Abstract: PURPOSE: To evaluate the effect of different polishing methods on microleakage of different resin composite restorations (Filtek Z350 and Filtek Z250). METHODS: Standardized preparations (the box-type cavities, 3 mm in length and width,2 mm in depth) were prepared at the cemento-enamel junction on buccal surface of 80 premolars. They were randomly divided into 2 groups, and restored with composites( Filtek Z350 or Filtek Z250). Based on polishing methods, the specimens of each group were randomly classified into 4 subgroups: no polishing, polishing with Sof-lex discs, polishing with Super-snap discs and polishing with diamond burs. After thermal circulation (2000 times, 5-55℃) and soaked for 24 hours in 2% methyl blue solution, the specimens were cut through the midline of the restoration, the microleakage at the occlusal margin and the gingival margin were observed under a stereomicroscope and the leakage depth was measured with Spot version 4.6 software package. The microleakage width and microleakage depth of different groups were analyzed with SPSS 17.0 software package for Mann -Whitney U test and Kruskal - Wallis test. RESULTS: The microleakage depth of Filtek Z350 groups was (0.655±0.486) mm,（0.626±0.497） mm,(0.634±0.345) mm and（0.875±0.283）mm, respectively. The microleakage depth of Filtek Z250 groups was (0.785±0.553) mm、(0.763±0.491) mm,(0.789±0.308) mm and (0.942±0.318) mm. The microleakage depth of specimens polishing with diamond burs was significantly deeper than that of other groups. There was no significant difference among specimens with no polishing, polishing with Sof-lex discs and polishing with Super-snap discs. CONCLUSIONS: The polishing system of Sof-lex discs and Super-snap discs have no significant influence on microleakage of resin composite restorations.

Key words: Microleakge, Composite resin, Polishing system