A randomized controlled clinical trial of 3-unit posterior zirconia–ceramic fixed dental prostheses (FDP) with layered or pressed veneering ceramics: 3-year results

Article

Reference

A randomized controlled clinical trial of 3-unit posterior zirconia–ceramic fixed dental prostheses (FDP) with layered or

pressed veneering ceramics: 3-year results

NAENNI, Nadja, et al .

Abstract

The aim of the present pilot study was to test whether or not posterior zirconia-ceramic fixed dental prostheses (FDPs) with pressed veneering ceramic exhibit less chipping than FDPs with layered veneering ceramics

NAENNI, Nadja, et al . A randomized controlled clinical trial of 3-unit posterior zirconia–ceramic fixed dental prostheses (FDP) with layered or pressed veneering ceramics: 3-year results.

Journal of Dentistry , 2015, vol. 43, no. 11, p. 1365-1370

DOI : 10.1016/j.jdent.2015.07.013 PMID : 26234623

Available at:

http://archive-ouverte.unige.ch/unige:79016

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

1 / 1

A randomized controlled clinical trial of 3-unit posterior zirconia – ceramic fi xed dental prostheses (FDP) with layered or pressed veneering ceramics: 3-year results

Nadja Naenni

*, Andreas Bindl

, Caroline Sax

, Christoph Hämmerle

, Irena Sailer

aClinicforFixedandRemovableProsthodonticsandDentalMaterialScience,UniversityofZurich, Zurich,Switzerland

bClinicofPreventiveDentistry,PeriodontologyandCariology,UniversityofZurichandPrivatePractice,Zurich,Switzerland

cPrivatePractice,Horgen,Switzerland

dClinicofFixedandRemovableProsthodonticsaandDentalMaterialScience,UniversityofZurich,Zurich,Switzerland

eDivisionofFixedProsthodonticsandBiomaterials,UniversityofGeneva,Geneva,Switzerland

ARTICLE INFO Articlehistory:

Received13December2014 Receivedinrevisedform9June2015 Accepted24July2015

Keywords:

Ceramics

Fixed-dentalprostheses Zirconia

Pressedceramic

ABSTRACT

Objectives:Theaimofthepresentpilotstudywastotestwhetherornotposteriorzirconia–ceramicfixed dentalprostheses(FDPs)withpressedveneeringceramicexhibitlesschippingthanFDPswithlayered veneeringceramics.

Methods:Fortypatients(13female,27male;meanage54years(range26.1–80.7years)inneedofone maxillaryormandibularthree-unitFDPinthesecondpremolarormolarregionwererecruitedand treatedattwoseparatecentersattheUniversityofZurichaccordingtothesamestudyprotocol.The frameworksweremadeoutofzirconiausingaCAD/CAMsystem(CerecSirona,Bensheim,Germany).The patientswererandomlyassignedtoeitherthetestgroup(zirconiaframeworksveneeredwithpressed ceramic;IPSe.maxZirPress,IvoclarVivadentAG,Schaan,Liechtenstein;n=20)orthecontrolgroup (layeredveneeringceramic;IPSe.maxCeram,IvoclarVivadentAG,Schaan,Liechtenstein;n=20).All FDPswereadhesivelycementedandevaluatedatbaseline(i.e.,cementation),at6monthsandat1and 3yearsofclinicalservice.Thesurvivalofthereconstructionwasrecorded.Thetechnicaloutcomewas assessedusingmodifiedUnitedStatesPublicHealthServices(USPHS)criteria.Thebiologicparameters analyzedatabutmentteethandanalogousnon-restoredteethincludedprobingpocketdepth(PPD), plaquecontrolrecord(PCR),bleedingonprobing(BOP),andtoothvitality(CO2).Datawasdescriptively analyzedandsurvivalwascalculatedusingKaplan–Meierstatistics.

Results:36patients(25female,11male;meanage52.3years)with18testand18controlFDPswere examinedafterameanfollow-upof36months(95%CI:32.6–39.1months).Comparisonofgroupswas donebyCrosstabulationshowingevendistributionoftherespectiverestoredteethamidstthegroups.

