Introduction With growing demand for expedited digital workflows in prosthodontics, high-speed sintering protocols have gained popularity. While the mechanical properties of dental zirconia under these protocols have been studied, the esthetic consequences—particularly changes in shade and translucency—remain inadequately understood. This study evaluated the effects of high-speed sintering on the optical, colorimetric, and compositional properties of 3Y-, 4Y-, and 5Y-yttria-stabilized zirconia (YSZ) across a full spectrum of shades, and identified factors contributing to esthetic changes critical for predictable clinical outcomes.

Methods A total of 144 disc-shaped specimens (n = 8) were prepared from 3YSZ, 4YSZ, and 5YSZ pucks in shades B1, A3, and C4. Each was subjected to conventional (~12 hours) or high-speed (~18 minutes) sintering. Specimens were polished to a 0.5-μm finish, with final dimensions of 14 mm in diameter and 1 mm thick. Density, phase content, porosity, translucency, contrast ratio, color, and elemental composition were quantified. Photographs were taken against a neutral gray background using a calibrated camera. Normality was assessed using the Shapiro–Wilk test. Non-parametric comparisons were performed using the Kruskal–Wallis test with Dunn’s post-hoc analysis (α = 0.05).

Results High-speed sintering significantly altered the optical properties of zirconia (p < 0.0001), reducing translucency—particularly in the C4 shade (p = 0.0009) and in 5YSZ (B1: p = 0.0126; A3: p = 0.0009; C4: p = 0.0003). Increased Porosity (p = 0.0199), especially in 5YSZ, contributed to the decline in translucency. Color shifts included increased L* and decreased b* values (p < 0.0001). Additionally, a* values for A3 and C4 shifted from positive to negative, indicating a red-to-green transition. ΔE₀₀ values exceeded clinical thresholds, particularly in C4 across all compositions. Fe₂O₃ concentrations decreased while NiO remained stable, suggesting that thermal pigment instability contributed to the colorimetric changes.

Conclusions High-speed sintering compromises zirconia esthetics, particularly in high-translucency and darker shades. 5YSZ offered no translucency advantage, exhibited greater shade deviation, and—due to its lower flexural strength—lacks justification for use under accelerated protocols. These findings highlight the need to optimize high-speed sintering protocols and customize shade guides to ensure esthetic reliability in prosthodontics.