Studies on Application of Shape Memory Alloy Plate for Internal Fixation of Jaws

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Ni-Ti alloy compression mini-plate was developed for rigid boneーfixation in oral surgery. The investigation of the mechanical properties of this plate and the biocompatibility of NiーTi alloy was performed to obtain basic data for its clinical application. Transformation temperatures of the alloys were measured to evaluate the effect of heat-treatment temperatures. Tensile and shape recovery tests were performed on four types of mini-plates, i. e., four-hole regular and long types Ni-49.49Ti (at%), five-hole regular type Ni-49.49Ti (at%), and Ni-49.26Ti (at%).The following results were obtained.1. Specimens with a heat-treatment at 500^ﾟC, for 30 minutes in both compositions showed adequate As points (about 25^ﾟC) and Af points (44-50^ﾟC) for clinical use.2. In the tensile and shape recovery tests, the 500^ﾟC heat-treated four-hole regular type plate showed better mechanical properties than the 440^ﾟC heat-treated one.3. The five-hole regular type plate of Ni-49.49Ti (at%) alloy had the best mechanical properties for clinical application, judging from the amount and the temperature of shape recovery.4. Ni-Ti alloy was evaluated for the biocompatibility by a cell culture method and showed relatively high cell attachment and growth. Its biocompatibility appears to be better than that of Vitellium.5. Ni-Ti and Vitellium showed almost the same tissue response in rats. Tumorigenicity of NiーTi was not always strong, but similar to that of Vittallium.It is concluded that NiーTi shape memory alloy miniーplates should be applied for internal bone ーfixation in oral surgery.