JPS58167503A - Investment material for dental casting - Google Patents

Abstract

PURPOSE:An investment material for dental casting, containing a ceramic, e.g. quartz glass, having increased density by heat-treating under high pressure as an investment material having a large amount of swelling in heating and a small amount of swelling in curing and a binder. CONSTITUTION:An investment material for dental casting,consisting of a high- density ceramic, e.g. quartz glass, and a binder, and obtained by hot-pressing the quartz glass at 10 GPa or below and 700 deg.C or below for 10min or less, cooling the resultant hot-pressed quartz glass to room temperature, and reducing the pressure to the ordinary pressure. Silicic acid may be further added to the resultant investment material, and therefore the shrinkage is reduced. Silicate glass consisting essentially of SiO2 glass and germanate glass consisting essentially of GeO2 or coesite, etc. may be used in addition to the quartz glass. EFFECT:Metallic molded articles of desired shape are obtained without requiring a means, e.g. absorbing or hardening swelling, etc.

Description

[Detailed description of the invention] This invention relates to investment materials for dental castings.

Dental metal molded products such as metal crowns and inlays are made by injecting a wax material into a plaster model from which an impression has been taken to form a wax mold, which is then buried in an investment material made of silicic acid powder, etc. The wax mold is eluted by heating the investment material 1- to form a cavity in the investment material, and into this cavity, hot water containing a molten dental casting alloy is poured, and then it is cooled and solidified to be cast. has been done. In the above casting process, when the investment material is heated to melt the wax mold in which it is embedded, the cavity formed by the wax mold also expands as the investment material expands, and this expanded cavity When the molten alloy is injected into the mold, it is cooled and solidified, shrinking and forming a metal molded product in the desired shape. However, conventionally used investment materials have relatively low density and low thermal expansion, such as silicic acid or cristobalite, so when the investment material hardens, it absorbs water and expands. Expand it further by means such as hardening expansion,
This compensated for the shrinkage of the casting alloy. However, if large water absorption expansion and hardening expansion are applied to the investment material when it hardens,
The investment material expands toward the opening of the cylindrical casting ring in which it is filled, so the amount of expansion in the vertical and horizontal directions is different, and the void space is deformed to form a metal molded product in the desired shape. The problem was that it was difficult to obtain.

In view of the above problems, there has been a need for investment materials that expand a large amount when heated and have a small amount of expansion when hardened.

As a result of intensive research in order to meet the above-mentioned demands, the present inventor found that
Ceramics such as quartz glass, which has been made denser by heat treatment under high pressure, expand significantly when heated to return to the original Ishiya glass, and I7 also found that the amount of shrinkage during the cooling process after heating is small. It was learned that the performance is suitable for dental casting investment material and I-.

That is, the present invention is a dental casting investment material characterized by being made of high-density ceramics densified by heat treatment under high pressure and a bonding material.

The densified ceramic used in this invention is manufactured by a high-pressure method, which is known as one of the means for growing single crystals of ceramics. For example, stone or glass, pressure 1
Pressure heat treatment is carried out under the conditions of 0 GPa or less, temperature of 700° C. or less, and heating time of 10 minutes or less, then cooled to room temperature 1, and then lowered to normal pressure. The density of high-density quartz glass is influenced by the above-mentioned pressure, and the relationship between pressure and density is shown in the graph of FIG. 1. 1st
As shown in the figure, normal quartz glass with a density of 2.21M is
The density starts to increase at a pressure of 30 Pa, and as the pressure increases, the density increases, and at a pressure of 8 GPa, the density increases to 2.6
17cII is obtained, and the higher the temperature during pressurization, the higher the density is achieved at a relatively lower pressure. Therefore, the desired density of high-density quartz glass can be obtained by appropriately selecting and combining the pressure and temperature during pressurization.

High-density quartz glass has a large amount of thermal expansion due to heating.
Furthermore, the amount of shrinkage during the cooling process after heating is small, and a specific example of thermal expansion during heating will be described below.

Octahedral pyrophyllite is used as a pressure medium, and in this pressure medium, a cylindrical quartz glass with a diameter of 10 WM and a length of 12 mm, a gelaphite heater, and a thermoelectric element made of an alloy of platinum/rhodium-87/18 are installed. This is assembled into a pair, attached to the MA-8 high pressure generator, and held in a 10,000 ton press at the appropriate pressure and temperature for 10 minutes at L, then allowed to cool naturally, and then reduced pressure to create high densities with different densities. Manufactured quartz glass.

Next, the high-density quartz glass was cut into a cylindrical sample with a length of 10 cm, and the coefficient of linear expansion (%) of this sample was measured and calculated using a thermal dilatometer (manufactured by Rigaku Denki Co., Ltd.!).

