[Study of mechanical properties of shape memory alloy plate for internal fixation of jaws].

Ni-Ti alloy compression mini-plate was developed for rigid bone-fixation in oral surgery. The investigation of the mechanical properties of this plate was performed to obtain basic data for its clinical application. Ni-49.49 Ti (at%) alloy and Ni-49.26 Ti (at%) alloy were used for the specimens. First, transformation temperatures of the alloys were measured to evaluate the effect of heat-treatment temperatures. Secondly, tensile and shape recovery tests were performed on four types of mini-plates, i.e., four-hole regular and long types Ni-49.49 Ti (at%), five-hole regular type Ni-49.49 Ti (at%) and Ni-49.26 Ti (at%). The following results were obtained. 1. Specimens with a heat-treatment at 500 degrees C, for 30 minutes in both compositions showed adequate As points (about 25 degrees C) and Af points (44-50 degrees C) for clinical use. 2. In the tensile and shape recovery tests, the 500 degrees C heat-treated four-hole regular type plate showed better mechanical properties than the 440 degrees C heat-treated one. However, in the four-hole regular type plate without heat-treatment, the shape memory effect was rarely found. 3. The five-hole regular type plate of Ni-49.49 Ti (at%) alloy had the best mechanical properties for clinical application, judging from the amount and the temperature of shape recovery. It is concluded that Ni-Ti shape memory alloy mini-plates should be applied for rigid internal bone-fixation in oral surgery.