Nitinol is a shape memory alloy, which is a special alloy that can automatically restore its plastic deformation to its original shape at a certain temperature, and has good plasticity.
In addition to its unique shape memory function, memory alloy also has excellent characteristics such as wear resistance, corrosion resistance, high damping and super elasticity.
Performance and characteristics
(1) Phase transformation and properties of Nitinol
As the name suggests, Nitinol is a binary alloy composed of nickel and titanium. Due to changes in temperature and mechanical pressure, there are two different crystal structure phases, namely austenite phase and martensite phase. The phase transformation sequence of nickel-titanium alloy cooling is parent phase-R phase-martensite phase. The R phase is rhombohedral, and the austenite is in the state when the temperature is high or when the load is removed. It is cubic and hard. The shape is relatively stable. The martensite phase is a state at a relatively low temperature or under loading. It has a hexagonal shape and is ductile, repeatable, unstable, and easily deformed.
(2) Special properties of Nitinol
Shape memory characteristics: Shape memory is when the parent phase of a certain shape is cooled from above Af temperature to below Mf temperature to form martensite, the martensite is deformed at a temperature below Mf, and heated to below Af temperature, accompanied by reverse phase transformation. The material will automatically restore its shape in the parent phase.
Superelasticity: The so-called superelasticity refers to the phenomenon that the sample produces a strain much larger than its elastic limit strain under the action of external force, and the strain can be automatically restored when unloaded.
Intraoral temperature change sensitivity: The corrective force of stainless steel wire and CoCr alloy orthopedic wire is basically not affected by the oral temperature.
Corrosion resistance: studies have shown that the corrosion resistance of nickel-titanium wire is similar to that of stainless steel wire
Anti-toxicity: Nitinol shape memory alloy has a special chemical composition, that is, it is an atomic alloy such as nickel-titanium, containing about 50% nickel, and nickel is known to have carcinogenic and cancer-promoting effects.
Gentle orthodontic power: currently commercially used orthopedic wires include austenitic stainless steel wires, cobalt-chromium-nickel alloy wires, nickel-chromium alloy wires, Australian alloy wires, gold alloy wires and titanium alloy wires.
Good shock absorption properties: The greater the vibration caused by the arch wire due to chewing and night molars, the greater the damage to the root and periodontal tissue.
(3) Clinical application of Nitinol wire:
1. It is used for the early alignment and leveling of the patient's dentition. Due to the superelasticity and shape memory properties of the Nitinol archwire and the lower stress-strain curve, the Nitinol archwire is routinely included in the treatment system as the initial stage in clinical practice. Arch wire.
2. Nitinol spring: Nickel-titanium push spring and extension spring are springs used for orthodontics of teeth. They are super-elastic and suitable for orthodontic treatment to open up the gap between teeth and pull teeth in different directions.
3. The LH archwire was researched and developed by Dr. Soma and others in Japan. "LH" is named from "LowHysteresis", that is to say, when the archwire is ligated to the bracket, it is produced when the archwire is activated. The difference between the stress and the stress generated when the arch wire slowly returns to its original shape when the tooth is moved is small.