FIG. 2 is a graph showing changes in linear expansion coefficients of silica glass having different densities. As seen in the graph of FIG. 2, the higher the density, the greater the rate of increase in the coefficient of linear expansion, and the higher the coefficient of linear expansion. and density 2.5571
M quartz glass has a linear expansion coefficient of approximately 4% after 2 hours from the start of heating.
It can be seen that even after reaching 10001], the expansion continues as the heating time is extended.

Figure 3 is a graph showing the relationship between temperature and coefficient of linear expansion when the heating rate of quartz glass with a density of 2.5 g and 79M is different. has been shown to increase.

FIG. 4 is a graph showing the relationship between heating time and coefficient of linear expansion when the heating temperature is increased in stages.

It can be seen that when the temperature is maintained at a given temperature, there is no significant difference in the evaluation time after the temperature is raised and the coefficient of linear expansion.

As can be understood from the graphs in Figures 2 to 4 above, the amount of expansion when high-density quartz glass is heated can be controlled arbitrarily by changing the degree of densification, heating temperature, heating time, etc. can.

When using the above-mentioned high-density quartz glass as an investment material for casting, the high-density quartz glass returns to the original quartz glass when heated, so thermal contraction in the cooling process after heating is extremely small. However, gypsum on high-density quartz glass,
The magnitude of thermal shrinkage during the cooling process can be adjusted by mixing a binder such as phosphoric acid or by further mixing silicic acid.

Figure 5 shows only high-density fused silica glass with a density of 2.5571M (graph A), and a mixture of 75 parts by weight of the high-density fused silica glass and 25 parts by weight of gypsum (α-casOa・7H-0) (graph B). ), and high-density quartz glass 37.5
A mixture of 37.5 parts by weight of silicic acid and 25 parts by weight of gypsum (graph C) was heated to 680 degrees and held at 1.7 degrees, and then cooling was started 2 hours after the start of heating. This is a graph. As shown in the graph in Figure 5, when using only high-density quartz glass, there is almost no thermal contraction during the cooling process, but when using gypsum or a mixture of gypsum and high-density quartz glass with the same amount of silicic acid, undergoes some thermal contraction during the cooling process. Furthermore, even when gypsum or gypsum and silicic acid are mixed, the coefficient of linear expansion reaches 1.7% 25 hours after the start of heating, and there is a tendency for further expansion.

The coefficient of linear expansion shown in Fig. 5 above is obtained by pulverizing high-density quartz glass in an agate mortar, adding 30% by weight of Honmaru, gypsum, and silicic acid to the powder, and kneading it.
Create a dry sample for the cylinder, and perform measurement calculation 1- in the same manner as above.
It is a value.

Although high-density quartz glass has been described below, the present invention is not limited thereto. Si, O*ga°
It is a silicate-based glass whose main component is Gem.
The spinel phase of germanate-based glass, aluminosilicate-based galanium, coesite, and MgβeQ4, which is 141j, is known to be highly densified in the same way as above, and exhibit similar thermal expansion characteristics. Therefore, it is included in the densified ceramics of the present invention.

As explained below, since this invention uses high-density ceramics as an investment material for casting, the amount of thermal expansion during heating is greater than that of conventional ceramics, so water absorption expansion, hardening expansion, etc. does not require any means. In addition, the amount of expansion of high-density ceramics depends on the degree of densification of the ceramics,
Since it can be adjusted by appropriately combining conditions such as heating temperature, heating time, heating rate, presence or absence of mixing of a binder, silicic acid, etc., it can be arbitrarily changed depending on the amount of casting shrinkage of the alloy material. Furthermore, since high-density ceramics have low shrinkage during the cooling process after heating, a metal molded product of a desired shape can be obtained, and the shrinkage can be reduced by mixing a binder, silicic acid, etc.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between pressure and density during the production of high-density quartz glass, and Figure 2 is a graph showing the relationship between heating time and coefficient of linear expansion for high-density quartz glass with different densities.
Figure 3 is a graph showing the same relationship as Figure 2 with different heating rates; Figure 4 is a graph showing the same relationship as Figure 2 with stepwise temperature increases; Figure 5 is for high-density silica glass only (A) , a mixture of high-density quartz glass and stone (1), and a mixture (C) of high-density quartz glass, gypsum, and silicic acid, the graph shows the relationship between linear expansion coefficient and time during the heating and cooling process. Patent applicant Toyoyo Moriwaki Takashi Goto Agent Patent attorney Takeo Sakano

Claims (1)

[Scope of Claims] [1] An investment material for dental casting, characterized by comprising high-density ceramics made densified by heat treatment of high-pressure knives and a binding material. [2] The dental casting investment material according to claim 1, wherein the high-density ceramic is high-density quartz glass. [3] The dental implant material according to claim 1, which is a mixture of high-density quartz glass, a binding material, and silicic acid.