rimental porcelain repair ed clinical conditions Nice H. J. Creugers, DDS, PhD,a Peter Arnd F. KByser, DDS, PhD.b
University of Nijmegen,Nijmegen,The Netherlands Twenty metal ceramic crowns on upper premolars in 12 patients were purposely fractured before seating with temporary cement. The fractured crowns were repaired in situ with an experimental porcelain repair system. The initial results ‘were satisfactory both esthetically and functionally. However, only 50% of the repairs were intact by th’e end of the la-month follow-up period. The system is considered to be suitable only for intermediate repairs of metal ceramic crowns that are in occlusal contact. (J PROSTHET DENT 1992;68:724-7.1
he metal ceramic crown combines the beauty of porcelain and the strength of metal alloys in a single restoration. Although the strength of porcelain and the bond strength to the metal substrate have improved greatly, some failures still occur under clinical conditions, The prevalence of porcelain fractures in metal ceramic crowns is approximately 5% in 10 years.‘, 2 The main reason for porcelain fracture is inadequate tooth preparation, which results in too little interocclusal space for metal substructure and porcelain. Improper design of the restoration in relation to the occlusion (that is, the margin between porcelain and metal) is a major cause of failure. Remaking of the crown or fixed partial denture is often inadvisable, and intraoral repair with a composite resin may be indicated. Several intraoral porcelain repair systems are available,3 but most of them have been only moderately successful. Clinical procedures for nearly all systems have been complex and time-consuming. Successful repair has been an even greater problem when the metal substructure has been exposed. An excellent overview of several adhesive intraoral porcelain repair systems is presented by Bertolotti et a1.,4 which along with other publications5s describes improved results by etching of porcelain with hydrofluoric acid or with aeidulated phosphate fluoride gels. Several improved intraoral porcelain repair systems are currently available, and most of them similar to the system under investigation, show acceptable in vitro bond values4yg-12 This study evaluated an experimental porcelain repair aAssociateProfessor, Trikon Institute for Dental Clinical Research, Departmentof Oral Function and ProstheticDentistry. bProfessor and Chairman, Prosthetic Dentistry. 10/1/39428
of Oral Function
system under stringent conditions in posterior teeth with regard to survival of the repairs and esthetic appearance. The porcelain repair system consisted of an experimental ceramic primer, Prisma Ceraprime; a bonding agent, Prisma Universal bond 2; and a composite resin, Prisma Fil (DeTreyiDentsply, Koblenz, Germany). MATERIAL
Twenty metal ceramic crowns were fabricated for maxillary premolars in 12 patients (11 women and one man). The crowns were made of a high-silver palladium alloy, Simidur S2 (Wieland, Pforzheim, Germany) and Shofu porcelain (Shofu, Kyoto, Japan). Before placement the porcelain of the facial cusps was purposely fractured by preparation of a groove in the porcelain followed by chipping of the porcelain with an instrument placed obliquely in the groove. The fractured sites were classified as follows: class I, fracture within the porcelain with no metal exposure; and class II, fracture including metal exposure. Fig. 1 and 2 show metal ceramic crowns with both types of fracture. The fractured crowns were luted temporarily with Temp-bond (Kerr, Basel, Switzerland) cementing material to allow the removal and repair of the crowns at the end of the study. The fractured crowns were repaired by three different clinicians with Ceramic Prime and Prisma Fil composite resin (Detrey/Dentsply). Damage to the crown and the repair were performed by different clinicians. The clinical protocol for the procedure is as follows. 1. Surface conditioning and creation of finishing bevels in porcelain with a diamond instrument 2. Isolation of the area with a cotton roll or rubber dam 3. Mixing of ceramic primer and etching gel (37% phosphoric acid) in a 1:l ratio and application of the mix onto the porcelain for 2 minutes
Fig. 1. Metal ceramic crowns on maxillary premolars show class I fractures. Grooves used to make the fracture can be seen. Fig. 2. Metal ceramic crown with class II fracture. Fig. 3. Metal ceramic crowns immediately after repair. Pig. 4. Repaired class II porcelain fracture.
4. Washing and drying of the porcelain surface and the exposed metal surface for 30 seconds each 5. Application and curing of Prisma Universal Bond 2 6. Building up of the cusps with Prisma Fil composite resin, light cured in 1 mm layers. When metal was exposed, an opaque layer of resin was applied before placement of the composite resin. 7. Finishing of the restoration with Shofu finishing disks Fig. 3 shows two crowns that have been repaired intraorally. Fig. 4 shows a repaired class II fracture. The total time for the repair procedure was recorded, including eventual deviations from the clinical protocol. The repaired crowns were evaluated for esthetics and survival of the repair. The esthetic appearance was assessedby means of the following index: Alpha. Color, shade, and/or transparency of the restoration match well with the crown. Brauo. A small but acceptable mismatch in color, shade, and/or translucency exists between restoration and crown; the margin of the restoration is visible.
Charlie. Unsatisfactory mismatch in color, shade, and/or translucency exists between restoration and crown. The patients were recalled at 2 weeks and 3, 6, and 12 months after repair of the crowns. All patients were in need of the restorations, agreed to participate in the study, and signed an informed consent. At the end of the study the crowns were removed and repaired by a dental technician. One crown could not be removed without damage and was remade.
RESULTS At the baseline of the study, 12 crowns showed a class I fracture and eight showed a class II fracture. The mean time needed for repair of the porcelain fracture was 25 minutes, ranging from 14 to 40 minutes. There was no significant difference between treatment times for repair of class I and class II fractures. One clinician was significantly slower than the others (31 vs 21 and 22 minutes). All 20 repairs matched well in color, shade, and translucency (alpha: n = 20). All crowns were in occlusion in the intercuspal po-
0% O-3 MONTHS
6. 7. Fig. 8. gration, Fig. 9.
5. Survival percentages of porcelain repairs during 12-month follow-up
Repair failure of class II fracture detected at 12-month recall. Repair failure of class I fracture at 9 months. Repair after 12 months shows surface wear of composite resin, marginal disinteand porosity. Repaired metal ceramic crowns on maxillary premolars at 12 months.
sition, whereas 20 Y0of the repaired sites extended into the occlusal area. The survival diagram of the repairs (50% failure rate) is shown in Fig. 5. Fig. 6 shows a failure in situ. Fig. 7 shows failure detail after the crown was removed. Failure occurred at the bonding interface between the crown and the resin restoration in all cases. No cohesive failures were found. Failures were divided equally between class I and class II fractures. Other baseline variables, such as occlusion and occlusal guidance, were distributed equal.ly between failures and nonfailures. Fifty percent of the nonfailed repairs showed discoloration at the margins at the E-month recall (bravo: n = 5; Fig. 8). Wear of the composite resin was seenin 80% of the specimens (Fig. 9). DISCUSSION
Intraoral repair of a porcelain fracture with the Prisma Ceraprime kit was performed easily. Results in the first 6 months of follow-up were acceptable with regard to esthetics and function. Substantial deterioration occurred in the period from 6 to 12 months. Failures showed no relation to recorded baseline variables such as type of fracture, occlusion, and occlusal guidance. The problem of wear and surface deterioration is not related to the repair system but to the use of microfilled composite resin (Prisma Fil) in this study. It could have been minimized if a (submicron) hybrid composite resin had been used. The survival rate (50%) at the end of the E-month evaluation period is too low to recommend use of the tested material for the occlusal repair of metal ceramic crowns.
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