JP2901175B2 - Titanium orthodontic parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium orthodontic part manufactured by a metal powder injection molding method.

[0002]

2. Description of the Related Art Conventional orthodontic parts are made of metal, ceramic or polymer resin.
Ceramics or polymer resins have excellent aesthetics compared to metal because their color tone is close to that of living teeth. Some ceramics are manufactured by powder injection molding. Stainless steel is generally used for the metal one because of its corrosion resistance, and is widely used because of its excellent mechanical properties. Metal products are manufactured by metal powder injection molding or cutting.

[0003] However, these orthodontic parts have the following problems. That is, the ceramic and polymer resin products have inferior mechanical properties to those of stainless steel products, and may be damaged during use and may damage the oral cavity. In addition, stainless steels are considered to be carcinogenic and allergic due to the effects of elements such as Ni contained therein (for example, "Dental metal material", special steel, 42
Vol. 11, No. P42).

Although it is known that Ti is excellent as a metal for biomaterials, its machinability is inferior, and it has been difficult to manufacture orthodontic parts having minute and complex shapes by machining. A method of manufacturing a titanium part by a metal powder injection molding method is disclosed in Japanese Patent Application Laid-Open No. 2-54733 or the like. However, it is necessary to obtain a characteristic required for the characteristics of a small and complicated orthodontic part. Was not enough.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and utilizes a metal powder injection molding method to provide a safe titanium orthodontic part having excellent mechanical properties. The purpose is to provide.

As a result of various studies on the present invention, a method for solving the above problems has been obtained. That is, the present invention provides: (1) a step of mixing a titanium raw material powder and a binder to obtain a mixture; (2) a step of molding the mixture by injection molding to obtain a molded body; and (3) a step of removing a binder in the molded body; (4) A titanium orthodontic part manufactured through a step of sintering a molded body from which a binder has been removed to obtain a sintered body, wherein the obtained sintered body has a carbon content of 0.25 wt% or less. , Oxygen: 0.
Comprises 6 wt% or less has a composition comprising the balance Ti and inevitable impurities state, and are relative density of 97.0% or more, the hardness
Saga H _RV 100-320, there is provided a titanium orthodontic parts elongation, characterized in der Rukoto 2% or more.

[0007]

The surface of the sintered body after sintering is oxidized or nitrided,
Alternatively, a modification treatment such as increasing the hardness and / or changing the color of the surface is advantageously performed by coating with gold or a gold alloy.

The titanium raw material powder used has an average particle size of 25.
μm or less, carbon content 0.25 wt% or less, oxygen content 0.
6 wt% or less is preferable.

The step of removing the binder is preferably performed in an inert atmosphere or under reduced pressure.

The step of sintering the compact from which the binder has been removed is preferably performed in a vacuum or in an inert atmosphere in the presence of a getter material. Further, the degreased molded body is preferably placed in another container in a sintering furnace for sintering.

[0012]

The orthodontic part made of titanium according to the present invention is manufactured by using a metal powder injection molding method and manufactured through the following steps. (1) Step of mixing a titanium raw material powder and a binder to obtain a mixture (2) Step of forming a mixture by injection molding to obtain a molded body (3) Step of removing the binder in the molded body and (4) Removing the binder Of obtaining a sintered body by sintering the compact

According to the present invention, it has been found that the mechanical properties, especially the tensile strength and elongation, of a sintered body, that is, an orthodontic part, are determined by the carbon and oxygen contents and the relative density of the sintered body. In other words, in order to obtain orthodontic parts that are carcinogenic and have a low risk of allergy at a general price and that satisfy the required mechanical properties, it is necessary to minimize the carbon content and the oxygen content, It is necessary to obtain a sintered body having a high density. When carbon and oxygen enter titanium, stable oxides or carbides are formed, which makes removal difficult. In addition, since the material is embrittled, elongation decreases and tensile strength generally decreases. Further, the strength and hardness of the sintered body are greatly affected by the density, and the mechanical properties are deteriorated due to the decrease in the density. Further, the impact resistance is significantly affected by the density, and at a density of 95% or less, the impact resistance is reduced to about one-tenth that of a non-porous material having the same material composition.

