Thermal rise during photopolymerization and degree of conversion of bulk fill and conventional resin composites

Background: Light curing of resin composite is associated with a thermal rise that may have harmful effect on the health of the vital pulp. In addition, desirable polymerization is important to achieve mechanical properties and clinical function. The purpose of this in‑vitro study was to compare the thermal rise under normal dentin during photopolymerization and degree of conversion (DC) of bulk fill and conventional resin composite using continuous high‑ and soft‑start mode. Materials and Methods: In this in‑vitro study, Cl I cavities with a dimension of 4 mm × 4 mm × 4 mm and remaining dentin thickness of 1 mm were prepared on 56 extracted human molars. The temperature rise during the light curing of conventional resin composite (Tetric N Ceram, Ivoclar Vivadent) by incremental filling technique and bulk‑fill resin composite (Tetric N Ceram Bulk Fill, Ivoclar Vivadent) by bulk‑filling technique were measured with a K‑type thermocouple wire. DC of both resin composites was measured using Fourier‑transform infrared spectroscopy. Data were analyzed using one‑way ANOVA, Tamhane and Duncan post hoc, two‑way ANOVA at the significance level of α = 0.05. Results: Photopolymerization temperature rise due to soft start mode and the first layer of conventional composite was higher than continuous high mode and bulk‑filling technique, respectively (P < 0.001). DC of conventional resin composite was higher than bulk‑fill composite (P < 0.001). Conclusion: Soft‑start mode produced higher thermal rise than continuous high mode and conventional resin composite showed higher DC than bulk‑fill composite.