Influence of polymerization technique on microleakage and microhardness of resin composite restorations

This study evaluated the influence of three polymerization techniques on microleakage and microhardness of Class II restorations using a microhybrid (Filtek Z250) and a "packable" resin composite (SureFil). The techniques, their respective light intensities and time used in relation to the resin composites, are: Conventional (C)--800 mW/cm2 for 40 seconds; Soft-Start (SS1)--75 mW/cm2 for 10 seconds plus 518mW/cm2 for 30 seconds; Soft-Start (SS2)-- 170mW/cm2 for 10 seconds plus 518 mW/cm2 for 30 seconds and Plasma Arc Curing (PAC)--1,468 mW/cm2 for three or six seconds. One hundred and fifty-two "Vertical Slot type Class II cavities" at the mesial and distal surfaces were prepared and divided into eight groups (n = 19). After the restorative procedures, the samples were thermocycled (1,000 cycles at 5 degrees C and 55 degrees C), then immersed in 2% methylene blue dye solution for four hours. The microleakage was evaluated and the results analyzed by the Kruskal-Wallis and Multiple Comparisons tests. Ten samples from each group were randomly selected, embedded in polyester resin, polished and submitted to the Knoop microhardness test. ANOVA (split-plot) and Tukey's test (p < 0.01) revealed significant differences among depths: the hardness at the top surface was significantly higher followed by the middle and bottom surfaces. There was no significant difference in microleakage among the techniques when microhybrid resin composite was employed. However, when using a "packable" resin composite, the conventional technique for polymerization was comparable to Soft-Start and better than PAC.