyintheetiologyofthedisease,while fracture ofthe restorationortooth canbe relatedpartially tothepresenceofasofterbaseundertherestoration,such asalining.Topreventfracture,thestrongestmaterialswith high fracturetoughnessshould beused. Long-termclinical trialswithnanofilledandlow-shrinkingcomposites,onthe other hand,are stillneededto provetheirsuitabilitytobe

98

usedinpatients.Meanwhile,itisunlikelythatthese materi-alswillprovideasignificantimprovement,asgoodresultsare alreadyachievedwiththecurrentlyavailableposterior com-positematerials.

Inconclusion,compositerestorationshavebeenshownto performfavorablyinposteriorteeth,withAFRsof1–3%.To improvethesuccessoftheserestorations,factorsrelatedto thepatientandoperatorareofprimaryimportance,indicating theneedforpreventionandaconservativeapproachtoward restorationreplacement.Theimprovementofmaterial prop-ertiesshouldaddressthepreventionofsecondarycariesand areductioninfractureincidence.

r

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