The effect of repeated firings on the color of an all-ceramic system with two different veneering porcelain shades

Statement of problem. Color matching between a restoration and natural teeth is a common clinical problem. Despite careful shade selection, color of the restoration may be affected by fabrication procedures. Purpose. The purpose of this study was to determine the color changes of an all-ceramic restoration with 2 different veneering porcelain shades after repeated firings. Material and methods. Twenty disc-shaped ceramic specimens, 4 mm in diameter with a 1-mm core thickness and 2 different veneering porcelain shades (A1, A3), were fabricated from a zirconia-based porcelain (DC-Zirkon) (n=10). Repeated firings (3, 5, 7, or 9 firings) were performed for the specimens, and color differences (Delta E) were determined using a spectrophotometer. Repeated measures ANOVA was used to analyze the data (number of firings, veneering porcelain color). The Tukey HSD test and paired 2-tailed tests were performed for multiple comparisons (alpha=.05). Results. The L*a*b* values of the ceramic system were affected by the number of firings (3, 5, 7, or 9) (P <.001) and the veneering porcelain shade (P <.001). Significant interactions were present between the number of firings and veneering porcelain shade for L* (P=.003) and b* (P=.042) values, but not for the a* value (P=.82). An increase in the number of firings of the specimens with both A1 and A3 veneering porcelain shades produced an Increase in the L* value, resulting in lighter specimens (P <.001). For both A1 and A3 veneering porcelain shades, the a* value decreased after repeated firings, which resulted in more green specimens (P=.002). The b* value did not change after repeated firings (P=.09) for the A1 veneering porcelain shade; however, it increased for the A3 veneering porcelain shade, which resulted in more yellow specimens (P=.001). Conclusions. The color of the all-ceramic specimens with different veneering porcelain shades is influenced by repeated firings. However, color changes that occurred are clinically acceptable.