Cryo-instrumentation technique: a temperature-modulated approach to improve the mechanical performance of NiTi endodontic instruments

Abstract

Background The mechanical behavior and shaping performance of heat-treated nickel–titanium (NiTi) rotary instruments are influenced by temperature-dependent phase transformation. Aim This study evaluated cryo-instrumentation technique, in which NiTi instruments are used under controlled cryogenic conditions, and assessed its effect on cyclic fatigue resistance, cutting efficiency, and canal centering ability of HyFlex CM instruments. Materials and methods Thirty-six samples were randomly allocated into two groups. In the cryo-instrumentation group, HyFlex CM instruments were surface-cooled with Endo-Frost® and used under intracanal cryogenic conditions at 2°C. In the body-temperature group, instruments were used at 37°C without surface cooling. Cyclic fatigue resistance was assessed using standardized artificial canals, and the number of cycles to fracture was calculated. Cutting efficiency was evaluated by measuring dentin reduction on pre- and post-instrumentation cone-beam computed tomography scans. Canal centering ability was assessed using standardized two-dimensional image superimposition at the coronal, middle, and apical thirds. Intergroup comparisons were performed with statistical significance set at p < 0.05. Results Instruments used under cryogenic conditions demonstrated significantly greater cyclic fatigue resistance than those used at body temperature (p < 0.001). Cutting efficiency did not differ significantly between the groups at any canal level (p > 0.05). Canal centering ability was significantly improved in the cryo-instrumentation group at the middle and apical thirds (p < 0.05), whereas no significant difference was observed at the coronal third. Conclusion The proposed cryo-instrumentation technique may enhance cyclic fatigue resistance and canal centering ability of HyFlex CM instruments without compromising cutting efficiency.