Abstract: PURPOSE: This in vitro study was aimed to evaluate the efficacy of intra-canal broken instrument removal using a new lasso device. METHODS: Mandibular molars that were freshly extracted within 6 months were used in this study. The teeth were examined under magnification to rule out cracks. Only teeth with closed apices and measured longer than 18 mm from cusp tip to root tip were chosen. Root curvature should be less than 90°. After root canal negotiation, 3 mm of a size 30#04 taper nickel titanium file, which was shortened by 5 mm before, was intentionally fractured in the coronal to mid-third of the mesial buccal canal. The teeth were randomly assigned to the lasso and ultrasonic group, each group had 20 teeth. All teeth underwent broken instrument removal procedures. The procedure time and removal success rate were recorded. Cone-beam CT(CBCT) was taken before and after instrument breakage, and after instrument removal. Root curvature, depth of fracture, level of broken instrument, and canal volume were recorded for each group. Statistical analysis was performed using SPSS 13.0 software package. RESULTS: There was no significant difference in terms of root curvature, depth of fracture, level of broken instrument and removal success rate between the two groups(P>0.05). The procedure time was significantly shorter and root canal volume increase was significantly less in the lasso group(P<0.01). CONCLUSIONS: The new lasso device for intra-canal broken instrument removal has a high success rate in this in vitro study. Its usage can preserve more root dentine and shorten treatment time. It can be an useful adjunct to ultrasonic instrument in removing broken instrument from the root canal.

Key words: Broken instrument, Root canal treatment, Removal, Ultrasonic, Lasso device