Abstract: Abstract：　Objective To evaluate the marginal microleakage of class-Ⅱrestorations separately with SonicFillTM composite and 3M FiltekTMZ350composite under self-etch and selective enamel etch conditions. Methods　Class-II cavities were prepared in 48 molars and randomly divided into 4 groups according to different composite and etch ways (n=12): Group A: Self-etch with 3M single bond Universal adhesive + 3M FiltekTM Z350; Group B: Selective enamel etch + 3M single bond Universal adhesive+3M FiltekTM Z350; Group C: Self-etch with Kerr Optibond Versa adhesive + SonicFillTM composite; Group D: Selective enamel etch + Kerr Optibond Versa adhesive + SonicFillTM composite. After thermocycling, the specimens were submitted to Methylene blue for 24 hours. Then each sample was sectioned into 4 pieces in mesio-distal direction. Dye penetrations were examined under stereomicroscope. Results　The differences which were statistically significant in the microleakage of gingival wall were that Group B less than Group A, Group D less than Group C, Group C less than Group A and Group D less than Group B. And the differences which were statistically significant in the microleakage of side wall were that Group B less than Group A, Group D less than Group C, Group C less than Group A and Group D less than Group B. Conclusions　 Less microleakage of class-Ⅱ restorations in posterior teeth has been found in SonicFillTM composite than 3M FiltekTMZ350composite. And it is suggested to use selective enamel etching to reduce the marginal microleakage while filling posterior teeth with big cavities.

Key words: SonicFillTM Ultrasonic Composite System, Microleakage, Selective enamel etching