Survivalratewas100%forbothtestandcontrolFDPs.Chippingoftheveneeringceramictendedtooccur morefrequentlyintest(n=8;40%)thanincontrol(n=4;20%)FDPs,albeitnotsignificantly(p=0.3).No furtherdifferencesofthetechnicaloutcomesoftestandcontrolFDPsoccurred.Inbothtestandcontrol grouphealthyconditionsandnodifferenceofthebiologicparametersattheabutmentandun-restored teethwasfound.

Conclusion:ZirconiaFDPswithpressedandlayeredveneeringceramicsexhibitedsimilaroutcomesat 3years.Atrendtomorechippingofthepressedveneeringceramic,however,wasobserved.

Clinical significance:Posteriorrestorationswithzirconiaframeworksareaviabletreatmentmethod.

Whenrestoringposteriorteethwithall-ceramicrestorations,careprovidersshouldbeawareofthe higherrateofchippingcomparedtothepublisheddataonconventionalmetal-ceramicrestorations.

ã2015PublishedbyElsevierLtd.

1.Introduction

Thedemandformetal-freereconstructionsisconstantlyrising andhasledtothedevelopmentofnewdentalmaterialssuchashigh- strengthceramiczirconia.Zirconiaexhibitsthehighestmechanical stabilityofallavailabledentalceramicsandhasatooth-resembling

* Correspondingauthorat:ClinicforFixedandRemovableProsthodonticsand MaterialScience,UniversityofZurichPlattenstr.11,CH8032Zurich,Switzerland.

Fax:+41446343456.

E-mailaddress:[email protected](N.Naenni).

http://dx.doi.org/10.1016/j.jdent.2015.07.013 0300-5712/ã2015PublishedbyElsevierLtd.

ContentslistsavailableatScienceDirect

Journal of Dentistry

j o u r n a l h o m e p a g e : w w w . i n t l . e l s e v i e r h e al th . c o m / j o u r n al s / j d en

colorwhichmakesitadvantageoustometal[1].Numerousclinical studiesshowgoodmedium-tolong-termperformanceofzirconia whenusedforthefabricationofframeworks[2–6].However,when comparedto metal-ceramicfixed dentalprostheses(FDPs), full- ceramicrestorationsshowsignificantlylowersurvivalratesafter 5years[7].Themainissueofthezirconia-basedrestorationsistheir highrateoftechnical complications,most specifically chipping ofthe veneeringceramic[7].

Rates of 54% ofchipping of zirconiaveneering ceramicwere reported,leadingtotheclinicalissuethatzirconia–ceramicFDPsare still much more prone to technical complications than metal- ceramicFDPs.[8].Despitethatmostoftheobservedchippingswere ofminorsizeandonlyfewarereportedtorequirereplacementofthe zirconia–ceramic FDPs [8], chipping of the zirconia veneering ceramicremainstobeamajorclinicalissue[8,2].

One recently introduced new and promising method for veneering zirconia frameworksis the process of heat pressing the veneering ceramic onto the zirconia framework. As heat treatingsignificantlyreducestheflexuralstrengthoftheceramic [9], this technique may help reducing the highchipping rates.

Whenapplyingthistechnique,thedesiredshapeoftheveneering coatingismodeledontotheframeworkusingwax.

Thereaftertheframeworkisembeddedaccordingtothelost- waxtechnique[10].Thismethodofferstheclinicaladvantageof havingthe possibility for an intraoral try-in of the restoration beforefinalisation.The anatomicalshape oftheplannedrecon- structioncanthusbeevaluatedpriortothepressing[11].