In order to obtain a titanium orthodontic part having sufficient mechanical properties aimed at by the present invention, the carbon content, the oxygen content and the relative density of the orthodontic part, that is, the sintered body, must be adjusted for the above reasons. It is limited to the following range. The reason will be described below.

First, regarding the carbon content, as is known for ingots, the toughness is remarkably reduced by an increase of about 0.4%, and the carbon content is reduced to 0 by the influence of oxygen content and density. If it exceeds 0.25 wt%, it is difficult to secure elongation of 2% or more, preferably 3% or more, which is considered necessary for orthodontic parts even with a sintered body having a low oxygen content and a high density. Therefore, the range of the carbon content of the orthodontic part of the present invention is set to 0.25 wt% or less.
Preferably, it is 0.15 wt% or less.

Similarly, the oxygen content was also examined. Since the maximum allowable oxygen content for securing the above elongation was 0.6 wt%, the range of the oxygen content of the orthodontic part of the present invention was set to 0%. 0.6 wt% or less. Preferably, it is 0.5 wt% or less.

The density of the sintered body greatly affects its mechanical properties, and a material having no pores is most preferable. However, the conditions required for densification are complicated, and it is economically necessary to obtain a material having no pores. And it is often difficult in the manufacturing process. Accordingly, as a result of intensive studies on the density required to obtain an orthodontic part having excellent mechanical properties, which is the object of the present invention, if the carbon and oxygen contents are satisfied, a density of 97% or more is obtained. It was clarified that various mechanical properties were satisfied.
Therefore, the relative density of the orthodontic part of the present invention is set to 97% or more.

The sintered body is used as an orthodontic part after post-processing such as surface polishing and shape modification. This orthodontic part is Ni,
It does not contain elements that cause allergy to the human body, such as Cr, and has higher mechanical properties than those made of ceramic or polymer resin. However, to such Warekake it does not occur, 2% or more preferably requires elongation of at least 3%, also the hardness (H _RV) is necessary 100-320.
This is because, when a strong force is applied to the component due to contact with food or the like during use, it is desirable to avoid cracking and deformation because the inside of the oral cavity is damaged by cracking and deformation.

The present invention determines the ranges of carbon content, oxygen content and relative density of the orthodontic parts, and utilizes a metal powder injection molding method to achieve these. This method can be realized by combining the raw materials and the conditions of each step. In this invention, it implements according to the following suitable conditions in each process. (1) Step of mixing a titanium raw material powder and a binder to obtain a mixture (2) Step of forming a mixture by injection molding to obtain a molded body (3) Step of removing the binder in the molded body and (4) Removing the binder Of obtaining a sintered body by sintering the compact

The method for producing the titanium raw material powder used in the present invention is not particularly limited. However, in order to obtain the target purity of the present invention, the purity and specific surface area of the titanium raw material powder,
The particle size is set as follows.

That is, the purity of the titanium raw material powder is an important property directly related to the purity of the product after sintering. Therefore, the carbon content and the oxygen content of the raw material powder are set to 0.25% or less and 0.6% or less, respectively, preferably 0.1% or less and 0.3% or less, respectively. Is desirably 99.5% or more. Since the oxygen content of the raw material powder tends to depend on the specific surface area of the powder, the specific surface area of the powder satisfying the oxygen content is generally 0.15 m ² / g or less.

The characteristics of these raw material powders are generally easier to obtain as the particle size of the powder is coarser. However, even if the purity is satisfied, it is difficult to obtain the orthodontic part of the present invention unless the relative density is 97% or more. In order to obtain a high density, the finer the particle size of the powder, the better. In addition, the microstructure of the contact part is important in order to obtain a small shape of the orthodontic part, especially a sufficient strength of the part that adheres to the teeth,
In order to obtain this at the time of molding, the presence of coarse particles is not preferable for realizing the present invention. Therefore, the particle size (average particle size) of the powder used in the present invention is desirably 25 μm or less.

