Effect of sequential versus continuous irradiation of a light-cured resin composite on shrinkage, viscosity, adhesion, and degree of polymerization.

PURPOSE: To examine the effect of a two-phase approach to light-curing, beginning with a period of low-intensity light followed by one of high intensity.
MATERIALS AND METHODS: Five different tests were performed in this investigation comparing variable irradiation with continuous irradiation of a resin composite. The tests were surface hardness, adhesion, shrinkage, viscosity, and residual monomer concentration/degree of polymerization. In each test, all specimens were fabricated with Pertaca resin composite.
RESULTS: The two-step light-curing approach, using different intensity distributions during polymerization, does not affect shrinkage, surface hardness, or residual monomer concentrations compared with the conventional continuous curing approach if the total irradiation dose is high enough to achieve complete polymerization. Adhesion values may be improved with the two-step approach over the continuous approach. The study supported the theory that material flow is higher using the two-step approach, which reduces contraction stresses in the cavity during polymerization and preserves marginal integrity.