Itisassumedthatthisnewtechniquemaybeadvantageousto conventional veneering procedures for different reasons. The pressingtechniquemaybelesstimeconsumingandlesstechnique sensitivecomparedtothemanuallayering.Furthermore,pressing oftheveneeringceramicmayofferbetteraccuracy,homogeneity and, hence, stability of the ceramic [12]. Whilst by manually layering veneering ceramic the inclusion of micro-pores and trappedair cannotbeavoided, theprocessingof theveneering ceramicusing thelost-wax techniquemayminimizeflaws and micro-pores[13].Theseintrinsicdefectsmayinducetheinitiation ofcracksduringclinicalloading.Asaresult,crack-propagationcan leadtochippingoftheveneeringceramicandevenframework- fracturesoftheall-ceramicFDP[14].

Untiltodayonlylimitedclinicaldataisavailableindicatingthat pressingtheveneeringceramicontozirconiaframeworksmaybe superior to the conventional layering technique. Two recent systematic reviews indicate promising clinical outcomes of zirconia–ceramic FDPswhenusingthis techniqueforveneering [8,2]The chippingrate was significantlylower withpressedas comparedtolayeredveneeringceramicbothforFDPswithzirconia andmetalceramicframeworks[8].

Interestingly,oneclinicalstudyofzirconiaFDPswithpressed veneeringceramicshowednochippingwhatsoeverofthepressed zirconiaveneeringceramicafterafollow-upperiodof40months [15].Yet,thisstudywasnotrandomizedandonlyalimitednumber ofpatientswereincluded.

Therefore,theaimofthepresentrandomizedcontrolledclinical pilotstudywastotesttheclinicaloutcomesofzircona–ceramic FDPsveneeredwithpressedandlayeredveneeringceramics.

ThehypothesiswasthatFDPswithpressedveneeringceramic exhibit less chipping than the ones with manually layered veneeringceramics.

2.Materialandmethods

2.1.Studydesignandpatientselection

This study was designed as a pilot randomized controlled clinicaltrial(RCT)toaccountforthelackofscientificinformation

aboutthetestedtypeofveneeringceramicforzirconia,therefore, no sample size calculation was performed. Two clinics at the CenterofDentalMedicineattheUniversityofZurich(KBTM,PPK/

SZCR)tookpartinthisinvestigationfollowingonestudyprotocol.

Patientsinneedofathree-unitFDPinthepremolarormolar region were recruited. If the patients presented with multiple toothgaps, thesite tobeincludedin this studywas randomly selected. The local ethical committee approved of all the proceduresand materials(Ref.Nr. StV02/09).Informed consent wasprovidedbyeachparticipant.

Inclusioncriteriaforpatientsandabutmentteethwere:

-goodgeneralhealth(nosystemicdiseasethatshouldnegatively influencetheclinicaloutcomes.)

-periodontallyhealthy(PlaqueIndicesandBleedingonProbing hadtobebelow20%previouslytotheprosthodontictreatment.) -no obvious signs or symptoms of bruxing and/or clenching (bruxismsuchasattritionsandexistingfracturesonthepatients naturalteethorreconstructions,nopainonmuscularpalpation or tendomyopathies, no pain causing joint sound, no self- reportedbruxingorclenching

-abutmentteethinneedofreconstruction(abutmentteethwith existingextensivecavities,fillingsorcrowns)

-abutment teeth either vital or with lege artis endodontic treatment(postand corebuild-upsincludedmetalpostsand compositebuild-up(incaseofsufficientendodonticfillingand postbuild-upthesewerewas left unchanged);or glass-fiber postandcompositebuild-upincaseofrenewalofanexisting postor

-insufficientremainingtoothstructure)

-non-vital abutment teeth with positive long-term prognosis upon clinical and radiological assessment (no peri-apical or apparentperiodontallesions)

Exclusioncriteriaforpatientsandabutmentteethwere:

-Patientsnotwillingorabletoachievesufficientoralhygiene(i.e., PIandBoPbelow20%).

Thepatientswererandomlyassignedtooneofthefollowing treatmentgroups:

Test group: 20 patients receiving a zirconia–ceramic fixed dentalprosthesis(FDP)withpressedveneeringceramic(IPSe.max ZirPress,IvoclarVivadentAG,Schaan,Liechtenstein).

