Alumina pre-sintered body for crown color and method for producing same, method for producing alumina molded body for crown color, and method for producing alumina granular body for crown color

Abstract

The present invention provides an alumina pre-sintered body for crown color, the alumina pre-sintered body containing: (A) an α-alumina powder material having an average primary particle diameter of 30-300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in a sintering aid; (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow colorant; and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red colorant, wherein the content of (B) Mg is 100-5000 ppm in terms of metallic magnesium mass with respect to (A) the α-alumina powder material. A sintered body having a thickness of 3.0 mm obtained by sintering the alumina pre-sintered body for crown color under the conditions of atmospheric pressure (1013 hPa) and 1450°C has an a*value of −5 to +4 and a b*value of +3 to +25 under a black background. A sintered body obtained by sintering the alumina pre-sintered body for crown color under the conditions of atmospheric pressure (1013 hPa) and 1450°C has a bending strength of 800 MPa or greater. According to the present invention, it is possible to provide an alumina pre-sintered body for crown color, with which it is possible to produce a sintered body satisfactorily reproducing a crown color and having a high strength.

Description

Preliminary sintered crown-colored alumina, method for producing the same, method for producing crown-colored alumina molded body, method for producing crown-colored alumina granules

[0001] The present invention relates to a preliminary sintered crown-colored alumina, a method for producing the same, a method for producing a crown-colored alumina molded body, and a method for producing a crown-colored alumina granules.

[0002] In dental restoration, various materials such as metals, ceramics, and resins are selected. Among them, ceramics are promising materials as an alternative to metals, and are used in crown restoration where esthetics are required. In particular, zirconia ceramics are widely used from the viewpoints of their strength and esthetics. Dental restoration using zirconia ceramics generally involves cutting a mill blank (material to be processed) made of a preliminarily sintered zirconia ceramic into a shape digitally designed in advance by a dental technician or dentist, followed by processes such as main sintering and polishing.

[0003] Dental restoration using zirconia ceramics is widely widespread, but there are still issues to be improved in terms of physical property balance, such as the tendency that strength decreases when esthetic properties (translucency) are enhanced. As ceramics other than zirconia ceramics, lithium disilicate glass ceramics are known as a material with excellent translucency, but their strength is not sufficient.

[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 preliminary sintered body that contains alumina (purity of 99.5% or more) having an average primary particle diameter of 50 to 300 nm, wherein D10 in the cumulative pore distribution is 20 nm or more and D90 is 90 nm or less, and it is described that the preliminary sintered body has excellent machinability and high translucency after sintering. Patent Document 2 discloses an invention relating to a dental oxide ceramic preliminary sintered body that contains alumina having an average circularity of primary particles of 0.81 or more, with a relative density of 43 to 63%, and it is described that the preliminary sintered body has excellent polishability, and the polished surface of the preliminary sintered body and the surface of the sintered body after sintering have high flatness and excellent esthetics.

[0005] Patent Document 3 discloses an invention relating to a dental alumina calcined body comprising high-purity alumina having an average primary particle diameter of 30 to 300 nm, a sintering aid, and a blue colorant, wherein the content of the sintering aid is 10 to 5000 ppm, and it is described that yellowing after sintering can be suppressed, and a sintered body having high light transmittance, linear light transmittance and high aesthetic properties can be provided even when sintering is performed under atmospheric pressure. Patent Document 4 discloses an invention relating to a dental alumina workpiece, wherein the average crystal grain size at a first point and a second point in specific sections from one end and the other end of the dental alumina workpiece are different from each other, and it is described that the sintered body after sintering is excellent in light transmittance, strength and linear light transmittance.

[0006] WO 2023 / 127559 pamphlet WO 2023 / 127561 pamphlet WO 2023 / 127562 pamphlet WO 2023 / 127564 pamphlet

[0007] In dental restoration, it is required from the viewpoint of aesthetics that the color tone of the restoration site and its surrounding area match. For example, when restoring a crown, a material that can well reproduce crown color is required. As described above, various studies have been conducted on alumina ceramics, and from the viewpoint of aesthetics, it is known that a blue colorant is blended as in Patent Document 3 to suppress yellowing after firing. However, in Patent Document 3, the combination of colorants and the like have not been studied in detail, and there was room for improvement in order to well reproduce crown color.

[0008] Therefore, an object of the present invention is to provide a crown color alumina pre-sintered body capable of producing a high-strength sintered body with good reproduction of crown color, and a method for producing the same.

