Abstract: Abstract：　Objective　To evaluate the cleaning ability of different kinds of ultrasonic irrigants and rinsing time after root canal preparation. Methods　Eighty maxillary anterior teeth with single -canal were randomly divided into eight groups. All root canals were prepared to F3 with Protaper by machine. The specimens were respectively irrigated with ultrasound for one minute and three minutes. Group A and B used compound chlorhexidine gargle; Group C and D: 3% H2O2 solution; Group E and F: distilled water; Group G and H: 17% EDTA solution. The teeth were split along buccolingual direction , and the presence of debris and smear layer in the cervical , middle and apical thirds of the root canals were evaluated with a scanning electron microscope. Results　When the specimens were irrigated for one minute with different kinds of irrigants, statistical analysis showed that there was statistically significant difference between Group G and the other groups for debris removal in the cervical and middle third of the root canals (P<0.05). In the apical third of the root canals, there was statistically significant difference between group G and group C (P<0.05), and the differences between group C and group A or E(P<0.05) were also statistically significant. When the specimens were irrigated for three minutes with different kinds of irrigants , statistical analysis showed that there was significant difference between the group H and the other groups for debris removal in the cervical and middle third of the root canals (P<0.05). In the apical third of the root canals , there was no statistically significant difference between group H and group D (P>0.05), but significant difference existed between group H and group B or F(P<0.05).When the specimens were irrigated for different time with the same irrigant, there was statistically significant difference in the middle and apical third of the root canals between group A and B(P<0.05). Statistically significant difference was found in the apical third of root canals between group C and D(P<0.05), but no statistical significance existed between group E and F or between group G and H(P>0.05).Conclusion The ultrasonic irrigation with 17% EDTA solution for one minute can effectively remove the smear layer and debris of root canal. The effect of 3% H2O2 and compound chlorhexidine gargle is not better than that of 17% EDTA, but the appropriate extension of rising time can enhance the effect of the apical third of root canal.

Key words: ultrasonic irrigation, scanning electron microscope ( SEM), ethylenediamine tetraaceticacid, smear layer