In vitro comparison of the load-bearing capacity of ceramic and metal-ceramic resin-bonded fixed dental prostheses in the posterior region.

STATEMENT OF PROBLEM: The clinical use of ceramic resin-bonded fixed dental prostheses (RBFDPs) in the posterior region is desirable for esthetic and biological reasons but has been associated with many technical problems, including fractures or chipping of the veneer. Although these problems may be overcome by using monolithic zirconia, information is lacking about the load-bearing capacity of resin-bonded monolithic zirconia restorations for replacing a molar. PURPOSE: The purpose of this in vitro study was to compare the load-bearing capacity (F(u)), the load at initial damage (F(1d)), and the failure pattern of posterior RBFDPs fabricated from monolithic zirconia (MZr), veneered zirconia (VZr), and veneered cobalt-chromium (VCo). MATERIAL AND METHODS: For the replacement of a maxillary first molar, 4 groups (n=8) of RBFDPs differing in prosthesis material and retainer design (MZr-IR-RBFDPs, VZr-IR-RBFDPs, MZr-WR-RBFDPs, and VCo-WR-RBFDPs; IR, inlay-retained; WR, adhesive wing-retained) were fabricated with anatomic congruence of the FDP-abutment complex. The RBFDPs were subjected to thermocycling (10000x6.5 degrees C/60 degrees C) and mastication simulation (30-degree oblique loading on the pontic; 1200000x108 N) and then loaded until failure in a universal testing machine (0.5 mm/minute). Test forces correlating with F(u) and F(1d) were recorded. Statistical analysis was performed by using 2-way analysis of variance (ANOVA), 2-way repeated measures ANOVA, and the Tukey honest significant differences post hoc test (2-sided alpha=.05). RESULTS: F(u) was significantly affected by retainer design (P<.001) and F(1d) by both retainer design (P<.001) and prosthesis material (P<.001). F(u) was more than 2000 N for WR-RBFDPs and more than 1000 N for IR-RBFDPs (Tukey test ranking: MZr-WR-RBFDPs = VCo-WR-RBFDPs > MZr-IR-RBFDPs = VZr-IR-RBFDPs). Ceramic RBFDPs failed by complete fracture in the connector region, whereas failure of VCo-WR-RBFDPs was limited to the ceramic veneer. F(1d) was significantly lower (P</=.004) than F(u) for veneered specimens only; F(1d) started at test forces below 500 N and coincided with veneer cracking. CONCLUSIONS: Load-bearing capacity suitable for the definitive restoration of a molar was observed for all groups. Veneered resin-bonded fixed dental prostheses, however, were susceptible to cracking of the veneer.