Effects of Light Curing on the Mechanical Properties and Shade Stability of a Dual-Cure Bulk-Fill Resin Composite

Despite the growing use of dual-cure bulk-fill resin composites (RCs), the influence of light-curing protocols on their polymerization and material behavior remains unclear. Understanding these effects is critical for optimizing clinical outcomes.

This study investigated degree of conversion, flexural strength, flexural modulus, water sorption and solubility, and shade stability of a dual-cure bulk-fill RC, Bulk-EZ Plus (BZ), compared to a light-cured bulk-fill RC, Filtek-One Bulk-Fill (FB).

Specimens were randomized into five groups: BZ self-cured (BZ-SC), BZ light-cured for 10-seconds (BZ-10), BZ light-cured for 20-seconds (BZ-20), FB light-cured for 20-seconds (FB-20), and FB light-cured for 40 seconds (FB-40). Degree of conversion was evaluated using FTIR spectroscopy, flexural strength and modulus, and water sorption and solubility were determined following ISO 4049:2019. Shade stability in coffee and distilled water was measured using a spectrophotometer after 24 hours, seven days, and 21 days. Two-way ANOVA assessed the effects of RC type and curing protocol. Shade stability was analyzed using repeated measures and three-way ANOVA (α = 0.05).

Light activation increased the flexural modulus of BZ (p = 0.012 and p = 0.001 for BZ-SC vs. BZ-10 and BZ-20, respectively) and flexural strength (p = 0.018 for BZ-SC vs BZ-20), and reduced water sorption (both p < 0.001) and solubility (p = 0.028 for BZ-SC vs. BZ-10 and p = 0.001 for BZ-SC vs BZ-20). Extending light exposure from 20 seconds to 40 seconds did not change the flexural strength and modulus, or water sorption and solubility of FB (all p > 0.05).

Light activation improved the physical and mechanical properties of the dual-cure bulk-fill resin composite (Bulk-EZ Plus), but increasing the light exposure time did not improve the properties of the light-cured bulk-fill material (Filtek-One Bulk-Fill).