[0009] The present inventors have conducted intensive studies to achieve the above object. As a result, the present invention provides a pre-sintered alumina body for crown color, which comprises high-purity α-alumina powder granules having an average primary particle diameter in a specific range, a specific amount of Mg derived from a sintering aid composed of a magnesium compound, and further contains a specific yellow-based colorant and a specific red-based colorant, wherein a of the sintered body after firing is ＊ value and b ＊We have found that the above problems can be solved by using a pre-sintered alumina body for tooth coloring with a specific range of values ​​and bending strength, and have completed the present invention. The present invention relates to the following [1] to [6].

[0010] [1] (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 the sintering aid, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, 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 alumina pre-sintered body for tooth coloring with a thickness of 3.0 mm obtained by firing the alumina pre-sintered body for tooth coloring at atmospheric pressure (1013 hPa) and 1450°C is measured against a black background. ＊ The value is -5 to +4, b ＊A pre-sintered alumina body for tooth coloring, wherein the value is +3 to +25, and the bending strength of the sintered body obtained by firing the pre-sintered alumina body for tooth coloring under atmospheric pressure (1013 hPa) and 1450°C is 800 MPa or more. [2] A method for producing a tooth-coloring alumina molded body, characterized by pre-sintering at 500 to 1000°C the alumina molded body for tooth coloring, 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; (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent; and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder. [3] A method for producing alumina molded articles for tooth coloring, comprising press-molding alumina granules for tooth coloring at 10 to 400 MPa, wherein the alumina granules for tooth coloring contain (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, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, the content of (B) Mg being 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and the aggregated particle diameter being 5 to 100 μm. [4] A method for producing alumina granules for tooth crown coloring, 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, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, 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 an alumina pre-sintered body for tooth crown coloring according to [1] above, characterized in that (A) α-alumina powder 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 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, and (C) at least one element selected from Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent. [6] (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 the sintering aid, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is the same as that of (A) α-alumina A method for producing a tooth-coloring alumina pre-sintered body according to [1] above, comprising: spray-drying an alumina dispersion slurry containing 100 to 5000 ppm of metallic magnesium on a granular base to obtain alumina granules for tooth coloring with aggregated particle size of 5 to 100 μm; press-molding the alumina granules for tooth coloring at 10 to 400 MPa to obtain a tooth-coloring alumina molded body; and then pre-sintering the tooth-coloring alumina molded body at 500 to 1000°C.

[0011] According to the present invention, it is possible to provide a pre-sintered alumina body for tooth coloring that can reproduce tooth color well and produce a high-strength sintered body, and a method for manufacturing the same.

[0012] [Alumina Pre-sintered Body for Tooth Crown Coloring] The alumina pre-sintered body for tooth crown coloring 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 more; (B) Mg as an element contained in the sintering aid; (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent; and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the α-alumina powder (A), and the alumina pre-sintered body for tooth crown coloring is sintered at atmospheric pressure (1013 hPa) at 1450°C to obtain a sintered body with a thickness of 3.0 mm, and a black background. ＊ The value is -5 to +4, b ＊ The alumina pre-sintered body for tooth coloring has a value of +3 to +25, and the sintered body obtained by firing the alumina pre-sintered body for tooth coloring under atmospheric pressure (1013 hPa) and 1450°C has a bending strength of 800 MPa or more.

[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 pre-sintered alumina for crown-colored dental restorations of the present invention (sometimes simply referred to as pre-sintered alumina) contains α-alumina powder and granules. The α-alumina powder and granules are an aggregate 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. When the average primary particle diameter of the α-alumina powder and granules is less than 30 nm, the aggregability of the α-alumina powder and granules increases, the dispersibility in the dispersion step decreases, and the yield during granule production tends to decrease; when the average primary particle diameter exceeds 300 nm, the strength (such as flexural strength) of the obtained sintered alumina 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 still more preferably 120 to 250 nm. The average primary particle diameter is measured using a scanning or transmission electron microscope. Specifically, it is measured as follows. That is, image analysis is performed on n alumina particles which are primary particles, 30 or more randomly selected, preferably 100 or more, from an electron microscope captured image with clear contrast where the outlines of the particles can be identified, to obtain the equivalent circular diameter (diameter of a circle having the same area as that of the target particle) X of each alumina particle ｉ and calculate the sum of X from the 1st to the nth particle ｉ : ΣX ｉ based on which, the average particle diameter X calculated by the formula X = (ΣX ｉ ) / n is meant.

[0016] The purity of the α-alumina powder and granules used in the present invention is 99.5% or higher. When the purity is lower than 99.5%, the strength (flexural strength) of the obtained sintered body tends to decrease. The statement that the purity of α-alumina powder and granules is 99.5% or higher means that the concentration of impurities contained in the α-alumina powder and granules is 0.5% by mass or less. The impurity concentration can be determined by a known measurement method such as ICP emission spectrometry. The purity of the α-alumina powder and granules is preferably 99.7% or higher, and more preferably 99.9% or higher.

