Prospective clinical study of zirconia posterior fixed partial dentures

Prospective clinical study of zirconia posterior fixed partial dentures: 3-year follow-up Irena Saikr, Dr M s d Dentl/AureI Feh& Or hned DeM/ Frank Filser, Dr Rer Nat3/Heinz LUthy, Prof emer, Or Rer Nat4/ Ludwig J. Gauckler,Prof, Or Rer NaPpeterSchgrer, Prof ernar, Dr Mad Dee/ Christoph Hans Franz Hamrnerle, Prof, Dr M e d Dent6 Object-: The purpose of thls prospective clinlcal cohort study was to determine the success rate of $to 5unlt posterlor fixed partial dentures (FPDa) with zirconla frameworks after B years of function. M e t h a d and Materials: Forty-five patients In need of at least 1 FPD to repIace 1 to 3 posterlor teeth were Included. The frameworks were produced by means of a prototype computer-asslsted rnanufacfure system. They were milied with a precisely calculated Increase in size out of presintekd zirconla blanks and subsequently shrunk to the required size. Flfty-seven FPOs were cemented using eitherVariollnk or Panavia TC cement. Clinical and radiographic examinations were performed at baseline, 12,24, and 36 months after cernentatlon. Statistical analysls was performed by descrtptlve st&i&w and t h e Kaplan-Mebr suwlvat analysis. Comparisons of problng depth,Plaque Index, and bleeding on probing betwean test (abutment) and control (mntratateral) teeth were done with the McNemar test. R e s u h Thirtydx patlents with 46 FPDs were avaIC able for examination after 38 months, No fractures occurred, rendering a 100% success rate of the rirconla frameworks. Seven FPDs had to be reptaced bcauae of biologlc and technical problems. The suwlval rate, therefore, was 84,8%. Secondary caries was found in 10.9% of the FPDs. and chippinq of the veneering ceramic was found in 13.0%. mere were no significant differences regarding the problng depth in test and control teeth. Conclusion: Zlrconia frameworksdemonstrated suff iclent stablllty for replacement of pasterior teeth. However, the hiQh rates of technical problems should be reduced by further d d o p m e n t s of the prototype processingtechnqlogy. ( Q u i m n c e In€2006;37S85-693)

f b y words: ceramic, flxed partial denture. framework,.zirconla

'Senlor Lecturer.Clinlc for Flxed and Rcrnwable Pmsthodontlu and Denml Materlals.School of Dentlstry, UnlvmlIy of Zurlch, Switzerland. aPrtuare Practice. Zurich. Swherland. IMaterlal SclerPtlst Deparrment of Materlak, Swlss Federal

Institute of Tuhnol0gy, mncn, SMQerhnd.

'Material S c I e n t l s ~

Olnit

for

FIwd

and

Removable

Prosthgdmtlcs and Dentel Mateffala, School of Denttrtry. UnSverslty of Zurich, Swlmriand 'DM*as@d: Former Chair, Cllnic for Fixed and Remwable P~lsthodontlcsm d Dental Mmterifs, School of Dentistry,

Unlwrsky of Zurlch, Swlkedand. 6Profersor and

Chair. Cllnit

br

Flxed and Removable

Prosthodentlcs and Dental Mazerists. School of Dentfstry. Unlvcrslty of Zurich, S w l a e i l a o d

Irprlntraqrurtr:Or Irena Saller,tlinlc for namd and Removable Pmsthodonscs and Dental Materlafs, Schml of Dentlstry. Universkiy of Zurich. Plartenrtrasse 1 1,8032 Zuilch, Swieerland. Fax41 44 634 43 05. E-malh trena.raller@ zmkunlzh.ch Thlc paper was

presenred at the IADR meetlnq in Gothenbufg,

5wedcn.ln June 2003.

