Dynamic cyclic fatigue resistance of RACE EVO in S-shaped canal with different angles of access: An in vitro study

Abstract

Abstract Introduction: Nickel–titanium instruments annually undergo improvements to enhance the cyclic fatigue lifespan, especially with challenging canals. This study examines RACE EVO instrument in an S-shaped double-curvature canal in different angles of insertion 0°, 20°, and 40° to investigate the behavior of the heat-treated instruments in challenging canals. Materials and Methods: A total of 30 instruments were assigned to three groups (Group 0°, Group 20°, and Group 40°). RACE EVO instruments were tested in artificial canals. The canals had two curvatures: an apical one which its parameters are 70° angle and 2 mm radius and a coronal one which its parameters are 60° angle and 5 mm radius. The test was done using a cyclic fatigue apparatus. A statistical study was done by one-way analysis of variance groups, and Tukey’s honestly significant difference/Tukey–Kramer with a level of significance (α) was adjusted to 0.05. Results: The time until failure was reduced by the increase in the angle of insertion; however, Group 20° and Group 40° were not significantly different. All the instruments were broken apically. The scanning electron microscopic analysis showed typical characteristics of cyclic fatigue failure. Conclusions: Increasing the inclination during the insertion reduced the resistance of the RACE EVO instruments to cyclic fatigue failure despite the surface heat treatment of the instrument.