Abstract: Objective To evaluate the cleaning efficacy of 3 different root canal irrigating methods with scanning electronic microscopy(SEM).Methods Thirty extracted permanent teeth with single straight root canals were randomly divided into 3 groups.All the root canals were conventionally accessed,pulp removed and instrumented with crown down instrumenting technique using Protaper NiTi files(Densply,USA) and NaOCl(5.25%,1 mL) was used to flush the canals before further instrumentation.The final step was done with 3 different canal cleaning methods.Group A: Ultrasonic irrigation by placing the ultrasonic file of the ultrasonic device for root canal therapy(Odontoson2M,Denmark) at the junction of point middle third and apical third of the canal,take care to keep the file from touching the canal wall.Group B: Conventional syringe irrigation by placing the injector at the junction of the middle third and apical third,keep away from the canal wall,Irrigating the canal with 20 mL of NaOCl(5.25%);Group C: Use of cotton applicator to wipe the canal ten times with a cotton applicator soaked with NaOCl(5.25%).Then all the canals in the 3 groups were flushed with 2mL of water and dried.The following work was to resect the tooth crown along the enamel-dentine junction and split the tooth in to two buccal-lingually.The cleaning efficacy of the 3 groups was evaluated with a scanning electronic microscope and the grading was done with the reference of Abbott Evaluating Standard concerning the smear layer,dentine debris on the root canal wall and the dentine tubule opening.The cleaning efficacy was observed among groups at different sites as well as that of each group at different sites,and analyzed statistically with the assistance of SPSS 11.5 statistics analyzing software.Results Crown third: The difference was of no statistical significance among groups(P>0.05);Middle third and apical third: The differences among groups were of statistical significance and among the three groups,Group A did better than Groups C and B(P<0.05) while Group A did better than Group B(P<0.05).It was clearly seen that cotton applicators did poorly,while ultrasonic irrigation offered the most favorable outcome in cleaning root canal.Conclusion Ultrasonic irrigation does the best in cleaning the smear layer on the canal wall and cotton applicators do the worst.

Key words: smear layer, root-canal irrigation solution, scanning-EM