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-in filtrated 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) LA-B 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.