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 3 mm) superelastic NiTi wires, focusing on force at 0.5 mm after deactivation after deflection by 1, 2, 3 and 4 mm.

Materials and methods

Three-bracket bending tests using a 10 N load cell with 1 mm/min crosshead speed and 8 mm span were performed at 37 °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 3 mm (SB1, SB2 and SB3, respectively) were deflected by 1, 2, 3 and 4 mm. Deactivation forces (N) at 0.5 mm 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 1 mm deflection. No bent NiTi wires had linear load deflection graphs; hysteresis was observed after 2, 3 and 4 mm 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 0.5 mm 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 1 mm deflection can produce an active light deactivation force to level severely displaced teeth.