Comparison of cyclic fatigue of a reciprocating file system at different angles of rotation

Aim: Chemomechanical cleaning is one of the most critical stages of root canal treatment, and the incidence of file fracture significantly reduces the success rate of root canal treatment. The aim of this study is to compare the cyclic fatigue resistance of Reciproc Ni-Ti rotary files when operated at three different reciprocal angles. Material and Method: 45 pieces of Reciproc R25 canal files were tested in artificial canals with 60° curve, 5-mm curvature radius and 1.5-mm diameter, carved into a stainless steel block. A static model was preferred. The files, checked with a stereo-microscope, were randomly separated into 3 groups. Reciprocal angles of CCW 150°-CW 30° (Group 1), CCW 180°-CW 60° (Group 2) and CCW 210°-CW 90° (Group 3) were selected respectively. The duration of process until the fracture of files was determined with a chronometer. The lengths of fractured pieces were measured with a digital caliper. After the cyclic fatigue test, two samples from each group were examined with Scanning Electron Microscope (SEM) to determine the signs of cyclic fatigue. Results: The distribution of data was examined with Levene's test for equality of variances, and one-way analysis of variance (ANOVA) was applied to the normally distributed groups (p<0,05). Since there was a statistically significant difference (p=0,001) between the groups, Tukey's HSD post-hoc two-way comparison tests were used. While there were statistically significant differences between Group 1 and Group 2 (p=0,001) and Group 1 and Group 3 (p=0,001), there was no significant difference between Group 2 and Group 3 (p=0,376). Group 1 displayed the highest resistance to cyclic fatigue. There was no statistically significant difference between the lengths of fractured files in the Groups according to the one-way analysis of variance (ANOVA) (p=0,847). Conclusion: In our study, it has been observed that the reciprocal angles of CCW 150°-CW 30°, also suggested by the manufacturer, have the highest fracture resistance against cyclic fatigue.