The effect of light curing intensity on bulk-fill composite resins: heat generation and chemomechanical properties

OBJECTIVES: The aim of this study was to assess the effect of light curing intensity and wavelength spectrum on heat generation and chemomechanical properties of bulk-fill composites. METHODS: Four bulk-fill restorative materials (Filtek bulk-fill, Tetric PowerFill bulk-fill, Beautifil Bulk restorative and Admira Fusion X-tra were used in this study. A total of 100 cylindrical specimens of each composite (n = 25/group) were prepared, then cured using monowave light curing unit (LCU) with a single light intensity of 1470 mW/cm(2), and polywave LCU with three different light intensities (1200,2100, 3050mW/cm(2)). The temperature change during polymerisation was measured by five K-type thermocouples placed in each 1 mm layer from top to bottom. Hardness and degree of conversion of composites at each level were evaluated. Results were statistically analysed. RESULTS: The use of polywave LCU resulted in statistically higher peak temperatures ranging between 31.4–63.5 °C compared to the temperature generated by monowave LCU ranging between 29.5–60 °C (p < .05). Curing using polywave LCU with the highest light intensity of 3050 mW/cm(2) caused the highest peak temperature irrespective of the composite types. There was no significant difference in hardness with different light curing intensities and curing times, regardless of the bulk-fill resin materials (p > .05). A positive correlation was also found between the hardness and the DoC of the four bulk-fill composites. CONCLUSION: The change in temperature during polymerisation of bulk-fill composites were found to be proportional to the increase in light curing intensity. Mechanical properties of the bulk-fill composites were dependent on the composition and the type of photoinitiators.