Dental alumina pre-sintered body, method for producing same, method for producing dental alumina molded body, and method for producing dental alumina granules

Abstract

The present invention is a dental alumina pre-sintered body comprising (A) α-alumina powder particles that have an average primary particle diameter of 30-300 nm and a purity of 99.5% or more, (B) Mg as an element contained in a sintering aid, and (C) at least one element that is selected from the group consisting of Ce, Dy, Pr, Nd, and Y and that serves as an additive for improving translucency, the content of the Mg (B) being 100-5000 ppm with respect to the α-alumina powder particles (A) in terms of mass of metallic magnesium, wherein: the contrast ratio (Yb / Yw) of a sintered body having a thickness of 1.0 mm obtained by firing said dental alumina pre-sintered body at 1450°C under atmospheric pressure (1013 hPa) is 0.20-0.35; and the bending strength of the sintered body obtained by sintering said dental alumina pre-sintered body at 1450°C under atmospheric pressure (1013 hPa) is 800 MPa or more. According to the present invention, it is possible to provide a dental alumina pre-sintered body which has high translucency and from which a high-strength sintered body can be produced.

Description

Dental alumina pre-sintered body and method for manufacturing the same, method for manufacturing a dental alumina molded body, method for manufacturing dental alumina granules

[0001] The present invention relates to a dental alumina presintered body and a method for producing the same, a method for producing a dental alumina molded body, and a method for producing dental alumina granules.

[0002] In dental restorations, a variety of materials are used, including metals, ceramics, and resins. Among these, ceramics are a promising alternative to metals and are used in procedures such as crown restorations where aesthetics are important. Zirconia ceramics, in particular, are widely used due to their strength and aesthetic appeal. Dental restorations using zirconia ceramics generally involve cutting a mill blank (workpiece) made of a pre-sintered zirconia ceramic body into a digitally designed shape by a dental technician or dentist, followed by processes such as final sintering and polishing.

[0003] While dental restorations using zirconia ceramics are widely used, there are still issues that need improvement, such as the tendency for strength to decrease when aesthetics (translucency) is enhanced, and the balance of physical properties. Besides zirconia ceramics, lithium disilicate glass ceramics are known as a material with excellent translucency, but their strength is insufficient.

[0004] In recent years, high-purity alumina ceramic materials have been proposed as a technology to solve the above problems. Patent Document 1 discloses an invention relating to a dental oxide ceramic calcined body containing alumina (purity of 99.5% or more) with an average primary particle diameter of 50 to 300 nm, and in which the cumulative distribution of pores has a D10 of 20 nm or more and a D90 of 90 nm or less, and it is described that it has excellent machinability and high light transmittance after sintering. Patent Document 2 discloses an invention relating to a dental oxide ceramic calcined body containing alumina with an average primary particle circularity of 0.81 or more, and a relative density of 43 to 63%, and it is described that it has excellent polishability, and that the polished surface of the calcined body and the surface of the sintered body after sintering have high flatness and excellent aesthetics.

[0005] Patent Document 3 discloses an invention relating to a calcined dental alumina body, comprising high-purity alumina with an average primary particle diameter of 30 to 300 nm, a sintering aid, and a blue-based coloring agent, wherein the sintering aid content is 10 to 5000 ppm. It is stated that this invention suppresses yellowing after sintering, and provides a sintered body with high translucency and linear light transmittance even when sintered under atmospheric pressure, resulting in a highly aesthetic product. Patent Document 4 discloses an invention relating to a dental alumina workpiece, wherein the average crystal grain size differs at a first and second point in a specific interval from one end and the other end of the dental alumina workpiece, and it is stated that the sintered body after sintering has excellent translucency, strength, and linear light transmittance.

[0006] International Publication No. 2023 / 127559 Brochure International Publication No. 2023 / 127561 Brochure International Publication No. 2023 / 127562 Brochure International Publication No. 2023 / 127564 Brochure

[0007] In dental restoration, it is necessary to adjust the translucency depending on the restoration site from an aesthetic standpoint; for example, high translucency is required for restoration of the incisal edge. As mentioned above, various studies have been conducted on alumina ceramics, and from an aesthetic standpoint, it is known that blue-based colorants are incorporated to suppress yellowing after firing, as described in Patent Document 3. However, in the example of Patent Document 3, when a blue-based colorant is incorporated and its amount is increased, b ＊ The value increased, while the light transmittance decreased. Therefore, there was room for improvement in effectively enhancing the light transmittance of alumina ceramics.

[0008] Therefore, the present invention aims to provide a dental alumina pre-sintered body that has high light transmittance and can be manufactured into a high-strength sintered body, and a method for manufacturing the same.

