[Effect of different polishing time on microleakage of resin composite restorations]

To evaluate the effect of different polishing time on microleakage of different resin composite restorations (Filtek Z350 and Filtek Z250).

Standardized preparation (the box-type cavities, 3 mm in length and width,2 mm in depth) was performed at the cemento-enamel junction on buccal surface of 80 premolars.They were randomly divided into two groups,and restored with composite resin(Filtek Z350 or Filtek Z250). According to polishing time, the specimens of each group were randomly classified into four subgroups. They were the subgroups of no polishing, polishing immediately after restoring, polishing after 10 minutes and polishing after 24 hours. All of the restorations were polished with Sof-lex discs. After thermal circulation 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 degree and microleakage depth of different groups were analyzed with SPSS 17.0 software package for Mann -Whitney U test and Kruskal -Wallis test.

The microleakage depth of Filtek Z350 groups were(0.655±0.486)mm,(0.626±0.497)mm,(0.648±0.370)mm and (0.639±0.453)mm,respectively. The microleakage depths of Filtek Z250 groups were (0.785±0.553)mm,(0.763±0.491)mm,±0.749±0.608)mm and (0.715±0.588)mm,respectively. No significant differences (P>0.05) of microleakage was found among the different groups and subgroups.

The polishing system of Sof-lex discs have no significant influence on microleakage of resin composite restorations at different polishing time.