Off-axis sliding contact reliability and failure modes of veneered alumina and zirconia

Objective: All-ceramic dental crowns are popular because of their esthetics and biocompatibility. However, they often chip or fracture when subjected to repeated occlusal loading. Considerable efforts to improve the materials are being done through the study of fatigue and failure modes. The vast majority of fatigue studies have been conducted with uniaxial loading and no sliding action. We hypothesized different failure modes for porcelain veneered Y-TZP and that the reliability of porcelain veneered Y-TZP is higher than that of porcelain veneered alumina when subjected to fatigue under 30° off-axis sliding Y-TZP and alumina plates were porcelain veneered and cemented to aged composite blocks as a model for an all-ceramic crown on dentin. Methods: Specimens (n = 21 per group) were fatigue at 30° off-axis with a hard sphere sliding contact in water, by means of a mouth-motion simulator apparatus. Results: Although no difference between groups was found, the failure modes differed and there was a tendency to higher reliability for Y-TZP compared to alumina for a mission of 50,000 cycles at 150 N load. Significance: Failure modes for alumina specimens were deep penetrating partial cone cracks and cementation internal surface radial cracks. Y-TZP specimens showed only surface damage with deep penetrating partial cone cracks extending to the veneer core interface, with no cementation surface radial cracking, which overall agrees with clinical finding. Angled sliding contact appears to better simulate oral function.