Mechanical Properties of Curved Nickel-Titanium Orthodontic Archwires Prepared by Cold Bending and Heat Bending Techniques

Abstract

Curved nickel-titanium (NiTi) orthodontic archwires are widely used in deep bite and open bite correction because of their extraordinary properties of shape memory and superelasticity. The aim of this study were to investigate the mechanical properties of curved NiTi archwires prepared by two different techniques; cold bending and direct electric resistance heat treatment (DERHT) bending and compare those properties to preformed curve NiTi archwires. Preformed curve archwires, 0.016x0.022 inch, were served as a control (group1). Plain archwires were curved into similar geometry as control by fingers (group2) and under the application of DERHT (group3). The three-point bending test was performed to analyze unloading force, springback and stiffness of archwires. Surface hardness was measured by Vickers micro-hardness test. The result showed that the unload force of all sample groups were similar. However, the stiffness and spring back properties of group2 and group3 were significantly higher than those of group 1(p<0.05). Moreover, surface hardness of cold forming technique and preform-curved NiTi archwire was slightly lower than those obtained from DERHT bending technique. Based on these results, the cold bending technique could provide the curved archwire with similar mechanical properties to the preform-curved NiTi archwire. Therefore, the cold bending technique was acceptable to be used as a chair-side orthodontic NiTi wire bending.