JPH04200460A - Dentition orthodontic component and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an orthodontic component made of ceramics and a method for manufacturing the same.

(Prior Art) Conventionally, translucent aluminum oxide products have been used as ceramic orthodontic parts that are bonded to tooth surfaces because of their good appearance.

However, since orthodontic parts have three-dimensionally complex shapes, conventional ceramic orthodontic parts are made by sintering ceramic powder after bush-forming, and then cutting. It was manufactured by.

Also, aluminum oxide alone is not translucent, so a small amount of magnesium oxide is added as a sintering aid to translucent aluminum oxide products.

The role of magnesium oxide is to suppress the growth of crystal grains in the final stage of sintering and promote the disappearance of pores contained within the sintered body.

However, in the conventional aluminum oxide products mentioned above, there is a large variation in crystal grain size, the size of unavoidable residual pores is large, and it is not possible to obtain a sufficiently satisfactory degree of translucency. It also lacked strength. The cause of these problems is thought to be that conventional aluminum oxide products are molded using a press molding method. In other words, in the press molding method, pressure is not applied uniformly to the compact, and the packing density of the metal oxide powder varies in various parts of the compact.As a result, the density (pores) in the sintered final product (sintered compact) (corresponding to the size and number of crystals) and grain size vary in each part, so it is difficult to think about it. In addition, with press forming, it is difficult to directly obtain a complex three-dimensional shape, so cutting is performed after sintering, or hair cracks may occur on the surface of the sintered body during cutting. However, this also caused the destruction of orthodontic parts during use.

(Problem to be solved by the invention) Therefore, instead of using the press molding method, by the injection molding method,
A method for manufacturing orthodontic parts is being considered. In this method, a mixture of ceramic powder and an organic binder is molded into a predetermined shape by injection molding, the binder is removed from this molded body, and the final product is finished by sintering, which requires no mechanical processing. Orthodontic components with three-dimensionally complex shapes are manufactured without any process.

However, even with this injection molding method, only products with unsatisfactory translucency and mechanical strength are obtained. This is thought to be caused by the large amount of binder used for injection molding. That is, depending on the type of binder used, the binder is removed after injection molding, and remains even after sintering, resulting in a decrease in translucency. Also, the use of a large amount of binder makes it difficult to uniformly disperse the magnesium oxide used in a small amount into the aluminum oxide, resulting in unsatisfactory light transmittance of the product.

Therefore, an object of the present invention is to provide an orthodontic component with excellent translucency and mechanical strength, and a method for manufacturing the same.

Another object of the present invention is to provide a method for manufacturing orthodontic parts with excellent translucency and mechanical strength using an injection molding method.

(Means for achieving the object) According to the present invention, magnesium oxide 0.02 to 0.08
An orthodontic component is provided, characterized in that it is made of a sintered body having a composition in which the weight is 1% and the balance is aluminum oxide, and the crystal grain size is 5 to 40 μm.

Further, according to the present invention, a metal oxide mixed powder of magnesil oxide and aluminum oxide prepared to have a magnesium oxide content of 0.02 to 0.08% by weight is added with a glass transition temperature of 10% by weight.
A step of uniformly dispersing magnesium oxide by mixing acrylic resin at a temperature of 0° C. or lower to a total weight of 1 to 10 96; A binder material consisting of a wax with a temperature of 50 to 90°C and a thermoplastic plastic with a melt flow rate of 100 to 300 g/10 minutes is used, and the total amount of the binder material and the acrylic resin is 35 to 70% by volume of the total. a step of injection molding the kneaded material into a molded object of a predetermined shape; a step of removing the acrylic resin and the binder material from the molded object; and a step of removing the acrylic resin and the binder material from the molded object. The molded body from which the material has been removed is heated to 1600 to 2
A method of manufacturing an orthodontic component is provided, comprising the step of firing at 000°C.

The orthodontic component of the present invention has excellent light transmission f1 and mechanical strength, and as described above, it is manufactured by injection molding using a specific thermoplastic as a binder material. be.

Metal oxide mixed powder In the present invention, a mixed powder of magnesium oxide and aluminum oxide is used as a starting material.

The composition of this mixed powder is magnesium oxide powder or 0.0
It is important that the amount is 2 to 0.08% by weight, with the remainder being aluminum oxide powder. If the composition is outside this range, satisfactory translucency cannot be obtained. That is, in order to exhibit translucency, it is necessary that the relative density of the sintered body obtained by sintering, which will be described later, be at least 99%. As mentioned above, magnesium oxide suppresses the growth of crystal grains in the final stage of sintering, thereby promoting the disappearance of bores inside the grain boundaries and improving the sintered density, and also increases the size of the crystal grains. It acts to equalize the height. Therefore, magnesium oxide plays a major role in the "translucent property". For example, a magnesium oxide content of less than 0.02% by weight is insufficient to exhibit such an effect, and the density of the sintered body is not high enough.
It does not have sufficient translucency to be used as orthodontic parts. If the amount exceeds 0.08% by weight, magnesium oxide or a composite oxide of magnesium oxide and aluminum oxide will be formed at the grain boundaries of the sintered body, causing light scattering and reducing the translucency and mechanical properties. The strength decreases, making it unsatisfactory as an orthodontic component.