Controlgroup:20patientsreceivingaFDPwithconventionally layeredveneering ceramic(IPS e.max CeramMargin,IPS e.max Ceram Dentin and Enamel, Ivoclar Vivadent AG, Schaan, Liechtenstein).

Patientswererandomlyassignedtothetreatmentmodalityand therespective clinic bymeansof a random listwitheven and unevennumbers.The40patientswereevenlydistributedbetween thetwocenters.

2.2.Clinicalprocedures

The patients were treated between September 2009 and January 2010.The abutment teeth were preparedaccording to the guidelines for all-ceramic FDPs. After completion of the preparationthevitalabutmentteethweretreatedwithadentine adhesive system (Syntac Classic, Ivoclar Vivadent AG, Schaan, Liechtenstein)tosealthedentinaltubules.Impressionsweretaken withanA-siliconeimpressionmaterial(President,ColtèneWhale- dent,Altstätten,Switzerland/Honigum,DMG,Hamburg,Germany) performingdouble-mixtechnique.Theimpressionoftheopposite jaw was taken with alginate. Provisional restorations were fabricatedchair-side using a composite material (ProTemp, 3M

1366 N.Naennietal./JournalofDentistry43(2015)1365–1370

ESPE, Seefeld, Germany) and cemented with an eugenol- free temporarycement(Freegenol).

2.3.Frameworkfabrication

TheFDPswerefabricatedbyspecializeddentaltechnicianswho hadreceivedtraininginthenewveneeringtechniquepriortothe startofthestudy.Theimpressionswerepouredwithscanstone (Camtech-Roc,Picodent,Witterfürth,Germany)andthecastswere scanned using a CAD/CAM scanner (inEOS Scanner, Sirona, Bensheim, Germany). The frameworks were virtually designed bymeansofthecorrespondingsoftwareoftheCAD/CAMsystem (CerecV2.6R2005Sirona,Bensheim,Germany).Theframeworks weremilledoutofY-TZPpartiallysinteredzirconiaceramicblanks (IPS e.max ZirCAD, Ivoclar Vivadent AG, Schaan, Liechtenstein) withthechair-side millingunitof theCAD/CAM system (inLab milling unit, Sirona, Bensheim, Germany). After milling the frameworksweresinteredtofulldensityin ahigh-temperature furnace(NaberthermLHT02/16,Lilienthal,Germany).

Beforeveneering,theframeworkswereclinicallycheckedwith specialemphasistofit,shapeandsizeoftheconnectorsandthe anatomicalsupportoftheveneeringceramics.

2.4.Veneeringprocedures

Testgroup:aftersintering,theframeworkswerecleanedwith water. They were then coated with a liner (IPS e.max Ceram ZirLiner,IvoclarVivadentAG,Schaan,Liechtenstein)andbakedat 960Ctoachievebetterbondbetweenframeworkandveneering ceramic.Theframeworksinthisgroupwereveneeredwithpressed veneering ceramic (IPS e.max ZirPress, Ivoclar Vivadent AG, Schaan, Liechtenstein). The procedures for over-pressing were performed according to the lost wax technique following the manufacturer’s directions. In brief, a wax-up of the desired anatomical shape of the veneering ceramic was modeled onto eachframework.Aminimalthicknessoftheveneeringceramicof 0.7mm was provided. The frameworks with wax-ups were embedded in investment compound (IPS PressVEST, Ivoclar VivadentAG,Schaan,Liechtenstein)andthenplacedinafurnace (EP600,IvoclarVivadent,Schaan,Liechtenstein)at850Ctoburn outthe wax.Theveneering ceramicingots (IPSe.max ZirPress, Ivoclar Vivadent AG, Schaan, Liechtenstein) were heated and pressed onto the frameworks at 900–910C according to the

manufacturer’sdirections.ThefinishingoftheveneeredFDPswas performedmanuallyusingdiamond burs,paintingcolors anda glazingceramic(IPSe.maxCeramGlazePaste,IvoclarVivadentAG, Schaan,Liechtenstein).

