Influence of the light curing unit and thickness of residual dentin on generation of heat during composite photoactivation.

The aim of this study was to determine the effect of different types of composites (Filtek Z250, Esthet X and Filtek Supreme) and dentin thicknesses (0.5 or 1.0 mm) on the generation of heat during photoactivation by QTH (conventional halogen light), LED (light emitting diode), and PAC (xenon plasma light) light-curing units. Temperature changes were recorded with a thermocouple type K connected to a digital thermometer. Twenty chemically polymerized acrylic resin bases were prepared in order to guide the thermocouple and to support the dentin disks. On the acrylic resin base, elastomer molds of 2.0-mm thickness were adapted. The temperature increase was measured after composite photoactivation and the matrix was stored at 37 degrees C. After 24 hours, photoactivation was performed again and the temperature increase was measured. Obtained data were analyzed by ANOVA and Tukey's test (alpha= 0.05). The mean temperature increase produced by QTH was significantly lower than that of the other photoactivating units (P < 0.05), due to its low radiant exposure. There were no significant differences among the samples with regard to dentin thickness and type of composites (P > 0.05). The immediate temperature rise was statistically higher when compared to the increase after additional polymerization (24 h), in all groups (P < 0.05). Light intensity and exposure time appeared to be the most important factors causing temperature change.