Resistance to torsional failure and cyclic fatigue resistance of ProTaper Next, WaveOne, and Mtwo files in continuous and reciprocating motion: An in vitro study

AIMS: The purpose of this study was to evaluate the resistance to torsional failure and cyclic fatigue resistance of ProTaper Next (PTN), WaveOne, and Mtwo files in continuous and reciprocating motion. SETTINGS AND DESIGN: Randomized control trial in a tertiary care setting. SUBJECTS AND METHODS: A total of 10 new size 25.06 taper PTN X2, 25.06 taper Mtwo files, and 25.08 taper WaveOne primary files each was selected. A custom fabricated cyclic fatigue testing device with a 70° angle of curvature and 3 mm width; curvature starting at 6 mm from the tip was used. All instruments were rotated and reciprocated till fracture occurred and time till fracture of each instrument was recorded in seconds. For torsional failure testing 5 mm tip of each file was embedded in composite resin block and uniform torsional stresses (300 rpm, 2.0 Ncm) were applied repetitively by an endodontic motor with auto stop mode until file succumbed to torsional failure. Number of load applications leading to failure was recorded. STATISTICAL ANALYSIS USED: Data were analyzed using t-test for equality of means, Pearson correlation, and ANOVA test. RESULTS: All the files showed superior resistance to cyclic fatigue in reciprocating motion when compared with continuous rotation mode. WaveOne primary files displayed maximum resistance to cyclic fatigue both in continuous and reciprocating motion. WaveOne primary files also demonstrated maximum resistance to torsional failure followed by PTN with Mtwo files exhibiting least resistance. CONCLUSIONS: Operating files in reciprocating motion enhances their cyclic fatigue resistance. WaveOne files showed maximum resistance to cyclic fatigue and torsional failure due to their cross-sectional diameter coupled M-Wire technology.