RESUMO
Objective To evaluate the results of different methods in removing the root canal gutta percha.Methods Select 60 man-dibular premolars with step-back techinique during root canal prepartion,and the mandibular premolars were stored for 2 weeks after AH-plus paste and gutta percha cold lateral condensation.And then they were randomly divided into 3 groups to remove the root canal filling.Group A were given manually cleaning and shaping with stainless steel instruments combined with chloroform.Group B were given Pro Taper nickel ti-tanium system.Group C were given Pro Taper nickel titanium system combined with microscopic ultrasound technology.The completion time of the 3 groups were recorded and the root canal wall cleanliness of the 3 groups were carefully observed.Results The competition time and amount of debris of apical foramen in group C were both significantly less than those of group A and group B,with statistically significant difference (P <0.05).And the cleanliness of root canal wall of group A was significantly better than that of group A and group B (P <0.05). Conclusion During the root canal retreatment,mechanically use Pro Taper nickel titanium system combined with microscopic ultrasound technology can improve the work efficiency and the cleanliness of root canal wall.