Biaxial Flexural Strength of Zirconia-based Ceramic with Different Core:Veneer Ratio

Objective: To investigate the biaxial flexural strength (BFS) of zirconia-based ceramic (Cercon®) with different thickness of core: veneer ratio. Material and method: Fifty specimens, 15 mm. in diameter and 1.2 mm. in thickness, were fabricated following manufacturer's recommendations. The specimens were prepared and divided into 5 groups of 10 specimens. Group 1 was made of core:veneer = 1:0 (core material alone), group 2 was at ratio 2:1 (core thickness = 0.8 mm.), group 3 was at ratio 1:1 (core thickness = 0.6 mm.), group 4 was at ratio 1: 2 (core thickness = 0.4 mm.) and group 5 was at ratio 0:1 (veneer porcelain alone). All specimens were subjected to piston on three ball test following ISO 6872:1995. All tests were carried out on the Instron 5566 with crosshead speed of 1.0 mm/ min and calculated for BFS. Result: The means BFS ± SD of group 1 - 5 were 921.48±106.86 MPa, 1009.49 ±98.72 MPa, 895.68±92.96 MPa, 768.08±73.17 MPa, 70.49±8.54 MPa, respectively. ANOVA and Tamhane test revealed that there was no statistically significant difference among the BFS of group 1, group 2 and group 3 (P>0.05) but the BFS of these groups was significantly higher than the BFS of group 4 and group 5 (P<0.05). The BFS of group 5 was significantly lower than other groups (P<0.05). Fracture at core-veneer interface can be observed in all core-veneer composite specimens. Conclusion: At the thickness of 1.2mm, core and veneer ratio at 1: 0, 2: 1 and 1: 1 did not affect the BFS of zirconia-based ceramic, while decreasing the ratio to 1: 2, the BFS decreased significantly.