Optical Stability of Injectable Resin Composites with Different Shade-Matching Strategies

This study evaluated the effects of aging, coffee staining, and bleaching on the optical properties of injectable resin composites with varying filler types, resin matrix compositions, and shade-matching strategies. Six injectable resin composites and one conventional microhybrid composite were evaluated (n = 20 per material; 140 specimens in total). For each material, specimens were randomly allocated to two subgroups (n = 10): thermocycling or 12-day coffee staining followed by in-office bleaching. Disc-shaped specimens were fabricated, and baseline color, whiteness index, and translucency were recorded. Data were analyzed using repeated-measures ANOVA and one-way ANOVA, followed by Tukey’s HSD post hoc test for between-material comparisons (α = 0.05). Significant differences among materials were observed after aging, staining, and bleaching (p < 0.001). After aging, the multi-shade nanofilled FSF, group-shade nanohybrid NSF, and conventional microhybrid GDA showed the lowest color changes, whereas the one-shade composites showed the highest. Coffee staining reduced whiteness and translucency in all groups, with the greatest whiteness loss observed in the one-shade composites. Bleaching reduced staining-induced discoloration in all materials, most markedly in the one-shade nanohybrid CBF; however, residual color differences relative to baseline remained above the acceptability threshold in all materials. After bleaching, translucency in the supra-nanospherical OBF and EBF composites exceeded baseline values beyond the perceptibility threshold. Within the limitations of this in vitro study, the evaluated resin composites exhibited material-dependent changes in color, whiteness, and translucency following artificial aging, coffee staining, and bleaching, with incomplete recovery of baseline optical properties after bleaching.