Effect of stepped exposure on quantitative in vitro marginal microleakage.

PURPOSE The aim of this in vitro study was to evaluate the effect of a soft-start curing mode on microleakage MATERIALS AND METHODS Standardized Class V cavities were prepared within all the margins in the buccal enamel or dentin surface of sound, freshly extracted inferior bovine incisors. Forty preparations were filled with a restorative system (Single Bond and Filtek Z250, 3M ESPE, St. Paul, MN, USA). Ten restorations of each group were made on both types of substrates and polymerized with a conventional curing technique (600 mW/cm2/40 s) or with a soft-start technique (150 mW/cm2/10 s + 600 mW/cm2/30 s). All specimens were thermocycled 3000 times and then immersed in methylene blue 2% for 12 hours. The specimen microleakage was quantitatively determined in a spectrophotometer. RESULTS The soft-start technique resulted in statistically significant less microleakage for each substrate (p < .05). The conventional groups exhibited 6.1 (dentin) to 15.4% (enamel) more leakage compared with the soft-start groups. When compared with the enamel margins, the dentin margins demonstrated greater microleakage: from 15.5% greater with the conventional light-curing mode to 25.6% greater with the soft-start light-curing mode. CONCLUSIONS The polymerization technique using a very low initial intensity (150 mW/cm2/10 s) decreased the microleakage of composite resin restorations. CLINICAL SIGNIFICANCE A soft-start light-curing approach to resin composite polymerization resulted in less microleakage at enamel and dentin margins in Class V cavities compared with resin composite restorations polymerized using a conventional light-curing approach.