Introduction:

Low marginal adaptation and therefore micro-leakage, is one of the weaknesses of bulk fill resin composites. Pre-heating of composite resins reduces their viscosity, thus, increasing the marginal adaptation and decreasing their micro-leakage.

Objectives:

The aim of this study was to examine the effect of pre-heating on micro-leakage of bulk fill composite resins in dentin margins of class II restorations.

Material and methods:

This in-vitro study was conducted on 39 extracted human molars. Class II cavities were prepared on teeth’s proximal surfaces. Teeth were divided randomly into three groups, which were restored using three different composites: Group 1 – X-tra fil composite; Group 2 – Opus Bulk Fill composite; and Group 3 – Gradia Posterior composite. Each group included 2 sub-groups: at room temperature and after one pre-heating cycle at 50°C. The teeth were placed in fuchsin solution for 24 hours and were examined for micro-leakage under a stereoscopic microscope. Mann-Whitney U and Kruskal-Wallis tests were applied with SPSS 16 software. P-value of less than 0.05 was considered significant.

Results:

Pre-heating reduced micro-leakage significantly (p < 0.001). There was no significant difference in micro-leakage of different composites (p < 0.05).

Conclusions:

Pre-heating to 50°C decreases micro-leakage in the dentin margin of class II restorations in bulk fill composites (X-tra fil and Opus Bulk Fill) and conventional composite (Gradia Posterior). Investigating the effect of various pre-heating procedures, such as different temperatures, duration, and repeated pre-heating on physical and mechanical features of bulk fill materials, is suggested for future studies.