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 instrumentseparation. Reciproc-Blue is a thermally-treated NiTi single reciprocating systemcoated by an oxide layer caused by the thermomechanical process improving fatigueresistance. Aim: To evaluate the effect of different kinematics on the cyclic fatigueresistance of the Reciproc-Blue file and examine the influence of different canalcurvatures on its cyclic fatigue resistance. Method: Eighty new Reciproc-Blue filesdivided 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 curvature45°and 60°angles. All instruments were operated until the fracture occurred, Cyclicfatigue resistance was determined by recording the time to fracture in seconds. Datawere statistically analyzed by applying ANOVA test followed by Post Hoc Tukey test at95% significance level. Results: all reciprocating motions yielded a significant increasein time to failure when compared to continuous rotation in both canal curvatures. Therewas a significant difference in time to failure among all reciprocating groups in bothcanal curvatures. All experimental groups revealed greater cyclic fatigue resistanceat 45°compared to 60°angles of curvature. There was no significant difference inthe length of the fractured fragment for all tested groups in both canal curvatures.Conclusion: Movement kinematics has a significant influence on the cyclic fatiguelife of Reciproc-Blue instruments. Also, Increasing the angle of progression for eachreciprocation cycle decreases the cyclic fatigue resistance of NiTi instruments.