In 1940, gold arch wire, cobalt-chromium alloy wire and stainless steel round wire. In 1960, martensite stabilized alloys: mostly Ti-Ni alloys were made after deformation in martensitic state. This kind of arch wire has low stiffness and can produce lighter orthodontic force. There is no martensitic transformation caused by stress or temperature, so there is no memory effect and superelasticity. In 1980, Chinese and Japanese nickel-titanium alloy archwires were austenite-activated alloys: austenite was present in any state, and there was no martensite state caused by temperature in or out of the mouth. The martensite state could only be caused by stress and had superelasticity, but did not have shape memory function. This kind of arch wire has excellent resilience and low stiffness, and can produce weak orthodontic force. Major features are from the initial start to the final stage, the force generated is constant, in the treatment of early teeth irregularity, the effect is better. The removal point is not bendable at room temperature, and is not easy to weld. If the company is used as the main arch wire, it often causes unwanted expansion or contraction of the arch, and it is difficult to establish a good arrangement of premolars and molars.
In 1990, martensite activated nickel-titanium alloy: TTR is lower than or very close to the oral temperature, and exists in a multivariate state at room temperature, which is easy to deform. When placed in the oral cavity, martensite caused by stress and room temperature simultaneously transforms to austenite, i.e. shape memory function and superelasticity exist. It is easy to deform at room temperature (about 25 C) and below, but when it reaches a certain temperature (about 32 C), it will return to the original preform, showing the characteristics of shape memory and superelasticity. The Smart Brand of Beijing Saint Matt Technology Co., Ltd. and NitinolHA Brand of 3M Company are typical representative products. Thermally activated nickel-titanium archwire can be easily shaped and placed in the bracket because of this characteristic. When activated by the temperature and heat of the receptor in the oral cavity, it can produce shape restoring force and provide the required strength for orthopedics. Because the thermally activated nickel-titanium orthodontic wire has the characteristics of “softening in cold and becoming elastic in heat activation”, patients can change the orthodontic force by means of cold and hot water in mouth under the guidance of doctors, which is more convenient for Orthodontists and reduces the discomfort of initial orthodontic treatment. Increased thermodynamic nickel-titanium alloy: TTR temperature is higher than oral temperature, about 40 degrees Celsius, so that when the nickel-titanium archwire is placed in the mouth, it is still in a pluralistic state, the archwire is relatively soft, and austenite transformation occurs only when the mouth contains hot water. Therefore, the orthodontic force is weaker and can be used as the initial arch wire for adult patients and periodontal patients. The copper-nickel-titanium wire produced by Omcro and the Japanese low-lag L-H nickel-titanium arch wire have this property. Clinical application of Ti-Ni alloy wire:
- NiTi spring
NiTi push spring and pull spring are springs used in orthodontics. They have the characteristics of nickel-titanium superelasticity. They are suitable for opening up the gap between teeth and pulling teeth in different directions in orthodontic treatment. When the nickel-titanium coil spring is extended by 1 mm, about 50 g of force can be produced. Nickel-titanium coil springs have high elastic properties, which can produce a relatively soft and stable sustaining force under tension. The attenuation of force is very small, which can produce ideal orthodontic force for clinical tooth movement. It meets the physiological requirements. Compared with stainless steel wire of the same diameter, nickel-titanium wire spring has a high elasticity and a very low permanent deformation rate, and its release of orthodontic force is 3.5-4 times less than that of stainless steel wire of the same diameter. Therefore, in the application of orthodontic treatment, patients not only have light pain, soft and lasting sensory strength, but also reduce the time of re-examination, shorten the course of treatment and improve the curative effect. It is a new excellent mechanical device in orthodontic treatment.
- Arch wire of dental orthodontic system
Because of the superelasticity, shape memory and low stress-strain curve of nickel-titanium alloy arch wire, nickel-titanium alloy arch wire is routinely used as the initial arch wire in orthodontic system, so that patients’discomfort will be greatly reduced. Due to several different straight wire orthodontic techniques, MBT technology recommends using 0.016 inch thermally activated nickel-titanium alloy arch wire (HANT wire), DEMON self-locking bracket technology recommends using copper-containing thermally activated nickel-titanium alloy arch wire (transformation temperature is about 40 degrees), O-PAK orthodontic technology recommends using 0.016. Inch superelastic nickel-titanium alloy archwire is used for early alignment and leveling.
