Effects of core and veneer thicknesses on the color of CAD-CAM lithium disilicate ceramics

Abstract

Statement of problem. The color of dental ceramics is important for achieving successful esthetic restorations. However, insufficient studies are available of the color of recently introduced computer-aided design-computer-aided manufacturing (CAD-CAM) lithium disilicate ceramics as functions of the core and veneer thicknesses. Purpose. The purpose of this in vitro study was to evaluate the effects of the thickness of different core and veneer thicknesses on the color of CAD-CAM lithium disilicate ceramics. Material and methods. A total of 42 specimens from 2 groups of 7 ceramic cores at 3 thicknesses (0.8, 1.0, and 1.2 mm) were fabricated. The veneer was fabricated at 3 thicknesses (0.3, 0.5, and 0.7 mm). The group name was based on the name of the ceramic core (IPS e.max CAD; lithium disilicate (LDI, IPS Empress CAD; leucite-reinforced glass-ceramic [LR)), and the associated number was determined by the combined thicknesses of the core and the veneer: 1=0.8+0.7; 2=1.0+0.5; and 3=1.2+0.3. The color coordinates and the color differences were calculated using a spectrophotometer. The color difference was analyzed using the CIEDE2000 chrominance and the acceptability threshold. Two-way ANOVA was used to identify the color difference based on the core/veneer thicknesses, and the Tukey honest significant differences and Games-Howell tests were conducted to verify the Delta E-00 differences of the group (alpha=.05). In addition, regression analysis was carried out to estimate the causal relationship between the independent variables and the chrominance. Results. At a certain thickness, the color differences of LD1, LR1, and LR2 were not clinically acceptable based on the thicknesses of the core and the veneer. Results of 2-way ANOVA demonstrated that the different thicknesses of core/veneer combination significantly affected the color difference (P<.05). A significant interaction was present between the thickness and the material (P<.05). The results of multiple regression analyses showed that the average color difference of LR increased by 0.019 as the thickness of the core decreased by 0.2 mm. Conclusions. The color is influenced by the thicknesses of the core and the veneer. With a certain thickness, the color differences increased as the thickness of the core decreased, and lithium disilicate ceramics were less vulnerable to standard deviation of color difference compared with the leucite-reinforced ceramics.