Surface, Colorimetric, and Optical Properties of New-Generation Lithium Disilicate Ceramics

Lithium disilicate-based glass-ceramics (LDC) are widely used for esthetic restorations, yet their surface and optical behavior can vary depending on the composition and surface treatment procedure. The purpose of this study was to compare the surface, colorimetric, and optical properties of LDC materials with different compositions after being subjected to polishing or glazing.

Rectangular specimens were prepared by sectioning four compositions of LDC CAD/CAM blocks (IPS e.max CAD [IPS], Amber Mill [AM], Amber Mill Direct [AMD], Initial LiSi [ILS]). Baseline surface roughness (Ra), color, translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP) and gloss (GU) values were recorded. Each group was divided into two subgroups according to surface treatments, one undergoing glazing and the other polishing, followed by post-treatment measurements (n = 10). Color change (ΔE00) for each group was calculated based on the CIEDE2000 formula. In addition to baseline and final Ra, TP, CR, OP, and GU measurements, the changes in these parameters (ΔRa, ΔTP, ΔCR, ΔOP, and ΔGU) were calculated by subtracting the baseline values from the final values obtained after polishing or glazing. One extra specimen from each group was prepared for scanning electron microscopy (SEM) analysis. Mann-Whitney U, Kruskal-Wallis H, and Wilcoxon signed-rank tests were used for statistical analysis (α = 0.05).

The surface, colorimetric, and optical properties differed significantly based on the type of LDC material and the surface treatment method. The Ra values of IPS, AMD, and ILS decreased significantly after glazing compared to polishing (p = 0.016), which was confirmed by SEM analysis. Both surface treatments significantly reduced Ra values compared with baseline across all material groups (all p ≤ 0.013). Glazing resulted in higher mean ΔE00 values than polishing for IPS (p = 0.011) and ILS (p = 0.0001). For IPS, TP values were lower in the glazed specimens than those that were polished (p = 0.001), whereas the opposite trend was observed for CR values (p = 0.001). Regardless of the LDC material type, glazing produced significantly lower OP values (all p ≤ 0.041) and higher GU values (all p ≤ 0.023) than polishing.

Surface, colorimetric, and optical properties of LDC materials varied depending on the surface treatment method and material composition. While both surface treatments effectively reduced surface roughness, glazing enhanced surface gloss and opalescence more prominently, but induced material-specific color changes. Glazing also enhanced the translucency of IPS e.max CAD compared to other LDC materials.