Influence of Light Energy Density on Heat Generation during Photoactivation of Dental Composites with Different Dentin and Composite Thickness

OBJECTIVE The aim of this study was to determine the influence of different energy densities on the heat generated during photoactivation of Filtek Z250 (3M/ESPE) and Z100 (3M/ESPE) composite resins with different dentin and composite thickness. MATERIAL AND METHODS The temperature increase was registered with a type-K thermocouple connected to a digital thermometer (Iopetherm 46). A chemically polymerized acrylic resin base was prepared to serve as a guide for the thermocouple and as a support for 0.5-, 1.0-, and 1.5-mm-thick bovine dentin discs. Circular elastomer molds (1.0 mm-height x 3.0-mm diameter or 2.0-mm height x 3.0-mm diameter) were adapted on the acrylic resin base to standardize the composite resin thickness. A conventional halogen light-curing unit (XL 2500, 3M/ESPE) was used with light intensity of 700 mW/cm(2). Energy density was calculated by the light intensity applied during a certain time with values of 28 J/cm(2) for Z100 and 14 J/cm(2) for Filtek Z250. The temperature change data were subjected to three-way ANOVA and Tukey's test at 5% level. RESULTS The higher energy density (Z100) promoted greater temperature increase (p<0.05) than the lower energy density (Filtek Z250). For both composites and all composite thicknesses, the lowest dentin thickness (0.5 mm) yielded significantly higher (p<0.05) temperature increase than the other two dentin thicknesses. The 1-mm-thick composite resin layer yielded significantly higher (p<0.05) temperature changes for both composites and all dentin thicknesses. CONCLUSIONS Temperature increase was influenced by higher energy density and dentin/composite thickness.