JPH06279054A - Transparency control of glass ceramic artificial teeth - Google Patents

Abstract

PURPOSE:To provide a controlling method for transparency of artificial glass ceramic teeth capable of controlling transparency in a wide range without lowering the strength of the glass ceramic artificial teeth. CONSTITUTION:The subject method consists of the first temperature elevating process in which temperature of glass ceramic containing 8-11 (wt.) % Li2CO3, 20-80% MgO, 11-15% Al2O3, 35-45% SiO2 and 10-15% Na2SiF6 is elevated at constant elevating rate, the first holding process in which the glass ceramic is kept at a temperature adjusted within around the temperature precipitating mica crystal for a given period of time, the second temperature elevating process in which the temperature is elevated at a constant rate and the second holding process in which the glass ceramic is kept at 9 higher temperature than that of beta-spodumene crystal precipitation for a given period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the transparency of glass-ceramic (crystallized glass) artificial teeth.

[0002]

2. Description of the Related Art Recently, a glass-ceramic (crystallized glass) artificial tooth having an appearance closer to that of a natural tooth has been developed in place of a metal material such as an alloy which has been used as a crown material, and has been practically used clinically. Has been used.

Such a glass-ceramic artificial tooth is manufactured by the following method. First, glass prepared with an appropriate composition is melted and poured into a lost wax mold shaped into a crown shape to be molded. Next, the obtained transparent glass crown is reheated at a temperature near the crystal precipitation temperature to precipitate crystals, and a translucent crown with a cloudy appearance close to that of a natural tooth is obtained. Various kinds of glass-ceramic artificial teeth have been invented depending on crystals to be precipitated in the above-mentioned crown manufacturing process. Among them, (mica)-(β-sporium) -based glass ceramics produced by precipitating mica and β-sporiumene crystals are excellent artificial teeth having both machinability of mica and mechanical strength of β-sporium. is there.

By the way, since the transparency of natural teeth varies from person to person, various degrees of transparency are required even when manufacturing artificial teeth. In addition, different transparency is required depending on the part of the tooth such as the front tooth and the back tooth. Therefore, different transparency is also required.

Conventional (mica)-(β-spodium)
In the production of artificial teeth made of glass ceramics, a method of adjusting the maximum temperature is adopted to control the transparency. For example, in the process of heating under normal crystallization heat treatment conditions at 13 ° C./min to 750 ° C., holding at this temperature for 2 hours, further raising the temperature to 900 ° C. at 4 ° C./min, and then cooling. If you need something more transparent, the maximum temperature is 900 ° C to 890 ° C or 880 ° C.
The heat treatment was performed under the condition of lowering the temperature to control the transparency.

[0006]

However, the method of controlling the transparency by adjusting the maximum temperature as in the above-mentioned conventional method has the following problems. That is, as the degree of transparency is increased, the degree of crystallinity is lowered and the strength is deteriorated. In other words, controlling the transparency by adjusting the maximum temperature means changing the crystallinity.
When the heat treatment is performed under the condition that the maximum temperature is lowered in order to obtain higher transparency, the crystallinity is lower than that when the heat treatment is performed at a higher temperature. Therefore, while the purpose of crystal precipitation is to increase the strength, a decrease in crystallinity means a decrease in strength.

Another problem with the method of controlling the transparency by adjusting the maximum temperature is that the obtained transparency is limited. In other words, since it becomes cloudy at the first temperature holding (750 ° C.) of the heat treatment, even if the maximum temperature is adjusted, it is not possible to obtain transparency higher than that at the first holding temperature. Therefore, in order to obtain higher transparency, there is a limit in the conventional transparency control method by adjusting the maximum temperature.

An object of the present invention is to provide a method for controlling the transparency of a glass-ceramic artificial tooth, which can control the transparency in a wide range without lowering the strength of the glass-ceramic artificial tooth.

[0009]

A method for controlling transparency of a glass-ceramic artificial tooth according to the present invention is 8-11% by weight of Li ₂ CO ₃ , 20-28% of Mg.
O, 11-15% Al ₂ O ₃ , 35-45% SiO
_A first heating step of heating the glass ceramic containing ₂ and 10 to 15% of Na ₂ SiF ₆ at a constant heating rate;
A first holding step of holding for a certain period of time at a temperature adjusted within a range around the mica crystal precipitation temperature, a second temperature rising step of heating at a constant temperature rising rate, and a constant temperature above the β-spodiumene crystal precipitation temperature. A second holding step of holding for a time is provided.

The method for controlling the transparency of the glass-ceramic artificial tooth according to the present invention allows the temperature in the first holding step to be kept constant and the temperature rising rate in the first heating step to be lowered to increase the transparency. To do.

The method for controlling the transparency of the glass-ceramic artificial tooth according to the present invention is allowed to further include a step of holding for a certain period of time near the nucleation temperature before the first holding step.

According to the present invention as described above, it is possible to provide a method for controlling the transparency of a glass-ceramic artificial tooth which can control the transparency in a wide range without lowering the strength of the glass-ceramic artificial tooth.

