JPH0685787B2 - Method of manufacturing orthodontic bracket - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an orthodontic bracket which is used in orthodontics and has excellent aesthetics and high strength.

[Prior Art] Since a bracket bonded to each tooth is strongly pulled by a metal wire or the like during orthodontics, it is required to have high strength and high toughness so as to prevent breakage or chipping. Conventionally, stainless steel has been widely used as an orthodontic material that meets these conditions, but stainless steel has a drawback in that it has metallic luster and is visually conspicuous and lacks aesthetics.

Therefore, as a means for solving this drawback, Japanese Patent Laid-Open No. 64-258
Japanese Patent Publication No. 47 discloses an orthodontic bracket using single crystal alumina. Japanese Unexamined Patent Publication No. 64-46451 discloses an orthodontic bracket using single crystal zirconia containing yttria. In addition,
Japanese Unexamined Patent Publication No. 64-52448 discloses an orthodontic bracket using ceramics having spinel type crystals composed of magnesium oxide and aluminum oxide.

[Problems to be Solved by the Invention] However, although the single crystal alumina described in JP-A-64-25847 has excellent transparency, it is aesthetically pleasing, but the processing cost is high and its strength is high. Directional,
Since it has low toughness, it has the drawback of being easily cracked or chipped.

Further, the single crystal zirconia containing yttria described in JP-A-64-46451 and the spinel type crystal ceramics described in JP-A-64-52448 have transparency,
Although it is excellent in aesthetics, it has the drawback of low mechanical strength and risk of fracture.

Therefore, an object of the present invention is to provide a method for manufacturing an orthodontic bracket having high aesthetics, high toughness, and high mechanical strength.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and a method for manufacturing an orthodontic bracket according to the present invention includes yttria in an amount of 1.7 to 3.2 mol% and a crystalline system. Is a step of molding a zirconia powder composed of monoclinic crystals and tetragonal crystals to obtain a molded body, and a step of sintering the molded body at 1200 to 1400 ° C. to produce a zirconia sintered body (B). And a step (C) of heat-treating the sintered body at 1000 to 2000 atm at 1100 to 1400 ° C.

Furthermore, Co, Cr, Mn, Ce, Cd, Sr, Fe, C in the zirconia powder
0.5w total of one or more of u, Zn, Sb, V, Ni oxides
It is characterized by containing t% or less.

Hereinafter, the present invention will be described in detail.

The method for manufacturing a bracket of the present invention includes the above-mentioned step (A),
It includes (B) and (C).

Step (A) Step (A) is a step of forming a zirconia powder containing yttria in an amount of 1.7 to 3.2 mol% and having a crystal system of monoclinic and tetragonal, to obtain a formed body. Is done.

A high-purity aqueous solution of zirconium oxychloride containing no harmful elements such as arsenic and mercury and an aqueous solution of yttrium chloride were used, and the yttria concentration in terms of oxide was 1.7-3.2mo.
Mix to give 1%, and use the well-known coprecipitation method, hydrolysis method,
The precipitate obtained by the thermal decomposition method is dried, calcined at 800 to 1000 ° C., and then pulverized by a ball mill, an attrition mill or the like to obtain a raw material powder. Co, Cr, Mn, Ce, Cd, Sr, Fe, C contained in the bracket to reduce the coloring or sintering temperature.
Regarding the oxides of u, Zn, Sb, V, and Ni, if necessary, they may be mixed at the same time as the above aqueous solution, for example, as an aqueous solution of a water-soluble salt such as chloride to form an oxide in the bracket manufacturing process. it can. The raw material powder thus obtained is composed of monoclinic crystals and tetragonal crystals, and is a powder having good sinterability in which constituent elements having an average primary particle size of 0.1 μm or less are uniformly distributed. Further, the same raw material powder can be obtained by a metal alkoxide method, a sol-gel method, or a vapor phase method.