[0017] The content of α-alumina powder in the alumina pre-sintered body for tooth crown coloring 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 alumina temporary sintered body for tooth coloring of the present invention contains Mg (magnesium). The Mg is an element contained in the sintering aid contained in the alumina temporary sintered body for tooth coloring. That is, the alumina temporary sintered body for tooth coloring 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 alumina pre-sintered body for tooth coloring 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. The amount of Mg is preferably 300 to 3000 ppm, and more preferably 500 to 2500 ppm, by mass as metallic magnesium relative to the α-alumina powder. The amount of Mg is adjusted by the amount of magnesium compound added as a sintering aid when manufacturing the alumina pre-sintered body for tooth coloring.

[0020] <(C) Yellow-based coloring agent> The alumina temporary sintered body for tooth crown coloring of the present invention contains a yellow-based coloring agent. By using the yellow-based coloring agent in combination with the red-based coloring agent described later, the resulting sintered body can reproduce tooth crown color well and also has increased strength. By incorporating the yellow-based coloring agent, the b of the resulting alumina sintered body is improved compared to when it is not incorporated. ＊ This is a coloring agent that increases the value. The yellow coloring agent in this invention is at least one element selected from the group consisting of Ce (cerium), Dy (dysprosium), Ni (nickel), and Sm (samarium). By using such a specific yellow coloring agent, the b of the sintered body described later can be increased.＊ This makes it easier to adjust the values ​​to a specific range and reproduce tooth color. The yellow coloring agent is preferably at least one element selected from the group consisting of Ce and Ni. By selecting such a yellow coloring agent, the strength of the resulting tooth-colored alumina sintered body can be further increased.

[0021] The content of yellow coloring agent (in oxide equivalent) in the alumina temporary sintered body for tooth crown coloring is not particularly limited, but is preferably 1 to 2000 ppm, more preferably 3 to 1500 ppm, and even more preferably 5 to 800 ppm by mass relative to the α-alumina powder granules. The content of the yellow coloring agent is an oxide equivalent value. The oxides used when calculating the oxide equivalent content of Ce, Dy, Ni, and Sm are, respectively, CeO ２ , Dy ２ O ３ NiO, Sm ２ O ３ That is the case.

[0022] The content of the yellow coloring agent can be adjusted by the amount of the raw material for the yellow coloring agent used as a raw material when producing the alumina sintered body. The raw material for the yellow coloring agent is the elemental source of the yellow coloring agent (Ce, Dy, Ni, Sm). The content of the yellow coloring agent can also be measured by ICP emission spectroscopy or other methods using the alumina sintered body as an analytical sample.

[0023] Examples of raw materials for yellow colorants used when producing alumina sintered bodies include cerium compounds containing Ce, dysprosium compounds containing Dy, nickel compounds containing Ni, and samarium compounds containing Sm. Examples of the above compounds include salts and complexes containing the aforementioned elements. Examples of raw materials for yellow colorants 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; nickel compounds such as nickel chloride, nickel nitrate, nickel sulfate, nickel acetate, and nickel hypophosphite; and samarium compounds such as samarium chloride, samarium nitrate, samarium sulfate, samarium phosphate, and samarium acetate.

[0024] <(D) Red-based coloring agent> The alumina temporary sintered body for tooth crown coloring of the present invention contains a red-based coloring agent. By using the red-based coloring agent in combination with the yellow-based coloring agent described above, the resulting sintered body can reproduce tooth crown color well and also has increased strength. By incorporating the red-based coloring agent, the alumina sintered body obtained has a higher strength compared to when it is not incorporated. ＊ This is a coloring agent that increases the value. The red coloring agent in this invention is at least one element selected from the group consisting of Ho (holmium), Er (erbium), Cr (chromium), Mn (manganese), Cu (copper), and Eu (europium). By using such a specific red coloring agent, the a of the sintered body described later can be ＊ This makes it easier to adjust the values ​​to a specific range and reproduce tooth color. The red coloring agent is preferably at least one element selected from the group consisting of Cr and Mn. By selecting such a red coloring agent, the strength of the resulting alumina sintered body can be further increased.

[0025] In particular, it is preferable to select at least one element from the group consisting of Cr and Mn as the red coloring agent, and at least one element from the group consisting of Ce and Ni as the yellow coloring agent. By combining specific red and yellow coloring agents in this way, the strength of the resulting alumina sintered body is effectively improved. The reason for this is not entirely clear, but it is presumed that the alumina sintered body is densely packed while suppressing the growth of particle size due to the inclusion of multiple specific elements.

