JP2008086633A - Orthodontic wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an orthodontic wire which is designed to shorten the treatment period, ease pain, and bring no odd feeling about its color, has a high strength, low elasticity, and is ductile enough to remain unbroken in being bent for treatment, and has a low friction coefficient, a long-lasting stable spring property, and a color that matches that of teeth. <P>SOLUTION: This wire, made of a βtype Ti alloy of high strength and low elasticity called rubber metal, after being wiredrawn in a cold or warm working process, and shaped into a wire with a circular or oval cross section, is coated with a group IVa, group Va, or group VIa nitride film, carbide film, carbonitride film, or metal film having gold or white color closer to teeth color by means of a physical vapor deposition method. With the control on the drawing and film-forming conditions, the wire becomes free from twists or bends, having a high strength, a low elasticity, an enduring ductility high enough to prevent fracture in being bent, and a long-lasting stable spring property with a low friction coefficient. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a wire provided for orthodontic treatment of teeth.

As a treatment for malocclusion of people with poor tooth occlusion and poor tooth alignment, a strong wire such as Co-Cr strong wire or stainless steel wire or NiTi alloy wire is pressed against the tooth for a long time to correct it. I have been.

However, these strong steel wires and alloy wires have high strength and at the same time have a high modulus of elasticity, and when these wires are pressed against the patient's teeth, they feel pain against the high stress that was pressed. There were many things. In addition, it was necessary to continue treatment for a long period of 1 to 3 years until correction was completed. NiTi contains Ni and its use has been restricted due to allergy problems. In addition, these wires have a gray metallic color, and there is a sense of discomfort with the color of the teeth when the mouth is opened.

Recently, a β-type Ti alloy called rubber metal having high strength and low elastic modulus has been developed and disclosed in Japanese Patent No. 3375083. If this material can be used as an orthodontic wire, it will be possible to relieve pain that has been felt by patients. However, when this alloy is drawn into a wire, it cannot be avoided that the alloy is greatly bent. When heating is performed to correct this curvature, there has been a problem that it becomes brittle and breaks during bending during treatment. Furthermore, the coefficient of friction was high and it was difficult to move along the teeth during treatment. In addition, it had a gray metallic color, and the discomfort with the tooth color when the mouth was opened was not improved. Furthermore, there is a problem that the strain amount of the wire subjected to a load during a long-term treatment is large and a constant stress cannot be applied. Because of these problems, it was not used as an orthodontic wire.
Japanese Patent No. 3375083

In the past, it has been required to shorten the treatment period for orthodontic treatment, to relieve the pain received from the wire during orthodontic treatment, and to spend the treatment period without any discomfort in color. For this purpose, the strength of the straightening wire is not only high, but also has a low modulus of elasticity, has a ductility that does not break when the wire is bent for treatment, and the wire is curved for easy handling. In addition, it is required that the stress applied to the tooth is reduced little when a certain strain is applied to the wire during a long-term treatment. Furthermore, the orthodontic wire is required to have a color that does not cause a sense of incongruity with the teeth and that the wire has a low coefficient of friction so that the wire can move to an appropriate position along with the correction of the teeth. Further, it is desired that the wire can surely hit along the tooth and can give an appropriate torque to the tooth.

  The present invention uses, as a material, a β-type Ti alloy having a high elasticity of 800 MPa or more and a low elastic modulus of 70 GPa or less while having a high strength of 800 MPa or more, instead of a strong wire or a NiTi alloy wire conventionally used as an orthodontic wire. After this is drawn in cold or warm, it is processed into a wire with a circular or rectangular cross-sectional shape, and then using a physical vapor deposition method, it has a beautiful gold color or white color close to the color of teeth, IVa group, It has been found that the above-mentioned problems can be improved by coating a Va group and VIa group nitride thin film, carbide thin film, carbonitride thin film or metal thin film.