As for the binder used in the present invention, it is preferable to use a binder having a low oxygen content because the transfer of oxygen to the titanium powder at the time of debinding is more easily prevented. In the present invention, the kind of the binder to be used is not particularly specified because it can be suppressed. Typically, EVA, PP, PE, P
Resins such as BMA; and further, these include WAX,
A plasticizer and the like can be included.

First, the above-mentioned titanium raw material powder and a binder are mixed. In this step, a kneader such as a general kneader or a general heating mixer can be used. The selection of the mixer can be arbitrarily selected according to the powder and binder characteristics to be used, and is not particularly specified in the present invention. preferable. For this purpose, it is important to apply a sufficient shearing force to the mixture during kneading and to incorporate a binder to improve the wettability with the surface of the metal powder.

Next, the mixture of the titanium raw material powder and the binder thus obtained is injection molded by an injection molding machine. In this molding step, since the physical properties of the mixture change depending on the physical properties and the mixing ratio of the titanium raw material powder and the binder, it is necessary to perform molding using a molding machine and molding conditions according to the physical properties. Not specified.

Generally, the mold used for molding is the same as the plastic mold, but the orthodontic part of the present invention has a fine and complicated shape. It is preferable to apply the molding technology of parts, and similarly, a mold needs a mechanism for smoothly operating a large number of slides. Also,
It is desirable that the shape of the back surface of the bonding portion be a shape including a part of a cylinder or a sphere in order to smoothly operate the slide of many fine parts and to enable sufficient bonding with the teeth.

The structure of the molding die of the present invention is not particularly limited as long as it can obtain a target shape. However, in order to satisfy economic efficiency and sufficient adhesion to teeth, the gate width is set to 1 mm using a hot runner or the like. It is desirable to do the following.

Next, the binder is removed from the obtained molded body. This step is not particularly limited because it depends on the selection of the binder. However, in general, it is necessary to remove the binder promptly so that the carbon contained in the binder does not stay in the titanium powder constituting the molded body or the floor plate of the molded body. Therefore, it can be said that it is desirable to remove at a relatively low temperature (for example, 100 to 350 ° C.).

Further, in order to accelerate the degreasing, it is effective to carry out the treatment under reduced pressure or in an inert atmosphere from the viewpoint of suppressing an increase in the oxygen and carbon contents. Further, it is also effective to place the powder in a reactive atmosphere or environment that accelerates the decomposition of the polymer resin constituting the binder in a relatively low temperature range in which the transfer of oxygen and carbon in the powder is difficult to proceed.

Finally, the compact from which the binder has been removed is sintered. A major problem in this process is how to suppress the increase in powder having a high affinity for oxygen and a large surface area. In particular, orthodontic parts are complicated in shape and therefore have a large surface area for their weight, and are apt to penetrate carbon, oxygen, etc., and sufficient properties cannot be obtained by known sintering methods. As a result of intensive studies on this problem by the inventors, the oxygen content of the sintered body after sintering is basically determined by how low the oxygen potential of the environment in which the compact after debinding is installed is kept. I got the conclusion. In order to keep the oxygen potential at the time of sintering low, it became clear that the furnace structure, the atmosphere, the material of the bottom plate, and the like had a great influence, and desirable conditions for realizing the present invention were obtained.

The heating method and atmosphere of the sintering furnace used in the present invention are not particularly limited. However, in order to suppress an increase in oxygen in the debindered (degreased) molded body, the structure is desirably sinterable in a vacuum or an inert gas atmosphere. In order to suppress these, it is desirable to further provide a container (preferably made of graphite) inside the furnace container and insert a degreased molded product into the container and perform sintering treatment. It is desirable that a substance capable of absorbing oxygen and carbon is provided as a getter in the vicinity of the molded body in the container. The amount and material of the getter are selected depending on the positional relationship with the molded body, the material of the floor plate, and the shape of the container. Was.

