Statement of problem: Flexural and shear strength between ZrO(2) cores and veneering porcelains require investigation to facilitate clinical use.
Purpose: The purpose of this study was to assess the strength of ZrO(2) 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 ZrO(2) (Lava) and high-noble alloy (Olympia) were fabricated for 4-point flexural testing and shear testing. IPS d.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 ZrO(2) 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 ZrO(2) cylinders to produce shear specimens. The flexural and shear specimens were divided into 4 groups (n=10); metal ceramic and ZrO(2) with and without thermal cycling. Thermal cycling was performed at 5 degrees C and 55 degrees 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 ANOVA 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 ZrO(2) thermal cycled groups, with a higher value 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 ZrO(2) 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. ZrO(2) 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 ZrO(2) groups. There was a significant difference between the metal ceramic and ZrO(2) groups in shear. Thermal cycling did not have a clear effect among different groups in both tests.