Inthetestgroup10FDPswereslightlymodifiedoutofesthetic reasonsbysuperficiallyreducingthepressedveneeringceramicat thebuccalsidebyapproximately0.5mmandbylayeringonecoat ofveneeringceramicontothesurface.

AtalltestFDPsthefinishingfiringstepoftheglazingceramic (IPSe.maxCeramGlazePasteandGlazeandStainLiquid,Ivoclar VivadentAG,Schaan,Liechtenstein)wasperformedat725C.

Controlgroup:accordingtotheproceduresinthetestgroup the zirconia frameworks were cleaned with water after the sinteringprocess.Toachievebetterbondbetweenframeworkand veneeringceramicagaintheframeworkswerecoatedwithaliner (IPS e.max Ceram ZirLiner, Ivoclar Vivadent AG, Schaan, Liechtenstein),and bakedat 960C ina furnace.The respective veneeringceramics(IPSe.maxCeramMargin,IPSe.maxCeram Dentinand Enamel,IvoclarVivadentAG,Schaan, Liechtenstein) werethen appliedin layersontotheframeworksand baked at 750C respectively 725C according to the manufacturer’s directions.Aconventionalfurnacewasused(OralDesign,Austro- matM,Dekema,Freilassing,Germany).

Theveneeringceramic wasfinallysmoothenedand polished withpumiceandpolishingliquid(KMGPoliermittel,CandulorAG, Wangen,Switzerland).

2.5.Cementation

Beforecementation themarginal fit,inter-proximal contacts and theocclusionofthefinalFDPswereclinicallychecked.The internalsurfacesoftheFDPswerecleanedwithalcoholandthe abutmentteethwerecleanedwithfluoride-freepumice(Cleanic Prophypastefor Cleaningand Polishing,Kerr HaweSA,Bioggio, Switzerland).

AllFDPswereadhesivelycementedwithresincement(Panavia 21TC,Kuraray,Japan).Accordingtothemanufacturer’sdirections oftheresincementadentinprimer(EDPrimer,Kuraray,Japan) wasappliedtothedentin.Nopre-treatmentofthezirconiasurface wasperformed.Aftercementation,theocclusionwasadjustedif needed and any reshaped surfaceswere meticulously polished withceramicpolishers(Kometnos.9425,9426,9547,Brasseler).

Table1

ThetechnicaloutcomewasassessedusingmodifiedUnitedStatesPublicHealthServices(USPHS)criteria[17].

Alpha(A) Bravo(B) Charlie(C) Delta(D)

Framework fracture

Nofractureofframework Veneering

fracture

Nofracture Chipping,butpolishingpossible Chippingdowntoframework Newreconstructionis mandatory

Occlusal wear

Nowearfacetsonrestoration andopposingteeth

Smallwearfacets(diameter<2mm)on restorationand/oropposingteeth

Wearfacets(diameter>2mm)on restorationand/oropposingteeth

Newreconstructionis needed

Marginal adaptiation Probedoesnotcatch Probecatchesslightly,butnogap

detectable

Gapwithdentinorcement exposure

New reconstructionisneeded Anatomical

form

Idealanatomicalshape;good proximalcontact

Slightlyover-orundercontoured;weak proximalcontact

Highlyover-orunder-contoured;open proximalcontact

Newreconstructionis needed

Radiographs Novisiblecementationgapon X-ray

Minorgapvisible

Patient satisfaction Verysatisfied Temporarilynotsatisfied(e.g.,

postinsertionsensitivity)

Notsatisfiedtolerable discomfort

Notsatisfied intolerable discomfort ordislike

2.6.Baselineandfollow-upexaminations

Atbaseline(upto2weekspost-cementation),andagainafter 6 months,1 and 3 years of function the FDPs were examined clinicallyandradiologically.Beforehandacalibrationmeetingwas heldwheretheexaminingdentistswereinstructedandtrained.In ordertoavoidbiastheFDPswereexaminedbytwoclinicianswho werenotinvolvedinthereconstructivetreatment.Survivalofthe FDPswasassessedanddefinedasFDPinsituatfollow-upvisit withorwithoutmodification.

