Cyclic fatigue analysis of twisted file rotary NiTi instruments used in reciprocating motion

Gambarini G, Gergi R, Naaman A, Osta N, Al Sudani D. Cyclic fatigue analysis of twisted file rotary NiTi instruments used in reciprocating motion. International Endodontic Journal, 45, 802806, 2012. Abstract Aim To evaluate the cyclic fatigue fracture resistance of engine-driven twisted file (TF) instruments under reciprocating movement. Methodology A sample of 30 size 25, 0.08 taper NiTi TF instruments was tested in a simulated canal with 60 degrees angle of curvature and a 3 mm radius. During mechanical testing, different movement kinematics were used at a constant speed, which resulted in three experimental groups (each group n = 10). The instruments from the first group (G1) were rotated until fracture occurred. The instruments in the second (G2) and third group (G3) were driven under reciprocating movement with different angles of reciprocation. The time of fracture for each instrument was measured, and statistical analysis was performed using one-way analysis of variance followed by Tukeys Honestly Significant Different test. Results Reciprocating movement resulted in a significantly longer cyclic fatigue life (P < 0.0001) when compared with continuous rotation. No difference was found between reciprocation 150 degrees clockwise/30 degrees counterclockwise (CW/CCW) and 30 degrees CW/150 degrees CCW. Conclusions The reciprocating movement was associated with an extended cyclic fatigue life of the TF size 0.25, 0.08 taper instruments in comparison with conventional rotation.