Do irrigating solutions influence the cyclic fatigue resistance of heat-treated NiTi instruments? an in vitro study

Nickel-titanium (NiTi) instruments have advanced root canal preparation through enhanced precision. Thermal pretreatment improves both flexibility and cyclic fatigue resistance (CFR). While irrigating solutions are essential for decontamination, they may also affect the properties of heat-treated NiTi instruments. This study aimed to evaluate the impact of different irrigating solutions on the cyclic fatigue resistance of heat-treated NiTi files.

Four heat-treated reciprocating NiTi-files were analyzed: EdgeOne R-Utopia, Reciproc Blue, Procodile Q and CC One Blue. Files were immersed (5 min; 37 °C and 60 °C) in 5.25% sodium hypochlorite (NaOCl), 17% ethylenediaminetetraacetic acid (EDTA), 96% ethanol, NaOCl + EDTA, distilled water, or left in a no-immersion control group. CFR was measured in an artificial root canal (60° curvature, 5 mm radius), and fragment length (FL) was documented. The surface features of the fragments were assessed through scanning electron microscopy.

File system, irrigating solution, and temperature significantly influenced CFR (p < 0.001). Across all immersion conditions, the CFR reached its highest value with Procodile Q (37 °C distilled water) and its lowest with EdgeOne R-Utopia (60 °C NaOCl + EDTA). EDTA reduced CFR across all files, particularly at elevated temperatures and when combined with NaOCl. Microscopy revealed micropitting and roughened surfaces, particularly on CC One Blue (60 °C NaOCl), as well as material degradation and heterogeneous surfaces with NaOCl + EDTA.

Heat-treated NiTi instruments are influenced in their mechanical and metallurgical behavior by the chemical and thermal impact of irrigating solutions. Heated EDTA and NaOCl + EDTA were detrimental, while Procodile Q demonstrated the highest CFR. Within the limitations of this study, exposure to irrigating solutions, particularly heated EDTA and NaOCl + EDTA, reduced the cyclic fatigue resistance of heat-treated NiTi files. Clinically, prudent selection and temperature control of irrigants may help preserve instrument performance and reduce the risk of file fracture during root canal preparation.