Effect of thickness on optical properties of monolithic CAD-CAM ceramics

Objective: To compare the effect of material and thickness on the color stability and relative translucency parameters (RTP) for monolithic ceramics subjected to coffee thermocycling. Methods: Four specimens each at thicknesses of 0.5, 0,7 and 1mm were sectioned from monolithic ceramics [preshaded monolithic zirconia (MonZr), lithium disilicate (LDS) and zirconia reinforced lithium silicate (ZLS)]. The specimens were glazed and subjected to 5000 coffee thermocycling. The color coordinates of specimens were determined with a spectroradiometer and color differences and RTP values were calculated with CIEDE2000 color difference and TPCIEDE2000 formulas. ANOVA was used to analyze CIEDE2000 color difference and RTP values (alpha = .05). Results: For the color difference data, the 2-way ANOVA revealed a significant interaction between material and different thickness (P = .002). Except for 0.5mm thick ZLS material, all materials in all thicknesses studied presented color changes within the clinically acceptable limits after coffee thermocycling. For the RTP data, the 3-way ANOVA revealed a highly significant interaction between material and different thicknesses (P < .001). Conclusions: Material type and thickness can be expected to affect color change and relative translucency of the restorations made with preshaded MonZr, LDS and ZLS materials. Except for 0.5mm thick ZLS material, color changes of all studied materials were within the clinically acceptable limits. Except ZLS material, color changes of other materials were not significantly affected by thickness. Staining in coffee was not found to affect translucency, and the materials' translucency parameters were ranked from high to low as LDS, ZLS and MonZr at each thickness studied.