[0026] The content of red coloring agent (in oxide equivalent) in the alumina pre-sintered body for tooth crown coloring is not particularly limited, but is preferably 1 to 2000 ppm, more preferably 5 to 1000 ppm, and even more preferably 10 to 500 ppm, on a mass basis relative to the α-alumina powder granules. The content of the red coloring agent is expressed in oxide equivalent. Note that when calculating the oxide equivalent content of Ho, Er, Cr, Mn, Cu, and Eu, the oxides are as follows: ２ O ３ Er ２ O ３ , Cr ２ O ３ Mn ３ O ４ CuO, Eu ２ O ３ That is the case.

[0027] The content of the red coloring agent can be adjusted by the amount of raw materials for the red coloring agent used as raw materials when producing the alumina sintered body. The raw materials for the red coloring agent are the elemental sources of the red coloring agent (Ho, Er, Cr, Mn, Cu, Eu). The content of the red coloring agent can also be measured by ICP emission spectroscopy or other methods using the alumina sintered body as an analytical sample.

[0028] Examples of red coloring agents used as raw materials when producing alumina sintered bodies include holmium compounds containing Ho, erbium compounds containing Er, chromium compounds containing Cr, manganese compounds containing Mn, copper compounds containing Cu, or europium compounds containing Eu. Examples of the above compounds include salts and complexes containing the aforementioned elements. Examples of raw materials for red colorants include holmium compounds such as holmium chloride, holmium nitrate, holmium sulfate, holmium oxalate, and holmium acetate; erbium compounds such as erbium chloride, erbium nitrate, erbium fluoride, and erbium acetate; chromium compounds such as chromium chloride, chromium nitrate, chromium fluoride, chromium sulfate, and chromium acetate; manganese compounds such as manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate; copper compounds such as copper chloride, copper fluoride, copper bromide, copper sulfate, copper nitrate, copper oxalate, and copper acetate; and europium compounds such as europium chloride, europium nitrate, europium fluoride, and europium acetate.

[0029] <Other Elemental Components> The alumina temporary sintered body for tooth coloring of the present invention may contain other components besides the above-mentioned components (A) to (D), to the extent that it does not impair its performance. For example, it may contain other elemental components other than the elements indicated by (C) yellow coloring agent and (D) red coloring agent above. More specifically, the alumina temporary sintered body for tooth coloring of the present invention may contain, as other elemental components, at least one element selected from the group consisting of Nd (neodymium), Co (cobalt), Pr (praseodymium), Li (lithium), and Zr (zirconium). In particular, containing either or both Nd and Co as other elemental components can further increase the strength of the resulting tooth coloring alumina sintered body.

[0030] When the alumina pre-sintered body for tooth coloring contains other elemental components, the content of these other elemental components (in terms of oxides) is not particularly limited, but is preferably 0.1 to 200 ppm, more preferably 0.5 to 100 ppm, and even more preferably 1 to 50 ppm, on a mass basis relative to the α-alumina powder. The content of other elemental components is expressed in terms of oxides. Note that when calculating the oxide content of Nd, Co, Pr, Li, and Zr, the oxides used are Nd, Co, Pr, Li, and Zr, respectively. ２ O ３ Co ２ O ３ , Pr ２ O ３ Li ２ O, ZrO ２ The content of other elemental components can be adjusted by the proportions of raw materials used when producing the alumina pseudosintered body. The content of other elemental components can also be measured using the alumina pseudosintered body as an analytical sample by ICP emission spectroscopy or other methods.

[0031] When incorporating other elemental components into alumina pre-sintered bodies for dental crown coloring, it is preferable to use neodymium compounds containing Nd, cobalt compounds containing Co, praseodymium compounds containing Pr, lithium compounds containing Li, and zirconium compounds containing Zr as raw materials for incorporating other elemental components during the production of the alumina pre-sintered body. Examples of the aforementioned compounds include salts and complexes containing the aforementioned elements.

[0032] <a ＊ value, b ＊ Value > The alumina sintered body of the present invention, with a thickness of 3.0 mm, was fired under atmospheric pressure (1013 hPa) and 1450°C (2-hour anchoring), and the value of the alumina sintered body under a black background. ＊ The value is between -5 and +4, and b ＊ The value is between +3 and +25. Alumina sintered body is such a ＊ Value and b ＊ Being a value makes it easier to reproduce tooth color. (a) ＊ The value is preferably -3 to +4, and more preferably -1 to +3. (See b above) ＊The value is preferably +4 to +20, and more preferably +5 to +18. a of the alumina sintered body ＊ Value and b ＊ The value can be adjusted by the type and amount of yellow and red colorants used. ＊ Value and b ＊ The value represents chromaticity in the CIELab color system and is an index of hue and saturation. ＊ Value and b ＊ The value is measured using a spectrophotometer. Also, a ＊ Value and b ＊ The values ​​are measured against a black background. A black background is defined as a surface with a lightness of 1 or less according to the Munsell color system and a spectral reflectance of 10% or less at wavelengths of 380 to 780 nm.

