Nickel titanium alloy is a binary alloy composed of nickel and titanium. Due to the change of temperature and mechanical pressure, there are two different crystal structure phases, namely austenite phase and martensite phase. The phase transition sequence of nickel-titanium alloy is parent phase -R phase - martensite phase. The R phase is rhomboid, the austenite is the state at high temperature, or when the load is removed, the cube, hard. The shape is stable. While the martensite phase is the state of relatively low temperature or loading, hexagonal, ductile, repetitive, not very stable, easy to deformation.
Shape memory characteristics: shape memory refers to that when martensite is formed after the parent phase of a certain shape is cooled from above AF temperature to below MF temperature, the martensite is deformed below MF temperature and heated to below AF temperature, accompanied by reverse phase transformation, the material will automatically recover its shape in the parent phase.
Hyperelasticity: The so-called hyperelasticity refers to the phenomenon that the strain of the sample under the action of external force is far greater than its elastic limit strain variable, and the strain can automatically recover when unloading.
Sensitivity to temperature changes in the oral cavity: The orthodontic power of stainless steel wire and CoCr alloy dental orthodontic wire is basically not affected by the temperature in the oral cavity.
Corrosion resistance: Studies show that the corrosion resistance of nickel-titanium wire is similar to that of stainless steel wire.
Anti-toxicity: the special chemical composition of nickel-titanium shape memory alloy, that is, it is an atomic alloy of nickel-titanium, containing about 50% nickel, which is known to have carcinogenic and cancer-promoting effects.
Soft healing power: currently commercially available tooth orthodontic wires include austenitic stainless steel wires, cobalt-chromium-nickel wires, nickel-chromium wires, Australian wires, gold wires and nickel-titanium wires.
Good shock absorption: the greater the vibration caused by mastication and night bruxism to the arch wire, the greater the damage to the root and periodontal tissue.
