The effect of ceramic thickness and number of firings on the color of ceramic systems: an in vitro study.

STATEMENT OF PROBLEM Although all-ceramic restorations are widely used, there is a lack of information on how color is affected by fabrication procedures. Color matching problems may be encountered in a definitive restoration despite careful shade selection. PURPOSE The aim of this study was to evaluate the effect of dentin ceramic thickness and repeated firings on the color of glass-infiltrated aluminum-oxide (In-Ceram) and leucite-reinforced (IPS Empress) all-ceramic systems using a colorimeter. MATERIAL AND METHODS Twenty-one disc-shaped specimens, 10 mm in diameter with a 0.6-mm core thickness and 0.5-, 1-, or 1.5-mm dentin ceramic thickness, were made from each of 2 ceramic systems (n=7) . Repeated firings were performed for each group, and the color differences were compared with the color after the initial firing. Color differences among ceramic specimens were measured using a colorimeter (XL-20 Colorimeter), and data were expressed in Commission Internationale d'Eclairage (CIE) LAB system coordinates. Repeated-measures analysis of variance was used to analyze the data (number of firings, ceramic brand, and ceramic thickness) for significant differences. The Tukey honestly significant difference test and paired 2-tailed tests were used to perform multiple comparisons (alpha=.05). RESULTS The L( *)a( *)b( *) values of ceramic systems were affected by the number of firings (3, 5, or 7) (P<.01) and ceramic brand (In-ceram or IPS Empress) (P<.01). L( *) and a( *) values were affected by ceramic thickness (0.5, 1, or 1.5 mm) (P<.01); however, b( *) value was not affected by ceramic thickness (P=.075). Significant interactions were present in L( *), a( *), b( *) values between number of firings and ceramic brand (P<.01), and between ceramic brand and ceramic thickness (P<.05). Significant interactions were present between number of firings and ceramic thickness (P<.01) in L( *) and b( *) values but not in the a( *) value (P=.379). CONCLUSION The analysis revealed that there were substantial changes in L( *)a( *)b( *) color data as the number of firings increased, which resulted in perceptual color changes in L( *)a( *)b( *) color parameters.