Investigation of the effects of different surface applications on color stability, whiteness index, and surface roughness of bleach-shade resin composites

Aim: The aim of this in-vitro study is the investigation of the effects of different surface treatments on the color stability, whiteness index, and surface roughness of bleach-shade resin composites after immersion in coffee. Material and Method: In this study, four bleach-shade resin composites Estelite Asteria (BL), Brilliant EverGlow (BL Trans), G-aenial A'chord (BW), Opallis (E-Bleach L) and one multi-shade composite Filtek Z250 (A2) were used. A total of 300 specimens were prepared, with 60 specimens from each composite and immersed in coffee for 12 days. The specimens were divided into six subgroups based on surface treatment procedures: one-step polishing (OptraGloss), two-step polishing (NovaTwist), bleaching (WhitenessHP), bleaching followed by one-step polishing, bleaching followed by two-step polishing, and a control group. Color and surface roughness measurements were performed at three stages: before staining (t0), after staining with coffee (t1), and after surface treatments (t2). Color change was calculated using the CIEDE 2000 and whiteness index CIELAB-based Whiteness Index for Dentistry (WID) formula. Statistical analyses were performed using the Kruskal-Wallis H and Dunn tests, Robust ANOVA, and Spearman correlation analysis (p<0.05). Results: After staining with coffee, all specimens exhibited clinically unacceptable ΔE₀₀ values (ranging from 5.52 to 10.45) and a decrease in WID values. Among the tested materials, Asteria showed the highest color stability after staining, while Brilliant EverGlow and G-aenial A'chord demonstrated the highest WID values. The highest surface roughness (Ra) values were observed in the bleaching-only groups, whereas the lowest Ra values were found in the one-step polishing groups. Bleaching alone provided limited color recovery; however, combined treatments (bleaching followed by polishing) led to significantly improved surface smoothness, resulting in meaningful enhancements in both color and whiteness. A weak correlation was found between ΔE₀₀ and ΔRa from t0 to t1, a moderate correlation from t1 to t2, and a strong positive correlation between ΔE₀₀ and ΔWID (p<0.05). Conclusion: The bleaching combined with two-step polishing, as well as the two-step polishing groups alone, enhanced color recovery and whiteness values; however, they also resulted in increased surface roughness. The combination of G-aenial A'chord and one-step polishing was identified as the most clinically advantageous interaction in terms of color stability, surface roughness, and whiteness index. Keywords: Resin composite, Bleach shade, Color stability, Surface roughness, Polishing, Bleaching