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Clinical application of nickel titanium alloy wire

1. Due to the superelasticity and shape memory properties of nickel titanium alloy arch wire, as well as its lower stress-strain curve, nickel titanium alloy arch wire is currently commonly used in clinical practice as the initial arch wire included in the orthodontic system for early alignment and leveling of patient dentition. This greatly reduces patient discomfort. Due to the existence of several different straight wire orthodontic techniques, MBT technology recommends the use of 0.016-inch thermally activated nickel titanium alloy (HANT wire), DEMON self-locking bracket technology recommends the use of copper containing thermally activated nickel titanium alloy (phase transition temperature is around 40 degrees Celsius) produced by Omcro company, and O-PAK orthodontic technology recommends the use of 0.016-inch super elastic nickel titanium alloy (HANT wire) for early alignment and leveling.

2. Nickel titanium spring: Nickel titanium push and pull springs are a type of spring used for orthodontic treatment, with the special properties of nickel titanium superelasticity, suitable for orthodontic treatment to open up gaps between teeth and pull teeth in different directions. The nickel titanium spiral spring can generate approximately 50g of force when extended by 1mm. Nickel titanium spiral springs have high elastic properties and can generate relatively soft and stable sustained force under tension. The attenuation of force is minimal and can generate ideal orthodontic forces that meet the clinical requirements for tooth movement. Meets physiological requirements. The high elasticity and extremely low permanent deformation rate of nickel titanium wire tension springs result in a 3% difference in the released corrective force compared to stainless steel wires of the same diameter 5-4 times. Therefore, in the application of orthodontic treatment, patients not only have mild pain and a soft and long-lasting feeling of strength, but also have reduced follow-up time, shortened treatment courses, and improved efficacy, making it a new and excellent mechanical device in orthodontic treatment.

3. L-H bow wire was developed by Dr. Soma and others in Japan and produced by Tomy Company. "LH" is named after "LowHysteresis", which means the stress generated when the wire is ligated to the bracket, that is, when the wire is activated. The difference between the stress generated when the wire slowly returns to its original state when moving teeth is very small. The lag is very small. SOMA et al. compared the stress-strain curves of LH wire and other nickel titanium alloy wires, and found that L-H wire has the smallest hysteresis range, which gives the wire the advantages of low load and sustained light force. At the same time, the initial slope of the curve is low, indicating low stiffness of the wire. The hysteresis curves of other types of nickel titanium alloy wire indicate greater rigidity, indicating that L-H wire has obvious mechanical advantages. Due to the higher proportion of titanium content in the nickel titanium component of LH wire compared to general nickel titanium arch wire, it is called titanium nickel wire, and experiments have shown that its shock absorption effect is strong. Another characteristic of LH nickel titanium wire is that it can be bent and heated and shaped using a heat treatment instrument. Therefore, LH nickel titanium wire can also be treated from aligning and leveling, opening and closing the bite to closing the gap, and in the final completion stage, with one arch wire on top and one arch wire on the bottom. As long as the arch wire is bent to the desired shape in each stage, it can be shaped using a heat treatment instrument to enhance hardness. At present, L-H arch wire is used in clinical practice for expansion treatment, correcting open jaw, deviated jaw, and inverted jaw. Due to its sustained stability and softness in strength, the effect is good. At the same time, J-hooks are often used in conjunction to improve the weakness of softer arches. Although MEAW technology has ideal results in correcting upper malocclusion, the complex arch wire bending often discourages many physicians.

Therefore, some physicians have adopted a rocking chair type nickel titanium arch wire with vertical traction of the front teeth, which is similar to the mechanical system. Although this has a similar effect, they always feel that when compared with MEAW, the movement of each independent tooth is not as good as MEAW technology. The reason is that the rocking chair type nickel titanium wire is a continuous arch wire and cannot be bent. Therefore, the angle of bracket bonding and the curvature of the rocking chair of the arch wire determine the angle of each tooth, unlike in MEAW technology where there is more room for individual adjustment of the angle of each tooth. Using LH nickel titanium to bend the rocking chair, and then using a wire shaper to bend it in the mouth, the effect is quite ideal. Although I have often come into contact with the term thermal activation, I have little knowledge about it. I searched for relevant knowledge in a book, hoping to increase everyone's understanding of thermal activated nickel titanium wire.

There are two main aspects to describe the hardness of nickel titanium wire. The martensitic state refers to the state where the wire is the softest and has the highest degree of bending. The austenitic state refers to the hardest state of the arch wire. This is the state of the wire at room temperature. The martensitic state of the arch wire undergoes significant changes when heated, transforming into an austenitic state, known as thermal activation. Although similar changes may occur in the austenite state of the arch wire, the degree of change is relatively small and almost imperceptible.

The wire in martensitic state has much better elasticity than that in austenitic state, which means it has a strong ability to recover to its initial shape after deformation and is not easily broken; The force generated by the austenitic state of the wire is 42% higher than that of the martensitic state, but the force released by the martensitic state of the wire is more persistent and constant.

The elastic deformation ability of the two types of arch wires is similar, but the martensitic state of the arch wire can undergo temporary deformation at room temperature and recover to its initial shape in oral temperature environment, thus greatly improving its actual deformation range.

Thermally activated arch wire is an ideal choice for early treatment, as it has a wide range of actual deformation and soft and long-lasting strength, making it suitable as the initial arch wire. In theory, it should be fully seated in the brackets of severely misaligned teeth. Both round and rectangular wires can be used as initial bow wires.

Advantages of thermally activated nickel titanium wire:

1. Less patient pain:

This is due to the gradually increasing force value and the final light force. Controlled thermal activity can prevent a sudden increase in force value when eating hot drinks or food. Patients can alleviate excessive force value by drinking cold water.

2. Less bracket detachment and ceramic bracket rupture:

This is due to the gradually increasing light force of the applied force. This type of wire is ideal for ceramic brackets. Bowstring can maintain its martensitic state at low temperatures, which helps to further reduce the initial force value and make the placement of bowstring easier.

3 Bow wires with less breakage:

Due to its softness compared to the austenitic state of the arch wire, it is not easy to break under stress.

4 chair side work hours reduced:

Due to its large deformation range, it can reduce the number of adjustments and the replacement of bow wires.

5. Shortened treatment time:

Preliminary studies have shown that early torque control and the use of light and sustained force can shorten the overall treatment time, while early use of rectangular wire on straight wire brackets can directly move teeth towards their ideal position.

Disadvantages:

Unable to effectively maintain the shape of the dental arch, it is best not to use it to close gaps, as the force of the elastic ring and spiral spring can cause the arch wire to deform and the teeth to tilt. In addition, although thermally activated nickel titanium wire can shorten the working time next to the chair, the time for moving teeth is longer, and doctors should patiently wait for the arch wire to fully exert its function. Objective: To compare the stiffness, elasticity, strength, and fatigue resistance of Australian wire, American orthodontic steel wire, imitation Australian wire, domestic stainless steel wire, and heat-treated domestic stainless steel wire, in order to provide a basis for the rational selection of orthodontic steel wire in clinical practice. Method: The mechanical properties such as elastic modulus, elastic limit, rebound angle, tensile strength, torsional strength, and fatigue strength of the five commonly used orthodontic steel wires in clinical practice were tested and compared.

The results obtained comparative data on the stiffness, elasticity, strength, and fatigue resistance of five types of orthodontic steel wires. Conclusion: In clinical practice, steel wires should be selected reasonably based on the needs of different orthodontic timing and the different characteristics of steel wires.

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