A comparative investigation of cyclic fatigue resistance of four different nickel ti̇tanium rotary file systems

The aim of this study is to compare the cyclic fatigue resistance of ProTaper Next, Hyflex CM, TF-Adaptive and 2Shape nickel titanium rotary file systems with different alloy properties and production methods, and to investigate the surface changes due to cyclic fatigue by scanning electron microscopy. In our study, 120 files were used in 4 groups, each having 30 files. To ensure standardization, files with apical diameter and taper angle of #25/.06 of each rotary file system were selected. Static model test setup, in rpm and torque values according to the manufacturer's instructions, files were rotated in artificial root canals with 60° angle of curvature, 5 mm radius and 1.5 mm inner diameter, until the files failed. The time for failure of files was recorded with a digital chronometer and multiplied by the rotation speed to calculate the number of cycles. Distrubution of data were evaluated by using Kolmogorov-Smirnov test. One-way analysis of variance (ANOVA) tests were applied to compare the data which were observed to be in normal distribution and Bonferroni post hoc analysis was used to determine the source of the differences. According to the results of statistical analysis of our study, the number of cycles for the failure of files were compared between groups; significant differences were found between groups. The number of cycles for failure of files were recorded from highest to lowest as; Hyflex CM, TF-Adaptive, Protaper Next, 2Shape respectively. Failure surfaces were examined by scanning electron microscopy and failures were determined as a result of cyclic fatigue. The cyclic fatigue resistance was found highest in Hyflex CM system, whilst lowest in 2Shape file system. Factors such as production patterns, alloy properties and the phase in which the files were produced may affect the lifespan of the file systems.