Possibility of Bypassing Three Fractured Rotary NiTi Files and Its Correlation with the Degree of Root Canal Curvature and Location of the Fractured File: An In Vitro Study.

Introduction: This study aimed to evaluate the success rate of bypassing three NiTi rotary files (RaCe®, Hero 642®, and K3®), fractured in various root canal locations of extracted mandibular molars with two different canal curvatures. Materials and Methods: Ninety freshly extracted human first or second mandibular molars were selected. Three millimeters of the file tip (RaCe®, Hero 642®, and K3®), was fractured intentionally in the mesiobuccal root canal of each tooth by weakening the file in the last 3 mm of files #30 with 4% taper and preparing the root canals with two different degrees of curvature (n=30). Then, bypass possibility of the fractured files was evaluated using #8, #10, and #15 K-files and compared in different groups. In addition, the rate of accidental procedural errors was compared between these groups. Data were analyzed with univariate analysis and logistic regression models at a significance level of 0.05. Results: The overall success rate of bypassing was 61.1%. RaCe® files had the highest and the K3® files had the lowest bypass possibility rates (P=0.01); the greater the degree of canal curvature, the less successful the bypass procedure (P=0.01). The fracture of the files used to bypass was the most prevalent error. Conclusion: Based on this in vitro study the type of fractured file and the amount of canal curvature affected the success rate of the bypassing technique. In RaCe® files and the mild curvature group, the success rate was the highest.

Success of ultrasonic technique in removing fractured rotary nickel-titanium endodontic instruments from root canals and its effect on the required force for root fracture.

INTRODUCTION: Fracture of rotary nickel-titanium files is a real concern among endodontists; it affects the long-term prognosis of treatment. Ultrasound is a favorable technique for removing broken files, although it may result in some complications. The aim of this study was to determine the success rate of ultrasonic technique in removing file fragments and to evaluate its influence on the force required to fracture a tooth root. METHODS: An in vitro study was carried out on 70 extracted maxillary premolars. In the experimental group a #30/.04 taper Hero file was guided into the canal to break and lodge therein. The lodged file was removed by ultrasonic vibration and use of a dental operating microscope. The canals were instrumented with Hero files by using crown-down technique and then obturated. All the teeth were prepared for mechanical testing in Testometric machine to measure the required force for root fracture. The Fisher exact test and independent two-sample t test were used to analyze data. RESULTS: Ultrasonic technique exhibited a success rate of 80% in removing broken files. Success rate in the roots with file fracture before the curve was 11.5 times more than that of file fracture cases beyond the curve. Other factors such as bypass possibility did not affect success rate. The average time required for removing file fragments was 36.3 ± 7.15 minutes, which did not significantly differ in different file locations within the canal. According to mechanical test results, ultrasonic application did not significantly affect the required force for root fracture. The force required to fracture a root did not significantly differ in various file locations. Vertical fracture in the buccolingual direction (split tooth) was the most incident fracture pattern. Procedural errors observed in this study predominantly included transportation, perforation, and craze line. CONCLUSIONS: Ultrasonic technique was successful in removing 80% of fractured rotary files and did not significantly affect the required force for root fracture.