Next, the above raw material powder is molded using a known molding method such as a rubber pressing method, a mold molding method, an extrusion molding method, an injection molding method,
Obtain a molded body.

The molded body produced by the rubber pressing method, the die molding method, and the extrusion molding method may be calcined before the main sintering in the step (B) and primary processed into the shape of an orthodontic bracket. it can. In addition, when the molded body is produced by injection molding, the shape of the molded body is the shape of the desired orthodontic bracket, and therefore no post-processing is required.

Step (B) In the step (B), the molded body obtained in the step (A) is treated with 1200
This is a step of producing a zirconia sintered body by sintering at ˜1400 ° C., and is performed as follows, for example.

After degreasing the molded body obtained in step (A), 20 to 100 ° C
The temperature rises from 1200 to 1400 ℃ at a heating rate of
Sintering is performed by holding for 10 minutes to 3 hours, cooled to about 600 ° C. at a rate of 200 to 500 ° C./hour, then naturally cooled and cooled to room temperature to produce a zirconia sintered body. If the sintering temperature is less than 1200 ° C, the sintering is insufficient, and if it exceeds 1400 ° C, it is particularly noticeable for the material with a low yttria content and high toughness. The tetragonal crystal becomes unstable, a dense sintered body cannot be obtained, and corrosion resistance also deteriorates. Thus, a sintered body having a desired composition, crystal structure and crystal grain size can be obtained. However, this sintered body has a porosity of 0.7 to 1.7%, and it is difficult to obtain sufficient mechanical strength and aesthetics.

Therefore, the next step (C) is required.

Step (C) In the step (C), the sintered body obtained in the step (B) is processed to 1000
This is a process of heat treatment at 1100 to 1400 ° C. under 2,000 atmospheres.

This step (C) is called HIP treatment (hot hydrostatic treatment) and is preferably carried out for 10 minutes to 3 hours in the present invention. The HIP treatment crushes the pores of the sintered body to make it dense with a porosity of 1% or less, and further improves the incompleteness of crystal grain boundaries, resulting in improved translucency and other aesthetics. The HIP process must be performed in a non-reducing atmosphere. This is because zirconia is colored black or brown when reduced. In addition, if carbon or carbide is present in the atmosphere, similar coloring may be observed, so it should be avoided.

Next, if necessary, the HIPed sintered body is processed into a desired orthodontic bracket.

According to the present invention, an orthodontic bracket having high toughness and mechanical strength can be obtained by using a zirconia sintered body as a material. That is, when this zirconia sintered body receives a stress from the outside, a part of the tetragonal zirconia component undergoes a phase transformation to a monoclinic structure locally, thereby relaxing the energy for destroying the material (stress-induced The transformation strengthening mechanism) acts on the phase transformation part, so that high toughness and high strength are developed.

In the zirconia sintered body that constitutes the bracket for orthodontics, the average crystal grain size of tetragonal zirconia is 0.12 to 0.5μ.
It is preferably m. The reason is that if the thickness is less than 0.12 μm, the phase stability of the tetragonal zirconia is too good, so that the stress-induced transformation strengthening action is difficult to work and it is difficult to form a dense sintered body. Phase stability deteriorates, and corrosion resistance decreases when immersed in high temperature steam during sterilization or in body fluid for a long time.
This is because when stress is applied to the material, a phase transformation occurs along the crystal grain boundaries throughout the material, so that grain boundary destruction may occur.

And as described above, the average crystal grain size of tetragonal zirconia is 0.
If it is 12 to 0.5 μm, the phase stability of the tetragonal crystal is high, so that the tetragonal zirconia content is practically preferably 50 mol% or more in order for the stress-induced transformation strengthening mechanism to act effectively.

