Abstract: Abstract: Objective To evaluate the efficiency of instrumentation and the amount of extruded apical debris with new WaveOne system in preparing root canals. Methods 40 mandible teeth with single root canal were randomly divided into 4 groups and prepared by K-file, BLx, ProTaper Universal and WaveOne, respectively. The extruded apical debris during the preparation were collected and measured. Then combined with the time for preparation, all data were comprehensively compared and evaluated. Results The amount of apical debris of K-File group was the largest, followed by the WaveOne group. There was no significant difference between the BLx and ProTaper groups (P>0.05), and there were significant differences among the other groups (P<0.05). The WaveOne group took the shortest time to prepare, followed by the BLx group, then the ProTaper group, the K-File group needed the most time, and the differences among groups had statistical significance (P < 0.05).Conclusion WaveOne has advantages in the amount of the extruded apical debris compared with the hand K-File, but doesn’t surpass the other two kinds of traditional titanium with Niti instruments. Compared with the other three instruments, WaveOne has the best root canal preparation efficiency.

Key words: Key words：　the new Niti instrument, root canal preparation, the extruded apical debris, root canal preparation time