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 hi gh intensity. Materials and Methods: Five different tests were perform ed in this investigation comparing variable irradiation with continuou s irradiation of a resin composite. The tests were surface hardness, a dhesion, shrinkage, viscosity, and residual monomer concentration/degr ee of polymerization. In each test, all specimens were fabricated with Pertac(a) resin composite. Results: The two-step light-curing approac h, using different intensity distributions during polymerization, does not affect shrinkage, surface hardness, or residual monomer concentra tions compared with the conventional continuous curing approach if the total irradiation dose is high enough to achieve complete polymerizat ion. Adhesion values may be improved with the two-step approach over t he continuous approach. The study supported the theory that material f low is higher using the two-step approach, which reduces contraction s tresses in the cavity during polymerization and preserves marginal int egrity.