Effect of Shade and Light-Curing Intensity on Bulk-Fill Composite: Heat Generation and Chemo-Mechanical Properties (In Vitro Study)

The aim of this study is to assess the effect of shade and light-curing intensity on the heat generation and degree of conversion of bulk-fill composite. A commercially available bulk-fill composite resin was used in this study. A total of 250 cylindrical specimens of each composite shade (n = 25/group) were prepared (125 for testing heat generation and 125 for testing degree of conversion, then cured using a monowave light-curing unit (LCU) with a single light intensity of 1470 mW/cm2 and a polywave LCU with three different light intensities (1200, 2000, and 3000 mW/cm2). Heat generation during polymerization was measured by five K-type thermocouples placed in each 1 mm layer from top to bottom. FTIR was used for evaluating the degree of conversion. Regarding heat generation, significant differences were seen in layers 4 and 5. Curing types and times also showed significant impacts on heat generation and the degree of conversion. Heat generation relates more to curing time than light intensity. Darker shades generate and retain more heat. Lighter shades exhibit higher degrees of conversion with longer curing.