JPH1036136A - Ceramic for dentistry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic used for dentistry, simple in handicraft operations and having high strength and excellent brightness. SOLUTION: This ceramic for dentistry contains at least one kind of oxide selected from the group consisting of silicon dioxide, magnesium oxide, aluminum trioxide, titanium dioxide, calcium oxide, and the oxides of phosphorus, vanadium and tantalum as a main component, and satisfies SiO2 : 40-50wt.%, MgO: 12-26wt.%, Al2 O3 : 6-19wt.%, TiO2 : 10-14wt.%, CaO: 7-19wt.% and M2 O5 : 0.05-0.1wt.%, when the main components are converted into SiO2 , MgO, Al2 O3 , TiO2 , CaO and M2 O5 (M=P, V, Ta) and when their contents are expressed by weight percents.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel composition of dental ceramics.

[0002]

2. Description of the Related Art As a material used for restoring a tooth partially lost due to erosion or the like, a composite material composed of an inorganic substance and an organic substance, called a combo resin, a metal or a ceramic is used. In particular, metals and ceramics are used for bridges requiring high strength, that is, irremovable prostheses that compensate for missing teeth. Among them, ceramics are highly evaluated as restoration and prosthetic materials because of their excellent wear resistance and aesthetic properties.

However, since ceramics are generally brittle and cannot withstand particularly large bending forces, a method of baking ceramics called a metal-baked porcelain on a surface of a metal casting has been conventionally used. However, in recent years, bending strength, which has been regarded as a disadvantage of ceramics, is gradually improving, and all-ceramic crowns (also called full ceramic crowns) in which all parts of restorations or prostheses are made of ceramics. Came to attention. All-ceramic crowns are by far the most aesthetically superior to metal-fired porcelain. This is because the baked porcelain has a metal layer inside and does not transmit light, so it cannot reproduce the transparency of natural teeth.On the other hand, all-ceramic crowns are made of translucent material that transmits light. That's why. Therefore, the market for all ceramics has been expanding in recent years.

The material used for the all-ceramic crown is a material called glass ceramic in which crystal particles are precipitated in glass matrix, or a composite of glass ceramic and ceramic powder such as alumina and zirconia. In particular, glass ceramics are characterized in that a transparent feeling similar to that of natural teeth can be obtained by adjusting the refractive indices of crystals and glass matrix. This transparency is greatly affected by the size of the crystal. In general, the smaller the difference in the refractive index between the precipitated crystal and the glass matrix, and the smaller the size of the precipitated crystal, the more transparent it becomes.
Aesthetically superior.

[0005] Glass ceramics are prepared by a two-stage heat treatment in which a nucleus forming step of depositing microcrystals of several tens of nm called crystal nuclei from mother glass and a crystallization step of growing the deposited crystal nuclei. The strength of glass ceramics is strongly affected by the morphology of the structure, such as crystallinity and crystal morphology. In general, it is said that the higher the content (crystallinity) of precipitated crystals and the more uniform and fine the crystal grain size, the higher the strength of glass ceramics. The initial conditions of crystallization, ie, nucleation conditions, have a subtle effect on these.

[0006] General methods for producing a crown made of glass ceramics are roughly classified into a build-up method and a casting method.

[0007] In the build-up method, since ceramic powder is raised on a double model and sintered, a complicated device is not required, and a restoration can be produced in a short time, which is simple.

The porcelain (porcelain) generally used at present for the build-up method is a glass ceramic on which leucite is deposited. Since the operation of sintering is used in the build-up method as described above, many bubbles remain. Therefore, the bending strength is about 70 MPa, which is not sufficient as a crown material.

In order to solve this problem, a method has been proposed in which alumina and zirconia are sintered in advance by embedding to form a ceramic skeleton, and the skeleton is impregnated with glass. Although some methods exhibit a bending strength of 500 MPa or more by this method, a great deal of time is required for glass impregnation. Further, there is a disadvantage that the strength varies greatly depending on the method of impregnation, and it is difficult to stably obtain physical properties. In addition, a difference in refractive index occurs between the ceramic used for the skeleton and the impregnated glass, and it is difficult to obtain a color tone similar to natural teeth.

