Effect of different kinematics on the cyclic fatigue resistance of Reciproc Blue file in different canal curvatures

Introduction: Ni-Ti instruments used in reciprocation reduce instrument separation. Reciproc-Blue is a thermally-treated NiTi single reciprocating system coated by an oxide layer caused by the thermomechanical process improving fatigue resistance. Aim: To evaluate the effect of different kinematics on the cyclic fatigue resistance of the Reciproc-Blue file and examine the influence of different canal curvatures on its cyclic fatigue resistance. Method: Eighty new Reciproc-Blue files divided into four groups (n=20) according to the reciprocation angles 150°CCW– 30°CW, 210°CCW–30°CW, 90°CCW–40°CW and 360°CCW(continuous-rotation), each group was subdivided into two subgroups (n=10) according to the canal curvature 45°and 60°angles. All instruments were operated until the fracture occurred, Cyclic fatigue resistance was determined by recording the time to fracture in seconds. Data were statistically analyzed by applying ANOVA test followed by Post Hoc Tukey test at 95% significance level. Results: all reciprocating motions yielded a significant increase in time to failure when compared to continuous rotation in both canal curvatures. There was a significant difference in time to failure among all reciprocating groups in both canal curvatures. All experimental groups revealed greater cyclic fatigue resistance at 45°compared to 60°angles of curvature. There was no significant difference in the length of the fractured fragment for all tested groups in both canal curvatures. Conclusion: Movement kinematics has a significant influence on the cyclic fatigue life of Reciproc-Blue instruments. Also, Increasing the angle of progression for each reciprocation cycle decreases the cyclic fatigue resistance of NiTi instruments.