SEM study of simulated clinical use for four nickel–titanium rotary endodontic files

Nickel–titanium (NiTi) rotary endodontic instruments are the major medical devices currently used for root canal therapy. Recently marketed NiTi files are manufactured using thermomechanical processes that improve fatigue resistance and flexibility, which are critical for clinical performance. This study employed a simulated clinical model to compare the wear and fracture of three such rotary instrument products (ProFile Vortex Blue™, ProTaper Gold™ and Coltene HyFlex ® CM™), with a previously introduced product (ProFile Vortex™) serving as a control. Files were examined by scanning electron microscope (SEM) at four positions along their length before use and through three simulated clinical procedures on extracted teeth. Wear and deformation were evaluated by two experienced clinicians. Files were categorized as usable, visually unacceptable and microscopically unacceptable, and results were analysed statistically. Three files fractured, and nine files plastically deformed. Many unused instruments were judged to be microscopically unacceptable. There were no significant effects for brand and amount of use for files remaining visibly useful. Microscopically useful instruments were significantly affected by the number of uses. It was concluded that no observed wear or distortion pattern limited multiple file uses and that poorly manufactured surface condition was not necessarily a precursor to failure. Controlled‐memory instruments tended to deform plastically and present minimal fracture risk.