JPH0541585B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plaster mold material for use in molding a denture base by compression molding using a thermoplastic resin.

Conventionally, methods for manufacturing denture bases using compression molding methods include molding using a mixture of acrylic monomers and polymers, followed by polymerization at room temperature or under heating; however, compression molding methods using thermoplastic resins is not known about. The present inventor developed the compression molding method and filed a patent application earlier.
56-99892).

The method is to place the thermoplastic resin for the denture base on the plaster mold in the lower flask, place it in a constant temperature heating tank, soften it with hot air, then fit it with the plaster mold in the upper flask and perform compression molding. This is the way to obtain.

In the conventional compression molding method using a mixture of acrylic monomers and polymers, a rice cake-like mixed resin is put into a prepared mold, the top and bottom of the flask are closed, and the flask is placed in a flask press. Polymerization is carried out at room temperature or by heating, but since the boiling point of acrylic monomers is 100°C, polymerization is usually carried out at temperatures below 100°C. Therefore, the heat resistance of mold materials for denture base molding is sufficient at 100°C, and materials with relatively high heat resistance such as alpha-type hemihydrate gypsum, beta-type hemihydrate gypsum, silicone-based materials, and agar were used. .

However, in the compression molding method using the thermoplastic resin, it is necessary to heat and soften the thermoplastic resin on the plaster mold in the lower flask, so the temperature of the plaster mold is also raised to 200°C to 400°C. Therefore, a material that can withstand temperatures of approximately 400°C is required for the plaster mold.
In the above-mentioned hemihydrate gypsum silicon-based materials, agar, etc.
It was found that when heated to 200℃ to 400℃, there was an extremely large decrease in strength and rigidity, making it unusable.

The object of the present invention is to provide a plaster mold that has good moldability in the above-mentioned compression molding method, that is, can withstand pressure molding at a temperature that softens the thermoplastic resin, and that allows the molded denture base to be easily taken out after cooling. The goal is to provide materials for

As a result of research, the present inventors have discovered that good results can be obtained by using a mixture containing alpha hemihydrate gypsum and silicon dioxide in a specific ratio, and have arrived at the present invention.

That is, in the present invention, alpha-type hemihydrate gypsum is
This is a plaster-type material for molding a denture base made of thermoplastic resin, which is made of a mixture of silicon dioxide at a ratio of ~80% by weight and silicon dioxide at a ratio of 50 to 20% by weight.

The alpha-type hemihydrate gypsum used in the present invention is dihydrate gypsum ( _CaSO4 .
It is obtained by wet heating (e.g. lightly baking at 120-130℃ in an autoclave with steam applied to it) and is expressed by the chemical formula α _- CaSO ₄ 1/2H ₂ O. be. Beta-type hemihydrate gypsum (β-
CaSO ₄ 1/2H ₂ O).

The silicon dioxide used in the present invention is generally
It is expressed as SiO ₂ and is sometimes called silica, silicic anhydride, or monosilicic acid. Allomorphs of silicon dioxide include cristobalite, quartz, tridymite, and fused silicic anhydride.

The blending amount is 40 ~ alpha type hemihydrate gypsum.
A mixture of 90% by weight and 60 to 10% by weight of silicon dioxide is effective. In other words, when using a mold material obtained from a mixture containing more than 90% by weight of alpha-type hemihydrate gypsum and less than 10% by weight of silicon dioxide, the strength of the gypsum mold will decrease significantly at temperatures that soften the thermoplastic resin. , damage to the plaster mold occurs during pressurization, making it impossible to perform good molding. Furthermore, if the alpha-type hemihydrate gypsum is less than 40% by weight and the silicon dioxide content is more than 60% by weight, the mechanical strength is low even at room temperature and cannot be used.

Furthermore, when beta-type hemihydrate gypsum is used instead of alpha-type hemihydrate gypsum, the strength is insufficient and good denture base molding cannot be performed.

Only when the alpha-type hemihydrate gypsum and silicon dioxide of the present invention are mixed in the above ratio, it has the strength to withstand the high temperature and pressure conditions of compression molding,
Moreover, when the molded product is taken out after cooling, the plaster mold is brittle, and the plaster can be easily destroyed and removed, and the molded denture base can be taken out smoothly and in a short time without any damage. This property is due to alpha-type hemihydrate gypsum of 50 to 80% by weight,
When the silicon dioxide content is 50 to 20% by weight, it is more effective and is more preferable.

Furthermore, when heating the thermoplastic resin, gypsum contracts due to dehydration phenomena, while silicon dioxide expands, so that in the case of molds using the mixture according to the invention, the contraction of gypsum and the expansion of silicon dioxide are offset. It has been found that this method has the advantage that there is no major change in the dimensions of the mold cavity, and that a denture base with dimensions that are faithful to the original shape can be obtained. Among the silicon dioxides used in the present invention, cristobalite in particular exhibits a phenomenon in which it expands more at temperatures above 200°C than quartz, tridymite, and fused silicic anhydride, but its temperature dependence is small. This is preferable because the change in mold cavity dimensions due to fluctuations in temperature conditions is small and a denture base that is more faithful to the original shape can be obtained.

