In Vitro Effect of Thickness of Veneering Ceramic on Color Parameters of Zirconia All-Ceramic Restorations

Statement of the Problem: Controversy exists regarding the effect of porcelain thickness on color of restoration. Purpose: This study sought to assess the effect of thickness of the veneering ceramic on color parameters of zirconia all-ceramic restorations. Materials and Method: This in vitro experimental study was conducted on 30 discs measuring 10mm in diameter and 0.5mm in thickness fabricated of A3 shade of ZIRCAD zirconia using computer-aided design/computer aided manufacturing (CAD/CAD) system. Discs were divided into three groups (n= 10). Disc-shaped metal molds measuring 10mm in diameter and 1, 1.5 and 2mm in height were used to fabricate IPS e.max veneering ceramic in 1, 1.5 and 2mm thicknesses. After applying porcelain and firing, the color parameters (CIE L*a*b*) were measured using a spectrophotometer in three phases of zirconia core, dentin porcelain and glazing. Color difference (Delta E) was compared among the three groups. Data were analyzed using ANOVA and Tukey's test. Results: By an increase in the veneering ceramic thickness from 0.5 to 1.5mm, Delta E changed from 10.78 to 13.45 units. The highest Delta E was noted in presence of 1.5mm thickness of dentin porcelain. A significant difference was noted in Delta E among the three groups (p= 0.000); Delta E in presence of 1.5mm thickness of the veneering porcelain was significantly higher than that in the other two groups (p< 0.05). Conclusion: Significant improvement in color occurs by an increase in thickness of the veneering ceramic, and 1.5mm thickness of veneering ceramic is favorable for use in the clinical setting.