Mechanical behavior of a Y-TZP ceramic for monolithic restorations: effect of grinding and low-temperature aging

• Two stimuli that Y-TZP monolithic restoration is submitted clinically were studied.
• Grinding showed not to be detrimental to biaxial flexure strength of Y-TZP.
• Low temperature aging did not promote deleterious impact at biaxial flexure strength of Y-TZP.
• An increase in m-phase content was observed for control group (notable increase) and ground groups (less intense increase).
• Low temperature aging did not affect roughness, while grinding promoted increase as function of grit size.

This study aimed to investigate the effects of grinding with diamond burs and low-temperature aging on the mechanical behavior (biaxial flexural strength and structural reliability), surface topography, and phase transformation of a Y-TZP ceramic for monolithic dental restorations. Disc-shaped specimens (Zirlux FC, Ivoclar Vivadent) were manufactured according to ISO 6872 (2008) and divided in accordance with two factors: “grinding — 3 levels” and “LTD — 2 levels”. Grinding was performed using a contra-angle handpiece under constant water-cooling with different grit-sizes (extra-fine and coarse diamond burs). LTD was simulated in an autoclave at 134 °C, under a pressure of 2 bar, over a period of 20 h. Surface topography analysis showed an increase in roughness based on surface treatment grit-size (Coarse > Xfine > Ctrl), LTD did not influence roughness values. Both grinding and LTD promoted an increase in the amount of m-phase, although different susceptibilities to degradation were observed. According to existing literature the increase of m-phase content is a direct indicative of Y-TZP degradation. Weibull analysis showed an increase in characteristic strength after grinding (Coarse = Xfine > Ctrl), while for LTD, distinct effects were observed (Ctrl < Ctrl LTD; Xfine = Xfine LTD and Coarse = Coarse LTD). Weibull moduli were statistically similar between all tested groups. Within the limits of this current study, it was feasible to notice that both aging in autoclave for 20 h (LTD) and grinding showed not to be detrimental to the mechanical properties of Zirlux FC Y-TZP ceramic.