Relationship between flexibility and physical, chemical, and geometric characteristics of rotary nickel-titanium instruments

ObjectiveThe purpose of this study was to assess the influence of both the metallurgic and the geometric characteristics of nickel-titanium endodontic instruments on their flexibility.Study designProTaper Universal (PTU), K3, and EndoSequence (ES) instruments were evaluated. Their chemical composition and phase constitution were characterized by conventional analytical techniques. Instrument diameter and cross-sectional area were evaluated by image analysis. Flexibility was evaluated in bending tests according to the ISO 3630-1.ResultsK3 presented the highest average bending moment (MB), followed by PTU and ES. A linear relationship was found between MB and the instrument's diameter and cross-sectional area at 3 mm from the tip. Alloy chemical compositions were similar among the files, but transformation temperatures were lower for K3 instruments, which presented only austenite as a constituent phase.ConclusionNickel-titanium instruments from different manufacturers have unequal behavior related to their flexibility properties. Manufacturing processes changed the phase constitution and transformation temperatures of the instruments investigated and may also have influenced their flexibility.