Color changes of monolithic zirconia block before and after sintering

Abstract

The aim of this study was to compare the color changes of three monolithic zirconia blocks by two shades before and after sintering. A total of 60 cuboid-shaped HT (H) and A2 (A) shade zirconia specimens (8.0×8.0×5.0 mm) were fabricated for the following materials: Razor (RZ) (RZ_H, RZ_A), Zenotec (ZN) (ZN_H, ZN_A), and Anatomic Coloured (AC) (AC_H, AC_A). A spectrophotometer was used to measure color coordinates (Commission Internationale de l'Eclairage [CIE] L*a*b*) before sintering. Sintering was done in the same condition. The color after sintering was evaluated, and color differences (ΔE*) before and after sintering were calculated. For comparisons, statistical analyses were conducted using a one-way analysis of variance (α=0.05). The ΔE* of the HT shade was significantly higher in the RZ_H (19.29±0.49) and AC_H (19.37±0.25) than in ZN_H (14.11±0.28). The ΔE* of A2 shade showed statistically significant difference in all groups, with RZ_A being the highest (28.39±0.51), followed by AC_A (23.01±0.43) and ZN_A (21.12±0.85). All materials had the largest ΔL* with decreasing direction. It indicated that the specimen darkened after sintering. The ΔL* in all materials was larger in the A2 group than in the HT group, and ΔE* was also larger in the A2 group. Within the limitations of this study, we conclude that after sintering of zirconia, the color change was the greatest in lightness, and the degree and pattern of change were different depending on the material and shade.