As a Ti alloy having a strength of 800 MPa or more and an elastic modulus of 70 GPa or less, a β-type Ti alloy containing a large amount of a Va group element has been developed. Despite having a high strength of 800 MPa or more, this material has a low elastic modulus of 70 GPa or less, and even when wire is drawn, unlike conventional metals, there is little work hardening, It maintains almost the same high strength and low elastic modulus. For this reason, it can follow a tooth with low force, and can be easily bent into a shape suitable for orthodontic treatment. In addition, the small elastic modulus contributes to giving a stable force to the teeth with little change in holding stress against changes in strain due to tooth movement. A strength of less than 800 MPa is not preferable because the strength is insufficient and a long period of time is required for dental correction. When the elastic modulus is 70 GPa or more, the patient feels pain when the wire is pressed against the teeth.
In order to achieve the object of the present invention, it is important to use a β-type Ti alloy having a strength of 800 MPa or more and an elastic modulus of 70 GPa or less as the material of the straightening wire.

Orthodontic wires include a single wire used along with teeth and a coil spring wire used for applying further stress to the single wire. Generally, a circular shape is most frequently used as the cross-sectional shape of the wire. However, when the straightening wire is used as a single wire, the rectangular shape is easier to fix along the teeth than the circular shape. In addition, since it is possible to apply torque to the teeth to be corrected, many options are given to the correction method of the corrector, and short-term correction is possible. However, in this case, if the initial line is twisted, not only the rectangular surface but also the part where the corner hits the tooth can not be brought into close contact with the tooth over the entire length of the wire. Torque is applied to the teeth. Therefore, it is important that the wire is not twisted.
When the cross section is rectangular, the mouth of the wire may be damaged by touching the corners of the wire. In order to prevent such an accident, it is necessary to provide a radius of R0.03mm or more at the corner of the rectangular wire.
When it is used as an inner coil spring wire of an orthodontic wire, it does not need to be rectangular in particular, and may be circular. In this case, if the wire diameter exceeds 1 mmφ, the strength of the spring becomes too high, so it is necessary that the wire diameter be 1 mmφ or less.

This β-type Ti alloy wire has a gray metallic color like conventional straightening wires, and it is inevitable that the patient feels uncomfortable when the patient opens his mouth as in the conventional case. In addition, the frictional resistance of the wire is as high as around 1.0, and the point that the teeth are difficult to move along the wire remains the same. In order to solve these problems, in the present invention, a nitride thin film, a carbide thin film, a carbonitride thin film, or a metal thin film of IVa group, Va group and VIa group is coated using a physical vapor deposition method. Group IVa and Va group nitrides include TiN and ZrN, which show a beautiful gold color or a light golden color with white added. Group IVa, Va and VIa metal thin films show a white color close to the color of the teeth. In addition, CrN, which is a VIa group nitride thin film, shows a glossy metallic color, and the type of film can be selected according to patient preference. By attaching the wires covering these teeth to the teeth, the uncomfortable feeling that is felt with conventional orthodontic wires is reduced. Among these, TiN, which is a nitride of Ti, or metal Ti can be coated on the Ti alloy wire with the best adhesion. In addition, the CrN film has a feature that the coefficient of friction is lower than that of TiN, and the wire is easily moved during correction.

In addition to physical vapor deposition, there are chemical vapor deposition and plating methods as methods for coating the above-mentioned film. However, chemical vapor deposition requires a high processing temperature. Will become brittle. In addition, the plating method does not have high adhesion, and there is a possibility that the film may be peeled off when the wire is bent for treatment. On the other hand, in the physical vapor deposition method, a nitride, carbonitride, carbide or metal thin film can be coated with good adhesion at a relatively low temperature.
Even in the physical vapor deposition method, the temperature rises during processing due to radiant heat from the raw material target. When the temperature of the wire is heated to 320 ° C. or higher during the treatment, the β-type Ti alloy wire is embrittled and broken when it is bent to 150 ° or higher during treatment. It is necessary for the orthodontic wire to maintain ductility that does not break even when it is bent at 150 ° or more. For this reason, the temperature of the wire must not exceed 320 ° C. during the coating process.

