Comparison of the load-deflection characteristics of 0.012 '' heat-activated, superelastic and bent superelastic nickel titanium wires

Purpose: To compare the characteristics and load-deflection graphs of 0.012 '' heat-activated NiTi, superelastic NiTi and bent (bends placed at 1, 2 and 3mm) superelastic NiTi wires, focusing on force at 0.5mm after deactivation after deflection by 1, 2, 3 and 4mm. Materials and methods: Three-bracket bending tests using a 10N load cell with 1mm/min crosshead speed and 8mm span were performed at 37 degrees C. Three groups of wires, 0.012 '' heat-activated NiTi wires (HANT), superelastic NiTi wires (S), and superelastic NiTi wires with bends placed at 1, 2 and 3mm (SB1, SB2 and SB3, respectively) were deflected by 1, 2, 3 and 4mm. Deactivation forces (N) at 0.5mm after deactivation were compared using ANOVA. Results: Bent NiTi wires produced lighter forces than superelastic and heat-activated NiTi wires (P<0.05). Superelastic and heat-activated NiTi wires had linear load-deflection graphs at 1mm deflection. No bent NiTi wires had linear load deflection graphs; hysteresis was observed after 2, 3 and 4mm deflection in all NiTi groups. Increasing the number of bends and deflection appeared to inactivate NiTi wires. Conclusions: After any deflection, all bent NiTi wires produce lighter forces at 0.5mm after deactivation than superelastic NiTi and heat-activated NiTi wires. This study indicates bending a NiTi wire close to a displaced tooth with up to 1mm deflection can produce an active light deactivation force to level severely displaced teeth. (C) 2018 Elsevier Ltd and The Japanese Orthodontic Society. All rights reserved.