Effect of Simulated Toothbrushing on Surface Roughness, Color Stability, and Gloss of Two Single-Shade Composite Resins

This in vitro study evaluated and compared the surface roughness, color stability, and gloss of two single-shade composite resins after simulated toothbrushing, and investigated the correlations among these parameters. Twenty disk-shaped specimens (n = 10 per group) were prepared from two single-shade composite resins (Material A and Group B) and subjected to simulated toothbrushing up to 15,000 cycles. Surface roughness (Ra) was measured at baseline and after 5000, 10,000, and 15,000 cycles. Color parameters (CIE Lab*) and gloss (60°) were measured at baseline and after 15,000 cycles. Color change was calculated using the CIEDE2000 formula (ΔE00). Data were analyzed using two-way mixed ANOVA, t-tests, and Pearson correlation analysis (α = 0.05). Both materials showed progressive increases in surface roughness. Material B exhibited significantly higher Ra values than Material A from 10,000 cycles onward (p < 0.01). After 15,000 cycles, Material B demonstrated significantly greater color change (ΔE00: 2.21 ± 0.18 vs. 1.48 ± 0.13; p < 0.001), exceeding the acceptability threshold (ΔE00 = 1.8), while Material A remained clinically acceptable. Material B also showed greater gloss reduction (60% vs. 35%; p < 0.001). Strong correlations were found between surface roughness and both gloss change (r = −0.919) and color change (r = 0.826). Material A demonstrated greater resistance to surface degradation and better preservation of optical properties compared to Material B. Surface roughness was identified as the common underlying factor driving both color instability and gloss reduction in single-shade composites. Clinical Significance: Not all single-shade composites perform equally under mechanical aging. Clinicians should consider the filler technology and long-term surface stability when selecting single-shade composite resins for clinical use.