On the other hand, in the state in which the β-type Ti alloy is drawn, the processing stress is inherently curved, so that the β-type Ti alloy is greatly curved. Even if the processing method is optimized, it is difficult to avoid bending of 10 mm or more per 200 mm. It remains difficult to use as an orthodontic wire if it is largely curved. When processing into a coil spring, if there is a large bend, processing becomes difficult. In the present invention, when the above thin film is coated on a wire obtained by drawing a β-type Ti alloy having a strength of 800 MPa or more and an elastic modulus of 70 GPa or less, bending is performed per 200 mm by heating the wire to 250 ° C. or more. It was found to reduce to 7 mm or less.
However, when the temperature is set to 320 ° C. or higher, as described above, the wire becomes brittle. Therefore, it is necessary to control the temperature during the coating process to a narrow range of 250 ° C. or higher and 320 ° C. or lower.

In addition, by coating this β-type titanium alloy in the above temperature range, the relaxation in which the stress decreases with the passage of time when a certain strain is applied can be reduced. I found out that it is possible to reduce the size. These characteristics are important for orthodontic wires that move teeth under stress over a long period of time, and the deterioration of the spring characteristics of the wire itself over time is extremely small, providing stable stress to the teeth for a long period of time. Make it possible.

The film thickness need not be specified, but in order to give a gold or white color to the entire wire surface, it is preferably 0.05 μm or more. Further, when the wire is thickened, the film is easily peeled when the wire is bent, and it is necessary to lengthen the coating treatment time, so that the thickness is desirably 2 μm or less.

In order to move teeth along the wire to an appropriate position for orthodontic treatment, it is important that the frictional resistance of the wire surface is low. The friction resistance of the conventional wire material and β-type Ti alloy used as a raw material by the present invention is not low.

In order to reduce the frictional resistance of the wire surface, it is first necessary to make the surface roughness Rz 2.0 μm or less. The surface roughness after processing into a wire should be less than or equal to the aforementioned surface roughness, and the surface roughness should not be greatly increased when the film is coated. There are an ion plating method and a sputtering method as physical vapor deposition methods for coating the film. However, when the ion plating method is used, the maximum particle size of around 1μm is scattered from the raw material target being processed and is easily contained in the film, so the surface roughness after processing into a wire is close to Rz2.0μm. In this case, the surface roughness after coating the film may exceed Rz 2.0 μm. In contrast, in the sputtering method, there is almost no scattering of large particles, and the surface roughness after being processed into a wire can be maintained almost as it is. In order to obtain a smooth film having a surface roughness of Rz 2.0 μm or less, a sputtering method is preferred as the coating method.

A frictional resistance can be lowered by coating the surface of the β-type Ti alloy with the above-described thin film while making the surface roughness Rz 2.0 μm or less. Among the thin films described above, a nitride, carbonitride, or carbide film has a lower frictional resistance than a metal thin film. By reducing the frictional resistance, it becomes easier for the teeth to move along the wire during tooth correction, which greatly contributes to shortening the treatment period.

According to the present invention, the orthodontic treatment can be completed in a significantly shorter period than before. In addition, the pain during orthodontic treatment can be eased and the treatment period can be spent without any discomfort in appearance.

A β-type Ti alloy having high strength but low elasticity is processed into a wire having a circular or rectangular cross section in the cold state. The processed wire can be processed without causing twisting, but it is inevitable that the wire is greatly curved. This is attached to an ion plating apparatus or a sputtering apparatus to cover a nitride thin film, carbide thin film, carbonitride thin film or metal thin film of IVa group, Va group and VIa group. When coating these films, it is important to perform the coating treatment while controlling the temperature in the range of 250 to 320 ° C. As a result, it is possible to produce an orthodontic wire that is high in strength but has a low elastic modulus, a small sag when subjected to a load for a long period of time, a low friction coefficient, and a straight and beautiful color. By using this wire to correct the teeth, there is no pain for the patient when attaching the wire, and there is no sense of discomfort with the color of the teeth. Can be completed.

