Torsional properties of commercial nickel-titanium wires during activation and deactivation.

This study evaluated torsional moments on activation and deactivation in commercial, nickel-titanium wires that are intended for use in the initial phases of orthodontic treatment. Nine commercial, rectangular nickel-titanium wires (0.017 x 0.025 in) were tested in torsion. One wire was conventional nickel-titanium, and the others were superelastic nickel-titanium wires. The specimens were tested in a torsiometer for rotations between 10 and 40 degrees in activation and deactivation. Wires E27, RF and R had the highest moments during activation and deactivation, without evidence of the plateau typical of the superelastic effect. Plateaus of constant moment were observed for wires C27, C35, E35, MO, NS, and NI. Torsional moments varied among superelastic nickel-titanium wires, even with wires that had the same transition temperature range. Some superelastic wires had torsional moments that were comparable with conventional nickel-titanium wires.