الفهرس 
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Abstract
Aim: The present in vitro study aimed to evaluate the success rate, the dentin loss using cone beam computed tomography and time taken for a separated instrument retrieval using different retrieval techniques (Ruddle technique with ET25 ultasonic tip, Terauchi file retrieval kit and Endo Rescue kit).
Method: sixty freshly extracted human mandibular first molars were selected, and a 4 mm portion of #25/.04 taper Fanta Blue file were fractured in the middle third of mesiobuccal canals. The teeth were then scanned using a CBCT image system to determine the root canal volume and dentin thickness before retrieval. The samples were divided randomly into three groups: group A (separated instruments retrieved by Ruddle technique using ET25 ultrasonic tip), group B (separated instruments retrieved using Terauchi file retrieval kit) and group C (separated instruments retrieved using Endo Rescue Kit). Then, another CBCT scan was taken to determine the root canal volume and dentin thickness after retrieval. The success rate, changes in root canal volume, changes in remaining dentin thickness, minimum dentin thickness and time taken for retrieval were recorded.
Results: Retrieval was successful in group A and B (70% and 80% respectively) without any significance difference between them. While, group C hadn’t any successful sample (p<0.0001). The root canal volume increased significantly in group A compared to group B (2.33±1.03 mm3 versus 1.28±0.78 mm3, P>0.0001). While, group C had the highest increase in the root canal volume 3.18±0.83 mm3. Dentin thickness changes and remaining dentin thickness after retrieval attempts were not significant between group A and B but the difference was highly significant as compared to group C. The mean time of retrieval in group A was (42.02±5.66 min). While, in group B the mean time was (42.42±3.35 min) with no significant difference between both groups (p=0.815).