[0010] The casting method requires a special casting machine because the crown is produced from the glass melt using centrifugal casting as in the case of metal casting. After that, a crystallization process called ceraming is performed, so that the entire process currently requires a minimum of about 8 hours, which is complicated. The casting method can obtain a glass-ceramic having a high degree of crystallinity, but on the other hand, as described above, requires a dedicated casting machine and requires a long time in the manufacturing process.

Examples of glass ceramics for crowns using a casting method include, for example, Japanese Patent Application Laid-Open Nos.
Mica glass that precipitates mica crystals like 77340, or calcium metaphosphate glass like JP-A-62-36042 and JP-A-63-21236, and is cast at the same casting temperature as metal. There are possible glass ceramics.

Particularly, in Japanese Patent Application Laid-Open No. 03-177340, 500MP
Although a composition having a strength reaching a is exemplified, mica-based glass ceramics have a drawback that the quality tends to vary due to scattering during casting due to the inclusion of fluorine. Calcium metaphosphate glass has a low mechanical strength and a composition in which the glass is easily eluted, and thus has a problem in long-term use in the oral cavity.

In the case of using casting, entrainment is involved,
It is easy to cause casting defects in a broad sense such as reaction with a mold material. Since glass is active in the melt, it reacts with the contacting mold material to locally change the composition or cause surface roughness. These casting defects tend to cause a decrease in strength and deterioration of aesthetics.

In addition, in the casting method, the cooling rate in the mold is generally partially different, so that in the case of glass ceramics, the difference in the cooling rate of the glass tends to cause a change in the structure. This structural change has a great influence on the subsequent nucleation step. Nucleation is a very sensitive process and is affected not only by the cooling rate but also by the nucleation temperature. In the casting method, the nucleation step is left to the user, so that it is difficult to reproduce desired physical properties at present.

As a method for solving these problems, a press molding (heating and pressing molding) method has been proposed. With the press molding method, the glass ceramic block that has been crystallized and processed is heated and softened at a temperature considerably lower than the casting temperature,
The crown is obtained by injection molding into a mold while applying pressure.

In the press molding method, the nucleation and crystallization steps can be performed in advance at the factory side, so that crown molding can be performed in a short time, and the technical operation is extremely easy. In the above-mentioned production method, since a high-viscosity material is injected into a mold at a low speed, it is the most excellent method for producing a ceramic crown at present without causing air bubbles and causing a reaction with the mold material.

At present, ceramic blocks commercially available for press molding are glass ceramics on which leucite is precipitated, like porcelain. Further, the manufacturing method is obtained by molding and sintering a glass powder, and basically a large number of bubbles exist in a ceramic block. For this reason, press molding proceeds easily, but due to residual air bubbles, the bending strength is about 200 MPa, which is not sufficient as a crown material.

Therefore, at present, there is no material which is easy to carry out technical operations and has high strength and can reproduce a color tone close to a crown.

Further, Dental Materials and Instruments Vol.12 p128 (1993)
Press-moldable CaO-Si for artificial crowns described in
O ₂ Fundamental Study on -MgO-based crystallized glass "and 19
In the "study of diopside of as a biological material" 94 years of the Ceramic Society of Japan in the Spring Annual Meeting Abstracts p75 described, viscosity diopside (CaO · MgO · 2SiO ₂₎ type of crystallized glass ceramics at 900 ℃ below It is reported that it can be press-formed due to flow and its bending strength is 400 MPa. However, since this glass ceramic has Ag ₂ O added as a nucleating agent, the silver colloid formed with the progress of crystallization grows and becomes gray black, and the brightness decreases,
Reproduction of crown color was difficult.

In addition, we have studied diopside glass ceramics composed of TiO ₂ and Al ₂ O ₃ instead of Ag ₂ O as a nucleating agent. In this system, blackness increases with progress of crystallization. Showed a trend.

Therefore, the technical operation is simple, high strength,
There is an urgent need to invent materials with excellent brightness.

[0022]

SUMMARY OF THE INVENTION An object of the present invention is to provide a dental ceramic which is easy to carry out in a technical operation and has high strength and excellent brightness.

[0023]

Means for Solving the Problems The present inventors have intensively studied to overcome the above technical problems. As a result, 850 ° C
At 900900 ° C., viscous flow occurs with crystallization and press molding is possible, and the strength is high, and M ₂ O ₅ (M = P, Ta,
It has been found that by adding V), a dental ceramic having high brightness and excellent aesthetics can be obtained, and the present invention has been completed.