[0009] The inventors diligently conducted research to achieve the above objectives. As a result, they discovered that the above problems can be solved by a dental alumina pre-sintered body containing high-purity α-alumina powder with an average primary particle size within a specific range, a specific amount of Mg derived from a sintering aid consisting of a magnesium compound, and a specific additive to improve light transmittance, wherein the contrast ratio (Yb / Yw) and flexural strength of the sintered body after firing are within a specific range, and thus the present invention was completed. The present invention relates to the following [1] to [6].

[0010] [1] A dental alumina pre-sintered body comprising: (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm in mass as metallic magnesium relative to the (A) α-alumina powder, wherein the contrast ratio (Yb / Yw) of a sintered body with a thickness of 1.0 mm obtained by firing the dental alumina pre-sintered body under atmospheric pressure (1013 hPa) at 1450°C is 0.20 to 0.35, and the bending strength of the sintered body obtained by firing the dental alumina pre-sintered body under atmospheric pressure (1013 hPa) at 1450°C is 800 MPa or more. [2] A method for producing a dental alumina molded body, characterized by pre-sintering a dental alumina molded body at 500 to 1000°C, comprising: (A) α-alumina powder or granules with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder or granules. [3] A method for producing a dental alumina molded body, comprising press-molding the dental alumina granules at 10 to 400 MPa, comprising: (A) α-alumina powder with an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and the aggregated particle diameter is 10 to 100 μm.[4] A method for producing dental alumina granules, comprising spray-drying an alumina dispersion slurry containing (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in a sintering aid, and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder. [5] A method for producing a dental alumina pre-sintered body according to [1] above, characterized by supporting (A) α-alumina powder or granules with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) a pre-sintered body containing Mg as an element included in a sintering aid, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder or granules, and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance. [6] A method for producing a dental alumina dispersion slurry according to [1] above, comprising: (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder; spray drying the slurry to obtain dental alumina granules with an aggregated particle size of 5 to 100 μm; press molding the dental alumina granules at 10 to 400 MPa to obtain a dental alumina molded body; and further pre-sintering the dental alumina molded body at 500 to 1000°C.

[0011] According to the present invention, it is possible to provide a dental alumina pre-sintered body that has high light transmittance and high strength, and a method for producing the same.

[0012] [Dental Alumina Pre-sintered Body] The dental alumina pre-sintered body of the present invention comprises: (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in the sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmission, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and the contrast ratio (Yb / Yw) of the sintered body with a thickness of 1.0 mm obtained by firing the dental alumina pre-sintered body under atmospheric pressure (1013 hPa) at 1450°C is 0.20 to 0.35. The dental alumina pre-sintered body is a dental alumina pre-sintered body in which the sintered body has a bending strength of 800 MPa or more, obtained by firing the aforementioned dental alumina pre-sintered body under atmospheric pressure (1013 hPa) and at 1450°C.

[0013] In this specification, unless otherwise specified, the notation "x to y" using numerical values ​​x and y shall mean "greater than or equal to x and less than or equal to y." If a unit is attached only to the numerical value y in such notation, that unit shall also apply to the numerical value x.

[0014] In this invention, a partially sintered body refers to a state in which a material has not yet become a fully sintered body during the sintering process. During the sintering process, a neck is formed where the constituent particles of the alumina powder granules of the raw material are partially joined together, and as it grows, open pores (i.e., holes open to the outside) are formed due to the voids between the particles. A partially sintered body refers to a state in which a large number of these open pores remain without disappearing.

[0015] <(A) α-Alumina Powder and Granules> The dental alumina pre-sintered body of the present invention (sometimes simply referred to as alumina pre-sintered body) contains α-alumina powder and granules. The α-alumina powder and granules are aggregates of α-alumina particles, which are primary particles. The average primary particle diameter of the α-alumina powder and granules is 30 to 300 nm. If the average primary particle diameter of the α-alumina powder and granules is less than 30 nm, the cohesiveness of the α-alumina powder and granules increases, the dispersibility in the dispersion process decreases, and the yield during granule production tends to decrease. If the average primary particle diameter is greater than 300 nm, the strength (such as bending strength) of the resulting alumina sintered body tends to decrease, and the light transmittance also tends to decrease. The average primary particle diameter of the α-alumina powder and granules is preferably 50 to 280 nm, more preferably 80 to 270 nm, and even more preferably 150 to 250 nm. The average primary particle diameter is measured using a scanning or transmission electron microscope. In detail, it is measured as follows: By performing image analysis on n primary alumina particles, which are 30 or more, preferably 100 or more, randomly selected from images taken with an electron microscope that clearly shows light and dark areas and allows for the identification of particle contours, the equivalent circular diameter of each alumina particle (the diameter of a circle with the same area as the target particle) is determined: X ｉ Find X from the 1st to the nth ｉ Sum of: ΣX ｉ Based on this, the equation is: X = (ΣX ｉ This refers to the average particle diameter X calculated by ) / n.

