FLEXURAL AND SHEAR STRENGTHS OF ZRO2 AND A HIGH-NOBLE ALLOY BONDED TO THEIR CORRESPONDING PORCELAINS

Statement of problem. Flexural and shear strength between ZrO2 cores and veneering porcelains require investigation to facilitate clinical use. Purpose. The purpose of this study was to assess the strength of ZrO2 and a high-noble alloy with corresponding porcelains. Material and methods. Forty rectanglar (12 x 10 x 3 mm) and 20 cylindrical (5 x 5 mm) specimens of ZrO2 (Lava) and high-noble alloy (Olympia) were fabricated for 4-point flexural testing and shear testing. IPS '.SIGN veneering porcelain for high-noble alloy and Lava Ceram, 2 mm thick, were fired, joining the 2 corresponding rectangles of high-noble alloy and ZrO2 to create flexural test specimens. The same types of veneering porcelains, 3 mm in thickness, were fired on 1 side of the corresponding high-noble alloy and ZrO2 cylinders to produce shear specimens. The flexural and shear specimens were divided into 4 groups (n=10); metal ceramic and ZrO2 with and without thermal cycling. Thermal cycling was performed at 5 C and 55 C for 5000 cycles with a 20-second dwell time. Flexural and shear tests were performed using a universal testing machine. Fractures were characterized using a stereomicroscope and SEM. Data were analyzed with a 1-way ANOVA and Tukey HSD post hoc test (alpha=.05). Results. The AN OVA revealed a significant difference among flexural groups (P=.008) and among shear groups (P<.001). In flexure, the Tukey HSD post hoc test revealed a significant difference (P=.005) between metal ceramic thermal cycled and ZrO2 thermal cycled groups, with a highervalue of 91.01 (22.33) MPa for the metal ceramic group. In shear, the Tukey HSD post hoc test revealed a significant difference between metal ceramic and ZrO2 groups, with a higher value of 82.00 (22.49) MPa for the metal ceramic group. Thermal cycling did not have a significant effect on flexure or shear strength. ZrO2 specimens failed cohesively within the veneering porcelain. Conclusions. There were no significant differences among the groups in flexure, except between thermal cycled metal ceramic and ZrO2 groups. There was a significant difference between the metal ceramic and ZrO2 groups in shear. Thermal cycling did not have a clear effect among different groups in both tests. (J Prosthet Dent 2008;100:274-284)