JPH072617A - Dental embedding material composition - Google Patents

Abstract

PURPOSE:To obtain a dental embedding material composition excellent in thermal expansion and hot strength. CONSTITUTION:This dental embedding material composition contains gypsum and a metaphosphoric acid salt. The composition further contains at least one kind of substance selected from the group consisting of cristobalite and quartz.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a dental investment material composition. More specifically, the present invention relates to an investment material composition capable of obtaining high thermal expansion when expanding a mold and having excellent hot strength.

[0002]

2. Description of the Related Art A molding method by casting is suitable for producing a complicated shape which is difficult to machine. In the dental precision casting method, a molding method by casting is also used. A wax pattern is embedded in an expansive refractory material called an investment material to create a mold, and after heating to remove the wax, pressure is applied to the mold to melt it. The method of pouring metal is used.

Conventionally, as a dental investment material for forming a dental investment material mold, a cristobalite type investment material containing gypsum and cristobalite as main components has been widely used. However, with such an investment material, if it is attempted to be formed by a so-called heat shock method in which it is suddenly placed in a high-temperature furnace and fired, cracks, cracks, breakage, etc. occur in the mold. In order to avoid this, there is a problem that slow preheating is required and a long time is required for the whole molding process.

In order to solve such a problem, a rapid heating type cristobalite type investment material has been developed. This investment material composition contains, as main components, for example, plaster of gypsum, cristobalite and quartz at 20% by weight or more, as described in JP-A-4-330006.
By using such an investment material composition, a mold excellent in thermal shock resistance was formed, and at the same time, the manufacturing time of the mold could be significantly shortened.

When the molten metal is poured into the mold thus produced for casting, the alloy becomes smaller than the mold due to solidification shrinkage (casting shrinkage). Therefore, it is necessary to make a mold larger than the wax pattern. Therefore, when casting the investment material composition, it is necessary to use a mold that is more expanded than the pattern.
The expansion of this mold depends in large part on the expansion of the investment material.

Conventionally, as a means for expanding the mold in the dental field, a method (total expansion method) that combines thermal expansion and hardening expansion of the investment material has been used, but the degree of dependence on hardening expansion is particularly large. However, since the curing expansion tends to change over time, a uniform overall expansion cannot be obtained, and there is a drawback that the fitting precision of the cast body varies. Therefore, in the total expansion method, it is preferable to increase the dependence on the thermal expansion that causes uniform expansion. However, in any of the above-mentioned conventional investment materials, heat shrinkage due to gypsum occurs at 400 to 500 ° C., and sufficient thermal expansion cannot be obtained, so it was difficult to increase the dependency on thermal expansion.

To increase the thermal expansion, it is preferable to increase the content of cristobalite in the investment material. However, in the above-mentioned conventional rapid heating type cristobalite type investment material composition, it is necessary to contain 20% by weight or more of cristobalite. However, in order to avoid a rapid expansion at around 250 ° C., the content of cristobalite is actually included. There is a limit to the amount, so it has not been fully effective. Further, each of the above-mentioned investment materials has a drawback that the hot strength is extremely low.

[0008]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned drawbacks, and an object thereof is to achieve sufficient thermal expansion against heat shrinkage due to gypsum and to improve hot strength. An object is to provide an excellent dental investment material composition.

[0009]

The dental investment material composition of the present invention contains gypsum and a metal salt of metaphosphoric acid, thereby achieving the above object.

[0010]

In the dental investment material composition of the present invention, gypsum is used as a binder and has the effect of increasing the strength of the investment material by binding other components. Therefore, the strength of the investment material depends on the content of the binder. Gypsum is used in the form of hemihydrate, and it is particularly preferable to use α-gypsum containing α-hemihydrate having less heat shrinkage. The gypsum used in the investment material composition of the present invention is 20% of the total composition.
It is preferably contained in the range of ˜40% by weight.

The composition of the present invention has an important point in that it contains a metal metaphosphate in order to enhance the thermal expansion and hot strength of the investment material. As described above, high thermal expansion can be obtained without excessively adding cristobalite, so that rapid thermal expansion at around 250 ° C. due to a large amount of cristobalite can be suppressed.

In a preferred embodiment, the metal salt of metaphosphoric acid is
It is contained in a proportion of 0.05 to 50% by weight based on the total composition. When the content of the metal metaphosphate is less than 0.05% by weight, an investment material composition having sufficient thermal expansion and hot strength cannot be obtained, which is not preferable. On the other hand, 50
When the content is more than weight%, the curing promoting effect acts excessively, which is not preferable. Examples of the metal salt of metaphosphate include aluminum metaphosphate and tin metaphosphate.

In a preferred embodiment, the investment material composition of the present invention further comprises cristobalite and / or quartz. Cristobalite and quartz are types of silica, and both are used as heat resistant materials. These impart the heat resistance to the investment material and further have the function of adjusting the thermal expansion. This is because the crystal morphology of cristobalite and quartz change at their respective transition points. For example, quartz changes from low temperature α-quartz to high temperature β-quartz at around 575 ° C. On the other hand, cristobalite transitions from low temperature α-cristobalite to high temperature β-cristobalite at 200 to 270 ° C.
When the α type changes to the β type, the density decreases and the volume increases, so that the crystal expands rapidly. Therefore, it is possible to compensate for the decrease in thermal expansion due to the thermal contraction of gypsum.

