Effect of treatments applied to monolithic zirconia with different thicknesses on surface roughness and bending strength before and after thermal aging

Objective: The aim of the present study is to investigate the effects of different surface treatments and thermal cycling on the surface roughness and biaxial flexural strength of monolithic zirconium samples prepared with different thicknesses. Method: In this study, a total of 160 VITA YZ ® HT brand monolithic zirconium samples were prepared in disk shape, 80 pieces of 1 mm thickness, 80 pieces of 2 mm thickness and 15 mm diameter. Half of the samples prepared in different thicknesses were subjected to thermal cycling. For all sample groups, 4 subgroups were created according to the surface finishing process (n=10). The subgroups were created as control (K), abrasion and polishing (AP), abrasion and glaze (AG), abrasion, polishing and glaze (APG). The surface roughness values ​​of the samples were measured with a tactile profilometer. Biaxial flexural strength was evaluated with the piston technique on three balls. Statistical analysis was performed with three-way Robust ANOVA. Results: In all samples, the average surface roughness was found to be the highest in the K and AP groups, and the lowest in the AG group. This difference was found to be statistically significant. The highest flexural strength values ​​were found in the APG group and the lowest in the K group. This difference was not found to be statistically significant. The effect of thermal cycling on surface roughness was found to be statistically significant, while its effect on flexural strength was not found to be significant. The effect of material thickness on surface roughness and flexural strength was found to be statistically significant. Conclusion: It was observed that thermal cycling application caused an increase in surface roughness value while decreasing the flexural strength. The increase in sample thickness was found to result in a decrease in surface roughness values, while leading to an increase in flexural strength values. Combined abrasion, polishing, and glazing reduced surface roughness and improved flexural strength. Key words: monolithic zirconium, surface finishing processes, thermal cycling, surface roughness, biaxial flexural strength