1. Shape memory performance (sm) refers to the formation of martensite when the parent phase of a certain shape is cooled from above af temperature to below mf temperature, the martensite is deformed below the mf temperature, then heated to below the af temperature, and then reversed The transformation causes the material to deform at a certain temperature. ll automatically restore its shape during the parent phase. The shape memory effect is actually a thermally induced phase transition process in nickel-titanium alloys.

2. The so-called super-elasticity means that the strain produced by the sample under the action of external force is far greater than the elastic limit strain, and the strain energy automatically recovers when unloaded. That is to say, in the mother phase state, due to the effect of applied stress, stress-induced martensitic transformation occurs, resulting in different mechanical behavior of the alloy from ordinary materials. Its elastic limit is much larger than that of ordinary materials, and it no longer follows Hooke's law. Compared to shape memory properties, superelasticity is independent of heat. In short, superelasticity means that within a certain range of deformation, stress does not increase with increasing strain. It can be divided into linear hyperelasticity and nonlinear hyperelasticity. In the former stress-strain curve, the stress-strain relationship is close to linear. Non-linear superelasticity is the result of stress-induced martensitic transformation and its inverse transformation during loading and unloading within a certain temperature range above Af, so it is also called phase transition pseudoelasticity. The pseudo-elasticity of nickel-titanium alloy phase transformation can reach about 8%. The superelasticity of nickel-titanium alloys changes with heat treatment conditions. When the arch wire is heated above 400 or dm, the superelasticity begins to decrease.

3. Oral temperature change sensitivity: The orthodontic force of stainless steel wire and CoCr alloy orthodontic wire is not affected by oral temperature. The orthodontic force of superelastic nickel-titanium alloy orthodontic wire changes with the change of oral temperature. When the deformation is constant. The orthodontic force increases with increasing temperature. On the one hand, it can accelerate the movement of the teeth, because changes in the oral temperature can stimulate blood flow in the blood stasis area caused by capillary blockage caused by the orthodontic device, so that the repairing cells get sufficient nutrition and maintain their function. Vigor and normal function during tooth movement. On the other hand, orthodontists cannot accurately control or measure orthodontic forces in the oral environment.

4. Corrosion resistance: Some studies have shown that the corrosion resistance of nickel-titanium wires is similar to that of stainless steel wires.

5. Anti-toxicity: Nickel-titanium shape memory alloy is a special chemical composition, namely atomic alloys such as nickel-titanium, which contains about 50% nickel. Nickel is known to have carcinogenic and carcinogenic effects. The oxidation of titanium in the surface layer generally plays a blocking role, which makes the nickel-titanium alloy have good biocompatibility. TixOy and TixNiOy on the surface can inhibit the release of nickel.

6. Soft orthodontic force: Currently commercial orthodontic wires include austenitic stainless steel wire, cobalt chromium nickel alloy wire, nickel chromium alloy wire, Australian alloy wire, gold alloy wire, and titanium alloy wire. The load-displacement curves of these orthodontic wires under tensile and three-point bending tests are discussed. Nitinol has the lowest and flatest unloading curve platform, indicating that this platform can provide the most durable and soft orthodontic force.

7. Good shock absorption performance: The greater the vibration of archwires during chewing and night molars, the greater the damage to roots and periodontal tissues. The results of different bow wire attenuation experiments show that the vibration amplitude of stainless steel wire is larger than that of super elastic nickel titanium wire, and the initial vibration amplitude of super elastic nickel titanium bow wire is only half of that of stainless steel wire. The good damping properties of archwires are vital to the health of the teeth, while traditional archwires such as stainless steel wires tend to increase root absorption.