Characterization of a bulk-fill resin-based composite by thermal analysis

The aim of this study was to evaluate through differential thermal analysis and thermogravimetry (TG-DTA) the thermal behavior of a bulk-fill composite, as a function of the curing depth; the objective was to verify whether it could be cured in greater increments with respect to the traditional dental composites. Samples of Tetric EvoCeram Bulk Fill (Ivoclar Vivadent) photopolymerized for 20 s at different curing depths (1-10 mm) have been analyzed, five samples of each layer, through the TG-DTA. The thermogravimetric curve (TG), the differential thermal analysis (DTA), and the first derivative of loss of mass (DTG) have been analyzed. The average temperature at which 5 % of mass loss occurred and the percentage of the average mass loss between 250 and 350 °C have been recorded. Analysis of variance and Bonferroni/Dunn test have shown statistically significant differences for what concerning all parameters analyzed in the first four layers versus the others. There were no significant differences in the thermal behavior of samples comprised between 1 and 4 mm. On the contrary, samples higher to 6 mm seemed to be not enough polymerized; 5-mm layers presented and intermediate polymerization. The TG-DTA has shown that this material shows the same thermal behavior in the first 4 mm if photopolymerized and for this reason it could be used in increment until 4 mm thickness.