The Effect of Repeated Firings on the Color of Dental Ceramics and Their Color Stability Submitted to Colored Solution

Introduction & Color matching between restoration and natural teeth is a common clinical problem. Despite careful shade selection, color of the restoration may be affected by fabrication procedures such as number of firing. Moreover, color stability is an important factor to ensure the long-term clinical success of ceramic restorations. There is a lack of information about color change of ceramic restoration affected by colored beverages, such as coffee colorants. The purpose of this study was to evaluate the effects of repeated firings and type of ceramic system on the color stability of dental ceramic exposed to a coffee beverage. In an experimental in vitro study, ninety disc-shaped specimens (10 mm in diameter with 0.5 mm core thickness and 1.5 mm dentin veneering thickness) from three ceramic system(PFM, IPS Empress 2, Zirconia-based) were made. Each system, based on the number of firings(3,5,7) was divided into 3 groups, then after repeated firings, half of each group was immersed in distilled water and another half in coffee (n=5). Color readings were determined with a colorimeter before and after firings and immersion in solutions, and L*, a*, and b* coordinates and total color variation (ΔE) were analyzed. ΔE was calculated using the formula ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2. A repeated measure ANOVA was used to analyze the data. The Tukey HSD test were performed for multiple comparisons (α=0.5). The ΔE values of the ceramic system were affected by the number of firings (3, 5, 7) (P<0.005) and the type of porcelain system (P<0.005). Significant interactions were present among the number of firings and the type of porcelain system (P=0.000). An increase in the number of firings produced an increase in the ΔE values but only for IPS system, the number of firings (3-5) was clinically significant (ΔE > 3).The average ΔE values were higher for those with less firings(3-5) than for those with more firings(5-7).The beverages and it’s interaction by the number of firings and type of porcelain system did not cause significant changes statistically(P> 0.005). The type of porcelain system and number of firings affected the color of the ceramic material tested. Coffee beverage did not produce any perceptible changes on the final color (ΔE< 3).