In the present invention, the magnesium oxide powder, aluminum oxide powder, etc. used for preparing this mixed powder are as follows:
It is possible to use commercially available products, or it is preferable to use highly purified products in order to exhibit translucency. In addition, in order to improve the sintered density and express good translucency, the average particle size of these should be 0, ■-ll1
It is desirable to use one within the range of m. If a powder with an average particle size larger than 1 μm is used, it will be difficult to increase the density of the final product, sintered body, and the translucency may be unsatisfactory. If this method is used, the amount of binder used for injection molding increases, and as a result, the initial packing density of the ceramic powder becomes low, which may make it difficult to obtain a high-density sintered body.

Preparation of a kneaded material for injection molding In the present invention, a mixed material for injection molding is prepared by adding an acrylic resin to the metal oxide mixed powder described above to form a uniform mixture, and then adding a binder material and kneading. It is used for the preparation of

The acrylic resin used here has a surfactant-like effect, and by blending this acrylic resin before mixing with the binder material, the magnesium oxide powder becomes the aluminum oxide powder. The advantage of uniform dispersion is achieved. This acrylic resin is 1 to 10% based on the total amount of metal oxide powder.
It is used in proportions by weight, in particular from 2 to 6% by weight. If the amount of acrylic resin used is less than 1% by weight or more than 10% by weight, magnesium oxide will not be uniformly dispersed in the aluminum oxide powder, and as a result, the final product (
The translucency of the sintered body varies depending on the part.

In addition, this acrylic resin has a glass transition temperature (T
g) or below 100°C. If an acrylic resin with a glass transition temperature higher than 100° C. is used, the molded product obtained by injection molding, which will be described later, will be hard and brittle, leading to problems in handling. Specific examples of acrylic resins include methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate,
Cyclohexyl acrylate, 2-ethylcyclohegycyl acrylate, propyl acrylate, hydroxyethyl acrylate/L, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, 2-ethyl methacrylate/L Polymers such as hexyl, t-butyl methacrylate, glycidyl methacrylate, 2-hydroxyethyl methacrylate, and lauryl methacrylate can be mentioned, and these can be used alone or in a blend of two or more,
Furthermore, two or more of the above-mentioned polymers can be copolymerized and used.

The above-mentioned acrylic resin and metal oxide powder can be mixed by various methods known per se, or the most suitable method is to prepare granular powder using a spray dryer, which is often used in fine ceramics. .

The mixture containing the acrylic resin is mixed with a binder material to form a kneaded material for injection molding. The binder material used is one that is effective in injection molding as described below, and has a softening point (JIS K 7206) or 50
It consists of waxes in the range of ~90°C and thermoplastics in the range of 100-300 g/10 min.

The above-mentioned waxes contribute to fluidity during injection molding, and if their softening point is lower than 50°C, the cycle time of injection molding will be longer, and the waxes will easily soften, making it difficult to work during molding. This may cause inconveniences such as poor sexual performance. Further, if the softening point is higher than 90° C., the fluidity decreases and the thermal decomposition point increases, resulting in a decrease in binder removal properties. Examples of such waxes include paraffin wax, microcrystalline wax, low molecular weight polyester wax, modified wax, and atactic polypropylene.

Furthermore, the thermoplastic plastic contributes to maintaining the shape of the molded product after injection molding, and has an MFR of 100g/
If it is less than 10 minutes, the injection moldability will be unsatisfactory, and if it is more than 300 g/10 minutes, the strength and shape retention of the injection molded product will be poor.

Examples of such thermoplastic plastics include polyethylene, polypropylene, ethylene-vinyl nitride copolymer, ethylene-acrylate copolymer, and polystyrene.

The ratio of these waxes and thermoplastics varies depending on the type, and generally the ratio is 4:1 to 1 on a weight basis.
14, particularly preferably 3.1 to 13.

The binder material made of the waxes and thermoplastic plastic mentioned above needs to be used at a ratio of 35 to 70% by volume based on the kneaded material, based on the total amount with the acrylic resin. If it is less than 35% by volume, the fluidity of the mixed material will decrease and injection molding will be difficult, and if it exceeds 75% by volume, it will be very difficult to remove the binder and the translucency of the final product will decrease. cause inconvenience.

