Damage sensitivity of dental zirconias to simulated occlusal contact

Objective. Mechanical damages can occur from dental restoration processing and fitting, or while it is in-service. This study evaluates the damage sensitivity of translucent zirconia (5Y-PSZ) relative to conventional 3Y-PSZ following mouth-motion simulations at various loads. Methods. 5Y-PSZ and 3Y-PSZ discs were adhesively bonded to a dentin-like substrate and divided into groups according to the load (50 N or 200 N) and number of cycles (up to 10(6)) used in the chewing simulation. Specimens were mounted with 30 degrees inclination in an electrodynamic mouth-motion simulator, and subjected to contact-slide-liftoff cyclic loading in water. Surface and sub-surface damages were analyzed using a sectioning technique. After the simulation, specimens were removed from the substrate and loaded with the damaged surface in tension for biaxial strength testing to assess their damage tolerance. Results. The strength of both ceramics underwent significant degradation after mouth- motion simulations. For 5Y-PSZ, the strength degradation was greater (similar to 60%) and occurred at a lower number of cycles than 3Y-PSZ. Herringbone cracks emerged on 3Y-PSZ and 5Y-PSZ surfaces under a 200-N load after 50 and 10 cycles, respectively. Meanwhile at a 50-N load, cracks formed at similar to 1000 cycles in both ceramics. Further increasing the number of cycles only had moderate effects on the strength of both ceramics, despite an increase in surface and sub-surface damage. More significantly, a 50-N occlusal load can debase the zirconia strengths as much as a 200-N load. Significance. Surface flaws produced during the chewing simulation are capable of significant strength degradation in zirconia, even after a small number of low-load cycles. (C) 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.

Automated summary

This study evaluated the damage sensitivity and strength degradation of translucent zirconia under mouth-motion simulations. The results showed that 5Y-PSZ exhibited greater strength degradation compared to 3Y-PSZ, with 50 N load significantly affecting the zirconia strengths.