The porosity of the zirconia sintered body forming the bracket is preferably 1% or less as described above. The reason is that if it exceeds 1%, the strength is lowered, the light-transmitting property is not obtained, the phase stability of the tetragonal zirconia is deteriorated, and the corrosion resistance is lowered. Although the physical properties of the zirconia sintered body vary depending on the properties of the raw material powder, the molding conditions, the sintering temperature, the sintering conditions such as pressure, the zirconia sintered body having the above-mentioned performance has a content of yttria which is a stabilizing substance. , As described above, when it is 1.7 to 3.2 mol%. 1.7mo
If it is less than 1%, tetragonal zirconia is unstable and a dense sintered body cannot be obtained, and if it exceeds 3.2 mol%, the toughness is remarkably reduced.

According to a preferred embodiment of the present invention, Co, Cr, Mn, Ce, Cd, Sr, F
Sum of one or more of e, Cu, Zn, Sb, V, Ni oxides
By containing 0.5 wt% or less, blue, pink, yellow,
It can be colored green or the like. Saturation, hue, and brightness are controlled by the type and content of oxides, but 0.5w
If it exceeds t%, the color tone becomes dark, which is not preferable. Also C
The sintering temperature can be lowered by adding a small amount of oxides such as r, Ni, Cu, Mn, and Zn to the raw material powder, and the average crystal grain size of tetragonal zirconia of 0.12 to 0.5 μm described above can be obtained. A sintered body can be easily obtained.

The hardness of the zirconia sintered body that constitutes the bracket is 900-1250 kg / mm ² in terms of Vickers hardness, which is considerably softer than that of alumina, but in some patients the bracket comes into contact with the mating teeth and the relationship between the tooth quality and the alignment of teeth. Since it may abrade the opposing teeth, the hardness is softer than natural teeth or close to the hardness of natural teeth (substantially Vickers hardness 100-700 kg / m
The wear can be prevented by providing the coating layer made of the material of m ² ). If the thickness of this coating layer is less than 50 μm, the coating layer will be worn away, and if it exceeds 300 μm, there will be inconvenience such as peeling from the bracket sintered body.
50-300 μm is good. As the coating layer, a polymer resin such as epoxy resin or polyurethane resin is used alone or alumina,
A mixture of inorganic material powder filler such as magnesia and silica, and crystallized glass obtained by breaking out fine crystals of mica are used.For example, direct dip coating, brush coating or epoxy adhesive is used for zirconia firing. Covered with a body.

EXAMPLES Next, the present invention will be described in more detail based on examples.

Example 1 Step (A) A zirconia powder containing 2.5 mol% yttria and a purity of 99.5% was mixed with 0.1 wt% of an aqueous solution of cadmium chloride having a purity of 98% in terms of oxide to remove water by evaporation. After that, it was fired at 950 ° C. to prepare a raw material powder. The powder was composed of monoclinic zirconia and tetragonal zirconia, the tetragonal zirconia content was 54.3%, and the specific surface area was 15 m ² / g.

Next, the above raw material powders spheroidized by using a spray dryer were molded into a bracket shape and a test piece shape for measuring physical properties by a mold molding method to obtain a molded body.

Step (B) The obtained molded body is heated in an electric furnace at a temperature rising rate of 100 ° C./hour for 140
Raise the temperature to 0 ° C, hold at that temperature for 2 hours and sinter
It was cooled to about 600 ° C. at a rate of ° C./hour and then cooled to room temperature in the furnace. The specific gravity of this sintered body is 6.0, that is, the porosity is
It was 1.6%.

Step (C) The pressure of this sintered body is 2000 in argon gas containing 1% oxygen.
HIP treatment was performed at 1400 ° C. for 90 minutes under atmospheric pressure. as a result,
The tetragonal zirconia content of the sintered body was 95 mol%, the average particle size was 0.45 μm, and the specific gravity was 6.09 (porosity 0.2%). The bracket-shaped sintered body was barrel polished to a glossy yellow bracket. It was made. The bending strength of the test sintered body was measured by JIS R1601, and the fracture toughness was measured by the IM method using Vickers indentation. Met.

