Blue Thermomechanical Treatment Optimizes Fatigue Resistance and Flexibility of the Reciproc Files

Introduction: The aim of the present study was to evaluate the influence of Blue thermal treatment on the bending resistance and cyclic fatigue of conventional M-Wire Reciproc files (VDW, Munich, Germany). The roughness pattern and the microhardness of the files were also assessed. Methods: Flexibility of standard Reciproc R25 files and the corresponding Blue prototypes was determined by 45 bending tests according to the ISO 3630-1 specification. Instruments were also subjected to cyclic fatigue resistance, measuring the time to fracture in an artificial stainless steel canal with a 60 angle and a 5-mm radius of curvature. The fracture surface of all fragments was examined with a scanning electron microscope. The roughness of the working parts was quantified by using a profilometer, and the microhardness test was performed using the Vickers hardness tester. Results were statistically analyzed using the Student t test with a level of significance set at P <.05. Results: Reciproc Blue instruments presented a significantly longer cyclic fatigue life and significantly lower bending resistance than the original Reciproc instrument (P <.05). Regarding the roughness pattern, there was no significant difference between Reciproc Blue and the original Reciproc instruments (P>.05), whereas Reciproc Blue revealed significantly lower microhardness than the original Reciproc instrument (P <.05). Conclusions: Reciproc Blue nickel-titanium showed improved all-around performance when compared with conventional M-Wire superelastic nickel-titanium, demonstrating improved flexibility and fatigue resistance, and reduced micro hardness while maintaining similar characteristics of the surface.