[0016] The purity of the α-alumina powder used in this invention is 99.5% or higher. If the purity is less than 99.5%, it becomes difficult to adjust the contrast ratio of the resulting sintered body to a predetermined range. A purity of 99.5% or higher for the α-alumina powder means that the concentration of impurities contained in the α-alumina powder is 0.5% by mass or less. The concentration of impurities can be determined by known measurement methods such as ICP emission spectrometry. The purity of the α-alumina powder is preferably 99.7% or higher, and more preferably 99.9% or higher.

[0017] The content of α-alumina powder in the dental alumina pre-sintered body of the present invention is not particularly limited, but is, for example, 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0018] <(B) Mg> The dental alumina pre-sintered body of the present invention contains Mg (magnesium). The Mg is an element contained in the sintering aid contained in the dental alumina pre-sintered body. That is, the dental alumina pre-sintered body of the present invention contains a sintering aid made of a magnesium compound. Examples of magnesium compounds include magnesium oxides, nitrates, acetates, hydroxides, and chlorides, with oxides (magnesium oxide) being preferred. A single magnesium compound may be used, or multiple compounds may be used in combination.

[0019] The amount of Mg (amount of magnesium element) in the dental alumina pre-sintered body is 100 to 5000 ppm by mass as metallic magnesium relative to the α-alumina powder. If the amount of Mg is less than 100 ppm or more than 5000 ppm, the strength of the resulting alumina sintered body tends to decrease. Also, if the amount of Mg is less than 100 ppm, the light transmittance of the resulting sintered body tends to decrease. The amount of Mg is preferably 300 to 3000 ppm by mass as metallic magnesium relative to the α-alumina powder, and more preferably 500 to 1500 ppm. The amount of Mg is adjusted by the amount of magnesium compound added as a sintering aid when manufacturing the dental alumina pre-sintered body.

[0020] <(C) Additive for improving light transmittance> The dental alumina pre-sintered body of the present invention contains an additive for improving light transmittance. The additive for improving light transmittance is an additive that, when compounded, results in a lower contrast ratio (Yb / Yw) compared to the case where it is not compounded. The additive for improving light transmittance in the present invention is at least one element selected from the group consisting of Ce (cerium), Dy (dysprosium), Pr (praseodymium), Nd (neodymium), and Y (yttrium). By using such an additive that improves specific light transmittance, the light transmittance of the sintered body can be improved, and furthermore, strength such as bending strength can also be increased. Among these, the additive for improving light transmittance is preferably at least one element selected from the group consisting of Ce and Y. By selecting such an additive for improving light transmittance, the light transmittance and strength of the obtained dental alumina sintered body can be further enhanced. In particular, selecting Y as the additive for improving light transmittance can greatly improve the light transmittance of the sintered body.

[0021] The content (oxide equivalent value) of the additive for improving light transmittance in the dental alumina pre-sintered body is not particularly limited, but based on mass relative to α-alumina powder granules, it is preferably 1 to 1000 ppm, more preferably 10 to 500 ppm, and still more preferably 30 to 300 ppm. The content of the additive for improving light transmittance is expressed as an oxide equivalent value. The oxides used when calculating the oxide equivalent content of Ce, Dy, Pr, Nd, and Y are respectively CeO ２ , Dy ２ O ３ , Pr ２ O ３ , Nd ２ O ３ , Y ２ O ３ .

[0022] The content of additives that improve light transmission can be adjusted by the amount of light-transmitting additive raw materials used as raw materials when producing the alumina sintered body. These light-transmitting additive raw materials are the elemental sources for the light-transmitting additives (Ce, Dy, Pr, Nd, Y). The content of light-transmitting additives can also be measured using the alumina sintered body as an analytical sample by ICP emission spectroscopy or other methods.

[0023] Examples of translucent additives used as raw materials when producing alumina sintered bodies include cerium compounds containing Ce, dysprosium compounds containing Dy, praseodymium compounds containing Pr, neodymium compounds containing Nd, and yttrium compounds containing Y. Examples of these compounds include salts and complexes containing the aforementioned elements. Examples of raw materials for light-transmitting additives include cerium compounds such as cerium chloride, cerium nitrate, cerium acetate, and cerium sulfate; dysprosium compounds such as dysprosium chloride, dysprosium nitrate, dysprosium fluoride, dysprosium sulfate, dysprosium carbonate, and dysprosium acetate; praseodymium compounds such as praseodymium chloride, praseodymium nitrate, praseodymium acetate, and praseodymium sulfate; neodymium compounds such as neodymium chloride, neodymium fluoride, neodymium nitrate, neodymium acetate, and neodymium sulfate; and yttrium compounds such as yttrium chloride, yttrium nitrate, yttrium acetate, yttrium sulfate, and yttrium carbonate.

