Effect of different CAD/CAM cutting depths on the post-fatigue load-bearing capacity of novel multilayer zirconia restorations.

Abstract

OBJECTIVES\nTo investigate the post-fatigue load-bearing capacity of restorations milled at various cutting depths in a novel strength- and color-gradient multilayer zirconia CAD/CAM disk.\n\n\nMETHODS\nIdentical crowns were divided into 4 groups (n=25 per group): crowns milled at 3 CAD/CAM cutting depths in multilayer zirconia disks as 3 experiment groups and homogeneous zirconia crowns as a control group. The color differences between various cutting depths were measured. In each group, crowns were tilted at 15° and subjected to fatigue loading for various numbers of cycles (0, 106, 2\u202f×\u202f106, 3\u202f×\u202f106 or 4\u202f×\u202f106, n=5 per subgroup). All surviving crowns were subsequently submitted to a static fracture test to determine load-bearing capacity. The data were analyzed by ANOVA and Weibull distribution analysis. Failure modes were observed with SEM.\n\n\nRESULTS\nFor a novel multilayer zirconia, a deeper CAD/CAM cutting depth corresponded to a higher load-bearing capacity but a darker color. After 106 cycles of fatigue loading, there was not a significant reduction in fracture load. However, after 4\u202f×\u202f106 cycles, the load-bearing capacity of all crowns decreased significantly by approximately 50%. For multilayer and homogeneous zirconia materials, similar failure mode and Weibull modulus were identified.\n\n\nCONCLUSIONS\nRestorations can be milled at various CAD/CAM cutting depths in a novel multilayer zirconia disk depending on the durability and aesthetic requirements. The load-bearing capacity of multilayer restorations degraded significantly after 4\u202f×\u202f106cycles of fatigue loading, but not after 106cycles.\n\n\nCLINICAL SIGNIFICANCE\nFor a novel multilayer zirconia disk, a posterior restoration can be milled from the middle or bottom of the disk to improve its load-bearing capacity. For an anterior restoration, to meet the aesthetic requirements, milling the entire thickness of a multilayer disk is recommended.