Effects of porcelain thickness on the flexural strength and crack propagation in a bilayered zirconia system

Objective: this study evaluated the influence of porcelain (vm9,vita zahnfabrik,germany) thickness on the flexural strength and crack propagation in bilayered zirconia systems (yz,vita zahnfabrik,germany). material and methods: thirty zirconia bars (20.0×4.0×1.0 mm) and six zirconia blocks (12.0×7.5×1.2 mm) were prepared and veneered with porcelain with different thickness: 1 mm,2 mm,or 3 mm. the bars of each experimental group (n=10) were subjected to four-point flexural strength testing. in each ceramic block,a vickers indentation was created under a load of 10 kgf for 10 seconds,for the propagation of cracks. results: the results of flexural strength were evaluated by one-way anova and tukey’s test,with a significance level of 5%. the factor “thickness of the porcelain” was statistically significant (p=0.001) and the 1-mm group presented the highest values of flexural strength. the cracks were predominant among the bending specimens with 1 and 2 mm of porcelain,and catastrophic failures were found in 50% of 3-mm-thick porcelain. after the indentation of blocks,the most severe defects were observed in blocks with 3-mm-thick porcelain. conclusion: the smallest (1 mm) thickness of porcelain on the zirconia infrastructure presented higher values of flexural strength. better resistance to defect propagation was observed near the porcelain/ zirconia interface for all groups. higher flexural strength was found for a thinner porcelain layer in a bilayered zirconia system. the damage caused by a vickers indentation near and far the interface with the zirconia shows that the stress profiles are different. © 2017,faculdade de odontologia de bauru. all rights reserved.