Two-step curing: influence on conversion and softening of a dental polymer

Objectives. The study investigates the influence of two-step curing of a BisGMA/TEGDMA based polymer on degree of conversion (DC) and on hardness before and after 1 day ethanol storage. Methods. The specimens were pre-cured at 25, 50, 100, 200, or 400 mW/cm2 for 10, 20, or 40 s. The final cure as well as the cure of the control group was carried out at 750 mW/cm2 for 20 s. DC was determined on thin films by FTIR. Hardness was determined on disks by the method of Wallace. Results. At intermediary energy densities of the pre-cure, the DC was reduced as compared to that of the control group. The hardness before ethanol storage was not influenced by the curing mode. Except for the lowest and the two highest energy densities of the pre-cure, the two-step curing mode resulted in polymers that after ethanol storage were softer than the control polymer. Significance. Two-step curing of resin composites may result in polymers with increased susceptibility to the action of softening substances in food and beverage.