[0024] The alumina pre-sintered body of the present invention may contain other components besides the above-mentioned components (A) to (C) to the extent that it does not impair its performance.

[0025] <Contrast Ratio (Yb / Yw)> The contrast ratio (Yb / Yw) of the alumina sintered body (alumina sintered body) with a thickness of 1.0 mm, obtained by firing the alumina sintered body of the present invention under atmospheric pressure (1013 hPa) and 1450°C, is 0.20 to 0.35. If the contrast ratio (Yb / Yw) is greater than 0.35, the light transmission is insufficient, and the aesthetics may be reduced depending on the restoration site. If the contrast ratio (Yb / Yw) is less than 0.20, the color of the adhesive material (dental cement material) cannot be obscured during adhesion to the tooth structure, which may reduce the aesthetics. The above contrast ratio (Yb / Yw) is preferably 0.22 to 0.33, and more preferably 0.25 to 0.32. The contrast ratio (Yb / Yw) can be adjusted by the type and content of additives that improve light transmission. The contrast ratio is defined as the ratio of the Y value (Yw) under a white background and the Y value (Yb) under a black background: the Yb / Yw value. The Y value is the Y value in the tristimulus system of the XYZ color system. A white background is a background with a lightness of 9.5 or higher according to the Munsell color system, and a black background is a background with a lightness of 1 or lower according to the Munsell color system.

[0026] <Bending Strength> The bending strength of the sintered body (alumina sintered body) obtained by firing the alumina pre-sintered body of the present invention under atmospheric pressure (1013 hPa) and at 1450°C is 800 MPa or more. If the bending strength is less than 800 MPa, defects such as breakage are likely to occur when applied to applications requiring strength. The bending strength of the above alumina sintered body is preferably 850 MPa or more, and more preferably 900 MPa or more. The upper limit of the bending strength of the above alumina sintered body is not particularly limited, but the bending strength is, for example, 1500 MPa or less. The bending strength is biaxial bending strength and can be measured by the method described in the examples.

[0027] [Method for producing dental alumina pre-sintered body] In the present invention, the following method for producing a dental alumina pre-sintered body can be provided. That is, the method for producing a dental alumina pre-sintered body of the present invention comprises: (A) an α-alumina powder and granular material having an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in the sintering aid, (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd and Y as an additive for improving light transmittance, The method for producing a dental alumina pre-sintered body is characterized by pre-sintering a dental alumina molded body, in which the content of (B) Mg is 100 to 5000 ppm in terms of mass as metallic magnesium relative to the (A) α-alumina powder and granular material, at 500 to 1000°C.

[0028] The dental alumina molded body used in the method for producing a dental alumina pre-sintered body is preferably produced using dental alumina granules as a raw material.

[0029] <Dental Alumina Granules> The dental alumina granules in the present invention comprise: (A) an α-alumina powder and granular material having an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in the sintering aid; (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd and Y as an additive for improving light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm in terms of mass as metallic magnesium relative to the (A) α-alumina powder and granular material. The granules are obtained by spray-drying an alumina dispersion slurry having the above composition.

[0030] The alumina-dispersed slurry is prepared by dispersing the aforementioned α-alumina powder and granular material, a magnesium compound serving as a sintering aid, and a raw material for a light-transmitting additive in a solvent. The dispersion treatment can be performed using a mixing device such as a ball mill, a bead mill, or a rotation-revolution stirrer. If necessary, additives may be added to the alumina-dispersed slurry. The solvent (dispersion medium) contained in the alumina-dispersed slurry includes water, and may also contain organic solvents such as ethanol, isopropyl alcohol, and dimethylformamide. The amount of the solvent (dispersion medium) used is usually 25 to 300 parts by mass relative to 100 parts by mass of the α-alumina powder and granular material. The slurry concentration of the alumina-dispersed slurry is usually 25 to 80% by mass. Examples of additives that may be optionally blended into the alumina-dispersed slurry include dispersants, plasticizers, binders, defoamers, and release agents.

[0031] The alumina-dispersed slurry prepared as described above contains (A) α-alumina powder and granular material having an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in the sintering aid, and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd and Y as an additive for improving light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm in terms of mass as metallic magnesium relative to the (A) α-alumina powder and granular material. Details of the components (A) to (C) contained in the alumina-dispersed slurry, and the respective contents of (B) Mg and (C) the additive for improving light transmittance relative to the component (A) in the alumina-dispersed slurry, are the same as those described in the aforementioned "dental alumina pre-sintered body".

