Color, whiteness, and surface roughness changes of group-shade and single-shade composite resins during a şalgam-induced staining and bleaching cycle: a longitudinal in vitro study

INTRODUCTION: Resin composites may undergo discoloration and surface degradation after exposure to acidic pigmented beverages, while bleaching may further affect their properties. This study evaluated color difference (ΔE₀₀), whiteness index (WIᴅ), and surface roughness (Ra) of conventional, group-shade, and single-shade composites during a şalgam-induced staining and bleaching cycle.
METHODS: Disk-shaped specimens (8 × 2 mm) were prepared from five resin composites (n = 10/group). Measurements were performed at baseline (T1), after 24 h (T2) and 1 month (T3) of şalgam immersion, and 1 day (T4) and 10 days (T5) after bleaching with 35% hydrogen peroxide. ΔE₀₀ and WIᴅ were determined spectrophotometrically and Ra using a contact profilometer. WIᴅ changes were analyzed using Friedman tests, between-material differences using Kruskal–Wallis and Dunn–Bonferroni tests, and material-by-time interactions using rank-based permutation tests.
RESULTS: Significant material-by-time interactions were detected for ΔE₀₀ and WIᴅ (both p < 0.001) and Ra (p = 0.049). At T3, Essentia Universal (S1) showed the greatest discoloration (ΔE₀₀ = 11.47 ± 2.75), whereas OptiShade (G2) showed the lowest (3.39 ± 0.25). After bleaching, Filtek Easy Match (G1) showed the greatest whitening recovery (82%), while S1 showed the lowest (−21%). Surface roughness increased after staining, particularly in S1, and decreased after bleaching.
DISCUSSION AND CONCLUSION: The tested composites showed material-dependent variability in color stability, whiteness recovery, and surface roughness. Group-shade composites showed more consistent overall performance, whereas single-shade composites showed greater variability. Material selection should consider long-term esthetic behavior in addition to initial shade matching.

Keywords: Single-Shade Composite, Group-Shade Composite, Tooth Bleaching