Comparison of the time required to create secondary fracture of separated file fragments by using ultrasonic vibration under various canal conditions.

INTRODUCTION: Nickel-titanium files often separate because of mechanical fatigue. The purpose of this study was to determine safe preparation techniques for separated file removal by using ultrasonics. METHODS: Fifty nickel-titanium file fragments were divided into 5 groups. An ultrasonic tip was activated on a file fragment positioned between dentin blocks simulating several canal conditions: Group 1 consisted of the fragment protruding from a pair of straight dentin blocks. For group 2, the fragment was also positioned between 2 straight dentin blocks except one block was positioned 1 mm more apically than the other block, simulating a troughed area that is often created during file removal attempts. For groups 3-5, the fragment was positioned similarly as group 2 but between blocks with 30°, 45°, and 60° curvatures, respectively. The time it took for secondary fracture to occur was recorded, and the data were statistically analyzed. RESULTS: Fragments with dentin wall supporting on the opposite side of ultrasonic activation site resisted fracture significantly longer than those without it. Fragments in 30° and 45° curved blocks took significantly longer to fracture than the other groups (Fisher protected least significant difference, P < .05). CONCLUSIONS: Secondary fracture of separated files appeared to be reduced when the ultrasonic tip was applied to the inner curvature of the canal.

Evaluation of the efficiency of a new file removal system in comparison with two conventional systems.

A novel file-removal system (FRS) was designed to address weak points of conventional file-removal methods. The purpose of this study was to compare file-removal time and dentin removal rates among the FRS, the Masserann kit (Micro-Mega, Besancon, France), and an ultrasonic file-removal method. Ninety extracted mandibular incisors with separated nickel titanium files were divided into 3 groups of 30 teeth each. Groups 1, 2, and 3 had file-removal attempts made by using the Masserann kit, a CPR-7 titanium ultrasonic tip (Obtura-Spartan Corp., Fenton, MO), and the FRS, respectively. Each group had three operators removing the separated files. Pre-/postoperative digital radiographs were downloaded into image analyzing software that calculated the amount of dentin removed. The FRS needed less time and had less dentin loss than the others (p<0.05). There were statistical differences between the experienced operator and less experienced operators regarding the file-removal time and the dentin removal rates (p<0.05).

Removal of separated files from root canals with a new file-removal system: Case reports.

There have been many different devices and techniques developed to retrieve instruments fractured during endodontic procedures, but none of them can consistently remove separated instruments from root canals. Iatrogenic accidents such as perforation and canal destruction have been reported during the removal of separated instruments. The file removal process becomes even more difficult when breakage occurs in a curved canal or in the apical third of the canal. Four cases requiring removal of separated files from the apical third of curved canals are presented. All were successfully treated using a newly designed system and technique.