Torsional property and rotary fatigue fracture of Smart~ nickel-titanium endodontic instruments / 实用口腔医学杂志

ABSTRACT

Objective:To study the torsional property and rotary fatigue fracture of Smart K files and R reamers made of nickel-titanium alloy. Methods:The torsional property and rotary fatigue fracture behavior of Smart K files and R reamers were evaluated by means of specially-designed torsional device and simulated endodontic root canals system. The instrument surface and the rotary fatigue fractured surface were investigated by optical microscope and scanning electron microscope. Results:Compared with ANSI/ADA specification No.28, maximum torque values of Smart K and R endodontic instrument were higher. Tensile stresses on the outer surface of the endodontic instruments played a dominant role in fracture initiation during rotary fatigue fracture. The rotary numbers corresponding to rotary fatigue fracture decreased with the increase of the instrument size and curvature. Smart K and R endodontic instruments exhibited good ductility. Dimples were found on the fractured surface, and the fatigue fracture was the typical ductile fracture. Conclusion:Smartendodontic instruments have excellent torsional and rotary fatigue fracture resistance properties.