Effects of high-speed sintering on the translucency and color of dental zirconia with different shades and yttria contents.

Abstract

Purpose: This study evaluated the effects of high-speed sintering on the translucency and color of various yttria-stabilized zirconia (YSZ) compositions and identified factors influencing these properties to improve clinical predictability.

Materials and methods: A total of 144 disc-shaped specimens fabricated from 3YSZ, 4YSZ, and 5YSZ pucks in shades B1, A3, and C4 were sintered using conventional (∼12 h) or high-speed (∼18 min) protocols. Specimens were polished to a 0.5 µm finish and measured Ø13.75 mm × 1 mm. Porosity, phase content, translucency, color, and elemental composition were quantified (n = 8). Normality was assessed using the Shapiro-Wilk test. Pairwise comparisons were performed using Wilcoxon rank-sum tests where appropriate. The effects of shade, yttria content, sintering protocol, and their interactions were evaluated using factorial ANOVA (α = 0.05).

Results: High-speed significantly reduced translucency and diminished the translucency advantage of 5YSZ, particularly in darker shades. The reduced translucency was attributed to increased porosity. High-speed also produced lighter specimens (higher L^* values) with lower a^* and b^* values, indicating a shift toward greener, less yellow color coordinates. Color differences (ΔE₀₀) were greatest in C4-shaded specimens. Additionally, a distinct light-dark subgrouping was observed within the 4YSZ-B1 high-speed condition. Compositional analysis showed that HS reduced Fe₂O₃ levels while maintaining NiO, suggesting that color changes may be associated with Fe₂O₃ instability and increased porosity.

Conclusions: High-speed reduced translucency and altered clinically perceptible color in dental zirconia, especially in high-yttria contents and darker shades.