Effect of simulated mastication on the surface roughness of three ceramic systems

Statement of problem. Zirconia complete coverage crowns are being widely used as restorations because of their high strength and improved esthetics. Data are sparse about the change in surface roughness of this ceramic material after repeated mastication cycles of opposing enamel. Purpose. The purpose of this study was to investigate changes in the surface roughness after being subjected to 3-body wear-opposing human enamel of 3 types of ceramics: dense sintered yttrium-stabilized zirconia (Z); lithium disilicate (L); and a conventional low-fusing feldspathic porcelain (P) treated to impart a rough, smooth, or glazed surface. Material and methods. Twenty-four specimens of each of the Z and L ceramic were sectioned from computer-aided design and computer-aided manufacturing blacks into rectangular plates (15x12x2 mm). Twenty-four specimens of the feldspathic porcelain were formed into disks (12-mm diameter) from powders compressed in a silicone mold. All specimens (n=72) were prepared according to the manufacturers' recommendations. Specimens of each ceramic group were placed into 1 of 3 groups: group R, rough surface finish; group 5, smooth surface finish; and group G, glazed surface finish. A total of 72 specimens (9 groups with 8 specimens each) was placed in a 3-body wear simulator, with standardized enamel specimens (n=72) acting as the substrate. The changes in surface roughness of the ceramic specimens were evaluated after 50000 cycles. Data were analyzed by a repeated measures 3-way ANOVA mixed procedure with the Satterthwaite method for degrees of freedom and maximum likelihood estimation of the covariance parameters (alpha=.05). Results. Data showed that the PS group exhibited the largest change in surface roughness, becoming significantly rougher (P<.004), The LR group became significantly smoother (P=.012). Conclusions. The surfaces of monolithic zirconia ceramic and lithium disilicate did not become as rough as the surface of conventional feldspathic porcelain after enamel wear.