The cristobalite used in the composition of the present invention is preferably contained in the range of 20 to 60% by weight based on the total composition. When the content of cristobalite is less than 20% by weight, sufficient thermal expansion cannot be obtained, which is not preferable. On the other hand, when it exceeds 60% by weight, cracking may occur at a rapid temperature change. Incidentally, in the present invention, as described above, since the metal metaphosphate is contained, there is an advantage that the content of cristobalite can be reduced,
From this viewpoint, the more preferable content of cristobalite is 20 to 40% by weight.

Examples of the quartz used in the composition of the present invention include α-quartz, which is preferably contained in the range of 20 to 50% by weight based on 100% by weight of the total composition.
When the content of quartz is less than 20% by weight, sufficient heat resistance cannot be obtained, which is not preferable, while when it exceeds 50% by weight, curing reaction and operability are deteriorated, which is not preferable. In addition to the above-mentioned components, the composition of the present invention may use regulators such as curing accelerators and retarders.

The above curing accelerator accelerates the curing of the investment material,
It has the effect of increasing the strength of the investment material in a short time. Therefore,
Not only to control the expansion during curing and the curing time, but also to
It is possible to prevent heat shrinkage (due to gypsum) that occurs when heated to 00 to 450 ° C. Examples of the curing accelerator that can be used in the composition of the present invention include potassium sulfate, and examples of the retarding agent include potassium citrate and strontium chloride.
It is preferably contained in the range of 4.0% by weight.

The present invention will be described in more detail with reference to the following examples, but the following examples do not limit the present invention, and modifications may be made without departing from the spirit of the present invention. All are included in the technical scope of the present invention.

[0018]

Examples (Examples 1 to 8 and Comparative Example 1) 100 g of a sample consisting of a predetermined amount of gypsum and aluminum metaphosphate shown in Table 1
Then, 30 cc of water was added for 10 seconds, and further, manual kneading was carried out for 30 seconds, and vacuum kneading (a dental vacuum kneading machine, a rotation speed of 365 rpm, a vacuum pressure of 650 mmHg or more) was carried out for 30 seconds. An investment material composition was obtained. In the comparative example, a sample containing no aluminum metaphosphate was used.

With respect to the investment material compositions obtained in the above Examples and Comparative Examples, the room temperature was 23 ± 2 ° C., the humidity was 50 ± 10%,
A thermal expansion test was conducted under the condition of a water temperature of 20 ° C. That is,
Each investment material composition was poured into a mold for producing a thermal expansion test piece, and 2 hours after starting the introduction of water, it was taken out of the mold and set in TMA (manufactured by Rigaku Corporation). The thermal expansion was measured by TMA from room temperature to 700 ° C. at a temperature rising rate of 10 ° C./min. The measured data is analyzed by an analyzer to obtain a thermal expansion curve. The thermal contraction rate (%) of each test piece at 300 to 450 ° C. was measured from the obtained thermal expansion curve. The results are shown in Table 1.

[0020]

[Table 1]

As is apparent from Table 1, as the content of aluminum metaphosphate increases, the thermal contraction rate of the investment material composition of the present invention decreases and the thermal expansion rate thereof increases, so that the thermal expansion coefficient of the present invention increases. It was found that the composition can suppress heat shrinkage due to gypsum.

(Examples 9 to 11 and Comparative Examples 2 to 9) The investment material composition of the present invention was prepared in the same manner as in Example 1 except that the specified amounts of gypsum, quartz and aluminum metaphosphate shown in Table 2 were used. I got a thing. In the comparative example, a sample containing no aluminum metaphosphate was used. The compositions obtained in the above Examples and Comparative Examples were subjected to a thermal expansion test based on the above method. The results are shown in Table 2.

[0023]

[Table 2]

Even if the content of quartz was increased from 0.5 to 40.0% (Comparative Examples 2 to 9), the heat shrinkage ratio was reduced to 0.13% at the most, whereas the quartz was reduced. When Example 9 (content of aluminum metaphosphate: 1.0%) when the content of is fixed to 20.0% and Comparative Example 6 are compared, in Example 9, the heat shrinkage rate is 0.09%. It was found that the heat shrinkage was significantly improved. Similarly, Example 10 when the content of quartz was fixed at 5.0% (content of aluminum metaphosphate: 3.0%)
And Example 11 (content of aluminum metaphosphate:
20.0%), the heat shrinkage rate was further improved as compared with Comparative Example 4, and in Example 11, it decreased to −0.50%.