The blending method for obtaining the mixture according to the present invention is not particularly limited, and commonly used methods such as shaking and mechanical mixing can be used.

The mixture of the present invention may contain, if necessary, as long as it does not adversely affect the inherent strength and thermal properties of the mixture.
Small amounts of accelerators, retarders, colorants, etc. can be added to adjust the curing time.

The thermoplastic resin used in the present invention does not undergo thermal deterioration through the molding method, has an appropriate viscosity, has good moldability, and can be colored in a color similar to that of the gums. Therefore, it is required that the resin has appropriate rigidity and moisture resistance, as well as toughness that does not cause stress cracks during use. Therefore, polystyrene, polymethyl methacrylate, polymethylpentene-1, transparent nylon, polyethylene terephthalate, polycarbonate,
Polyarylate, polyester carbonate, transparent ABS resin, polysulfone resin, etc. are used, but polysulfone resins such as polysulfone and polyethersulfone have excellent moisture resistance, rigidity, stress cracking resistance, etc. preferable. The polysulfone resin used as a preferred embodiment in the present invention is defined as a polyarylene polyether polysulfone in which arylene units are located in a disordered or ordered manner with ether and sulfone bonds. for example UCC polysulfone Udel with the structure Polyethersulfone manufactured by ICI with the structure of
One example is Vichrex.

The present invention will be specifically explained below with reference to Examples, but these are merely illustrative of preferred embodiments and are not limited to the compositions of the Examples.

Example 1 After 70% by weight of alpha-type hemihydrate gypsum and 30% by weight of cristobalite were thoroughly mixed mechanically, the mixture was mixed with 0.25 times (weight ratio) water, and a wax denture base model was placed. Pour into a flask and let harden.

After the gypsum/cristobalite mixture has hardened, the wax is softened by heating and drained.
Polyethersulfone (ICI) having a volume corresponding to the wax is placed on the lower lid from which the wax has been removed.
Place a U-shaped molded product made of Victrex 200P (manufactured by Victrex 200P) colored to resemble gums, and blow hot air at 360°C to heat and soften. By pressing the upper lid part containing the removed artificial tooth onto the softened molded product, a polyether resin is applied to the cavity between the upper lid part and the lower lid part from which the wax has been removed. Insert the phone. After cooling, the metal frame of the flask was removed, and the polyethersulfone denture base integrated with the artificial tooth was taken out.

The extracted polyethersulfone denture base faithfully reproduced the shape of the wax model, had good surface gloss, and was sufficiently practical.
This indicates that the gypsum/cristobalite mixed type was able to sufficiently withstand the molding conditions without cracking or breakage even during 360°C hot air heating and pressure bonding. Furthermore, the gypsum mixture after molding could be easily removed from the molded product in water. Furthermore, due to the contraction of the gypsum and the expansion of the cristobalite, the dimensional change in the cavity where the wax model was removed was extremely small even during heating, so the denture base molded product was finished in dimensions that were extremely similar to the wax model.

Example 2 Alpha-type hemihydrate gypsum 60% by weight, tridymite
The molding was performed under the same conditions as in Example 1, except that the 40% by weight mixture was used as the plaster mold material for denture base molding, and when the molded product was removed from the plaster mold, it resembled the wax model as in Example 1. A good denture base with the following dimensions was obtained.

Comparative Example 1 Molding was carried out under the same conditions as in Example 1 except that a mixture of 95% by weight of alpha-type hemihydrate gypsum and 5% by weight of cristobalite was used as the plaster mold material for denture base molding. The mold was damaged, and compared to the wax model, the thickness and shape of the molded product were different, and the filling properties were insufficient, making it impossible to perform good molding.

Comparative Example 2 Molding was carried out under the same conditions as in Example 1 except that a mixture of 30% by weight of alpha-type hemihydrate gypsum and 70% by weight of cristobalite was used as the plaster mold material for denture base molding. The plaster mold was damaged during pressing, and good molding could not be achieved.

Comparative Example 3 Molding was performed under the same conditions as in Example 1, except that a mixture of 70% by weight beta-type hemihydrate gypsum and 30% by weight cristobalite was used as the plaster mold material for denture base molding. The plaster mold was damaged, and as in Comparative Example 1, good molding could not be performed.

Claims (1)

[Claims] 1. A thermoplastic resin denture base compression molding plaster molding material made of a mixture of 50 to 80% by weight of alpha-type hemihydrate gypsum and 50 to 20% by weight of silicon dioxide.