Technical outcomes were evaluated by means of modified United States Public Health Services (USPHS) criteria [17].

Parameterswereanalyzedindetail(Table1)Finally,thepatients wereaskedbythedentistwhetherornottheyweresatisfiedwith theestheticoutcomeandthefunctionalityoftheirFDPandthe respectiveanswer(yes/no)wasnoted(Table1).

The biological outcome was evaluatedby meansof probing pocketdepth(PPD),plaquecontrolrecord(PCR)[16]andBleeding on probing (BOP). These parameters were measured at test (abutment) and control teeth (un-restored analogous control teeth). The abutment tooth vitality was checked (CO2) and radiographsoftheabutmentteethweremade.

2.7.Statisticalanalysis

Data was analyzed descriptively. Survival and success rates weredeterminedaccordingtotheUSPHScriteriaandcalculated usingKaplan-Meier.Biologicaldatawasanalyzedusingthepaired t-test.DatawasanalyzedbySPSSversion17.0(SPSSStatistics,IBM, ArmonkNY,USA).

3.Results

Afterameanobservationperiodof36months(95%CI:32.6– 39.1m),36outoftheinitial40patientswereexamined(11male, 25female).Themeanageofthepatientsatthe3-yearfollow-up visitwas52.3years(95%CI:46.9–57.6years)inthetestgroupand 55.8years(95%CI:50.6–60.9years)inthecontrolgroup.

Fourpatients(2testand2control)werenotavailableforthe3- yearexamination.Theydidshowupforthe1-yearrecallandlater movedawaywithoutgivingnotice.TheFDPslost tothe3-year examination were replacing one maxillary molar and one mandibularpremolar(control)aswellasonemaxillarypremolar andonemandibularmolar(test).

The mean follow-up of the FDPs in the test group was 36.8months(95%CI:32.5–41.1m).Thecorrespondingfollow-up for the control group was 34.9 months (95% CI: 29.6–40.2m).

(Tables2a–2d) 3.1.FDPsurvival

NoframeworkfracturesoccurredandnoFDPwaslostdueto anotherreason. Hence,both test and controlFDPs had a 100%

survivalrate.

3.2.Technicaloutcomes

TechnicalevaluationoftheFDPsincludeddebonding,surface roughnessandchippingoftheveneeringceramicTable3.

Node-bondingoftheexaminedFDPsoccurred.

Surfaceroughnesswasobservedin18patients(14test(70%) and7control(35%)group)(p=0.056),whichshowedatendency towardstatisticalsignificance.Whenevaluatedregardingsurvival andtimebetweeneventofsurfaceroughnessandchipping,values didnotshowtobestatisticallysignificant.(p=0.487)

Chippingoccurredin33,2% ofallFDPs. Ofthese13,8%were minor(ratedB)and19,4%weremajor(ratedC).Atotalof8FDPs (40%) of thetest group and 4 FDPs(20%) of thecontrol group exhibitedchipping of theveneering ceramics.According tothe modifiedUSPHS criteria 3 chippingsfrom thetest group were minorand5weremajorInthecontrolgroupthechippingswere evenlydistributedwith2minorand2majorfractures(Table4).

Thedifferenceinmajorchippings(ratedC)wasnotstatistically significant (Breslow p=0.138) between the groups. All of the chippingswereclinicallypolishable.

3.3.Biologicaloutcomes

DifferencesinPPD,PCRandBoPweresatisticallynotsignificant butforPPD(0.003onesamplet-test).Anoverviewofthebiological evaluationisgiveninTable5.

None of the abutment teeth lost its vitality during the observationperiod.

3.4.Patientsatisfaction

Thepatientsinthetestgroupweresignificantlylesssatisfied withtheirFDPs(p>0.047Fisher’sExactTest).

Table2a

DetailedinformationonthenumberoftheFDPsandtheirrespectivelocation.