[0033] <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 1450°C (2-hour anchoring) 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.

[0034] The alumina temporary sintered body for tooth coloring described above can be obtained by the method for manufacturing the alumina temporary sintered body for tooth coloring described later.

[0035] [Method for Manufacturing a Pre-Sintered Alumina Body for Tooth Crown Coloring] The present invention provides the following method for manufacturing a pre-sintered alumina body for tooth crown coloring. That is, the present invention provides a method for manufacturing a pre-sintered alumina body for tooth crown coloring, characterized by pre-sintering a molded alumina body for tooth crown coloring at 500 to 1000°C, which contains (A) α-alumina powder or granules 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, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, 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.

[0036] In the method for manufacturing alumina temporary sintered bodies for tooth coloring, it is preferable to manufacture the alumina molded body for tooth coloring using alumina granules for tooth coloring as a raw material.

[0037] <Alumina Granules for Tooth Crown Coloring> The alumina granules for tooth crown coloring in the present invention are obtained by spray-drying an alumina dispersion slurry which contains (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, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder.

[0038] The alumina dispersion slurry is prepared by dispersing the above-mentioned α-alumina powder and granules, a magnesium compound as a sintering aid, a raw material for a yellow colorant, and a raw material for a red colorant in a solvent. The dispersion process can be carried out using mixing equipment such as a ball mill, bead mill, or orbital agitator. Additives may be added to the alumina dispersion slurry as needed. The solvent (dispersion medium) contained in the alumina dispersion slurry includes water, and may also include organic solvents such as ethanol, isopropyl alcohol, and dimethylformamide. The amount of solvent (dispersion medium) used is usually 25 to 300 parts by mass per 100 parts by mass of α-alumina powder and granules. The slurry concentration of the alumina dispersion slurry is usually 25 to 80% by mass. Additives that may be added to the alumina dispersion slurry as needed include dispersants, plasticizers, binders, defoamers, and release agents.

[0039] The alumina dispersion slurry prepared as described above contains (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, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder. Details of components (A) to (D) contained in the alumina dispersion slurry, and the respective contents of (B) Mg, (C) yellow coloring agent, and (D) red coloring agent relative to component (A) in the alumina dispersion slurry are the same as those described in the "Alumina Pre-sintered Body for Tooth Crown Coloring" above.

[0040] Alumina granules for tooth coloring can be obtained by spray-drying the alumina dispersion slurry prepared as described above. The spray-drying method can be employed in which the alumina dispersion slurry is sprayed in fine droplets using a high-speed airflow and dried, or in which the alumina dispersion slurry is dropped onto a disc-shaped rotating body rotating at a rotational speed of 1,000 to 50,000 rpm and blown off in a mist by centrifugal force.

[0041] The resulting alumina granules for tooth coloring are composed of multiple aggregated particles, each aggregated 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 alumina granules for tooth coloring 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 alumina granules for tooth coloring is within this range, molding defects in the molded product 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.

[0042] The alumina granules for tooth coloring contain (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 the sintering aid, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, 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 size is 5 to 100 μm. The details of components (A) to (D) contained in the alumina granules for tooth coloring, and the respective contents of (B) Mg, (C) yellow coloring agent, and (D) red coloring agent relative to component (A) in the alumina granules for tooth coloring, are the same as those described in the "Alumina Pre-sintered Body for Tooth Coloring" section above.

[0043] <Alumina Molded Body for Tooth Crown Coloring> The alumina molded body for tooth crown coloring in the present invention is preferably manufactured by molding alumina granules for tooth crown coloring. Examples of molding methods include press molding, extrusion molding, injection molding, and casting, with press molding being preferred. Examples of press molding 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.

[0044] The press pressure used during press forming is, for example, 10 to 400 MPa, preferably 100 to 300 MPa.

[0045] The shape of the alumina molded body for tooth coloring can be determined appropriately depending on the purpose, but typically disc-shaped (disk type) or rectangular or roughly rectangular (block type) shapes are common.

[0046] The alumina molded body for tooth coloring contains (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, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder. Details of components (A) to (D) contained in the alumina molded body for tooth coloring, and the respective contents of (B) Mg, (C) yellow coloring agent, and (D) red coloring agent relative to component (A) in the alumina molded body for tooth coloring, are the same as those described in the "pre-sintered alumina body for tooth coloring" above.

