Effects of sintering protocol and aging on the optical properties of multilayer zirconia

Monolithic zirconia prostheses have been sintered using speed protocols; however, data regarding their optical properties and aging behavior remain scarce. This study evaluated the color, translucency, and fluorescence of multilayer translucent zirconias subjected to different sintering protocols and aging. A total of 120 0.8-mm-thick disks were made from Lava Esthetic Fluorescent Full-Contour Zirconia (LE group), IPS e.max ZirCAD Prime Esthetic (ZC group), and IPS e.max CAD (LD group). The zirconia specimens were obtained from the incisal (I), transitional (T), and body/dentin (B/D) zones. Half of the specimens were sintered using a standard protocol, while the other half underwent speed sintering. All specimens were aged in an autoclave. The L*a*b* coordinates and 3D excitation-emission matrices (EEMs) were obtained. ΔE ₀₀ , ΔL’, ΔC’, ΔH’, TP ₀₀ , and ΔTP ₀₀ were calculated using CIEDE2000. Data were analyzed using Wilcoxon signed-rank, Mann-Whitney, and Kruskal-Wallis tests with Bonferroni correction (α = 0.05). EEM contour plots were evaluated by Parallel Factor Analysis (CP/PARAFAC). The LEB group showed the highest ΔE ₀₀ (4.47) after speed sintering. Aging increased color differences under both sintering protocols, accompanied by a reduction in lightness ( p  < 0.001). Translucency increased after speed sintering, except for ZCI. Reduced translucency was observed in ZCT, ZCD, and LD specimens after aging ( p  < 0.001). Speed sintering and aging reduced fluorescence, with a more pronounced effect in the LE group. Speed sintering protocols can alter the color, translucency, and fluorescence of multilayer zirconia over time when combined with aging.