Reconstructedtooth Molar(n) Premolar(n) Total(n)

Testgroup(pressed) 14 6 20

Maxilla 1 5 6

Mandible 13 1 14

Controlgroup(layered) 14 6 20

Maxilla 6 4 10

Mandible 8 2 10

Table2b

Detailedinformationonthereconstructionatthe3-yearexaminationonallocation ofthereconstruction.

Reconstructedtooth Molar (n)

Premolar (n)

Total (n)

Testgroup(pressed) 13 5 18

Maxilla 1 4 5

Mandible 12 1 13

Controlgroup(layered) 12 6 18

Maxilla 5 4 9

Mandible 7 2 9

Table2c

Detailedinformationonthereconstructionsatthe3-yearexaminationongender distribution.

Female (n)

Male (n)

Total (n)

Patients 25 11 36

Table2d

Detailedinformationonthereconstructionsatthe3-yearexaminationonwear time.

Age(mean) Observationperiod(mean) Controlgroup 52.3years(46.9–57.6years) 36.8m(32.5–41.1m) Testgroup 55.8years(50.6–60.9years) 34.9m(29.6–40.2m)

1368 N.Naennietal./JournalofDentistry43(2015)1365–1370

4.Discussion

The 3-year survival rate for both zirconia-ceramic FDPs veneeredwithlayeredandpressedveneeringceramicwas100%.

Noframeworkfracturesandnode-bondingoccurredwithinthe observationperiod.Thusthetwotestedtypesofzirconia–ceramic FDPsexhibitedfairlygoodoutcomesat3yearsoffunction.

ThetestandcontrolFDPsexhibitednodifferenceswithrespect tothetechnicaloutcomes.Atrendtowardsmorechippingofthe pressedveneeringceramiccouldbeobserved,yetthedifference didnot reachstatistical significance. The hypothesis, therefore, wasrejected.

Asshort-spanposteriorFDPswithframeworksmadeofzirconia exhibitverysatisfyingsurvivalratesof97.8–100%after3years,it hasbeenwidelyacceptedthatzirconiaisareliablematerialfor frameworks.[6,8]. Literatureshows that even afterobservation

times of 5–10years very few fractures of zirconiaframeworks occurred[5,6,18,19,20].

As opposed to this, chipping of the veneering ceramic still remainstobeamajortechnicalcomplicationofzirconia–ceramic FDPs[8].

Numerousattemptsweremadetoreducethechippingrateby developingnewveneeringceramicswithbetterintrinsicstability, improvingthechemicaladhesiontotheunderlyingframework,and adaptationofthemanufacturingtechniques(i.e.,pressing,CAD-on).

Instead of manuallylayering the veneering ceramic, in this study theceramic was appliedbypressing itonto thezirconia framework.Itwasassumedthatthistechniquewouldinduceless risk for chipping due to higher homogeneity of the ceramic [12,21,22].

The first published study onpressed veneering ceramic by Beuerandco-workersshowednochippingof3-unitzirconiaFDPs Table3

ThetechnicaloutcomewasassessedusingmodifiedUnitedStatesPublicHealthServices(USPHS)criteria.

Alpha(A) Bravo(B) overall

Marginaladaptation Overall

30% 70%

Occlusalwear

Testgroup 30% 70%

Controlgroup 65% 35%

Overall 47.5%

(Nowearfacetsonrestorationand opposingteeth)

52.5%

(Smallwearfacets(diameter<2mm)onrestoration and/oropposingteeth

Smallwearfacets(diameter<2mm)onrestoration and/oropposingteeth)

Breslow0.478 Fischer0.056%

(notsignificant)

Anatomicalform

Testgroup 90% 92.5%

Controlgroup 95%

Interproximalcontact

Testgroup 95% 92.5%

Controlgroup 90%

Radiographs

Testgroup 70.6% 78.4%

Controlgroup 85%

(NovisiblecementationgaponX- ray)

(Minorgapvisible)

Patientsatisfaction

Testgroup 75% Temporarilynotsatisfied

(e.g.,Postinsertionsensitivity)

Notsatisfied

intolerablediscomfortordislike

Controlgroup 100%

(Verysatisfied)

Table4

Detailedinformationonthechippingrate.

