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1) In 1940, gold bow wire, cobalt chromium alloy wire and stainless steel round wire.
2) In 1960, martensitic stabilized alloy: mostly nickel-titanium alloy was made after deformation in martensitic state. This kind of arch wire has low stiffness and can produce light correction force. There is no martensitic transformation caused by stress or temperature, so there is no memory effect and hyperelasticity.
3) In 1980, Chinese nickel-titanium alloy and Japanese nickel-titanium alloy arch wire, austenite-activated alloy: that is, in any state of austenite state, placed in the mouth and outside the mouth do not have martensite state caused by temperature, martensite state can only be caused by stress, has super elasticity, but does not have the shape memory function. This kind of arch wire has excellent resilience and low stiffness, which can produce weak correction force. It is characterized by a constant force generated from the initial initiation to the final stage, and is more effective in treating early teeth irregularities. The disadvantage is that it can not be bent into shape at room temperature and is not easy to weld.If used as the main arch wire, it can often cause undesirable arch expansion or retraction, and it is difficult to establish a good premolar and molar alignment.
4) In 1990, martensite-activated Nitinol: that is, TTR is lower than or very close to the oral temperature, it exists in a multiple state at room temperature and is easy to deform. When placed in the oral cavity, the martensite caused by stress and room temperature simultaneously changes to austenite, that is, it has shape memory function and super elasticity. It is easy to deform at room temperature (about 25℃) and below, but when it reaches a certain temperature (about 32℃), it will return to the original preformed shape, showing shape memory and superelasticity characteristics. Smart and Nitinol HA of 3M are typical representative products. Because of this characteristic, thermally activated nickel-titanium arch wire can be easily manipulated to form at or below normal temperature and placed in the bracket. When activated by body heat in the mouth, it can produce shape restoring force and provide the required force for orthopedics. Due to the characteristics of the heat-activated nickel-titanium orthodontic wire, which is "soft when cooled and elastic when activated by heat", patients can change the orthodontic force by using cold and hot water in the mouth under the guidance of doctors, which is more convenient for the orthodontic and reduces the discomfort of the initial orthodontic.
5) Thermodynamic nickel-titanium alloy: The TTR temperature is higher than the mouth temperature, about 40℃, so that when the nickel-titanium arch wire is placed in the mouth, it is still in multiple state, the arch wire is soft, and the austenite transformation occurs only when the mouth is filled with hot water. Therefore, the orthodontic force is weaker and can be used as the initial arch wire in adult patients and patients with periodontal disease. Omcro's copper-containing nickel-titanium wire and Japan's low-lag L-H nickel-titanium arch wire are examples of this property.
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