Objective: To evaluate the success rate of retrieving separated instrument, the root canal volume changes using cone-beam computed tomography and the retrieval time using Ruddle's technique, Terauchi file retrieval kit (TFRK) and Endo Rescue kit.

Methods: Sixty human mandibular first molars were selected, and a 4-mm portion of# 25/. 04 rotary files were separated in the middle third of moderately curved mesio-buccal canals. Teeth were randomly assigned into three groups (n= 20): R group, in which separated files were retrieved according to Ruddle's technique; T group, in which separated files were retrieved using TFRK and E group, in which separated files were retrieved using Endo Rescue kit. Values were analyzed using IBM SPSS. Results presented as mean±standard deviation and 95% confidence interval for the root canal volume and time and frequency (%) for success rate. Comparisons of differences in time, canal volume and success rate between groups were assessed.

Results: Retrieval was successful in R and T groups (70% and 80% respectively) without any significant difference between them (p= 0.715), while E group hadn’t any successful samples (0.0%) with significant difference compared to R and T groups (p< 0.001, p< 0.001). E group showed the highest increase in canal volume followed by R group, while T group exhibited the lowest increase in canal volume. There was no significant difference in the mean retrieval time between R and T groups (p= 0.815).

Conclusion: TFRK provides a more conservative way for retrieval of separated instrument from the middle third of moderately curved canals.