[0032] Spray-drying the alumina-dispersed slurry prepared as described above yields dental alumina granules. For the spray drying method, the following methods can be employed: a method in which the alumina-dispersed slurry is formed into fine droplets, sprayed and dried using a high-speed air flow, or a method in which the alumina-dispersed slurry is dropped onto a disc-shaped rotating body rotating at a rotational speed of 1000 to 50000 rpm, and the slurry is scattered into a mist by centrifugal force and then dried.

[0033] The resulting dental alumina granules are composed of multiple aggregated particles, each formed by the aggregation of multiple primary α-alumina particles. Any α-alumina particle constituting an aggregated particle is in contact with any other α-alumina particle constituting the same aggregated particle. The formation of aggregated particles can be confirmed, for example, by scanning electron microscopy. The aggregated particle diameter of the dental alumina granules is preferably 5 to 100 μm, more preferably 10 to 100 μm, and even more preferably 10 to 80 μm. When the aggregated particle diameter of the dental alumina granules is within this range, molding defects in the molded article can be suppressed. The aggregated particle diameter can be adjusted to a desired range by adjusting manufacturing conditions, such as the amount of dispersion medium used in the spray drying method. The aggregated particle diameter refers to the average aggregated particle diameter (median diameter in volume statistics) measured by laser diffraction-scattering.

[0034] The dental alumina granules contain (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher, (B) Mg as an element contained in the sintering aid, and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmission, wherein the content of (B) Mg is 100 to 5000 ppm in mass as metallic magnesium relative to the (A) α-alumina powder, and the aggregated particle size is 5 to 100 μm. Details of components (A) to (C) contained in the dental alumina granules, and the respective contents of (B) Mg and (C) additives to improve light transmission relative to component (A) in the dental alumina granules, are the same as those described in the "Dental Alumina Pre-sintered Body" above.

[0035] <Dental Alumina Molded Body> The dental alumina molded body in the present invention is preferably manufactured by molding dental alumina granules. Molding methods include press molding, extrusion molding, injection molding, and casting, with press molding being preferred. Press molding methods include uniaxial press molding and CIP (Cold Isostatic Pressing). Press molding may be carried out in multiple stages, and CIP (Cold Isostatic Pressing) molding may be performed after uniaxial press molding.

[0036] The press pressure used during press forming is, for example, 10 to 400 MPa, preferably 100 to 300 MPa.

[0037] The shape of dental alumina molded bodies can be determined appropriately depending on the purpose, but typically they are disc-shaped (disk type) or rectangular or nearly rectangular (block type).

[0038] The dental alumina molded body contains (A) α-alumina powder or granules with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher, (B) Mg as an element contained in the sintering aid, and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmission, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder or granules. Details of components (A) to (C) contained in the dental alumina molded body, and the respective contents of (B) Mg and (C) additives to improve light transmission relative to component (A) in the dental alumina molded body, are the same as those described in the "Dental Alumina Pre-sintered Body" above.

[0039] <Pre-sintering> A dental alumina pre-sintered body is obtained by pre-sintering the dental alumina molded body obtained as described above. The temperature during pre-sintering is generally lower than the temperature during main sintering, for example, 500 to 1000°C, preferably 550 to 900°C. During pre-sintering, heating causes a diffusion (adhesion, fusion) phenomenon of molecules and atoms on the surface of the alumina particles, resulting in a state where the constituent alumina particles are partially joined together (a state where a so-called neck is formed), thereby improving the strength of the pre-sintered body to a strength that is easy to handle and process. The dental alumina pre-sintered body obtained by pre-sintering is a microporous pre-sintered body having pores that open outwards. Before pre-sintering, degreasing treatment may be performed as needed. Here, degreasing treatment means a treatment to remove adsorbed water, dispersants, plasticizers, binders, defoamers, release agents, etc. contained in the dental alumina molded body by volatilization or decomposition.

[0040] Conventional methods known as degreasing and / or pre-sintering can be used without particular limitation and may be carried out continuously or in multiple stages. Furthermore, it is preferable to carry out the process in an oxygen-containing air atmosphere in order to efficiently remove organic matter. Degreasing and / or sintering can be carried out, for example, by heating in an electric furnace.

[0041] <Other Manufacturing Methods> As described above, a method for manufacturing a dental alumina pre-sintered body of the present invention has been explained, but other methods may also be employed. For example, a method may be employed in which an additive to improve light transmission is incorporated into the pre-sintered body after it has been manufactured without using an additive to improve light transmission. That is, a dental alumina pre-sintered body of the present invention may be manufactured by incorporating at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmission into a pre-sintered body, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder and granules, and (B) Mg is included as an element in the sintering aid, and the content of (B) Mg is 100 to 5000 ppm by mass relative to the (A) α-alumina powder and granules (hereinafter sometimes referred to as an uncolored pre-sintered body).