[0047] <Pre-sintering> A pre-sintered alumina body for tooth coloring is obtained by pre-sintering the alumina molded body for tooth coloring 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), and the strength of the pre-sintered body can be improved to a strength that is easy to handle and process. The pre-sintered alumina body for tooth coloring obtained by pre-sintering is a porous 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 alumina molded body for tooth coloring by volatilization or decomposition.

[0048] 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 pre-sintering can be carried out, for example, by heating in an electric furnace.

[0049] <Other Manufacturing Methods> As described above, the method for manufacturing alumina temporary sintered bodies for tooth coloring according to the present invention has been explained, but other methods may also be used. For example, a method may be adopted in which a temporary sintered body is manufactured without using (C) yellow coloring agent and (D) red coloring agent, and then (C) yellow coloring agent and (D) red coloring agent are supported on the temporary sintered body. In other words, the alumina pre-sintered body for tooth crown coloring of the present invention may be manufactured by supporting (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, and (B) a pre-sintered body containing Mg as an element in the sintering aid, wherein the content of (B) Mg is 100 to 5000 ppm in mass as metallic magnesium relative to (A) α-alumina powder (hereinafter sometimes referred to as an uncolored pre-sintered body) with (C) at least one element selected from Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent.

[0050] Uncolored pre-sintered bodies can be manufactured in the same manner as described in the above-mentioned method for manufacturing tooth-coloring alumina pre-sintered bodies, except that (C) yellow colorants and (D) red colorants are not used. Specifically, an uncolored tooth-coloring alumina dispersion slurry containing α-alumina powder and a magnesium compound as a sintering aid is spray-dried to obtain uncolored tooth-coloring alumina granules, which are then molded to obtain a tooth-coloring alumina molded body. The tooth-coloring alumina molded body is then pre-sintered to obtain a tooth-coloring alumina pre-sintered body (uncolored pre-sintered body). Methods for incorporating (C) yellow colorants and (D) red colorants into the uncolored pre-sintered body include immersing the uncolored pre-sintered body in a liquid in which the above-mentioned raw materials for the yellow colorant and red colorant are dissolved or dispersed, or dropping or coating the uncolored pre-sintered body with the liquid in which the above-mentioned raw materials for the yellow colorant and red colorant are dissolved or dispersed. As a result, the raw materials for the yellow colorant and the raw materials for the red colorant penetrate into the pores of the uncolored pre-sintered body, and the colorants are supported on the inside and surface of the pre-sintered body. The liquid in which the raw materials for the yellow colorant and the raw materials for the red colorant are dissolved or dispersed may be a liquid in which both the raw materials for the yellow colorant and the raw materials for the red colorant are dissolved or dispersed, or it may be multiple liquids in which the raw materials for the yellow colorant and the raw materials for the red colorant are dissolved or dispersed separately. The solvent (colorant solvent) constituting the liquid in which the raw materials for the yellow colorant and the raw materials for the red colorant are dissolved or dispersed is water and / or an organic solvent, and preferably water, alcohol-based organic solvents such as ethanol and isopropyl alcohol, or glycol-based organic solvents such as ethylene glycol and propylene glycol can be used. One type of solvent (colorant solvent) may be used alone, or two or more types may be used in combination. The concentration of each coloring agent raw material in the liquid in which the yellow coloring agent raw materials and the red coloring agent raw materials are dissolved or dispersed is not particularly limited. It is sufficient to adjust the concentration of each coloring agent in the alumina temporary sintered body for tooth coloring of the present invention to the desired concentration. However, it is preferable that the total amount of coloring agent raw materials be approximately 0.001 to 10% by mass relative to the solvent.

[0051] Furthermore, although a method using alumina granules for tooth coloring has been described in the method for manufacturing a pre-sintered alumina body for tooth coloring, it is also possible to manufacture it without using the aforementioned granules. For example, a mixture of α-alumina powder and granules, a magnesium compound as a sintering aid, a raw material for a yellow coloring agent, and a raw material for a red coloring agent may be molded to obtain a molded body of alumina for tooth coloring, and the molded body may be pre-sintered.

[0052] [Use of Alumina Pre-Sintered Body for Tooth Coloring] The alumina pre-sintered body for tooth coloring 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 alumina pre-sintered body for tooth coloring, a tooth colored alumina sintered body that can reproduce tooth color well can be obtained. The alumina pre-sintered body for tooth coloring to be sintered may or may not have been machined as described above. Generally, the alumina pre-sintered body for tooth coloring 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 resulting tooth-colored alumina sintered body reproduces tooth color well and has high strength, making it suitable for use as a dental prosthesis for restoring tooth crowns.

[0053] 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.

[0054] [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.

