Development of a Hallux Valgus Orthodontic Appliance Using Cu-Al-Mn Superelastic Alloy

Cu-Al-Mn alloy has better workability than Ni-Ti alloy [1] and it is expected to develop a plate product, which has been difficult to be produced so far in Ni-Ti. In 2011, we have commercialized the ingrown toenail clip using a Cu-Al-Mn thin plate [2]. This work was intended to develop a hallux valgus (HV) orthosis. The conventional orthotics are composed of rigid materials and cause pain in use. The stress plateau of superelasticity can provide flexible force to correct HV. However, the recoverable strain is small and work hardening occurs in the stress-strain curve in random textured Cu-Al-Mn alloy because of grain constraint [3]. In this study, we focused on the texture control in Cu-Al-Mn ternary alloy.

It was found that the recrystallization texture is developed when the heating rate after cold-rolling is slow and that good superelasticity with stress plateau is obtained in a polycrystalline plate. Furthermore, the fraction of low-energy boundaries increased and the resistance to stress corrosion cracking was improved. We developed a HV orthosis using the textured Cu-Al-Mn plate in collaboration with orthopedic surgeon and prosthetist. It was found from the clinical evaluations that the recovery force of superelasticity is enough high for correction of HV and flexible for a long period of use. As a result, the orthosis showed excellent correction effect.

[1] R. Kainuma et al. Metall. Mater. Trans. A, 27A (1996), 2187. [2]T. Tanaka et al. Materia 51 (2012) 108. (Japanese) [3] Y. Sutou et al. Metall. Mater. Trans. A, 33A (2002), 2817.