If necessary, the obtained sintered body is used after finishing processing such as surface polishing or shape modification, but the polished metal is glossy and has an aesthetic property of ceramic or polymer resin. Since it is inferior to the product, the surface can be modified by heat treatment or coating such as plating to change the state to a state close to the color of the tooth before use.

The surface can be modified by a method such as nitridation or oxidation by CVD, or plating by gold or a gold alloy. It is necessary to select a method that can satisfy the object of the present invention because the aesthetics can be improved by these techniques, but the biocompatibility is reduced due to the surface of the orthodontic parts having properties different from pure titanium.

Further, the effect of improving the surface hardness by the coating can be obtained, and the sliding property with the wire during orthodontic treatment can be improved.

[0035]

The present invention will be described in more detail with reference to the following examples.
Will be explained. (Example 1) The gas atomized pure titanium powder shown in Table 1 was used as the raw material.
Fee. Carbon and oxygen contents are determined by combustion analysis.
The average particle size is measured using a laser diffraction particle size distribution analyzer.
And the specific surface area was measured using the BET method.
About 30% by volume of thermoplastic resin (Mitsubishi Chemical
Seiko SB125, 50%), wax, (Japanese wax)
WAX130, 40%) Plasticizer (Nippon Rika Co., Ltd.)
Butyl phthalate, 10%) organic binder
And kneading at 130 ° C for 30 minutes using a pressure kneader.
And made a compound. The resulting compound
Measure the viscosity of the sample with a capillary-type viscosity measurement device.
As a result, the shear rate was 1216 at 150 ° C. ^-1When the viscosity is 1
100 Poise. Using this compound,
Orthodontics using an inline screw type injection molding machine
The product was molded. At the same time, pull for mechanical property measurement
A test piece was formed. Specifically, it is as follows.

(Molding conditions) The molding conditions were all set to the same condition A in the table. However, since the viscosity of the raw material compound differs depending on the raw material powder, only the injection pressure and the holding pressure during molding were changed and modified. Molding temperature 140 ° C Mold temperature 2
5 ° C.

The obtained molded body was placed in a reduced pressure atmosphere (10 to 10).
After heating to 200 ° C. in ⁻⁵ Torr), the temperature was raised to a maximum temperature of 280 to 450 ° C. for 12 hours in an argon gas stream to specifically remove the binder under the following conditions.

(Degreasing conditions) For degreasing, it is necessary to prevent oxidation of titanium powder from the atmosphere, to prevent intrusion of carbon and oxygen due to decomposition of the binder, and to reduce gas generation in the sintering furnace. is there. In degreasing condition A, the maximum temperature is 300 ° C, and in B, 350 ° C
C was 450 ° C. These conditions and atmosphere,
The properties of the degreased body are determined by a combination of conditions such as a heating rate and a binder type.

The debindered compact was placed in a sintering furnace on a smooth zirconia flooring plate, heated to 800 ° C. under a vacuum of 1 Torr or more, and then heated in argon gas under the following conditions. It was held at 1200 ° C. for 2 hours to perform sintering.

(Sintering conditions) In the condition A, the amount of Ti scrap getter charged was twice as much as the product weight, which was near the molded body, and then charged into a graphite box. In the condition B, the getter was set to a half of the product weight, and the same box as above was used. Condition C was performed under the condition that no getter or box was used.

The hardness of the obtained sintered parts and sintered test pieces was measured, and the mechanical properties were confirmed by the test pieces.

As a result, the oxygen content, the carbon content and the hardness of the part and the test piece were similar and coincided. Therefore, it was determined that mechanical properties equivalent to those of the test piece could be obtained. Table 1 shows the chemical composition, density, and mechanical properties of the obtained sintered body. The strength and elongation were measured with a dumbbell-shaped test piece using an autograph-type tensile tester. The hardness was measured with a micro Vickers hardness tester.