Next, in order to examine the effect of aluminum metaphosphate on the compressive strength, the above Comparative Example 2 and Example 1,
The compressive strengths of the investment material compositions of Comparative Example 3 and Example 2, Comparative Example 4 and Example 4, Comparative Example 5 and Example 5, Comparative Example 6 and Example 7, and Comparative Example 7 and Example 8, respectively, were measured. I decided to measure. That is, room temperature 23 ± 2 ° C, humidity 50 ± 10
%, Water temperature of 20 ° C., each composition was measured according to JIS T-6
Pour into a mold for compressive strength test piece production defined in 601.
One hour after starting the introduction of water, it was taken out of the mold and set in a furnace. Room temperature to 700 ° C at a heating rate of 30 ° C / min
And heated at 700 ° C. for 10 minutes, and then taken out of the furnace. The compression strength (Mpa) was obtained by measuring the maximum crushing strength of each test piece within 30 seconds using an autograph (manufactured by Shimadzu Corporation) under the measurement conditions of a crosshead speed of 1 mm / min. The results are shown in Table 3.

[0026]

[Table 3]

As is apparent from Table 3, since the compositions of Examples all have higher compressive strength than the compositions of Comparative Examples, the inclusion of aluminum metaphosphate increases the hot strength. I found out that

(Examples 12 to 19 and Comparative Examples 10 to 1)
4) An investment material composition of the present invention was obtained in the same manner as in Example 1 except that the prescribed amounts of gypsum, quartz, cristobalite, and aluminum metaphosphate shown in Table 4 were used. In the comparative example, a sample containing no aluminum metaphosphate was used. The thermal expansion test and the compressive strength test were performed on the compositions obtained in the above Examples and Comparative Examples based on the above methods. The results are shown in Table 4.

[0029]

[Table 4]

When the gypsum and quartz contents were the same and a part of cristobalite was replaced with aluminum metaphosphate, the change in the effect was as follows: Comparative Example 10 and Example 12, Comparative Example 11 and Example 13, Comparative Example 12 and Example 14, Comparative Example 1
3 and Example 15 and Comparative Example 14 and Examples 16-19, respectively.
It was found that the composition of each example containing a small amount of aluminum metaphosphate instead of cristobalite had a smaller heat shrinkage rate than the composition of the comparative example, and that the heat shrinkage due to gypsum could be suppressed. Also regarding the compressive strength, the composition of the present invention is 700 ° C. more than the composition of the comparative example.
It was possible to increase the hot strength in.

(Examples 20 to 22) 34 cc and 33 c per 100 g of a sample containing the components of the composition shown in Table 5.
An investment material composition of the present invention was obtained in the same manner as in Example 1 except that water of c or 36 cc was added over 10 seconds.

[0032]

[Table 5]

The physical properties of the compositions obtained in the above examples were evaluated by the following methods. The following physical property evaluations were all carried out under the conditions of room temperature 23 ± 2 ° C., humidity 50 ± 10% and water temperature 20 ° C. 1. Setting time The samples obtained in the above examples were measured according to JIS T-6601.
Pour into a cylindrical stainless steel ring specified in 1. and load a 300g Vickers needle 1mm from the top of the sample.
The time (min) until it stops entering above is measured.

2. Flowability test A cylindrical stainless steel ring defined by JIS T-6601 is placed on a glass plate, the sample obtained in the above-mentioned example is poured into this ring, and 2 hours from the start of water addition.
After a minute, gently pull up the ring to leave the kneading mud on the glass plate. After 1 minute, the maximum diameter value and the minimum diameter value of the kneaded mud contacting the glass plate were measured, and the average value was measured as the flow value (m
m).

3. Compressive strength test The samples obtained in the above-mentioned examples are JIS T-6601.
The test piece was poured into the mold for compressive strength test piece preparation specified in paragraph 30 and after 30 minutes from the start of introducing water, the test piece was taken out from the mold and
It was set in a furnace at 0 ° C., baked for 30 minutes, taken out of the furnace, and measured within 30 seconds. 4. Hardening expansion test It was measured according to the setting expansion test of JIS 6605-1987 (hard dental plaster).

5. Thermal expansion test According to the test method described above. 6. Conformance state The conformance state to the bridge was evaluated. The results are shown in Table 6.

[0037]

[Table 6]

The compositions of the respective examples are slightly different depending on the difference of water mixing ratio, but the coefficient of thermal expansion and 700
The hot strength at ℃ was high. Also, setting time, fluidity,
Good results were also obtained for the curing expansion coefficient. In addition, the conformity state to the bridge is Example 22 (mixed water ratio: 0.36)
Composition was the best.

[0039]

As described above, the dental investment material composition of the present invention can improve the thermal expansion and hot strength, and enables casting by the heat shock method. Further, by using such an investment material, a cast body having a smooth surface condition can be obtained.

Claims (3)

[Claims] 1. A dental investment material composition containing gypsum and a metal salt of metaphosphoric acid. 2. The investment material composition according to claim 1, further containing at least one selected from the group consisting of cristobalite and quartz. 3. The investment material composition according to claim 1, wherein the content of the metal metaphosphate is 0.05 to 50% by weight based on the total investment material composition.