That is, the present invention relates to silicon oxide, magnesia oxide, aluminum oxide, titanium oxide, calcium oxide,
And containing phosphorus, vanadium, and at least one oxide selected from the group consisting of oxides of tantalum as a main component, each of which is SiO ₂ , MgO, Al ₂ O ₃ , TiO ₂ ,
When converted to CaO and M ₂ O ₅ (M = P, V, Ta) and the content is expressed in percentage by weight, SiO ₂ : 40 to 50% by weight, MgO
: 12 to 26% by weight, Al ₂ O ₃ : 6 to 19% by weight, TiO
_2: 10 to 14 weight%, CaO: 7~16 weight%, M ₂ O
₅ : Dental ceramic (first invention) satisfying 0.05 to 0.1% by weight.

Another invention relates to silicon oxide, magnesia oxide,
Aluminum oxide, titanium oxide, calcium oxide, and at least one oxide selected from the group consisting of oxides of phosphorus, vanadium, and tantalum, each of which contains SiO ₂ , MgO, Al ₂ O ₃ , TiO _{2 2} , Ca
O, and _{M 2 O 5 (M = P} , V, Ta) when representing the content in terms to weight percentage to, SiO _2: 49-50 wt%, MgO:
15-16 wt%, Al ₂ O _3: 10~12 wt%, TiO _2:
12-13 wt%, CaO: 11 to 12 wt%, M ₂ O _5:
A dental ceramic satisfying 0.05 to 0.1% by weight (second invention).

The composition range of the dental ceramic of the present invention is as described above, and the details will be described below.

The amount of silicon oxide (based on SiO ₂ ) is 40 to 50% by weight, preferably 49 to 50% by weight. The content of Si0 ₂ is higher the viscosity of the glass exceeds 50%, it is difficult to obtain a homogeneous glass. When a crown is produced by a press molding method, a molding temperature is increased, and internal crystallization hardly occurs. Further, when it is less than 40%, the matrix glass becomes weak, and sufficient strength cannot be obtained.

The content of magnesium oxide (based on Mg0) is 1
It is 2 to 26% by weight, preferably 15 to 16% by weight. Mg0 is a crystal component and is an essential component. If the content of Mg0 exceeds 26%, the viscosity is increased, and crystallization remarkably progresses during molding, which hinders molding. Further, the viscosity of the glass becomes high, and melting and forming become difficult. Also, it is easy to devitrify during casting. 1
If it is less than 2%, internal crystallization is inhibited and only surface crystallization proceeds, which is not preferable.

The content of aluminum oxide (based on Al ₂ O ₃ ) is 6 to 19% by weight, more preferably 10 to 12% by weight. Al ₂ O ₃ is an essential component to obtain a more homogeneous glass material. If the content of Al ₂ O ₃ is less than 6%, the effect is not exhibited. On the other hand, if the content exceeds 19%, the melting temperature becomes high and defoaming and molding become difficult, which is not preferable. The anorthite (CaO · Al ₂
O ₃ · 2SiO ₂ ) crystals are likely to precipitate.

The content of titanium oxide (based on TiO ₂ ) is 10 to 14
%, More preferably 12 to 13% by weight. Ti
O ₂ acts as a nucleating agent. Further, it has the effect of lowering the melting temperature of glass, so that it is necessary to contain the glass in this range. If the content of TiO ₂ is less than 10%, there is no effect as a nucleating agent. On the other hand, if the content exceeds 14%, crystallization remarkably progresses during molding and molding is hindered, which is not preferable. Further, a marked coloring is observed, which is not aesthetically preferable.

The content of calcium oxide (based on CaO) is 7 to
It is 16% by weight. More preferably, it is 11 to 12% by weight. CaO is a crystal component and an essential component. By containing CaO in this range, diopside as a main crystal is precipitated. If the content of CaO is less than 7%, the amount of crystal precipitation decreases, and the main crystal phase changes to enstatite. In addition, the viscosity increases, which is not preferable. If the content exceeds 16%, internal crystallization is inhibited and surface crystallization takes precedence, which is not preferable.

