Impact of Simulated Gastric Acid and Surface Treatment on the Color Stability and Roughness of Zirconia

This in vitro study evaluated the impact of simulated gastric acid exposure on the optical (ΔE00, translucency parameter TP, contrast ratio CR) and surface (roughness Ra) properties of monolithic zirconia ceramics under varying sintering rates and surface treatments. Forty-eight disc specimens (10 mm × 10 mm × 1.0 mm) were randomly allocated into four groups (n = 12): slow sintering + polishing; slow sintering + glazing; fast sintering + polishing; and fast sintering + glazing. Specimens were aged in 0.06 M of HCl (hydrochloric acid) for 96 h, and all measurement parameters were assessed against white and black backgrounds before and after aging. Statistical analyses (Shapiro–Wilk, Kruskal–Wallis, Wilcoxon tests; α = 0.05) revealed that acid aging caused a significant increase in ΔE00 across all groups (p < 0.05), with the smallest change observed in the fast-sintering + glazing group and the largest in the slow-sintering + glazing group. Contrast ratios remained high in all groups (CR > 0.92), while only the slow-sintering + glazing group exhibited a significant reduction in TP (p < 0.05). Surface roughness decreased following aging in all groups, with the lowest Ra detected in the fast-sintering + glazing group. These results suggest that fast sintering combined with glazing enhances color stability and yields smoother surfaces under acidic conditions, recommending this protocol particularly for patients at elevated risk of increased oral acidity.