Further, kneading with the binder material can be easily carried out using a kneading device such as a kneader 1 or various mixers.

Injection molding Next, the kneaded material prepared in the above step is injected into a mold having a desired mold to obtain a molded product having the desired shape.

This injection molding can be carried out using the equipment and equipment used for ordinary injection molding of plastics as they are. Generally, the injection conditions are preferably heating temperature of 80 to 200° C., injection pressure of 500 to 2000 kg, and 10 f.

In the case of press molding, the compact is uniform (no stress is applied), the packing density of the ceramic powder is uneven, and the resulting sintered compact exhibits unsatisfactory translucency and mechanical strength. Since the present invention employs injection molding, such problems can be effectively avoided.

Binder Removal Next, the molded body is debindered to remove the binder material or the acrylic resin and binder material contained in the molded body.

This removal of the binder can be easily carried out by heating to a temperature higher than the decomposition temperature of the binder, etc., usually in the air or in an inert atmosphere such as nitrogen gas.

Firing treatment Following the binder removal described above, a firing treatment is performed.

In the present invention, it is necessary to perform this firing in a hydrogen atmosphere or in a vacuum. In general, in the final stage of firing, there are usually small bores within the grains, and it is important to eliminate these bores or improve the light transmission. In other words, when firing in hydrogen, some hydrogen will remain in the bore, but since hydrogen has excellent diffusivity, it can easily be discharged from the bore through grain boundaries and from the fired body. be done. As a result of this, the bore easily disappears due to ion diffusion. Furthermore, since there is almost no gas inside the bore in a vacuum, the bore is similarly easily annihilated by the diffusion of ions. Therefore, ceramics with excellent translucency can be obtained by firing in a hydrogen atmosphere or in a vacuum.

The firing temperature is 1,600 to 2,000℃, preferably 17
The temperature range is 00 to 1900°C. If the temperature is lower than 1600°C, the relative density of the obtained fired body will not be sufficiently improved, resulting in a decrease in translucency, and if the temperature is lower than 2000°C
When firing at a higher temperature, magnesium evaporates from the surface of the fired product, and as a result, the crystal grain size near the surface becomes abnormally large, or the relative density of the surface of the fired product does not improve, resulting in transparent It becomes white without becoming photosensitive.

Furthermore, the grain size of the sintered body is influenced by the sintering temperature and time when the method of the present invention is used. For example, when the firing temperature is set to 1,600 to 2,000°C according to the present invention,
It is preferable that the firing time does not exceed a maximum of 8 hours, particularly 4 to 7 hours. If the sintering time is too short, the crystal grain sizes will not be uniform, and if the sintering time is too long, abnormal grain growth will occur and the crystal grain sizes will also not be uniform.

Such firing is performed to such an extent that the relative density of the fired body is 99% or more.

Orthodontic parts The orthodontic parts of the present invention thus obtained have a composition of 0.02 to 0.08% by weight of magnesium oxide and the balance aluminum oxide, and have a crystal grain size of 5 to 40 μm. Due to its high magnesium content and crystal grain size, it has excellent translucency and mechanical strength. For example, in order to exhibit excellent light transmittance, it is desirable that the crystal grain size be large and uniform so that visible light is not scattered at grain boundaries. In this sense, single crystals are preferable. When single crystals break, they cause wall-to-wall fracture, resulting in very sharp surfaces, which can cause problems such as injuring the patient's mouth. It is unsuitable as an orthodontic component. Moreover, the price is also very high.

On the other hand, in order to increase mechanical strength, it is desirable that the crystal grain size is small. Since the crystal grain size of the sintered body constituting the orthodontic component of the present invention is in the range of 5 to 40 μm, both light transmittance and mechanical strength are satisfied.

(Example) Examples 1 to 5 Using magnesium oxide powder with an average particle size of 0.15 μm and aluminum oxide powder with an average particle size of 0.53 μm, the magnesium oxide content was varied as shown in Table 1. A mixed powder was prepared by changing the method.

Next, polybutyl methacrylate (glass transition temperature: 20°C) as an acrylic resin was added to the mixed powder so that the total amount was 5% by weight, and the mixture was granulated using a centrifugal spray dryer to prepare a uniform dispersion. did.

Each of these uniform dispersions contains a binder material containing paraffin wax (manufactured by Nippon Seiro Co., Ltd., 125, softening point 50°C) and low density polyethylene (manufactured by Sumitomo Chemical, Sumirikisen G308) in a weight ratio of 3:1. were added in a total amount of 40% by volume with the above acrylic resin, and a kneaded material for injection molding was prepared using a planetary mixer.

