Factors affecting ultrasonic removal of separated endodontic instruments: A retrospective clinical study.

Objective: The goal was to investigate the clinical value of two-dimensional radiographs and different radiographic measurement techniques before instrument removal with a microsonic technique. The aim was to find an easy-to-use technique for predicting the success of removal and case evaluation. Additionally the quality of root canal filling after instrument removal was assessed. Method and Materials: This retrospective study analyzed patients' records and preoperative and postoperative periapical radiographs made using the paralleling technique. On preoperative radiographs, canal access angle and Schneider and Weine angle of root canal curvature were measured and compared. The Schafer method was used for measuring the radius of curvature. In cases of successful removal taper, homogeneity and length of obturation were evaluated on postoperative radiographs. Results: A total of 123 cases of instrument removal were investigated. In total, 97 fragments (78.9%) were removed successfully. Statistical analysis was performed with Pearson's chi-square and Fisher's exact test (alpha < .05). The site of fragment relative to canal curvature, canal access angle, and Schneider angle significantly influenced the success of removal. The highest chance of removal failure was associated with > 20 degrees of canal access angle and > 40 degrees of Schneider angle. Only 26.3% of obturations met all technical standards. Altered taper could be identified in 64.2% and was always associated with ledge formation. Conclusion: Microsonic removal is a successful method to retrieve separated instruments. The use of only one radiographic measurement technique is not sufficient to precisely evaluate root canal anatomy, case difficulty, and chance of successful removal before instrument removal on a periapical radiograph. Postoperative root canal fillings are mainly substandard.