In addition to its own basic properties, nickel-titanium alloy also has special properties. Because of its special properties, it has broadened its application. Closer to home, the special properties of nickel-titanium alloys are generally as follows:
1. Shape memory characteristics: Shape memory is when the parent phase of a certain shape is cooled from above the Af temperature to below the Mf temperature to form martensite, the martensite is deformed at a temperature below Mf, and heated to below the Af temperature, accompanied by reverse phase. changes, the material will automatically return to its original shape. In fact, the shape memory effect is a thermally induced phase transformation process in Nitinol.
Superelasticity: The so-called superelasticity refers to the phenomenon that the sample produces a strain far greater than the elastic limit strain under the action of external force, and the strain can automatically recover when unloaded. That is, in the state of the parent phase, due to the action of external stress, the stress-induced martensitic transformation occurs so that the alloy exhibits mechanical behavior different from ordinary materials. Its elastic limit is much larger than that of ordinary materials, and it no longer obeys Gram's Law.
Corrosion resistance: Studies have shown that the corrosion resistance of nickel-titanium wire is similar to that of stainless steel wire.
Sensitivity to intraoral temperature changes: The orthodontic force of stainless steel wire and CoCr alloy orthodontic wire is basically not affected by intraoral temperature. The orthodontic force of superelastic nickel-titanium alloy orthodontic wire varies with oral temperature. When the amount of deformation is constant. As the temperature increases, the healing power increases. On the one hand, it can accelerate the movement of the teeth, because the temperature change in the oral cavity will stimulate the blood flow in the stagnant blood flow caused by the capillary stagnation caused by the orthodontic device, so that the repair cells are fully nourished during the movement of the teeth, maintain its vitality and normal function. Orthodontists, on the other hand, cannot precisely control or measure orthodontic forces in the oral environment.
Anti-toxicity: The special chemical composition of nickel-titanium shape memory alloy, that is, it is an atomic alloy such as nickel and titanium, containing about 50% nickel, and nickel is known to have carcinogenic and cancer-promoting effects. In general, the titanium oxide on the surface layer acts as a kind of barrier, making Ni-Ti alloys have good biocompatibility. The TiXOy and TixNiOy in the surface layer can inhibit the release of Ni.
Soft orthodontic force: Currently commercially used 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. Load-displacement curves for these orthodontic wires under tensile test and three-point bending test conditions. Nitinol has the lowest and flattest unloading curve platform, indicating that it can provide the most durable and gentle orthodontic force.
7. Good shock absorption characteristics: The greater the vibration of the archwire caused by chewing and night grinding, the greater the damage to the root and periodontal tissue. Through the results of different archwire attenuation experiments, it is found that the vibration amplitude of the stainless steel wire is larger than that of the superelastic NiTi wire, and the initial vibration amplitude of the superelastic NiTi archwire is only half of that of the stainless steel wire. Tooth health is very important, and traditional archwires, such as stainless steel wires, tend to aggravate root resorption.