Ceramics have a long history in fixed prOsthOdonttcs and operative dentistry for the achievement of optlmal e~thetlcs.~ Because of their superlor opticat quatities and material properties, a large number of allceramlc systems have been developed. Differences exist, however, between varlous classes af ceramic materials, As a result of these differencesthe various types of c o r n ics are utflized In dlverse c l l n l c l Indications. Qn the one hand, slHca-based ceramics, such as feldspathlc porcelain, offer excellent optical qualities and are, hence, applied in situations of highest esthetlc demands. Because of their lower mechanical stabiltty, on the other hand, they have to be reinforced either by a framework or by adhesive cemek tatlon to the underlying tooth structures. In addition, their indications are W t c Z e d to s i p

Q U I N T E S S E N C E INTERNATIONAL

gle c r ~ w n s . ~Non-silica-based -~ ceramics,

gies. tndustriatly prefabricated blanks of ddif-

such as alumina and afumlna-rirconia, exhib

ferent slrss can be milled to frameworks for

it higher rn-hanical

crowns and FPDs. First, the frameworks are either constructed In wax (mrnp~rassisted manufacture, or CAM) and subsequently scanned or digitally designed (computeralded design. ar CAD) after sGannlng the

stability. These materi-

als can be used for ceramic frameworks f a r fixed partial dentures (FPDs) under hlgher mechanical stress.',6 Of the ceramic materials available fordem tal FPDs, zlrcbnia offers the highest rnechanicat properties. It exRlbIts more than double the bending sb-ength and fraoture 'toughness than the other aeramlcs. The hending

strength and the fracture touQhnessof glassceramic (eg, Empress 1 ) amount to 182 MPa and 1.77 MPa rn1/2,respectively; the bending strength of alumina reaches 547 MPa and the fracture toughness 3.55 M P a rnt/2.sIn c o n t d , the bending strength of zirconia is 900 M P a , and its fracture toughness reaches 9 MPa m'/Z.7 In a recent in vltm study, the faiG urn probabilrty of FPDs with zlrconia frame works after a simulated layear dinical service was nearly zei-ona In another study assessing the stablllty of a glassceramic material (Empress) more than half of the initial strength was lost as a result of In vltro The flrst dental applications of zlmnla as either industrially prefabricated ceramic posts or Implant abutments for esthetically demanding cases exhibited very positive cllnicat lon@ternl m u k . In a retrospactive cllnlcal study Involving 79 teeth with jrconta posts, no fractures were observed after 4 years of cllnical ~ e r v i c e Similarly, .~ no fme tures of zirconla abutments on implants occurred during a 4-year observation perk ~ d l ndustrially . ~ prefabricated devices made out of drmnia also meal suocessful applications In medlclne, such as hip loint repla~smerlts.~~ Therefore. this ceramic seems pmrnislng for the appllcation as framework material for FPDs in anterior and posterior regions. Since zirconia ceramics oannot be processed in the dental laborsfow by tradt tlonal methods (powder/llquld appllcation), the framework have to be ground out of industrially prefabricated blanks. In addition, the manual grinding of densely sintered zimm nia I s a time-consuming procedure leading to a hlgh wear of rnltllng Instruments.Hence, contemporary methods utilize new computer-aided processing technol*

master cad. To overcome the difficulttes when milling densely slntered zlrconla, new techniques for pracesslng tirconia In the "soft," presintemd "green stage" have been developed. With these methods, the presiw tered ceramic blanks can easily be machined to indlvldual forms. Subsequently, these have to be sintered to full denstty to obtain the optimal material properties. Thls slnrering process leads to shrinkage, whlch has to be compensated for by enlarging the origlnal form prlor to machining. Thls Is achieved by means of specialized computer software." This manufacturing process reduces rnilllnq time and wear of the mllllng Instruments and, thus, reducss the overall m.A large variety of systems working with prestntered rlrconla are available today, leadirig to an Increased frequency of FPDs with zlrcan la frameworks.

Mo dlnlcal long-term studies lnvolvfng crowns and FPDs with zirconla frameworks are presently mallable. The alm of this prospedlve clinical cohort study was to determine survival and success rates of 3-to 5-unit posterior WDs with zirconia frame works.

METHOD AND MATERIALS Patients and FPDs FoHy-five patients In need of at least 1 FPD In the posteriar region of the maxilla or mandibte wera inltlally Included in the study. The following inclusldn crlteria were used for the selection of the participants: 1 to 3 p o s terior teeth missing, periodcrntally healthy abutment teeth, and balanced occtusal forces (no rnlssing antagonistio teeth). Patients were fnformed about the purpose of the study, the clinical procedures, and the makrlals to be used. Informed consent was obtained. Following patient history and cllnl-

cat and radiagraphiG examinations, patients underwent comprehensive dental care includfng the incorpor&ion of a totaI of 57 3to Sunk FPDs with zirconia frameworks.

