Comparative Evaluation of the Bending Flexibility of Heat-Treated Nickel–Titanium Endodontic Rotary Files: An In Vitro Study

Abstract

Objective: Nickel–titanium (NiTi) rotary instruments exhibit superior flexibility and fatigue resistance compared with stainless steel files due to their superelasticity and shape memory effect. This study compared the bending flexibility of three NiTi rotary endodontic files of identical size (#25/.06) manufactured using different thermal treatments: ProTaper Next (M-Wire), M3 Pro Gold (CM Wire with gold heat treatment), and E Flex Blue (Blue heat-treated NiTi). The null hypothesis was that there would be no difference in bending flexibility among the tested instruments.

Methods: Bending resistance was measured using a standardized cantilever bending test according to ISO 3630-1, a method widely employed for evaluating NiTi instrument flexibility. Forty-five files (n = 15 per group) were tested. Statistical analysis was performed using one-way ANOVA and Tukey’s post hoc test with significance set at P < 0.05, consistent with previous mechanical studies on NiTi instruments.

Results: E Flex Blue demonstrated significantly lower bending resistance (higher flexibility) compared with M3 Pro Gold CM and ProTaper Next (P < 0.001). M3 Pro Gold CM exhibited intermediate flexibility, while ProTaper Next showed the highest bending stiffness.

Conclusions: Within the limitations of this in vitro study, Blue heat-treated NiTi files demonstrated superior bending flexibility, supporting their potential clinical advantage in negotiating curved root canals, as previously suggested in recent metallurgical and mechanical investigations.