Using this kneaded material, the injection temperature was 90°C using an injection molding machine.
And injection molded under the conditions of injection pressure 600 kg/enr, a disc-shaped molded body with a diameter of 10 mm and a thickness of 2 mm (for translucency test), and a plate with a thickness of 3 mm, a width of 4, and a length of 25 mm. A shaped body (for measuring mechanical strength) was molded.

Next, the molded body was heated in an air stream to remove the binder (heating temperature: 500°C), and then fired in a hydrogen stream at a temperature of 1800°C for 6 hours to create a sintered body. (Example 1).

Table 1 shows the distribution of crystal grain sizes of the obtained sintered body.

Further, the translucency and mechanical strength of the sintered body were evaluated by the following methods.

Translucency: After polishing the surface of the sintered body obtained from the molded body for translucency testing with diamond and making the thickness uniform, it was measured using an absorbance meter for in-line transmission in the visible light region (300 nm - 110,100 nm). The measurement results are shown in Table 1.

The second in-line transmittance indicates the ratio of the intensity of transmitted light incident within a certain angle to the intensity of incident light when a parallel light beam of a certain intensity is incident on a sample of a certain thickness.

Mechanical strength: The sintered body obtained from the molded body for mechanical strength is made into a plate with a thickness of 2 mm.
The bending strength of each plate was measured after adjusting the dimensions to 4 mm in width and 20 mm in length. The results are shown in Table 1.

In addition, sintered bodies were prepared in the same manner as in Example 1, except that the magnesium oxide content was varied as shown in Table 1.
Examples 2-5). Table 1 shows the evaluation results of the crystal grain size distribution, translucency, and mechanical strength of the obtained sintered body.

Comparative Examples 1 to 5 Press molding (press pressure 1 ton/c) instead of injection molding
A sintered body was produced in exactly the same manner as above except that step m) was performed (Comparative Example 1).

Magnesium oxide content: 0.01% by weight and 1.0% by weight
A sintered body was produced in the same manner as in Example 1, except that % of metal oxide mixed powder was used (Comparative Example 2.3).

Furthermore, in Comparative Example 4, the sintering temperature was changed to 180°C in Example 1.
The sintering time at 0°C was 10 hours, and in Comparative Example 5, the sintering temperature was set at 2050°C for 6 hours, and the grain size distribution was outside the range of the present invention. A sintered body was created in the same manner as in Example 1.

Table 1 shows the evaluation results of the crystal grain size distribution, translucency, and mechanical strength of the obtained sintered body.

Table 1 Comparative Example 1 This is an example in which id press molding was performed.

The in-line transmittance is a measured value at a plate thickness of 1r+m.

Examples 6-9. Comparative Examples 6 to 10 The molds were changed using methods corresponding to Examples 1 to 4 and Comparative Examples 1 to 5, respectively, and the perspective view in Figure 1 and the sectional view in Figure 2 (A-A in Figure 1) were used. A sintered body in the shape of an orthodontic part that is often used in practice as shown in the cross section was prepared, and its translucency and mechanical strength were evaluated.

In this case, for translucency, in-line transmittance is measured from the arrow direction in Figure 2, and for mechanical strength,
Force was applied at a constant speed from the direction of the arrow, and the maximum strength at that time was evaluated. The results are shown in Table 2.

Table 2 Comparative Example 6 (This is an example in which surface press molding was performed.

Inline transmittance is 1t, measured value at 2.6 old plate thickness.

(Effects of the Invention) According to the present invention, by injection molding, it is possible to supply orthodontic components that are complex-shaped products with excellent translucency and mechanical strength.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the shape of the orthodontic component created in the example. FIG. 2 is a cross-sectional view of the orthodontic component shown in FIG.
It is.

Claims (2)

[Claims] (1) An orthodontic component comprising a sintered body having a composition of 0.02 to 0.08% by weight of magnesium oxide and the balance being aluminum oxide and having a crystal grain size of 5 to 40 μm. (2) Acrylic resin with a glass transition temperature of 100°C or less is added to the metal oxide mixed powder of magnesium oxide and aluminum oxide prepared so that the magnesium oxide content is 0.02 to 0.08% by weight. 1-10% by weight of
A step of uniformly dispersing magnesium oxide by mixing the magnesium oxide powder uniformly, adding a wax having a softening point of 50 to 90°C and a melt flow rate of 100 to 300 g/10 to the mixed powder in which magnesium oxide powder is uniformly dispersed. a step of adding and kneading a binder material consisting of a thermoplastic plastic such that the total amount of the binder material and the acrylic resin is 35 to 70% by volume of the whole; a step of injection molding into a molded object; a step of removing the acrylic resin and the binder material from the molded object; and a step of molding the molded object from which the acrylic resin and binder material have been removed in a hydrogen atmosphere or in a vacuum for 1600 minutes. ~2
A method for manufacturing orthodontic parts, comprising the steps of firing at 000°C.