Delayed Light Activation Improves Color Stability of Dual-Cured Resin Cements

To evaluate the color change caused by post-irradiation conversion (ΔE_24h and ΔE_8 days ) and artificial aging (ΔE_AGING ) of resin cements light activated through ceramics of different opacities immediately and 6 minutes after manipulating the material.

Resin cement disks (Allcem and LuxaCore) were light activated through ceramics (without ceramic, e.max HT, LT, and MO) immediately and 6 minutes after the manipulation (n = 10). Spectrophotometry was used to evaluate ΔE_24h and ΔE_{8 days} after 37˚C-dry-dark-storage for 24 hours and 8 days, and ΔE_AGING after 60˚C-water-storage for 24 hours. Data were analyzed with three-way ANOVA and Tukey's HSD (α = 0.05).

Regarding the post-irradiation color change, significant differences were found between the cements (p < 0.0001), light activation protocols (p = 0.037), and ceramics (p < 0.001). The immediate activation (16.2 ± 0.1) showed lower ΔE values than the delayed activation (16.5 ± 0.1). Ceramics influenced the ΔE values as follows: MO (14.0 ± 1.2) < LT (14.9 ± 1.2) ≈ HT (15.4 ± 1.2) < control (21.2 ± 1.2). Regarding ΔE_AGING , significant differences were found between cements (p < 0.001), light activation (p = 0.006), and ceramics (p < 0.001). The delayed activation (8.4 ± 0.1) showed lower values than the immediate activation (8.9 ± 0.1). Ceramic spacers influenced ΔE_AGING as follows: control (5.6 ± 0.2) < MO (6.6 ± 0.2) < HT (11.0 ± 0.2) ≈ LT (11.5 ± 0.2).

The delayed light activation resulted in increased color stability, while the ceramic interposition resulted in lower color stability.