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.., for 30 minutes in both compositions showed adequate As points (about 25..) and Af points (44. `50..) for clinical use.
2. In the tensile and shape recovery tests, the 500.. heat-treated four-hole regular type plate showed better mechanical properties than the 440.. 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.