[0042] Uncolored pre-sintered bodies can be manufactured in the same manner as described in the above-mentioned method for manufacturing dental alumina pre-sintered bodies, except that (C) an additive to improve light transmission is not used. That is, an uncolored dental alumina dispersion slurry containing α-alumina powder and a magnesium compound as a sintering aid is spray-dried to obtain uncolored dental alumina granules, which are then molded to obtain a dental alumina molded body. The dental alumina molded body is then pre-sintered to obtain a dental alumina pre-sintered body (uncolored pre-sintered body). Methods for incorporating (C) an additive to improve light transmission into the uncolored pre-sintered body include immersing the uncolored pre-sintered body in a liquid in which the above-mentioned light-transmitting additive raw material is dissolved or dispersed, or dropping or coating the uncolored pre-sintered body with the liquid in which the above-mentioned light-transmitting additive raw material is dissolved or dispersed. As a result, the additive to improve light transmission penetrates into the pores of the uncolored pre-sintered body, and the additive to improve light transmission is supported on the inside and surface of the pre-sintered body. The solvent (coloring agent solvent) constituting the liquid in which the light-transmitting additive raw material is dissolved or dispersed is water and / or an organic solvent, preferably water, an alcohol-based organic solvent such as ethanol or isopropyl alcohol, or a glycol-based organic solvent such as ethylene glycol or propylene glycol. One type of solvent (coloring agent solvent) may be used alone, or two or more types may be used in combination. The concentration of the raw material in the liquid in which the light-transmitting additive raw material is dissolved or dispersed is not particularly limited, and can be adjusted as appropriate so that the concentration in the dental alumina sintered body of the present invention produced is the desired concentration, but it is preferable that the amount of the light-transmitting additive raw material relative to the solvent be about 0.001 to 10% by mass.

[0043] Furthermore, although a method using dental alumina granules has been described for the manufacturing method of dental alumina pre-sintered bodies, the bodies may also be manufactured without using the granules. For example, a mixture of α-alumina powder, a magnesium compound which is a sintering aid, and a raw material for a translucent additive may be molded to obtain a dental alumina molded body, and the molded body may be pre-sintered.

[0044] [Use of Dental Alumina Pre-Sintered Body] The dental pre-sintered body of the present invention is used for the purpose of dental restoration and may be machined into an appropriate shape as needed. Machining can be performed using a CAD / CAM system. A CAD / CAM system refers to a system that uses computer-aided design to design desired three-dimensional shape data (CAD) and performs computer-aided manufacturing (CAM). By sintering (final sintering) the dental alumina pre-sintered body, a dental alumina sintered body with excellent light transmission and high strength can be obtained. The dental pre-sintered body to be sintered may be one that has been machined as described above, or it may not have been machined. Generally, the dental alumina pre-sintered body is machined before sintering. The temperature during sintering is, for example, 1200 to 1700°C, preferably 1300 to 1600°C. The pressure during final sintering can be, for example, atmospheric pressure in the range of 960 to 1060 hPa. The sintering time depends on the sintering temperature, but is usually about 5 minutes to 6 hours, preferably about 10 minutes to 4 hours. The dental alumina sintered body obtained as described above has high translucency and high strength, and can therefore be suitably used as a dental prosthesis, particularly for restoring the incisal edges of anterior teeth and the occlusal surfaces of molars.

[0045] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these examples.

[0046] [Measurement Method] The sintered bodies prepared by firing the pre-sintered bodies made in each example and comparative example at atmospheric pressure (1013 hPa) and 1450°C for 2 hours were measured as follows.

[0047] <Contrast Ratio (Yb / Yw)> The sintered body prepared as described above was made to a thickness of 1.0 mm, and the spectral reflectance was measured using a spectrophotometer (Tokyo Denshoku Co., Ltd., Spectrophotometer "TC-1800MKII") under a black background and a white background. The contrast ratio was measured by dividing the Y value (Yb) under the black background by the Y value (Yw) under the white background. Note that the smaller the Yb / Yw, the more transparent the material.