The dental ceramic of the present invention further contains at least one oxide of phosphorus oxide, vanadium oxide and tantalum oxide in addition to the above components. The content of these oxides (M ₂ 0 ₅ basis, M = P, V, Ta ) is 0.03 to 0.1
% By weight. These oxides, abolished the blackness of the glass due to oxygen defects and Ti ^{3+ Bruno} presence caused by TiO _{2 Roh} added, is essential for obtaining a glass having excellent aesthetic improvement lightness. If the content is less than 0.03, there is no effect
If it exceeds 0.1, coloring may be observed, and it may be difficult to adjust the color tone. Incidentally, a plurality of these oxides may be added.

The dental ceramics of the present invention may contain, in addition to the above essential components, metals such as Ce, Fe, Mn, Ni, Co, V, Cu, Cr, etc. for the purpose of coloring when used as a crown material. And at least one oxide as a coloring component. It can also be added to Zr0 ₂ to improve the transparency of the glass.

The dental ceramic of the present invention may contain fluorine. Fluorine has the function of lowering the viscosity of glass and promoting crystallization. When fluorine is added, the content is preferably less than 1% by weight.

The dental ceramic of the present invention is a crystallized glass (glass ceramic) containing a crystal phase in glass, and the crystal phase is composed of diopside as a main crystal. When the diopside is not included, it is difficult to achieve light transmission and high strength.

A typical production method of the dental ceramics of the present invention will be specifically described below. First, a glass raw material serving as a supply source of each of the above essential components is ground and mixed using a shaker mixer, a ball mill, etc., and then the mixture is filled in a platinum crucible and heated at 1500 ° C. for 2 hours using an electric furnace. Melts. Next, the molten glass is cast into a mold and gradually cooled to obtain a sample glass block. The glass produced in order to improve the uniformity of the obtained glass may be repeatedly crushed and re-melted.

The above glass raw material is not particularly limited, and powders of metal oxides, carbonates, hydroxides, nitrates, sulfates and the like generally used as glass raw materials can be used. In consideration of the finally obtained glass composition, the mixing ratio of the glass raw materials to be used is determined in advance by calculation. Specific examples of the glass raw material serving as a supply source of each essential component are described below.

The quartz as a raw material of silicon oxide (Si0 _2), cristobalite (Si0 _2), amorphous silica (Si0 ₂₎ are generally used. Magnesia (MgO), magnesite (MgCO ₃ ), and magnesium hydroxide (Mg (0H) ₂ ) are mainly used as raw materials for magnesium oxide. Magnesium sulfate as a refining agent (MgSO _4), magnesium nitrate (MgN0 ₃₎
Etc. may be added in small amounts. Alumina (Al ₂ O ₃ ), aluminum hydroxide (Al (0H) ₃ )
Are used. Rutile (TiO ₂ ), anatase (TiO ₂ ), or the like can be used as the TiO ₂ raw material. Calcium carbonate as a raw material for calcium oxide (CaC0 _3), calcium hydroxide (Ca (OH) ₃₎ is mainly used. The raw materials of the oxides of phosphorus, vanadium, and tantalum use the corresponding oxides, but inorganic salts such as nitrates and sulfates may be used. When phosphoric acid is added, calcium phosphate (Ca (PO ₄ ) ₂ ), magnesium phosphate (Mg (PO ₄ ) ₂ ) or the like can be used.

In addition to the above raw materials, for example, kaolin (Al
Compounds such as ₂ O ₃ · 2SiO ₂ · 2H ₂ O) and dolomite (MgCO ₃ · CaCO ₃ ) can also be used.

It is preferable that these raw materials do not contain impurities, but it is sufficient that each of the raw materials has a purity of at least 98% or more.

Next, the sample glass block obtained by the above method is heat-treated to precipitate diopside crystals, thereby obtaining a dental ceramic of the present invention having excellent brightness and close to the crown and having high strength.

The heat treatment method for depositing the diopside crystal is not particularly limited, but a typical method will be described below. The maximum temperature of heat treatment depends on the composition, but generally
850 ° C to 1000 ° C. In order to produce ceramics having better strength and lightness, a first-stage heat treatment (nucleation process) is performed in a temperature range of 700 ° C to 850 ° C, and then a second heat treatment is performed in a temperature range of 900 ° C to 1000 ° C. Generally, two-stage heat treatment (crystallization treatment) in which heat treatment is performed in stages or multi-stage heat treatment in which heat treatment is further carried out is used.

