Effect of photoactivation protocol and radiant exposure on monomer conversion and flexural strength of a resin composite after water and ethanol storage

The use of soft‐start photoactivation to reduce shrinkage stress has become widespread in restorative dentistry. However, an increased susceptibility to ethanol degradation of polymers formed by pulse‐delay photoactivation was reported. It was hypothesized that reductions in flexural strength after ethanol storage were related not only to low curing rates, but also to the radiant exposure employed. A commercial composite was subjected to different curing protocols (continuous at high irradiance, continuous at low irradiance, and pulse‐delay) and radiant exposures (6, 12, and 24 J/cm2). After 48 h, differences in degree of conversion were minimal and no differences in strength were detected among specimens stored in water. Ethanol storage caused significant strength reductions in pulse‐delay and low irradiance specimens that received 6 J/cm2. The results suggest that when low irradiances or pulse‐delay methods are used, a relatively high radiant exposure is necessary to originate a polymer network structure similar to that obtained by continuous high irradiance photoactivation. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006