Utility of Ni-Ti shape memory orthodontic wire.

The characteristic temperature dependence of recovery force was evaluated for a Cu-containing Ni-Ti shape memory wire with the nominal Af point being 40 degrees C. It exerted mild recovery force within the range of the proposed optimum force at the usual oral temperature. Larger forces were generated when it was heated to temperatures above Af: 40, 50 or 60 degrees C. By subsequently cooling to temperatures below Af, the force decreased again, and vice versa. The excellent reversibility, reproducibility and durability of the recovery force were also confirmed. These results indicate that the shape memory wire may be a reasonable material for a new concept of intermittent orthodontic treatment, in which mild force will be applied to the tooth for most of the daily hours and the tooth movement will be intermittently accelerated by larger forces generated only when the patient has hot foods or drinks.