As a device for heat treatment, a known heat treatment device, that is, an electric furnace or the like is suitably used.

The crystallization of the dental ceramic of the present invention can be carried out simultaneously with the injection into the mold at the time of molding or after the end of the injection into the mold. For example, in the former case, crystallization and injection are simultaneously achieved by heating to a viscosity of about 10 ⁶ boise (about 900 ° C.).
In the latter case, first, the mixture is heated to a temperature range such that the viscosity becomes 10 ⁹ poise (850 ° C.).
This is achieved by a two-stage heating process in which the crystallization zone is heated to 0-1000 ° C.

When the above two-stage heating step is used, it is possible to carry out the crystallization after removing the refractory model material from the heating furnace after the casting into the mold is completed.
Further, after the filling into the mold is completed, the crystallization can be performed under pressure or under reduced pressure.

The temperature range in which the first-stage heat-treated glass obtained by the above method is heated and softened usually has a viscosity during heating.
A temperature range of 10 ⁹ to 10 ⁶ boise is preferable. The temperature range to reach this viscosity is in the range of 850 ° C to 950 ° C. The heating temperature during molding is also in the same temperature range.

[0047]

As described above, according to the present invention _{Mg0-CaO-Al 2 0 3} -TiO 2 -Si0 2
Dental ceramic of the present invention containing glass M ₂ 0 ₅ system (M = P, V, Ta, etc.) to a specific range indicates a viscous flow behavior suitable for press molding, moreover strength, high brightness. Specifically, the technical operation is facilitated, and the doctor or the patient can use it with confidence. Further, since the lightness is high, by adding a coloring component to the glass as necessary, the glass exhibits a color close to a crown color, so that a color tone similar to that of natural teeth can be exhibited, which is useful as a crown material.

[0048]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The methods for measuring the properties and physical properties of the materials shown in the detailed description of the invention and in the examples are as follows.

For identification of the precipitated crystal, a uniform glass melt was prepared, and the glass melt was poured into a carbon mold to obtain a glass material. The glass material thus obtained was subjected to a heat treatment under the conditions shown in each table and then pulverized and analyzed by powder X-ray diffraction (RINT-1200, manufactured by Rigaku Corporation). The results are shown in each table.

For the water resistance and acid resistance tests, the heat-treated glass material described in each table was pulverized and classified so as to have a particle size of 420 to 590 microns, and 3 g was accurately weighed to obtain a test powder. The test powder was boiled for 1 hour with 100 ml of a test solution (0.01 N nitric acid solution or purified water), dried, and the reduction rate was calculated from the weight loss. The results are shown in each table.

The flexural strength was obtained by subjecting the glass material to the heat treatment shown in each table, finishing the surface to a mirror surface with a diamond paste to form a 2 mm × 3 mm × 35 mm test piece, and crossing it with a strength tester (Shimadzu Corp. EHF-F1). A three-point bending test was performed under the conditions of a head speed of 0.5 mm / min and a span distance of 20 mm to determine bending strength. The results of the treatment temperature, treatment time, and bending strength are shown in each table.

The following methods were used to evaluate the translucency and lightness of the obtained ceramics. The glass material was processed into a cylindrical shape with a diameter of 10 mm and a thickness of 2 mm in the same manner as in the case of identifying the precipitated crystal,
Apply the specified heat treatment, finish the surface to a mirror surface with diamond paste, and use the color difference meter (Nippon Denshoku Co., TC-1800MKII) to measure the ratio of the Y value measured against the blackboard to the Y value measured against the white plate. Calculate the contrast ratio,
L * was measured according to JIS Z 8729 to obtain lightness. The contrast ratio is more opaque as the numerical value is larger, and L *
Indicates that the larger the value, the brighter the color. The results are summarized in each table.

The moldability of the obtained glass material was evaluated as an injection rate using the following method. A glass material having a diameter of 10 mm and a height of 12 mm was prepared in the same manner as in the case of transparency and lightness, and subjected to a nucleation treatment at a predetermined temperature. 10mm x 10mm sheet wax (manufactured by GC)
No.28 0.35mm thick) and sprue (READY CASTIN made by GC)
G WAX 32 mm) to prepare a wax model, and this wax was buried using a quartz-based investment material (Matsufu Co., Ltd. OK powder) to obtain a mold. The sprue length was 5 mm, and the powder-liquid ratio of the investment material was 0.33. The above-mentioned glass ingot was set in this mold and evaluated by the injection rate into the mold. The results of temperature, injection pressure, injection time and injection rate at the time of injection are summarized in each table.