[0055] <a ＊ , b ＊> The sintered bodies (3.0 mm thick) obtained by firing the pre-sintered bodies prepared in each example and comparative example as described above were subjected to a spectrophotometer equipped with a standard light C light source (Tokyo Denshoku Co., Ltd.: TC-1800MKII) to measure the color tone of the reflected light under black background conditions, and CIEL was used. ＊ a ＊ b ＊ chromaticity a, expressed in a color system ＊ , b ＊ They obtained the following, respectively.

[0056] <Shade> "Shade" is divided into four color tones: A (red), B (yellow), C (gray), and D (brown). The intensity of each color is divided into four levels, and the numbers 1 to 4 are assigned so that the darker the color, the higher the number, resulting in a total of 16 types: A1 to A4, B1 to B4, C1 to C4, and D2 to D4. If the color falls into one of these 16 types, it is judged that the tooth color has been reproduced. For the sintered bodies (thickness 3.0 mm) obtained by firing the temporary sintered bodies prepared in each example and comparative example as described above, a shade guide (VITA Classical (product name) manufactured by VITA Corporation) was used to visually evaluate which rank of the above 16 color types it fell into. If it did not fall into any of the above 16 color types it was classified as "not applicable".

[0057] <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. 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).

[0058] The raw materials used in the examples and comparative examples are as follows:

[0059] <(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%

[0060] <(B) Mg> Magnesium oxide powder: 500A (manufactured by Ube Materials Co., Ltd.)

[0061] <(C) Yellow Colorants> The following compounds were used as raw materials for the yellow colorants: Ce source: Cerium(III) acetate monohydrate Ni source: Nickel(II) chloride hexahydrate Dy source: Dysprosium nitrate hexahydrate Sm source: Samarium nitrate hexahydrate

[0062] <Coloring agents not included in component (C)> As a source of Fe, iron(II) sulfate heptahydrate

[0063] <(D) Red Colorants> The following compounds were used as raw materials for the red colorants: Manganese(II) chloride tetrahydrate as the Mn source Chromium(III) chloride hexahydrate as the Cr source Holmium(III) acetate monohydrate as the Ho source Erbium chloride hexahydrate as the Erbium chloride hexahydrate as the Cu source Copper(II) nitrate trihydrate as the Cu source Europium(III) chloride hexahydrate as the Eu source

[0064] <Colorants not included in component (D)> Silver(I) chloride as an Ag source

[0065] <Other Elemental Components> The following compounds were used as raw materials to include other elemental components: Neodymium nitrate hexahydrate as the Nd source Co cobalt(II) chloride hexahydrate as the Co source Praseodymium nitrate n hydrate as the Pr source Li lithium nitrate Zirconium oxide octahydrate as the Zr source

[0066] <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) 2 g of magnesium oxide powder (500A, manufactured by Ube Materials Co., Ltd.), 6 g of anhydrous citric acid, and 123 g of pure water were stirred and mixed for 5 hours as a sintering aid, which is a source of Mg, to prepare a magnesium oxide dispersion. Next, 100 g of the alumina slurry, 48 g of pure water, 6.6 g of the magnesium oxide dispersion, 1.2 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 the yellow coloring agent (raw material for the yellow coloring agent) (cerium oxide: CeO ２ (D) As a raw material for red colorants (raw material for red colorants), 0.00321 g of manganese(IV) chloride tetrahydrate (manganese oxide: Mn ３ O ４An amount equivalent to 20 ppm of α-alumina powder was weighed and mixed and stirred for 10 minutes to prepare an alumina dispersion slurry for tooth coloring. The alumina dispersion slurry for tooth coloring was then spray-dried and granulated to prepare alumina granules for tooth coloring (aggregated particle size 36 μm). The alumina granules for tooth coloring were filled into a mold of a predetermined shape and uniaxially pressurized at a pressure of 200 MPa for 1 minute to produce an alumina molded body for tooth coloring. The alumina molded body for tooth coloring 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 pre-sintered alumina body for tooth coloring. Next, the temperature was increased from 700°C to 1450°C at a heating rate of 10°C / min, and after 2 hours of aging, it was allowed to cool to produce a tooth-colored alumina sintered body. The evaluation results are shown in Table 1.

[0067] <Examples 2-17, Comparative Examples 1-7> Except for appropriately changing the raw materials for yellow-based colorants, raw materials for red-based colorants, other elemental components, and their proportions so that the pre-sintered bodies shown in Tables 1-2 could be obtained, alumina pre-sintered bodies for tooth coloring were prepared in accordance with Example 1. The evaluation results for each are shown in Tables 1-2.

