Japanese NiTi alloy wire: use of the direct electric resistance heat treatment method.

Japanese nickel titanium (NiTi) alloy wire possesses excellent spring-back properties, shape memory and super-elasticity. In order to adapt this wire to clinical use, it is necessary to bend as well as to control its super-elastic force, and so a direct electric resistance heat treatment (DERHT) method was developed. An electric current is passed directly through the wire, thus generating enough heat to make it possible to bend it as well as to impart a change in the super-elastic force of the wire. With this DERHT method, the excellent spring-back properties of the wire are not diminished, and it is possible to apply an optimal force to each tooth with a single archwire.