Curing behavior of a nanocomposite as a function of polymerization procedure.

The purpose of this study was to analyze the curing behavior of a nanocomposite by assessing in real time the degree of cure at depths of 2 mm and 6 mm. The variation of hardness with depth, shrinkage stress, and curing time until gelation with 16 curing regimes was further investigated using one halogen and three LED curing units. In the present study, it was shown that the soft-start polymerization concept is still valid, even with high-power LED curing units. A soft cure polymerization resulted in reduced shrinkage stress while simultaneously keeping the degree of cure and mechanical properties constant. For all tested curing unit types, a short polymerization duration (10 seconds) was insufficient to cure the nanocomposite in deeper layers--since the variation of hardness with depth showed a discontinuity between the layers, thus accounting for a decreased hardness of up to 30%.