Prosthodontie procedures Experienced clinicians perfomed the treatments for all w p t 5 FPDs, whbh were

made by undergraduate students. Prep* ratron techniques were digMty modified to futifl the requlfements of the novel framework manufacturing method: Margin: ~imumferentidlyrounded shoulder/chamfer (I ,2 mrn in width) Internal and external preparation radii L 0.65 mm Tapering angle: 6 to 8 degrees for molars and premolars (1.0 degrees for canines) Occlusal reduckion: 1.5 to 2.0 mrn

After preparation, the teeth were desensk tized (Gluma, H e m u s Kulzer) and a fullerch impression was 'taken with a polyether material (Permadyne, Espe). Pmvlslonalswere fab ricaW (Protsmp Garant, Espe) and cemented wlth pravlslonal cement (TempBond,

KerrHawe). All frameworks were produced utilizing the direct ceramic machining (DCM) method. A detailed description ufthis proce dure was published el~ewhere.'~ Briefly, the Impressions were poured In dental stone (Fuj~Rock, GC), and framework were made out of tight-curing resin cornposlte (Tagis, lvoclar Vivadent). The following fremework dimensions, similar to the ones commonly used for rnHal-ceramic FPDs, were applled: Coping thickness: 0.5 mm Connector cross section: is mm2far 3-unit, 9 rn+ for +unit, and 11 mmzfor 5-unit

The morphology of the frameworks was mechafiically captured. For this purpose, a probe was mounted on a prototype macMne deslgnedfor the controlled rnllllng. The data obtained were digitized and enlarged by 25% using speciailzed computer softwere. This enlargement was done to compensate for sintering shrinkage. The frameworks were machined out of presintered zimonia blanks

using hard metal milts In the milling machine. Subsequently, they were slntered to full dew slty at 1,600°C. During stnterfng the frame works shrank to the dimensions of the resin composfie original. A new veneering ceramic with a coefFii cient of thermal expansion adjusted for zirce nia (CTE z'rrconia 11 X 10- K-*)was deveC nped. The frameworks were veneered using conventianal veneering tachniques. The interior surfaceq d the FPDs were abraded with aluminum oxide (granule size 110 mm, pressure 2 bar for 10 seconds, eccordlng to the developer's instructions) and cleaned wkh aalcohot Thereafter, they were adhesively cemented using of 2 cements: Variolink (Ivoclar Vivadent) and Panavia TC (Kuraray). The abutment teeth were preconditioned according to the m a n u facturer's instructions for each cement. The occlusion was adjusted as need&, and any reshaped surfaces were polished.

Baseline examination Probing pocket depths (PPD) were assessed at 4 s h s at the abutments Immediately after Insertion of the FPDs. Radiographs uf the abutmemt teeth and clinical phatqgraphs were taken, Abutment vitality was assessed using carbon dioxide.

Follow-up examination At 1 and 3 years after Incorporation. the FPDs were mmlned for framework fracture and for technical and biologb wmplicatlons, le, chipping or fracture of the veneering material, abutment fracture, marginal di* crepanoies, secondary caries, loss of vitality, and periapicallesions. In addition, the following periodontal parameters were assessed at abutment (test) and control teeth (contratatsral or opposing, notcrowned teeth): PPD, probtng attachment levels (PAL). Plaque Index (Ptl), bleeding on probing (BOP), and tooth mobiMy~Furthermore, vltalfty of both abutment and control taeth was W e d using carbon dlaxlds. OccIusal and functional relationships between FPDs and opposina Jaws were noted. Radiugraghs and clinical phgraphs were taken. Patients were asked whether they Ilked the esthetic outcome of their reconstru-

QU1NTES'SEvNCEINTERNATIONAL Sailer e t at

Fractu~e abutment t w t h * K l e r i e s .

-

5

Panda SC

4

3

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- - - - -

33.3

Variollnk

42

YmoIink

tion(8) and whether they Were satisfied with k function, with the option to answer yes or no. F~nally,irreversible hydrocolloid impressions of maxillae and mandibles were taken tcr fabricate study casts.

