Influence of Thermal Tempering Processes on Color Stability of Glassinfiltrated Monochrome and Multilayer 5 mol% Yttria Partially Stabilized Zirconia.

Introduction: This study investigated the effects of tempering on color stability of glassinfiltrated monochrome (Mo) and multilayer (Mu) 5 mol% yttria-partially stabilized zirconia (5Y-PSZ).

Materials and methods: 180 5Y-PSZ specimens (width-length-thickness = 10-20-2 mm) were prepared from Mo and Mu, comprising cervical (C) and incisal (I) zone, and sintered with traditional versus glass infiltrated technique with different tempering processes through slow (S: 5°C/min), normal (N: 35°C/min), and fast (F: 70°C/min) cooling. CIE-L*a*b*, color difference (ΔEdiff), and microstructures were evaluated. ANOVA and Tamhane's comparisons were determined for significant differences (p⟨0.05).

Results: Mo closely resembled MuI for L* and a*, but was similar to MuC for b* and ΔEdiff. MuC exhibited significantly higher L*, a*, and b*, but lower ΔEdiff than MuI. Glass infiltration and fast tempering significantly increased L*, and ΔEdiff, whereas decreased a*, and b*. Mu had higher color change than Mo, but both were within an acceptable threshold (ΔEdiff≤5.5).

Conclusions: Glass infiltration and tempering processes altered color, with greater influence on Mu>Mo. Glass infiltration and rapid tempering produced a whitechalky and less chroma due to smaller grain size and t→m transformation. Nevertheless, color alterations were still within acceptable limits, thus considered color stable.