Force-deflection properties of superelastic nickel-titanium archwires

This in vitro study compared the force-deflection behavior of 8 superelasti c nickel-titanium orthodontic wires (0.017 x 0.025 in) under controlled mom ent and temperature. To simulate leveling a lateral incisor, brackets and f irst molar tubes without tip and angulation were used. The wires (n = 5) we re ligated into stainless steel brackets attached to a plastic jig to simul ate a mandibular arch. A testing machine (instron) applied deflections of 0 .2 to 2.0 mm at 35 degreesC in the lateral incisor area. Force-deflection d iagrams were determined from the passive position to an activation of 2 mm and then during deactivation. Forces on deactivation at a deflection of 1 m m were compared by analysis of variance. Significant differences (P < .05) in forces were observed among wires. All wires exhibited superelastic behav ior, but in stratified loading levels.