Impact of Light-Curing Time for Bulk-Fill Composite in Proximal Box

Objectives: Bulk-fill composites are marketed for their ability to be cured to a depth of 4mm compared to 2mm for traditional light-cured composites. This study investigated the effect of light-curing duration on the depth of cure of bulk-fill composites in a proximal box simulating clinical placement.
Methods: Three bulk-fill composites (SDR: Dentsply SDR flow+; FTK: 3M Filtek Bulk Fill Flowable; EXF: GC EverX Flow) were placed in 60 typodont teeth with large MO preparations (4mm deep) against a Tofflemire matrix band, and cured from 1.5 mm above the occlusal surface using an LED curing light (Ivoclar Bluephase PowerCure) for 20 or 40 seconds. Depth of cure was measured by Vickers hardness on the proximal surface of the restorations at 0.5mm increment, from occlusal towards 4mm gingival depth, at 15min and 24hr after light-curing. ANOVA and pairwise comparisons were used to analyze results (n=10; alpha=0.05).
Results: Three-way ANOVA showed no statistically significant effect of material (FTK, EXF, SDR; p=0.709), but the effects of curing duration (20s or 40s) and measurement time (15min or 24hr) were significant (p<0.001). Pairwise comparisons indicated that all materials cured for 40s were significantly harder at 24hr. The table shows comparison of relative bottom hardness ratio (bottom hardness/max hardness of each material), which was significant for curing duration and measurement time in SDR and FTK, but not significant for EXF. After 24hr, restorations light-cured for 40s were significantly harder than those light-cured for 20s. All tested bulk-fill composites reached at least 70% of maximum hardness at 4mm depth with 40s cure at 24hr.
Conclusions: Light-curing bulk-fill composites for 40s instead of 20s resulted in a more thorough cure up to 4mm depth. Hardness at 24hr was higher than at 15min, indicating that the tested composites did not reach their full potential immediately following placement.