[Studies on new superelastic NiTi orthodontic wire. (Part 1) Tensile and bend test (author's transl)]

NiTi alloy has attracted the most public interest in recent years. This alloy has two unique properties, one is "shape memory effect" and the other is "outstanding elasticity". NiTi wire with the property of outstanding elasticity suggested it could be useful in orthodontics. Recently new NiTi alloy which had other characteristics of "superelasticity" was developed. In this study, new superelastic NiTi wire was examined to evaluate for use in orthodontics, in tensile and bend tests, compared with stainless steel, Co-Cr alloy and work hardened NiTi wire. The results obtained are as follows: (1) New superelastic NiTi wire showed unique stress-strain curve with a plateau from the strain of 2% to 5%, the unique deformation behavior was caused by stress induced transformation, and returned to almost zero strain as stress was reduced. (2) New superelastic NiTi wire showed an elongation of about 11%. In the cyclic tensile tests to the strain of 8%, new superelastic NiTi wire showed little permanent deformation of 0.5% after 10 cycles. (3) In bend tests, new superelastic NiTi wire showed lower than half load compared with stainless steel and Co-Cr alloy wires. Its permanent deformation was very little after 2 mm deflection. (4) The load-deflection curve of new superelastic NiTi wire showed almost constant load in the wide range of deflection. The results of this study indicate that new superelastic NiTi wire must be considered as a promising candidate for orthodontic arch wire.