[0013]

EXAMPLES Examples of the present invention will be described in detail below. The glass having the composition shown in Table 1 below obtained by melting was subjected to heat treatment under the conditions 1 to 5 shown in Table 2 below. Table 1 Li ₂ CO ₃ MgO Al ₂ O ₃ SiO ₂ Na ₂ SiF ₆ 8.6 8.8 11.8 37.1 14.3 Table 2 Condition Heat Treatment Process Condition 1 13 ° C / min → 750 ° C (2 hours) → 4 ° C / min → 880 ℃ condition 2 13 ℃ / min → 650 ℃ (2 hours) → 4 ℃ / min → 880 ℃ condition 3 4 ℃ / min → 650 ℃ (2 hours) → 4 ℃ / min → 880 ℃ condition 4 4 ℃ / min → 600 ° C (2 hours) → 4 ° C / min → 880 ° C Condition 5 4 ° C / min → 570 ° C (6 hours) → 4 ° C / min → 650 ° C (2 hours) → 4 ° C / min → 880 ° C

The transparency of the crystallized glass obtained under the above conditions was examined. The results are shown in Table 3 below. In addition, in Table 3, the order from the highest transparency is given. Also, condition 2
The bending strength and crystallinity of the crystallized glass obtained by the heat treatment under the condition 5 were examined. The results are shown in Table 4 below.

As is clear from Table 3, even if the maximum temperature during crystallization heat treatment is the same, different transparency can be obtained by controlling the heating rate and the holding temperature.

That is, comparing the heat treatments under the conditions 1 and 2, the transparency is increased by changing the initial holding temperature from 750 ° C. to 650 ° C. even though the rate of temperature rise and the maximum temperature are the same. You can Also,
Comparing the heat treatments of Condition 2 and Condition 3, the transparency can be increased by slowly increasing the temperature increase rate from the first holding temperature to 13 ° C./min to 4 ° C./min. Further, comparing the heat treatments under the conditions 3 and 5, the transparency can be increased by holding at 570 ° C. before reaching 650 ° C. for the first temperature rise, as compared with the case where the holding step is not performed.

As is clear from Table 4, the crystallized glass obtained by the heat treatment under the condition 2 having a relatively low transparency has the crystallinity of 43.4% and the heat treatment under the condition 5 having a high transparency. Crystallized glass has a crystallinity of 43.
At 3%, both have almost the same crystallinity regardless of the difference in transparency. Therefore, it is understood that the difference in transparency between the two is not simply due to the difference in crystallinity. Also,
The flexural strengths under Conditions 2 and 5 are not significantly different regardless of the difference in transparency, and the strength does not decrease as the transparency increases as in the conventional method.

It is considered that the difference in transparency due to each heat treatment condition in such an example is due to the size of crystal grains. That is, when the size of the crystal particles is about the visible light wavelength or less, the transparency is high. On the other hand, when the size of the crystal particles is about the wavelength of visible light, the visible light is scattered by the crystal particles and the transparency is lowered.

The size of the crystal particles depends on the size of the particles of mica crystals which precipitate at a temperature lower than that of β-spodium. The size of the mica crystal particles is determined by the temperature rising rate that passes near the mica precipitation temperature. For example, rather than raising the temperature all at once to the mica precipitation temperature or more, holding the mica at around the mica precipitation temperature precipitates finer mica crystal particles, and the transparency can be increased. What is caused by such an effect is the difference in transparency between Condition 1 and Condition 2 and Condition 3 and Condition 4 described above. Further, when the temperature is raised slowly to the initial holding temperature, finer mica crystal particles grow as compared with the case where the temperature is raised all at once, so that the transparency can be increased. The reason for this effect is the difference in transparency between the conditions 2 and 3 described above. Furthermore, rather than raising the temperature to the mica precipitation temperature all at once, it is possible to increase the transparency because fine mica crystal particles grow when held once near the nucleation temperature. The reason for this effect is the difference in transparency between Condition 3 and Condition 5 described above. It is considered that the transparency after the heat treatment for crystallization is determined by these crystallization mechanisms.

In the conventional method, since the temperature raising step near the mica precipitation temperature is fixed, there is no difference in the mica precipitation state, and the transparency is controlled by the crystallinity of the mica and the β-spodium which is subsequently precipitated. Was there. Therefore, in the conventional method, the crystallinity decreases as the transparency increases, and as a result, the strength also decreases. On the other hand, in this embodiment, since the transparency is controlled by the size of the crystal particles, the transparency can be increased irrespective of the decrease in the crystallinity which is a problem in the conventional method. Therefore, it is possible to solve the problem that the strength is lowered by increasing the transparency as in the conventional method.

Further, in the heat treatment method in which the mica precipitation state is fixed as in the conventional method, if the crystal particles of the mica that initially precipitates are large, the particles are already clouded considerably at that point, so that crystallization is finally achieved. After the heat treatment of (1) is completed, it is not possible to obtain at least higher transparency. On the other hand, in the present example, by growing finer mica particles, it is possible to obtain a crystallized glass having a higher transparency, so that it is possible to obtain a wider transparency as compared with the conventional method without causing a decrease in strength. it can. Although the nucleation temperature was set to 570 ° C. and held at that temperature in the above-mentioned embodiment, the nucleation temperature may be slightly changed when the glass composition is changed.

[0022]

As described above in detail, according to the present invention, the transparency of the glass-ceramic artificial tooth can be controlled in a wide range without lowering the strength, and various transparency such as front teeth and back teeth are required. It is possible to provide a method for controlling the transparency of a glass-ceramic artificial tooth.

Claims (1)

[Claims] 1. A Li ₂ CO ₃ content of 8 to 11% by weight,
20 to 28% of MgO, 11 to 15 percent of Al ₂ O _{3, 3}
5-45% SiO ₂ and 10-15% Na ₂ Si
A first heating step of heating the glass ceramic containing F ₆ at a constant heating rate; a first holding step of holding the glass ceramic at a temperature controlled within a range near the mica crystal precipitation temperature for a certain time; A method of controlling transparency of a glass-ceramic artificial tooth, comprising: a second temperature raising step of raising the temperature at a temperature raising rate; and a second holding step of keeping the temperature above the β-spodiumene crystal precipitation temperature for a certain period of time.