The effect of thickness on the contrast ratio and color of veneering ceramics.

Abstract

Objectives: The objectives of this study were to evaluate the effect of thickness on the contrast ratio and color of two veneering ceramics. Materials and methods: Square shaped specimens (15mm x15 mm) were prepared from A3 shade of Vita VM9 (V) and IPS e-max Ceram (E) at four different thicknesses i.e., 0.6mm,0.8mm,1.2mm,1.5mm (n=5). All specimens were finished flat on a milling machine to the required dimension using 100 µ m diamond coated disc. The contrast ratio (CR= Yb / Yw ) and color difference (∆ E= [(L*1 -L2 *)2 + (a*1 - a*2 ) 2 + (b*1 -b*2 )]2 ) 1/2 were measured with a spectrophotometer and calculated. The statistical analyses for the mean contrast ratio (CR) of all groups were performed by two-way ANOVA and Tukey multiple comparison test at α=0.05. Color differences (∆E*) were compared between different thicknesses for the same brand and between different brands at the same thicknesses. Results: The results showed that the mean CR increased significantly with the increase in thickness from 0.6 to 1.5mm for both veneering ceramics; the CR of V 0.6 (0.61±0.01) was the lowest whereas CR of V 1.5 (0.87±0.00) and E 1.5 (0.87±0.01) were the highest. The brands did not significantly influence the mean contrast ratio in each thickness of veneering ceramics. For both veneering ceramics, a decrease in L*and an increase in a*were observed when the thickness increased. No influence of increasing thickness on b*was observed. Conclusions: The contrast ratio of two veneering ceramics was significantly influenced by thickness irrespective of the brands. L* and a* were influenced by thickness but not b*. When the thickness of the veneering ceramic was increased in both the brands, color changes were observed as an increase in ∆E* value.