Effects of two bleaching systems and a whitening mouthwash on the color stability, surface roughness, and microhardness of CAD/CAM materials and a composite resin

The preservation of color stability and surface integrity of restorative materials after bleaching remains clinically important. This study evaluated the effects of different bleaching protocols on color change (ΔE₀₀), surface roughness (Ra) and microhardness (VHN) of three CAD/CAM materials IPS e.max CAD (IPS), VITA Suprinity (VS), GC Cerasmart (CS) and one supra-nano-filled composite resin, Estelite Sigma Quick (ESQ), following staining, bleaching, and re-staining procedures. A total of 160 specimens ( n = 40/material; 14.5 × 14.5 × 2 mm) were prepared. After baseline measurements, specimens were immersed in coffee at 37 °C for 14 days. Bleaching protocols included 25% hydrogen peroxide (Philips Zoom), 40% hydrogen peroxide (Opalescence Boost), whitening mouthwash (Colgate Optic White), and distilled water (control). ΔE₀₀ was calculated using the CIEDE2000 formula (α = 0.05), Ra was measured using confocal microscopy and VHN with a Vickers microhardness tester, and Post-bleaching re-staining was performed for 3 days. Normality and homogeneity of variances were assessed using the Kolmogorov–Smirnov and Levene’s tests, respectively. Since parametric assumptions were met, within- and between-group comparisons were performed using repeated-measures analysis of variance (ANOVA) within the general linear model framework. Bonferroni correction was applied for multiple comparisons, and statistical significance was set at p < 0.05. Discoloration followed the order ESQ > CS > VS ≥ IPS. Re-staining was significantly influenced by both material type and bleaching protocol ( p < 0.001). Surface roughness decreased significantly in CS, VS, and IPS ( p < 0.001). After bleaching, Ra increased only in CS treated with 25% hydrogen peroxide ( p = 0.030), whereas treatment with 40% hydrogen peroxide significantly reduced Ra in VS ( p < 0.001) and IPS ( p = 0.001). In contrast, the mouthwash protocol significantly increased Ra in IPS ( p = 0.002). Staining resulted in a significant reduction in microhardness in all CAD/CAM materials ( p ≤ 0.002), while ESQ showed no significant change. Bleaching further reduced the microhardness of both VS and IPS regardless of the bleaching agent used. Bleaching protocols exert material-dependent effects on surface properties and color stability. Resin-containing materials demonstrated greater discoloration, and high-concentration hydrogen peroxide significantly reduced microhardness in glass-ceramic materials. Material composition should be considered when planning bleaching in patients with existing restorations.