[0048] <Bending Strength> The pre-sintered bodies prepared in each example and comparative example were fired as described above to obtain test specimens consisting of disc-shaped sintered bodies with a diameter of approximately 16.9 mm and a thickness of approximately 1.2 mm. The test specimens were set in an Autograph (manufactured by Shimadzu Corporation), and the biaxial bending fracture strength was measured with an indenter radius of 0.7 mm, a support circle radius of 5 mm, and a crosshead speed of 1 mm / min. The bending strength was calculated using the following formula. Five test specimens were evaluated, and the average value was taken as the bending strength (MPa). Formula: σ = (-0.2387F)(X-Y) / (t ２ ) X=(1+ν)ln(r ２ / r ３ ) ２ +{(1-ν) / 2}(r ２ / r ３ ) ２ Y=(1+ν){1+ln(r １ / r ３ ) ２} + (1 - ν) (r １ / r ３ ) ２ The symbols above represent, respectively: σ: biaxial bending strength (MPa), F: load at fracture of the specimen (N), t: specimen thickness (mm), ν: Poisson's ratio (0.24 for alumina), r １ : Support circle radius (5 mm in this test), r ２ : Indenter radius (0.7 mm in this test), r ３ : Represents the radius of the test specimen (mm).

[0049] The raw materials used in the examples and comparative examples are as follows:

[0050] <(A) α-Alumina powder> - α-Alumina powder: NXA100 (manufactured by Sumitomo Chemical Co., Ltd.) Average primary particle size 150 nm, purity 99.99% - α-Alumina powder: NXA150 (manufactured by Sumitomo Chemical Co., Ltd.) Average primary particle size 200 nm, purity 99.99%・α-Alumina powder: AKP-20 (manufactured by Sumitomo Chemical) Average primary particle size 420 nm, purity 99.99%

[0051] <(B) Mg> Magnesium oxide powder: 500A (manufactured by Ube Materials Co., Ltd.)

[0052] <(C) Additives to improve light transmission> The following compounds were used as additives to improve light transmission: Ce source: Cerium(III) acetate monohydrate Y source: Yttrium(III) nitrate hexahydrate Dy source: Dysprosium(III) nitrate hexahydrate Pr source: Praseodymium(III) nitrate hexahydrate Nd source: Neodymium(III) nitrate hexahydrate

[0053] <Additives not included in (C) component> As a source of Fe, iron(II) sulfate heptahydrate

[0054] <Example 1> (A) 100 g of NXA100 (manufactured by Sumitomo Chemical Co., Ltd.), 0.5 g of a dispersant (SN Dispersant 5468, manufactured by Sunopco Corporation), and 62 g of pure water were mixed together. This was placed in a polyamide pot and ball-milled at 65 rpm for 6 hours to prepare an alumina slurry. Next, (B) 3.32 g of magnesium oxide powder (500A, manufactured by Ube Materials Co., Ltd.) and 66.3 g of pure water were dispersed in a bead mill at 2400 rpm for 30 minutes to prepare a magnesium oxide dispersion as a sintering aid, which is a source of Mg. Next, 100 g of the alumina slurry, 48 g of pure water, 2.1 g of the magnesium oxide dispersion, 2.5 g of binder (SA-261P, manufactured by Japan Coating Resin Co., Ltd.), 0.6 g of plasticizer (PEG400, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and (C) 0.01200 g of cerium(III) acetate monohydrate as a raw material for an additive to improve light transmission (raw material for light transmission additive) (cerium oxide: CeO ２A quantity equivalent to 100 ppm of α-alumina powder was weighed and mixed and stirred for 10 minutes to prepare a dental alumina dispersion slurry. The dental alumina dispersion slurry was then spray-dried and dried to prepare dental alumina granules (aggregated particle size 39 μm). The dental alumina granules were filled into a mold of a predetermined shape and uniaxially pressurized at a pressure of 200 MPa for 1 minute to produce a dental alumina molded body. The dental alumina molded body was heated from 25°C to 600°C at a heating rate of 10°C / min, then left to degrease for 30 minutes, and then heated to 700°C at a heating rate of 10°C / min for 2 hours of pre-sintering to produce a dental alumina pre-sintered body. Subsequently, the temperature was raised from 700°C to 1450°C at a heating rate of 10°C / min, left to cool for 2 hours, and then a dental alumina sintered body was produced. The results of each evaluation are shown in Table 1.

[0055] <Examples 2-6, Comparative Examples 1-4> Dental alumina pre-sintered bodies were prepared in accordance with Example 1, except that the raw materials for the additives that improve light transmittance (raw materials for light transmittance additives) and their proportions were appropriately changed to obtain the pre-sintered bodies shown in Tables 1-2. The evaluation results are shown in Tables 1-2.