Specific examples will be described below.

Example 1 A β-type Ti alloy coil containing 30% Nb, 0.7% Ta, 0.7% Zr, and 1.2% O and comprising the balance Ti was drawn. The material Ti alloy coil linearity was 0.65mmφ, the tensile strength was 860MPa, and the elastic modulus was 45GPa. Table 1 shows the cross-sectional dimensions and mechanical properties of the four types of wire drawn. Bending is evaluated by deviation from a straight line per 200mm length. No. A and No. D are round wires, and No. B and No. C have a rectangular cross section. Both have a strength of 800 MPa or more and an elastic modulus of 70 GPa or less, and the strength is higher than before drawing, but the elastic modulus has not changed significantly, and is a desirable property for orthodontic wire properties. The value has changed. In addition, no twist was observed. However, the wire in the pultruded state was greatly bent at 10 to 30 mm per 200 mm. This bending is then hindered when it is bent into a shape along the teeth or processed into a coil spring.

These drawn β-type Ti alloy wires were attached to a sputtering apparatus, evacuated to 4 × 10 ⁻³ Pa or less, and then heated to 300 ° C. with a heater. After 1 hour, Ar gas was introduced to 0.52 Pa, voltage was applied to the Ti, Zr or Cr target of the coating material to generate Ar plasma, and Ti, Zr and Cr were evaporated. Subsequently, nitrogen gas was introduced into the furnace so as to be 20% of the total gas amount. As a result, Ti, Zr or Cr and nitrogen reacted on the Ti alloy wire surface to form a Ti, Zr or Cr nitride film, respectively. During the film formation, the temperature of the wire increased, and after the film was formed for 5 minutes, the process of stopping the film formation for 3 minutes was repeated 2 to 6 times. The film thickness was 0.05 to 0.3 μm. Table 2 shows the bending, ductility, surface roughness and color tone of the β-type Ti alloy wires coated with these nitride thin films. Similar to Table 1, the curve is shown as a deviation from a straight line per 200 mm length. The bending after the film formation is 5mm or less per 200mm length, which is a significant improvement over the drawing process. The strength and elastic modulus of the wire coated with the nitride film are hardly changed compared to before the film is formed. The ductility was evaluated based on whether or not the wire was cut when it was bent by 150 °. The colors of TiN and ZrN were beautiful gold or platinum. All of the surface roughnesses were Rz 2.0 μm or less, and the friction coefficients were all smooth from 0.5 to 0.6.
CrN was a glossy metallic color with a low coefficient of friction of 0.30.

Example 2
The β-type Ti alloy wire No. B described in Example 1 was attached to a sputtering apparatus, evacuated to 4 × 10 ⁻³ Pa or less, and then heated to 300 ° C. with a heater. After 1 hour, Ar gas was introduced to 0.52 Pa, a voltage was applied to the Ti target of the coating material to generate Ar plasma, and Ti was evaporated. Subsequently, nitrogen gas and CH ₄ gas were introduced into the furnace so that each amount was 10% of the total gas amount. As a result, Ti, nitrogen and CH ₄ gas react on the Ti alloy wire surface to form a Ti carbonitride film, TiCN. If Ar gas and CH ₄ gas are introduced without introducing nitrogen gas, TiC is formed. In any case, since the temperature during film formation rises, the process of film formation for 5 minutes and then the film formation pause is repeated 5 times. The film thickness was 0.2 to 0.25 μm. Table 3 shows the bending, ductility, surface roughness and color tone of the β-type Ti alloy wire coated with these carbonitride thin films. Similar to Tables 1 and 2, the curve is shown as a deviation from a straight line per 200 mm length. The bending after the film formation is 5mm or less per 200mm length, which is a significant improvement over the drawing process. The strength and elastic modulus of the wire coated with the carbonitride film are almost the same as before the film formation. The ductility was evaluated based on whether or not the wire was cut when it was bent by 150 °. The surface roughness was less than Rz2.0μm, and the coefficient of friction was lower than that of TiN film.

