Effects of polishing or glazing on surface roughness and microhardness after milling CAD-CAM ceramic materials

Abstract

Objective: This study aimed to evaluate the surface roughness and microhardness of CAD-CAM ceramic blocks after different surface finishing protocols. Materials and methods: Three ceramics were evaluated: lithium disilicate, leucite-reinforced feldspathic and zirconia-reinforced lithium silicate. Ninety specimens were obtained and distributed into 3 groups (n=10): polishing (specimens were polished with an abrasive rubber kit); conventional glaze (according to the manufacturer's recommendations); and, extended glaze (the specimens were kept for 15 minutes at maximum firing temperature and the furnace was kept closed until reaching 200ºC). In all specimens, a drill was used to simulate the milling machine and thus obtain the initial roughness. Surface roughness was evaluated before and after the finishing protocols, while Vickers microhardness was performed only after the finishing protocols. Roughness data were analyzed to repeated measures two-way ANOVA and Bonferroni post-hoc test and ANOVA with Welch correction and Games-Howell test were used to analyze microhardness data (α = 0.05). Results: Both conventional and extended glazes showed greater smoothness for lithium disilicate and zirconia-reinforced lithium silicate ceramics, while for Empress, extended firing of the glaze provided greater surface smoothness. Regarding microhardness, there was no statistically significant difference among the protocols for the same material. The conventional glaze group made from lithium disilicate did not show a significant difference in microhardness values in relation to the other groups. Conclusion: The application of glaze improves the surface smoothness of the ceramics after milling procedure. There is no change in microhardness with different surface finishing protocols.