Abstract
Objective: The aim of this study was to evaluate whether the method of light curing could influence: (a) marginal sealing and resin composite adaptation to the cavity wall; (b) polymerization contraction rate; and (c) the hardness at the top and bottom surfaces of a body of resin composite. Methods: Standard cylindrical cavities, 1 mm deep and 3 mm in diameter were prepared on flat superficial dentin surfaces in bovine teeth. The teeth were bonded with one of two adhesive systems (Clearfil Photo Bond, and Super-Bond D Liner) and filled with a hybrid resin composite. The resins were cured using three light intensities of 600, 270 and 20 mW/cm 2, and various curing times. After thermal cycling, the specimens were subjected to a dye penetration test to evaluate marginal sealing and adaptation of the resin composite to the cavity walls. In addition, using the same curing conditions, the rate of polymerization contraction was measured. The difference of hardness over time of composite specimens was measured using Knoop hardness measurements taken at the top and bottom surfaces of resin specimens made in a Teflon mold the same dimensions as the cavity prepared in dentin. Results:When the composite was light cured with an initial light intensity of 270 mW/cm 2 for 10 s, a 5 s interval then a light intensity of 600 mW/cm 2 for 50 s, the best marginal sealing and cavity wall adaptation was observed compared with the other curing modes. Earlier hardening occurred at the resin composite base compared with the top surface of the composite, and most of the polymerization contraction was completed during the initial flowable stage of the resin composite. All other methods demonstrated results with some degree of marginal opening and cavity wall gap formation, the worst being 600 mW/s for 60 s. Significance: The use of a low initial light intensity (270 mW/cm 2) for 10 s followed by high intensity light (600 mW/cm 2) for 50 s provides the best adaptation of resin composite to cavity walls and possibly the least polymerization contraction stress.
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