Reciprocating Torsional Fatigue and Mechanical Tests of Thermal-Treated Nickel Titanium Instruments

Introduction: This study aimed to evaluate the mechanical properties of Reciproc, Reciproc Blue, One RECI, and R-Motion, specifically focusing on their flexibility and buckling resistance and to assess their torsional fatigue behavior under 2 different reciprocation angles (150 degrees/30 degrees or 70 degrees/30 degrees). Methods: A total of 160 instruments (40 per brand) were tested. Flexion and buckling tests were conducted using a Universal testing machine (DL 200 MF). For the flexion test, instruments were positioned at a 45 degrees angle and flexed toward the ground plane. In the buckling test, the load was applied along the instrument's axis. A 20 N load cell and a test speed of 15 mm/s were used for both tests. Torsion test was performed using a torsiometer. The test speed was 100 rpm and the instruments were driven by an endodontic motor in 150 degrees/30 degrees and 70 degrees/30 degrees reciprocating angles. One-way analysis of variance post hoc Tukey tests and Student's t test were used for statistical comparisons (a = 5%). Results: The instruments exhibited significant differences in flexibility (P < .05), with One RECI demonstrating the highest flexibility and Reciproc the lowest. In terms of buckling resistance, Reciproc showed the highest values, while One RECI had the lowest (P < .05). Reciproc and Reciproc Blue displayed greater torque to fracture compared to One RECI and R-Motion (P < .05). Reducing the reciprocation angle did not affect the torque to fracture (P > .05). However, the reduced angle of 70 degrees/30 degrees significantly increased the time to fracture for all instruments when compared to angle of 150 degrees/30 degrees (P < .05). Conclusions: The tested instruments demonstrated notable differences in their mechanical performance, highlighting variability in flexibility, buckling resistance, and torsional behavior. Reducing the reciprocation angle prolonged the time to fracture without affecting maximum torque, underscoring the influence of reciprocation kinematics on instrument performance. (J Endod 2025;51:359- 366.)