Effect of light-curing modes on degree of conversion and color stability of flowable bulk-fill composites: an in vitro experimental study

Abstract

Objectives: This study aims to evaluate the impact of light-curing modes on the degree of conversion (DC) and color change (CIEDE2000 color difference, ΔE00) of different flowable composite resins. Methods: A total of 120 specimens (n = 10 per group) were prepared from four materials: G-aenial Universal Injectable (GUI; GC), Estelite Bulk Fill Flow (EBF; Tokuyama Dental), Tetric N-Flow Bulk Fill (TNF; Ivoclar Vivadent), and Filtek Bulk Fill Flowable (FBF; 3M ESPE). The specimens were polymerized using an LED light-curing unit under three light-curing modes: standard (1,000 mW/cm², 20 seconds), high-power (1,400 mW/cm², 3 × 4 seconds), and extra-power (3,200 mW/cm², 2 × 3 seconds). The DC was quantified using Fourier transform infrared spectroscopy. Color measurements were performed at baseline, and on the 7th and 14th days after immersion in coffee, using a spectrophotometer. The ΔE₀₀ was calculated using the CIEDE2000 formula. The data were analyzed using IBM SPSS software (α = 0.05). Results: Material type and light-curing mode significantly affected both the DC and ΔE00 (p < 0.05). All composites exhibited lower DC in the extra-power mode compared to the high-power mode. On day 14, the extra-power mode resulted in significantly greater discoloration in TNF, FBF, and EBF compared to the high-power mode (p < 0.05). Conclusions: Although curing with the extra-power mode saves time, it may result in a lower DC and an increase in ΔE00 in flowable composite resin.