The Effect of Repeated Firings and Ceramic Thickness on the Color of Ceramic Systems

Objectives: : Shade matching and color stability is a crucial stage for the long term esthetic success of a restoration. The thickness of porcelain veneering materials and the number of firings may affect the color of the restoration.The purpose of this study was to investigate the color changes of two all-ceramic systems with two different veneering porcelain shades after recurrent firing procedures
Methods: 42 disc-shaped specimens; 10 mm in diameter with a 0,5 mm core thickness and three different dentin thickness (0,5mm-1mm-1,5mm ) were made from each all-ceramic system ( ZR and IPS e-Max) with 2 different porcelain veneering shades (A1,A3). The recurrent firing procedure (1,3,5,or 7) were repeated for each specimens and color differences were (∆E) measured with a spectrophotometer (Vita Easyshade). All the data were expressed in CIElab System. Analysis of variance was used to determine the effect of veneer thickness and on the color parameters. The Duncan test and paired 2-tailed tests were used for multiple comparisons (α=.05)
Results: As the ceramic thickness increased, significant decreases in L values (P‹.01) were recorded for IPS e-Max and ZR specimens. According to the results of Anova; all L* a*b* values of the ceramic systems were affected by the number of firing procesdures (1,3,5,or 7) (P‹.001). As the number of firings performed, both A1 and A3 veneering porcelain shades indicate an increase in the L* value, causing lighter specimens (P‹.001).For both A1 and A3 veneering porcelain shades; the a* value decreased but the b* value increased after repeated firings (P‹.01)
Conclusions: Different veneering porcelain shades with two different ceramic systems influenced by the repeated firing procedure. The color changes that determined are clinically acceptable.