The influence of distal-end heat treatment on deflection of nickel-titanium archwire

OBJECTIVE The aim of this in vitro study was to evaluate the deflection-force behavior of nickel-titanium (NiTi) orthodontic wires adjacent to the portion submitted to heat treatment. MATERIAL AND METHODS A total of 106 segments of NiTi wires (0.019 x 0.025-in) and heat-activated NiTi wires (0.016 x 0.022-in) from four commercial brands were tested. The segments were obtained from 80 archwires. For the experimental group, the distal portion of each segmented archwire was subjected to heat treatment (n = 40), while the other distal portion of the same archwire was used as a heating-free control group (n = 40). Deflection tests were performed in a temperature-controlled universal testing machine. Unpaired Student's t-tests were applied to determine if there were differences between the experimental and control groups for each commercial brand and size of wire. Statistical significance was set at p < 0.05. RESULTS There were no statistically significant differences between the tested groups with the same size and brand of wire. CONCLUSIONS Heat treatment applied to the distal ends of rectangular NiTi archwires does not permanently change the elastic properties of the adjacent portions.