Statement of Problem: Recently, investigators have presented new methods to reduce polymerization shrinkage of composite resin restorations. It is claimed that more powerful light cure systems associated with a change in radiation patterns, lead to improved mechanical properties and reduced microleakage.

Purpose: The aim of the present study was to evaluate the effects of two curing systems, known as Soft-Start, Pulse-Delay, on microleakage and degree of conversion of composite resin restorations.

Materials and Methods: To evaluate microleakage, dye penetration method in class V cavities was applied. 30 extracted human molars filled with three different curing techniques, namely conventional, Soft-Start and Pulse-Delay, were compared. Degree of conversion was measured by FTIR Spectroscopy method immediately after sample curing. Kruskal- Wallis and Mann-Whitney test were used to compare groups.
Results: The degree of microleakage in enamel and dentin among three groups was not significantly different, however, microleakage in gingival and occlusal walls showed a significant difference among Pulse-Delay curing (P=0.001) and Soft-Start curing (P=0.28) groups, meaning that leakage gingival in wall was significantly higher than occlusal wall. This difference was not significant in conventional group. Moreover, the degree of conversion was not statistically significant among three groups (P-0.909).
Conclusion: Soft-Start and Pulse-Delay curing systems, with a two intensity start curing light, do not provide better marginal adaptation in class V composite resin restorations. It should be mentioned that polymerization degree is not also reduced in these methods.