Thermal studies on different classes of clinical dental composites

Various classes of dental composites have evolved over the years for various clinical applications, differing mainly in the relative proportions of their individual components (BisGMA, TEGDMA, UDMA, fillers, etc.). Four classes of composites have been investigated here via DSC and TG (after curing with blue light from a halogen light-curing unit): a ‘microhybrid’, a ‘nanocomposite’, a ‘flowable’ and a ‘fluoride-releasing’ variety. The aims were to compare various thermal properties amongst the four classes and also to compare the quality of polymerization of halogen light cure. We concluded that the DSC scans of all the polymers showed no exotherms, signifying the absence of any residual reactivity. However, the scans showed onset of endothermic regions before glass transition temperature (GTT), which may signify structural rearrangements within the polymers. The overall enthalpy ranged from ?1.4 to ?50 J g^?1, with significant differences between the ‘fluoride-releasing’ variety and the rest. The ‘fluoride-releasing’ variety showed the largest endotherm, signifying greater mass loss than the rest. The GTT (129 °C) did not differ significantly amongst the composite types. These same parameters, on a second DSC run of the same samples, followed a pattern similar to the first run, albeit to a lesser degree in magnitude. Hence, no benefit was gained by heating after the initial ‘light’ cure. The initial and total mass losses were higher for ‘fluoride-releasing’ (19 and 46%) and ‘flowable’ (12 and 38%) types compared to ‘microhybrid’ (3 and 24%) and ‘nanocomposite’ (4 and 20%). In a clinical scenario, the ‘fluoride-releasing’ composite may adequately photopolymerize, given its use in thin layers. The microhybrid and nanocomposites might also polymerize well in thinner layers without the need for a secondary heat treatment. The ‘flowable’ variety on the other hand, is not recommended to be subjected to a secondary heat treatment, due to its inferior thermal stability.