[0068]

[0069]

[0070] <Example 18> (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) 2 g of magnesium oxide powder (500A, manufactured by Ube Materials Co., Ltd.), 6 g of anhydrous citric acid, and 123 g of pure water were stirred and mixed for 5 hours 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, 6.6 g of the magnesium oxide dispersion, 1.2 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 alumina dispersion slurry for tooth coloring. Furthermore, the uncolored alumina dispersion slurry for tooth coloring was spray-dried and dried to prepare uncolored alumina granules for tooth coloring. The uncolored alumina granules for tooth coloring were filled into a mold having a predetermined shape and uniaxially pressurized at a pressure of 200 MPa for 1 minute to produce an alumina molded body for tooth coloring. A tooth-coloring 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, and then heated to 700°C at a heating rate of 10°C / min for 2 hours of pre-sintering to produce a tooth-coloring alumina pre-sintered body (uncolored pre-sintered body). Next, the tooth-coloring alumina pre-sintered body (uncolored pre-sintered body) was immersed for 5 minutes in an aqueous solution in which 0.55 g of cerium(III) acetate monohydrate and 0.154 g of manganese(II) chloride tetrahydrate were dispersed in 460 g of water, and then dried at 100°C for 30 minutes to produce a tooth-coloring alumina pre-sintered body impregnated with a coloring agent. In the alumina pre-sintered body for tooth coloring, the Ce content (oxide equivalent) relative to the α-alumina powder was 100 ppm, and the Mn content (oxide equivalent) relative to the α-alumina powder was 20 ppm. The content of each element was measured by ICP emission spectrometry. Subsequently, the alumina pre-sintered body for tooth coloring was heated from 25°C to 1450°C at a heating rate of 10°C / min, and after 2 hours of aging, it was allowed to cool to produce a tooth colored alumina sintered body. The evaluation results are shown in Table 3.

[0071] <Examples 19-25> Except for appropriately changing the raw materials for yellow-based colorants, raw materials for red-based colorants, other elemental components and their proportions to obtain the pre-sintered bodies shown in Table 3, and further changing the colorant solvent as shown in Table 3, alumina sintered bodies for tooth crown coloring were prepared in accordance with Example 18. The evaluation results for each are shown in Table 3.

[0072]

[0073] From the results in Tables 1 and 3, the sintered bodies obtained by firing the alumina temporary sintered bodies for tooth coloring in each example containing the predetermined components (A) to (D) are a ＊ The value is -5 to +4, b ＊ The values ​​were in the range of +3 to +25, corresponding to one of the shades A1 to A4, indicating that the tooth color was reproduced well, and that the bending strength values ​​were also high. From the results in Table 2, the sintered bodies made from the provisional sintered bodies of each comparative example that did not contain at least one of the components (A) to (D) either did not correspond to a shade or had low bending strength values, failing to achieve both tooth color reproduction and strength.

Claims

1. (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 the sintering aid, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, 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 alumina pre-sintered body for tooth coloring with a thickness of 3.0 mm obtained by firing the alumina pre-sintered body for tooth coloring under atmospheric pressure (1013 hPa) and 1450°C, a black background ＊ The value is -5 to +4, b ＊ A pre-sintered alumina body for tooth coloring, wherein the value is +3 to +25, and the bending strength of the sintered body obtained by firing the aforementioned pre-sintered alumina body for tooth coloring under atmospheric pressure (1013 hPa) and 1450°C is 800 MPa or more.

2. A method for producing a tooth-coloring alumina molded body, characterized by pre-sintering at 500 to 1000°C the alumina molded body for tooth coloring, 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 a sintering aid; (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent; and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder.

3. A method for producing alumina molded articles for tooth coloring, 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; (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent; and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, 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; and press-molding these alumina granules for tooth coloring at 10 to 400 MPa.

4. A method for producing alumina granules for tooth crown coloring, 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 a sintering aid; (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent; and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder; and spray-drying the alumina dispersion slurry.

5. A method for producing a dental crown color alumina pre-sintered body according to claim 1, characterized in that (A) α-alumina powder 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 in the 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, and (C) at least one element selected from Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent.

6. (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 the sintering aid, (C) at least one element selected from the group consisting of Ce, Dy, Ni, and Sm as a yellow coloring agent, and (D) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is the same as that of (A) α-alumina A method for producing a tooth-coloring alumina pre-sintered body according to claim 1, comprising: spray-drying an alumina dispersion slurry containing 100 to 5000 ppm of metallic magnesium by mass relative to alumina powder to obtain alumina granules for tooth coloring with aggregated particle size of 5 to 100 μm; press-molding the tooth-coloring alumina granules at 10 to 400 MPa to obtain a tooth-coloring alumina molded body; and further pre-sintering the tooth-coloring alumina molded body at 500 to 1000°C.

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