Abstract: Objective: To evaluate the effect of sonicfill system on microleakage of class Ⅱ resin filling. Methods: Fifteen extracted permanent molars with same caries in both mesial surface and distal surface were collected.One cavity was filled by sonicfill system (the experimental group), and the other cavity was filled by Herculite Précis nano resin with oblique layered filling technology (the control group). After 500 thermocycling, all samples were stained within 0.5% fuchsin solution for 24 hours, and teeth were mesio-distally cut along the tooth long axis.Stereomicroscope was employed to evaluate the dye penetration level (0-3) and scanning electron microscopy was used to observe the microleakage. Scores of dye penetration were analyzed by Mann-Whitney U test, and micro-crack width by SEM was analyzed by t-test. Results: There were significant differences in the Dye penetrationscores between two groups(P＜0.05). Microleakage of axial wall was significantly less than that of gingival wall(P＜0.05). The micro-crack widths between axial wall and gingival wall were significant differentbetween two groups(P＜0.01). Micro-crack width of axial wall was significantly less than gingival wall in each group(P＜0.01). Conclusion: Sonicfill system can effectively reduce the resin microleakage of class Ⅱ resin filling and the microleakage of axial wall is less than that of gingival wall.

Key words: Sonicfill , Bulk-fill, Microleakage