Example 3 A β-type Ti alloy coil made of 12% Ta, 9% Nb, 3% V, 6% Zr, 1% O balance Ti was drawn. The Ti alloy coil had a linear shape of 0.80 mmφ, a tensile strength of 840 MPa, and an elastic modulus of 46 GPa. Table 4 shows the cross-sectional dimensions and mechanical properties after drawing. The cross section is rectangular. Both have a strength of 800 MPa or more and an elastic modulus of 70 GPa or less. In addition, no twist was observed. However, the wire in the pultruded state was greatly bent at 10 to 20 mm per 200 mm.

These drawn β-type Ti alloy wires were attached to a sputtering apparatus, evacuated to 4 × 10 ⁻³ Pa or less, and then heated to 280 ° C. with a heater. After 1 hour, Ar gas is introduced to 0.8 Pa, electric power is applied to the raw material Ti and V targets to generate arc spots, Ti or V is evaporated, and Ti thin film or V thin film is formed on the Ti alloy wire surface. Vapor deposited. During film formation, the temperature of the wire increased, and after 5 minutes of film formation, the process of stopping film formation for 5 minutes was repeated 4 times to form a film for a total of 20 minutes. The film thickness was 0.8 μm. Table 5 shows the bending, ductility, surface roughness and color tone of the β-type Ti alloy wire thus coated with the Ti thin film or the V thin film. The bending of the wire is shown as a deviation from a straight line per 200 mm length. After film formation, all are 5mm or less, which is a significant improvement compared to the drawing process. The strength and elastic modulus of the wire coated with the metal film have hardly changed compared to before the film was formed. Moreover, the ductility evaluated by the presence or absence of cutting of the wire when bent by 150 ° was good. The color tone was white near the teeth.

Example 4
A compression coil spring having an outer diameter of 1.44 mm, a length of 50 mm, and a winding number of 125 was prepared using the wire coated with TiN on the 0.23 mmφ wire of Drawing No. D in Example 1 under the conditions described in Example 1. did. At the same time, a compression coil spring was prepared using a No. D 0.23 mmφ wire that was not coated. With respect to these two compression coil springs, the permanent strain generated in the springs when a compression load of 120 g was applied for 2000 hours at room temperature was measured. The result is shown in FIG. Those coated with TiN have a permanent set smaller by 30% or more than those without coating. Small permanent set means small spring sag and excellent durability, enabling stable orthodontics.

Example 5
The wire of the present invention indicated by No. B1 in Table 2 described above was used for orthodontic treatment of a 20-year-old woman. Compared to conventional strong wire, it was easier to process for orthodontic treatment. The force applied to the teeth was soft, and the pain that the patient had complained in the early stages of treatment was greatly reduced. By using the wire of the present invention, the process that required about 1 to 2 years in the treatment using the conventional strong wire was completed in 6 weeks because the tooth moving speed was about 10 times larger than the conventional one. In addition, the color tone is beautiful gold, and the uncomfortable feeling when opening the mouth was reduced.

FIG. 6 is a diagram showing a relationship between permanent strain and time when a compressive load of 120 g is applied to two types of coil springs.

Claims (1)

A β-type Ti alloy wire having a strength of 800 MPa or more and an elastic modulus of 70 GPa or less is coated with a nitride thin film, carbide thin film, carbonitride thin film or metal thin film of group IVa, Va and VIa. Orthodontic wire.