Heat Generation of Bulk-fill Composites Polymerized by Multipeak Versus Single Peak Light Curing Units

Background: Multipeak light-curing units (LCUs) are gaining popularity due to potential need to activate different photoinitiators. One of the risks associated with using LCUs is heat generation which can reach the pulp chamber through restorative materials and may cause an adverse pulp reaction. However, there is a limited data on heat generation potential of multipeak as compared to single peak LCUs. Objective: Evaluate the difference in heat generation, and transmission from single peak versusmultipeak LED-LCUs through dentin and different bulk-fill resin-based composites (BFRCs) at pulpal wall (PW). Materials and Methods: A single extracted sound human molar was used for standardized test set-up. A tunnel was prepared lingually to expose buccal-pulpal-axial-wall, and a box cavity, measured (2.5x3.5x3mm), was prepared buccally for BFRCs placement. A 0.5 mm remaining dentin thickness was left between PW and buccal cavity preparation. The PW was reflected to thermal-infrared-camera (Thermovision-A320, FLIR) via minimal-energy-loss mirror (λ/4 First Surface Mirror, Edmund Industrial Optics) to measure temperature changes on PW indirectly and on BFRC directly. Four multipeak LCUs (Bluephase G2, Ivoclar Vivadent; Bluephase PowerCure, Ivoclar Vivadent; D-Light Pro, GC Europe; Valo Cordless, Ultradent) and one singlepeak LCU (Demi Ultra, Kerr) were compared when photopolymerizing two BFRCs (Tetric EvoCeram Bulk Fill(TEB), Ivoclar Vivadent; Filtek One Bulk Fill Restorative (FOB), 3M ESPE). No bonding agent was used for easy removal of the BFRC after each cycle. BFRCs were photopolymerized for 10 seconds, and PW and BFRCs temperatures were recorded for 90 seconds. Four measurements were calculated for each LCU/BFRC combination: baseline to maximum temperatures (ΔT), time to reach maximum temperature (t), duration ofthe temperature above threshold (Δt), and heat transmission rate to PW (Q) using ThermoVision®ExaminIR™ (FLIR systems) software. Data were statistically analyzed using One-way ANOVA (p<0.001), Tukey’s post-hoc tests, and Tukey HSD tests. Results: In both BFRC groups, Valo Cordless, followed by Demi Ultra, generated significantly lower ΔT than other LCUs. Bluephase G2 has a significantly longer duration (Δt) in both BFRC groups. No significant difference was noted in (t) between groups. TEB had significantly higher temperature values (ΔT) and longer duration (Δt) when photopolymerized with all LCUs except Valo Cordless. FOB showed a significantly lowest Q when photopolymerized with Valo Cordless, while TEB showed the lowest Q when photopolymerized with Demi Ultra. Conclusion: Some LCUs can induce more heat generation and transmission than others and can impose an additional risk of pulp injury, but not necessarily between multipeak and single peak. Different BFRCs can heat up differently, and consequently can impose an additional risk of pulp injury.