Effect of High Intensity on Rapid Cure of Bulk-Fill Resin Composite

Objectives: The effect of rapid curing on the properties of bulk-fill composite resins containing addition-fragmentation chain transfer (AFCT) monomers, particularly in condensable and flowable types, remains underexplored. This study investigated the effects of rapid high-intensity polymerization on bulk-fill resin-based composites (RBCs) with AFCT monomers.
Methods: Two types of bulk-fill composites with different flows which are condensable (Filtek One Bulk Fill(Ffill) and Tetric Power Fill(Pfill)) and flowable (SureFill SDR Plus (SDR), Filtek Fill and Core Flowable Restorative (Fflow), and Tetric PowerFlow (Pflow)), were evaluated under high-intensity (3200 mW/cm² for 3 seconds) and standard (1000 mW/cm² for 20 seconds) curing protocols. The degree of conversion (DC), flexural strength (FS), and Vickers microhardness were evaluated. The elution of components was quantified with GC-MS. Cytotoxicity was assessed using a human gingival fibroblast cell line by WST-1 assay.
Results: The duration of the curing significantly affected DC values. SDR achieved the highest DC, with no significant differences between high-intensity (3 s) and standard (20 s) curing modes, whereas Ffill demonstrated a significant increase in DC with standard curing. Initiator elution correlated directly with DC, with higher residual monomers observed in 3 s. BHT (butylated hydroxytoluene) levels were highest in SDR, with notable reductions in Ffill and Fflow over time. FS was highest in Ffill and SDR groups, with Pfill showing no differences between curing times. Microhardness was significantly increased with longer curing, maintaining consistent top-bottom ratios in Pfill, SDR, and Pflow, while Ffill and Flow displayed lower uniformity. Cytotoxicity results indicated all materials exceeded ISO viability thresholds, but Ffill and Fflow exhibited lower cell survival rates than other groups.
Conclusions: The findings emphasize the potential of AFCT in enabling efficient curing while underscoring the necessity of optimizing curing protocols to improve the clinical performance and safety of bulk-fill resins in restorative dentistry. Further studies are needed to investigate long-term biocompatibility and assess the effects of rapid curing on material stability.