Example 2 Step (A) An aqueous solution of zirconium oxychloride having a purity of 99.5% or more and an aqueous solution of yttrium chloride having a purity of 99.5% were prepared so that the yttria concentration was 3.0 mol% in terms of oxide, and the total amount of oxide was converted. Cobalt oxide concentration 0.3 wt%, copper oxide concentration
A cobalt chloride aqueous solution having a purity of 98% and a copper chloride aqueous solution having a purity of 98% are added and mixed so as to be 0.2 wt%, and a precipitate obtained by adding an aqueous ammonia solution is dried, crushed and baked at 1000 ° C., Water was added and the mixture was pulverized with a zirconia ball mill for 24 hours. The raw material powder thus obtained was composed of monoclinic zirconia and 68 mol% tetragonal zirconia and had a specific surface area of 10 m.
It was ² / g.

Next, the raw material powder was molded by a rubber press method at a hydrostatic pressure of 2 ton / cm ² to obtain a molded body.

Step (B) The obtained molded body is heated in an electric furnace at a heating rate of 100 ° C./hour for 120 hours.
Raise the temperature to 0 ° C, hold at that temperature for 2 hours and sinter
It was cooled to about 600 ° C. at a rate of ° C./hour and then cooled to room temperature in the furnace. The content of tetragonal zirconia in this sintered body is 85 mol%, the average particle size is 0.2 μm, and the specific gravity is 6.02 (in porosity).
1.3%).

Step (C) This sintered body was ground into a bracket shape and a test piece for measuring physical properties, and subjected to HIP treatment at 1200 ° C for 90 minutes, resulting in a specific gravity of 6.1.
(Porosity is almost 0). The bracket-shaped sintered body was barrel-polished to produce a blue bracket having a translucent gloss. The bending strength of the test sintered body was measured according to JIS R1601, and the fracture toughness was measured according to the IM method.
a, Met.

Example 3 The bracket and the test piece for measuring physical properties produced in Example 2 were dipped in a liquid commercial polyurethane resin (RU-39 manufactured by Nippon Polyurethane Co., Ltd.) in which 10% by weight of the zirconia raw material powder produced in Example 2 was dispersed. After coating and curing, the surface has a thickness of 120 μm and a Vickers hardness of 150 kg / m.
A glossy bracket was created that formed a m ² coating layer to prevent abrasion of natural teeth. Strength of material due to coating layer formation,
There was no change in toughness.

Examples 4 to 11 Tables showing the material properties of brackets produced in the same manner as in Example 2 by changing the composition ratio, the sintered body firing temperature, and the HIP treatment temperature were used.
Shown in 1. The results of Examples 1 to 3 are also shown in Table-1.

[Effects of the Invention] As described above, according to the present invention, high toughness and high strength are less likely to cause breakage or chipping, and moreover, the color tone is closer to that of a natural tooth than that of metal, and a transparent feeling is obtained. Therefore, it is possible to manufacture an orthodontic bracket that is excellent in aesthetics, can form a coating layer as necessary, and can prevent wear of the opposing teeth.

Claims (3)

[Claims] 1. A step (A) of molding a zirconia powder containing 1.7 to 3.2 mol% of yttria and having a crystal system of monoclinic and tetragonal to obtain a molded body, and the molded body of 1200 to 1400. And a step (B) of producing a zirconia sintered body by sintering at 1000C, and a step (C) of heat-treating the sintered body at 1100 to 1400 ° C under 1000 to 2000 atm. Manufacturing method of orthodontic bracket. 2. A zirconia powder containing Co, Cr, Mn, Ce, Cd, Sr, Fe, C.
0.5w total of one or more of u, Zn, Sb, V, Ni oxides
The method for manufacturing an orthodontic bracket according to claim 1, wherein the content is t% or less. 3. The method for manufacturing an orthodontic bracket according to claim 1, wherein a coating layer is provided on the sintered body after the step (C).