Nochipping Minorchipping(polishable) Chippingtoframework TotalNo.Chipping

Testgroup(pressed) 10 3 5(27.7%) 8

Controlgroup(layered) 14 2 2(11.1%) 4

Total (77%) (13.8%) (19.4%) 36

Table5

BiologicaloutcomesTable5.

Plaqueindex(PI) Bleedingonprobing(BoP) Pocketprobingdepth(PPD)

Testgroup(pressed) 0.875 0.069 0.050

Controlgroup(layered) 0.1437 0.050 0.013

p-value 0.003 0.297 0.878

afteranobservationperiod of3-yearswhenveneeredwiththis technique[23].Heintzeandcoworkersstatedthatchippingofthe veneering ceramic occurred less frequently in pressed than in layeredceramics[8].Thesepositivefindingswerenotobservedin thepresentstudy.Thiswasinvastcontrasttoourexpectations.

Chippings within thetest group occurredto a similar or even slightly higher amount than in the group with the layered veneeringceramic.A possiblereasonfor thisdifference maybe thatinthepresentstudyanewmaterialwasusedandthatthe techniqueitselfwasatanearlystage.Inthefuturetheveneering procedureswouldprobablyneedsomerefinements.

In-vitrostudiesshowedthatthemainreasonforchippingwasa cohesive fracture of the veneering ceramic, meaning fractures happeningwithintheveneeringceramic[1,11].Thefactthatthe chippings occur within the veneering ceramic and not at the frameworkinterfaceallowsmostchippingstobepolishedrather thanhavingtoreplacethewholereconstruction.Thiswasthecase inthepresentstudyaswell,asallchippingscouldbepolishedand noneoftheFDPshadtobereplaced.Besidestheobservationfor chipping, the FDPs showed excellent technical and biologic integration.

Nostatisticallysignificantdifferencesofthebiologicoutcomes werefoundattestandcontrolFDPsbutforplaqueindices(PI).

Thesewerehigheratthecontrolthanatthetestteeth(p=.003).

Thismaybeexplainedbythefactthatceramicsarereportedtobe lesspronetoplaqueaccumulation.Anotherreasonmightbethat the patients were aware of their reconstruction and hence performed bettermechanical plaque-removal at thesites with thereconstruction.Thepatientsatisfactioninthepressedgroup waslowerduetoahigherincidenceofchippingsandoverallaless favourableaestheticoutcome.

Onthatscorethephysicalpropertiesofveneeringmaterialsare constantly being improved and new veneering techniques are developed. Recently Beuer et al. described a new veneering methodusingCAD/CAM-fabrication[12].Inanin-vitrosettingthe veneeringceramicwasmilled,sinteredtozirconiacopings(CAD- on-technique)andcomparedwithanatomicallyidenticalzirconia- basedcrownsveneeredbyeitherover-pressedorconventionally layered veneeringceramic. The fracture load of the CAD/CAM- veneered zirconia copings showed to be superior to the conventionallylayeredreconstructions [12]. Therefore thisnew veneeringmethodmaybeadvantageousintermsofcostreduction andchippingrate.WhethertheCAD/CAM-techniquewillleadto less chippings in all-ceramic reconstructions, remains to be investigatedinaclinicalsetting.

5.Conclusions

FDPs with zirconia frameworks and overpressed veneering ceramicsshowrelativelygoodshort-termsurvivalrates.Thereare differences though in technical outcomes when compared to conventional layering as chippings occurredmore often in the pressedgroup.Withinthisstudynosignificantbenefitcouldbe shownfortheoverpressingoftheveneeringceramicinall-ceramic reconstructions.

Further long-term studies are needed to show how the technical complications evolve over time. Furthermore, more clinicalstudiesareneededtoinvestigatewhetherthedevelopment

ofnewveneeringceramicsforzirconiaframeworkswillbeaviable alternativeoriftherewillbeatendencytowardsfull-anatomical zirconia-reconstructions.

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