Influence of different opacities on the color stability of composite resins: in vitro evaluation

Objective: To evaluate the influence of composite resin opacity on color stability, and to analyze the performance of the ΔEab and ΔE00 formulas in detecting color changes. Material and Methods: A total of 180 specimens (n = 20 per group) were fabricated using three opacity levels (translucent/incisal, enamel, and dentin) and three commercial composite resins: Vittra APS (FGM), Harmonize (Kerr), and Herculite Précis (Kerr). Specimens (7 mm × 1 mm) were prepared using a polytetrafluoroethylene mold between glass slides and light-cured with a Bluephase N unit (650 mW/cm2 for 40 s). All specimens were stored in distilled water at 37 °C until color evaluation. Color measurements were performed using an EasyShade digital spectrophotometer at 24 hours (baseline), 30, 60, and 90 days. Color stability was assessed through color variation (ΔE) according to the CIE system, using both ΔEab and ΔE00. Data were analyzed using a three-way ANOVA (opacity, resin, and time), followed by Bonferroni post-hoc testing (α = 0.05). Results: All composite resins exhibited clinically perceptible color changes (ΔE00 > 2.25) after 90 days. Vittra APS presented the highest values at 60 and 90 days (ΔE00 = 5.09 ± 1.77 and 5.12 ± 1.62, respectively), whereas Herculite Précis showed the best overall stability, particularly for the enamel shade (ΔE00 = 3.49 ± 1.10 at 90 days); Harmonize displayed intermediate values. Dentin-shade specimens exhibited the greatest color changes (ΔE00 up to 7.59 ± 1.24). Conclusion: Color stability was influenced by the interaction among composite resin brand, opacity, and aging time. More translucent shades exhibited less color alteration over time.