[0054] according to a first embodiment the glass material 92.08gSi0 _2, 28.16gMgO, 36.85gCaC
O ₃ , 31.04 g Al (OH) ₃ , 22.63 g TiO ₂ and 0.3 gMg (PO 4) ₂ were ground and mixed using a shaker mixer. These mixtures were filled in a platinum crucible and melted by heating at 1500 ° C. for 2 hours using an electric furnace. Next, the glass in a molten state was cast into a mold and gradually cooled to obtain a sample glass lump. The obtained sample glass lump is
The sample was placed in an electric furnace and subjected to a two-stage heat treatment at 700 ° C. for 5 hours and further at 850 ° C. for 40 minutes to precipitate microcrystals in the glass.
At this time, the temperature was raised at a rate of 300 ° C./h, and then allowed to cool to room temperature in the furnace.

The precipitated crystal phase of the obtained glass ceramic was identified by X-ray diffraction. As a result, it was confirmed that diobide was precipitated as a main crystal, and its bending strength was 40%.
It was 0 MPa. Table 2 shows the results of water resistance, acid resistance, injection rate, contrast ratio and L *.

Examples 2 to 8 Sample glasses having the compositions shown in Table 1 were prepared in the same manner as in Example 1, and were crystallized under the two-step heat treatment conditions shown in Table 1. Table 2 shows the results of the precipitated crystal, water resistance, acid resistance, injection property, contrast ratio and L * of the obtained glass. The precipitated crystal was diopside, as in Example 1. In this composition range, the bending strength, the injection rate, the contrast ratio, and the L * showed good results. The composition range of the two inventions resulted in molding at lower pressure.

[0057]

[Table 1]

[0058]

[Table 2]

Comparative Examples 1 to 10 Sample glasses having the compositions shown in Tables 3 and 4 were produced in the same manner as in Example 1, and were crystallized under two heat treatment conditions. Tables 3, 4 and 5 show various physical properties. Although all the glasses showed good results in terms of water resistance and acid resistance, the compositions shown in Comparative Examples 1 to 5 all proceeded with surface crystallization and could not obtain sufficient bending strength. In Comparative Example 7, the obtained glass block was devitrified (white turbidity), so that subsequent nucleation and other treatments were not performed. Comparative Example 6 was a case where no M ₂ O ₅ -based oxide was added, and the bending strength and the injection rate showed good results.
Lightness was lower than that of Example 1. Comparative Examples 8 and 9 are cases involving crystals other than diopside. In this case, the bending strength was reduced and the injection rate was also reduced. Also in Comparative Example 10, the injection rate was low.

[0060]

[Table 3]

[0061]

[Table 4]

[0062]

[Table 5]

Claims (2)

[Claims] Claims: 1. An oxide containing at least one oxide selected from the group consisting of silicon oxide, magnesia oxide, aluminum oxide, titanium oxide, calcium oxide, and oxides of phosphorus, vanadium, and tantalum. _{SiO 2, MgO, Al 2 O} 3, TiO 2, CaO, and M ₂ O
₅ (M = P, V, Ta) and expressed as a percentage by weight, SiO ₂ : 40 to 50% by weight MgO: 12 to 26% by weight Al ₂ O ₃ : 6 to 19% by weight TiO ₂ : 10-14% by weight CaO: 7 to 16 wt% M ₂ O _5: 0.03 to 0.1 wt% dental ceramics satisfying. 2. It contains, as a main component, at least one oxide selected from the group consisting of silicon oxide, magnesia oxide, aluminum oxide, titanium oxide, calcium oxide, and oxides of phosphorus, vanadium, and tantalum. _{SiO 2, MgO, Al 2 O} 3, TiO 2, CaO, and M ₂ O
₅ (M = P, V, Ta) and expressed in terms of percentage by weight, SiO ₂ : 49 to 50% by weight MgO: 15 to 16% by weight Al ₂ O ₃ : 10 to 12% by weight TiO ₂ : 12 to 13 wt% CaO: 11 to 12 wt% M ₂ O _5: 0.03 to 0.1 dental ceramics satisfying wt%.