[0056]

[0057]

[0058] <Example 7> (A) 100 g of NXA100 (manufactured by Sumitomo Chemical Co., Ltd.), 0.5 g of a dispersant (SN Dispersant 5468, manufactured by Sunopco Corporation), and 62 g of pure water were mixed together. This mixture was placed in a polyamide pot and ball-milled at 65 rpm for 6 hours to prepare an alumina slurry. Next, (B) 3.32 g of magnesium oxide powder (500A, manufactured by Ube Materials Co., Ltd.) and 66.3 g of pure water were dispersed in a bead mill at 2400 rpm for 30 minutes to prepare a magnesium oxide dispersion as a sintering aid, which is a source of Mg. Next, 100 g of the alumina slurry, 48 g of pure water, 2.1 g of the magnesium oxide dispersion, 2.5 g of binder (SA-261P, manufactured by Japan Coating Resin Co., Ltd.), and 0.6 g of plasticizer (PEG400, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed out and mixed and stirred for 10 minutes to prepare an uncolored dental alumina dispersion slurry. Furthermore, the uncolored dental alumina dispersion slurry was spray-dried and dried to prepare uncolored dental alumina granules. The uncolored dental alumina granules were filled into a mold having a predetermined shape and uniaxially pressurized at a pressure of 200 MPa for 1 minute to produce a dental alumina molded body. A dental alumina molded body was heated from 25°C to 600°C at a heating rate of 10°C / min, then degreased by holding it for 30 minutes. After that, the temperature was raised to 680°C at a heating rate of 10°C / min and pre-sintered for 2 hours to produce a dental alumina pre-sintered body (uncolored pre-sintered body). Next, the dental alumina pre-sintered body (uncolored pre-sintered body) was immersed for 5 minutes in an aqueous solution of 0.55 g of cerium(III) acetate monohydrate dispersed in 460 g of water, and then dried at 100°C for 30 minutes to produce a dental alumina pre-sintered body impregnated with an additive that improves light transmission. The content of the additive that improves light transmission relative to α-alumina powder in the dental alumina pre-sintered body (in oxide equivalent) was 100 ppm. The content of the additive that improves light transmission was measured by ICP emission spectrometry. Subsequently, the dental alumina pre-sintered body was heated from 25°C to 1450°C at a heating rate of 10°C / min, and after 2 hours of sintering, it was allowed to cool to produce a dental alumina sintered body. The evaluation results are shown in Table 3.

[0059] <Examples 8-16> Dental alumina sintered bodies were prepared in accordance with Example 7, except that the additives used to improve light transmittance were appropriately changed as shown in Table 3, and the coloring agent solvent was also changed as shown in Table 3. The evaluation results for each are shown in Table 3.

[0060]

[0061] The results in Tables 1 and 3 show that the sintered bodies produced by firing the dental alumina pre-sintered bodies of each example containing the specified components (A) to (C) had a contrast ratio (Yb / Yw) in the range of 0.20 to 0.35, exhibiting excellent light transmission and high flexural strength. The results in Table 2 show that the sintered bodies made from the pre-sintered bodies of each comparative example that did not contain at least one of the components (A) to (C) had poor light transmission or low flexural strength.

Claims

1. A dental alumina pre-sintered body comprising: (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in the sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmission, wherein the content of (B) Mg is 100 to 5000 ppm in mass as metallic magnesium relative to the (A) α-alumina powder; wherein the contrast ratio (Yb / Yw) of the sintered body with a thickness of 1.0 mm obtained by firing the dental alumina pre-sintered body under atmospheric pressure (1013 hPa) and 1450°C is 0.20 to 0.35; and the bending strength of the sintered body obtained by firing the dental alumina pre-sintered body under atmospheric pressure (1013 hPa) and 1450°C is 800 MPa or higher.

2. A method for producing a dental alumina molded body, characterized by pre-sintering a dental alumina molded body at 500 to 1000°C, comprising: (A) α-alumina powder or granules with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder or granules.

3. A method for producing a dental alumina molded body, comprising press-molding the dental alumina granules at 10 to 400 MPa, comprising: (A) α-alumina powder with an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and the aggregated particle diameter is 5 to 100 μm.

4. A method for producing dental alumina granules, comprising spray-drying an alumina dispersion slurry containing (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher, (B) Mg as an element contained in a sintering aid, and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder.

5. A method for producing a dental alumina pre-sintered body according to claim 1, characterized in that (A) α-alumina powder or granules with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) a pre-sintered body containing Mg as an element included in a sintering aid, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder or granules, and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance.

6. A method for producing a dental alumina pre-sintered body according to claim 1, comprising: (A) α-alumina powder with an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ce, Dy, Pr, Nd, and Y as an additive to improve light transmittance, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder; spray drying the alumina dispersion slurry to obtain dental alumina granules with an aggregated particle diameter of 5 to 100 μm; press molding the dental alumina granules at 10 to 400 MPa to form a dental alumina molded body; and further pre-sintering the dental alumina molded body at 500 to 1000°C.

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