Load-deflection characteristics of superelastic nickel-titanium orthodontic wires

Previous mechanical testing of orthodontic wires has, in many cases, failed to simulate some key features of the clinical environment. The purpose of this study was to investigate the load-deflection characteristics of 7 different 0.016-in initial alignment archwires (Twistflex, NiTi, and 5 brands of heat-activated superelastic nickel-titanium [HASN]) with modified bending tests simulating a number of conditions encountered clinically. Load-deflection tests were carried out on the wires with 5 different model designs, and data from selected points on the unloading phase of the generated graphs were statistically analyzed. Wire deflection was carried out at 3 temperatures (22.0 degrees C, 35.5 degrees C, and 44.0 degrees C) and to 4 deflection distances (1 mm, 2 mm, 3 mm, and 4 mm). Rankings were derived according to statistically significant differences in each test situation. The effects of model, wire, and temperature variation were all statistically significant. Twistflex and the 5 HASN wires produced a range of broadly comparable results, and NiTi gave the highest unloading values. Model rankings indicated that self-ligating Twin-Lock brackets produced lower friction than regular edgewise brackets. The authors recommend using the rankings from the mechanical test simulations to predict possible clinical performance of archwires.