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The aim of this study was to assess the degree of conversion and microleakage of a restorative composite in relation to the following variations on the photoactivation conditions: light intensity x exposure time and distance from the light source. Degree of conversion was analyzed on cylindrical specimens (5 mm in diameter and 2 mm in height), photoactivated according to one of the following methods: 600mW/cm x 40s; 400 mW/cm x 60 s or 200 mW/cm x 20s, followed by 500 mW/cm x 40s. The distance from the light source was also variable: 0, 3 or 7 mm. Therefore, nine experimental groups (n=3) were obtained. Energy density (power density x exposure time) for all groups was kept constant (24 J/cm). Specimens were then submitted to FT-Raman analyses (RFS 100/S, Burker, 4cm, 64 scans) for remaining double-bonds estimative, both on the top and on the bottom surfaces. The relation between 1610 and 1640 cm peaks (aromathic and aliphatic bonds, respectively) was taken into account. Statistical analyses (ANOVA and Tukey test, a=0,05) found significance for the distance from the light source, the surface considered and the interaction between photoactivation mode and distance from the light source. Degree of conversion (in %) was 58,29 (±2,87), 57,99 (±2,94) and 58,32 (±2,46) for 600, 400 and 200+500 mW/cm, respectively. For source distances of 0, 3 and 7 mm, values were 59,13 (±2,32) , 58,61 (±3,08) and 56,85 (±2,24), respectively. Top surfaces showed degree of conversion of 59,01 (±2,56), while for the bottom surface it was 57,40 (±2,67). For the microleakage test, the same composite was used for the restoration of class V cavities, made in 90 bovine incisors. The substrate was conditioned for 15 s with phosphoric acid (37%), then rinsed and gently dried. Prime & Bond NT (Dentsply/ Caulk) was then applied, according to the manufacturer’s instructions. Preparations were restored in bulk and photoactivated according to the procedures described for the degree of conversion analyses. The teeth were then stored for 24 in distilled water (37oC) before being submitted to the silver-nitrate microleakage protocol. The results were analyzed using scores, submitted to the KruskallWallis test. It could be observed that the two-step irradiation mode lead to less microleakage, when compared to the continuous modes. With exception to the specimens irradiated with 400mW/cm, higher microleakage was observed for smaller distances from the light source. Means for the microleakage scores ranged from 0,25 (±0,17) for the two-step groups, 7mm from the light source to 2,0 (±0,96) for 600mW/cm, 0mm. Power density did not influence neither the degree of conversion nor the microleakage. It could be concluded that photoactivation mode has an influence on the degree of conversion and on the microleakage. Key-words: degree of conversion, microleakage, polymerization.

"Influência do modo de fotoativação e da distância da fonte de luz no grau de conversão e microinfiltração de um compósito"