Statlstlcal anarysis Descriptive statistics were applied to the data. The v l s u a l f ~ i o nof the data was done using box plots. Patients lost to foIlow-up were censored. The following events and their time of occurrence were evaluat6d: loss of the reconstruotfon, cnipplng ofthe veneering ceramic, and carles development. Furthermore, caries was separately analyzed as a reason for loss of FPDs. The survival curves were estimated using the KaplanMeier survival analysis. In cases where the median survival time was reached, its standard error was reported. Otherwise, the mean survlval tlme togethar wRh its standard error was given. The comparisons of PPD, P11. and BOP between test and contml teeth were done by the McMsmar teet.16

RESULTS Thlrty-six pdients, 17 female and 79 male, with 46 zirconia FPDs (35 3-unit, 9 &unit, 2 5unit) were examined at the 3year recall. The WDs were examined cllnlcatly after a mean

Secongary caries ~eK%iW%h

Loss of retention

.

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---

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= -

Endodontic problems

observation period of 36.2 (f5.4) months. Seventeen FPDs had been luted with Varlolink (Ivoclar, Switzerland) and 29 wRh Panavla TC (Kuraray, Japan). Eighteen FF" were placed in the maxillae and 28 In - .mandibles of the patients. The first prernalar was replaced in 5 FPDs, the second premclar in 16, the first molar in 24, and the second molar In 1 FPD only. During the 3 years of clinical service, 9 patients with 11 3-unit FPDs were tost to fob Taw-up for dffferent reasons: 8 patients moved away or declined to further partlct pate in the study. One patient died 2 wars after cementation of the FPD. No framework fractures were observed. The succ-s rate of the ztrconia frameworks, therefore, was 100%. However, 7 FPDs (1 5.2%) had to be replaced because of technioal or biologic complIcatlons. These FPDs and the reasons for failure are presented In Tabfe 1. In 1 case, lass of retentJonoccurred In a Varialink-zernented FPD after a ctinical service time of 33.3 months. In another case, the FPD had not been properjy cemented initially and the marginal areas remalned unsealed. Therefore, sEiCondary caries occurred and tha FPD had to be remade after 44.1 months. Marglnai discrepancy (gap) and resulting secondary carles were the reason for 2 further losses. In 1 patient an abutment tooth had to be extracted because of ondodb~q& , g ~ Q ! p pand , In

I

Q U I N T E S S E N C E INTERNATIONAL S a i l e r et a1

,.,

.,.

~ i Ig .,., ,,, .l, ..lg ceramic up to the zirconia framework on the lingual part of the pontic reglon In a mandibular &unit FPO.

Flg 2 time

Kaplan-Meier cumulative survival ofthe veneering ceramic over

a n o t h e r patient

an abutment root was lost because of a longitudinal fracture. The seventh FPD was lost due to a large fracture of the veneering ceramic up to the framework (Fig I). The survival rate of t h e FPDs was

84.8%. In 13.0% of the cases (n = 6) chipping of

the veneering ceramic occurred after a mean service tlme of 37.2 (f0.6) months (Fig 2). The first chipping was diagnosed after 18.1 months and the latest after 38.3 months of clinical weartng. In 56.5% of the FPOs (n = 26), marginal discrepancies (gaps) were found. In 10.940 ( n 5) of the FPDs secondary caries In the marginal areas could be observed. There was n o statistically si~nificant association between the occurrence of marg-lnal gaps and secondary caries, however (P = .685, Fisher's exact test). Regarding the periodontal assessment, them were no statistically significant differences in the PPD between the test and the control teeth (Fig 3). Significantly more BOPpositive sites were found on test teeth, compared to the controls { P = .007, McNemar test). However, more PII-positive sltes were found on control teeth compared to the reconstructed teeth. This difference was only slightly significant {P = ,022,McNemar test). When BOP and PI1 were correlated, it appeared that o n the test sites, bleeding occurred frequently in piaque-negative sites, but no significant correlation between the 2

-

-

-

-3&pE SF

-

my.4-

=

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Fig 3 Box plot of pocket probing depths of the test abutments (TI = anterior,T2 = posterior) and control teeth (C1= anterior, C2 = posterior).

parameters could be found (Pearson correlation coefficient). All patients (lOOOh) were satisfled with the esthetics of the all-ceramic FPDs. Two patients (5.6%) were not satisfied with the functional aspects: 1 because of persisting temperature sensitlvlty (FPD was not properly cemented, no seal). the other because of occlusal problems (supraocclusion on reconstruction, pain).

. _

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