(Example 2) Table 2 shows a comparison with the conventional method. It is clear that the characteristics of the orthodontic part of the present invention are excellent methods satisfying mechanical characteristics and biocompatibility as compared with conventional ones. Compared to the ceramics and stainless steel parts of Comparative Examples 1 and 2, the aesthetics may be slightly inferior, but due to the excellent mechanical properties, there is little risk of breakage in the oral cavity. However, it is possible to avoid the possibility of carcinogenicity and allergicity due to the inclusion of Ni or the like such as stainless steel parts. Further, in the conventional attempts to apply titanium to orthodontic parts, it has been difficult to industrially produce titanium by the removal processing because of the poor machinability of titanium and the small and complicated shape of the part.
Similarly, in the production by metal powder injection molding, mechanical properties equivalent to those of ingots cannot be achieved, and it has been difficult to put them to practical use.

Table 2 shows the conventional production method again. These items 1 to 4 show the characteristics of general products manufactured by the respective companies.

The commercially available polymer resins and ceramics of Comparative Examples 1 and 4 are inferior to the examples of the present invention in that there is almost no elongation, and when the parts are broken, there is a danger of damaging the mouthpiece.

The components contained in the stainless steel parts of Comparative Examples 2 and 3 were substantially the same even if the processing method was different.
A material containing Ni and Cr is generally used to obtain corrosion resistance.
Excellent mechanical properties but may cause allergies.

Titanium is the most desirable material for achieving both mechanical properties and avoidance of allergy. However, as shown in Comparative Example 5, since the component shape is complicated and small, it is difficult to manufacture at a generally usable unit price when manufactured by cutting. Comparative Example 6 shows that the MI
As shown in the comparative example of Table 1, the characteristics of the titanium parts made of M are as follows.
It was difficult to use because of poor mechanical properties.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

The titanium orthodontic part of the present invention has a constant composition and density by using a metal powder injection molding method, so that its mechanical properties, bioadaptability and aesthetics are higher than those of the conventional one. Excellent and can be used without worrying about allergies and carcinogenesis.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ identification code FI C22C 14/00 (58) Fields investigated (Int.Cl. ⁶ , DB name) A61C 7/14 A61C 7/00 A61C 7/28 C61K 6/04 C22C 1/04 C22C 14/00

Claims (6)

(57) [Claims] (1) a step of mixing a titanium raw material powder and a binder to obtain a mixture; (2) a step of molding the mixture by injection molding to obtain a molded body; (3) a step of removing a binder in the molded body; 4) A titanium orthodontic part manufactured through a step of sintering a molded body from which a binder has been removed to obtain a sintered body, wherein the obtained sintered body has a carbon content of 0.25 wt% or less; Oxygen: 0.
Comprises 6 wt% or less has a composition comprising the balance Ti and inevitable impurities state, and are relative density of 97.0% or more, the hardness
Saga H _RV one hundred to three hundred and twenty, titanium orthodontic parts elongation, characterized in der Rukoto 2% or more. 2. The titanium raw material powder used has an average particle size of 25.
The orthodontic part made of titanium according to claim 1, which has a carbon content of 0.25 wt% or less and an oxygen content of 0.6 wt% or less. Wherein the step of removing the binder, titanium orthodontic component according to claim 1 or 2 carried out in an inert atmosphere or under reduced pressure. The method according to claim 4 wherein the step of sintering the molded body to remove the binder, under vacuum or under an inert atmosphere, titanium teeth according to any one of claims 1 to 3 carried out in the coexistence with getter material Straightening parts. 5. The titanium orthodontic part according to claim 4 , wherein the step of sintering the molded body from which the binder has been removed is carried out by further placing the molded body in another container in a sintering furnace. 6. A method of mixing a titanium raw material powder and a binder.
Engineering a to obtain a mixture step (2) mixture to obtain a molded article molded by injection molding
Extent and (3) removing the molded body of the binder process and (4) binder by sintering the molded body was removed sintered body
A titanium orthodontic part manufactured through a process of obtaining
The sintered body thus obtained has a carbon content of 0.25% by weight or less and an oxygen content of 0.2% by weight.
6% by weight or less, from residual Ti and unavoidable impurities
Having a relative density of 97.0% or more,
The surface of the compact after the sintering is modified.
Titanium orthodontic parts.