Torsional properties of nickel-titanium versus stainless steel endodontic files.

The purpose of this study was to evaluate and compare the torsional properties of stainless steel K-type .02 taper and nickel-titanium U-type .02 and .04 taper instruments. Torsion tests were performed on all three designs of instruments according to ANSI/ADA specification number 28. For each design, 20 instruments of each of three sizes (15, 25, and 35) were tested. The three parameters measured were maximum torque, torque at failure, and angular deflection. Stainless steel K-type .02 taper and nickel-titanium U-type .02 and .04 taper instruments met or exceeded specification standards for maximum torque. They also satisfied and far exceeded the standards for angular deflection at the failure point. The stainless steel instruments showed no significant difference between maximum torque and torque at failure, whereas both of the nickel-titanium instruments showed a significant differential between maximum torque and torque at failure.