Zirconia sintered body containing needle-shaped metal oxide

Abstract

The present invention provides a zirconia sintered body which is high in strength and can be subjected to machining. The present invention relates to a zirconia sintered body comprising zirconia, a stabilizer capable of inhibiting phase transition of the zirconia, a sintering aid, and a needle-shaped metal oxide. The aforementioned sintering aid comprises niobium pentoxide, and the content of the niobium pentoxide is preferably 5 to 15 parts by mass relative to 100 parts by mass of the total of the zirconia and the stabilizer. The aforementioned stabilizer comprises yttria, and the content of the yttria is preferably 2.5 to 10 mol% relative to the total number of moles of the zirconia and the yttria.

Description

Technical Field

[0001] This invention relates to processable zirconia sintered bodies. Background Technology

[0002] In recent years, sintered zirconia containing yttrium oxide has been used in dental materials such as dental restorations. These dental restorations are manufactured in various ways: zirconia particles are press-formed or formed using a slurry or composition containing zirconia particles to create a zirconia molded body with a desired shape, such as a disc or prism. This is then pre-fired to create a pre-fired body (milled blank), which is then cut (milled) into the target shape for the dental restoration, and further sintered. While sintered zirconia bodies possess excellent strength, they are often too hard to machine. Sometimes, the cutting machine (milling bar, etc.) stops automatically due to severe wear or increased machining load. In such cases, as described above, the pre-fired body (milled blank) is typically cut (milled) into the target shape for the dental restoration before further sintering.

[0003] However, this method requires the following steps: after taking a sample and machining it into the target shape for the dental restoration at a dental hospital, the pre-fired body of the target shape is sent to a dental laboratory equipped with a sintering furnace for sintering to obtain a sintered body. Then, the sintered body is sent back to the dental hospital for application in the patient's mouth to confirm the bite and make minor adjustments. Therefore, it takes a long time until the dental restoration is applied to the patient's teeth. For this reason, recent dental treatments not only aim to reduce energy costs but also to complete treatment without requiring patients to visit the dental hospital multiple times. From this perspective, sintered bodies that maintain excellent strength while being machinable have been studied (Patent Documents 1 and 2). Patent Document 1 discloses a zirconia sintered body where the sintering process is omitted, which reduces hardness and improves machinability by increasing the particle size after sintering.

[0004] Furthermore, Patent Document 2 discloses the shape of a fully sintered zirconia tooth crown preform. Compared to a typical block shape, the preform has a reduced processing volume, thus enabling it to be machined into a tooth crown shape without the need for post-processing sintering.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-127294

[0008] Patent Document 2: Japanese Patent Application Publication No. 2017-077454 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, as a sintered body, possessing both excellent strength and machinability is a trade-off, making it difficult to achieve both simultaneously. Therefore, the zirconia sintered body described in Patent Document 1 has low strength, and the balance between strength and machinability cannot be achieved, leaving room for improvement. Furthermore, the preform in Patent Document 2 reduces the processing involved, thus solving the problem of balancing machinability and strength. However, it produces a preform with a fixed size, making it unsuitable for cases exceeding that size and thus unsuitable for applications such as three-unit dental bridges, exhibiting a lack of selectivity in crown shape.

[0011] The purpose of this invention is to provide a zirconia sintered body with high strength and machinability.

[0012] means for solving problems

[0013] To achieve the aforementioned objectives, the inventors conducted repeated and in-depth research, and as a result, they were the first to discover that by sintering a zirconia shaped body containing zirconia, a stabilizer, a sintering aid, and needle-shaped metal oxides, a zirconia sintered body that balances strength and processability can be obtained. Furthermore, they were the first to discover that this yields a zirconia sintered body with selectivity in tooth crown shape. They also discovered that this zirconia sintered body is particularly suitable as a dental material, such as dental restorations. Based on these insights, the inventors conducted further repeated research, thereby completing this invention.

[0014] That is, the present invention relates to the following technical solutions.

[0015] [1] A zirconia sintered body comprising zirconia, a stabilizer capable of inhibiting the zirconia phase transformation, a sintering aid and a needle-like metal oxide.

[0016] [2] According to the zirconia sintered body described in [1], wherein the aforementioned sintering aid comprises niobium pentoxide,

[0017] The content of niobium pentoxide is 5 to 15 parts by mass relative to the total of 100 parts by mass of zirconium oxide and stabilizer.

[0018] [3] The zirconia sintered body according to [1] or [2], wherein the aforementioned stabilizer comprises yttrium oxide,

[0019] The content of yttrium oxide relative to the total molar percentage of zirconium oxide and yttrium oxide is 2.5–10 mol%.

[0020] [4] The zirconia sintered body according to any one of [1] to [3], wherein the aforementioned needle-shaped metal oxide has an aspect ratio of 1:3 to 1:55 (average fiber diameter: average fiber length).

[0021] [5] The zirconia sintered body according to any one of [1] to [4], wherein the content of the aforementioned needle-shaped metal oxide is more than 0 parts by mass and less than 10 parts by mass relative to the total of 100 parts by mass of zirconia and stabilizer.

[0022] [6] The zirconia sintered body according to any one of [1] to [5] has a Vickers hardness of 1050 HV or less.

[0023] [7] The zirconia sintered body according to any one of [1] to [6] has a failure toughness value of 5 MPa·m. 1 / 2 above.

[0024] [8] The zirconia sintered body according to any one of [1] to [7] has a three-point bending strength of 500 MPa or more.

[0025] [9] The zirconia sintered body according to any one of [1] to [8] has an average crystal grain size of 1 to 10 μm.

[0026]

[10] The zirconia sintered body according to any one of [11-[9], wherein the aforementioned needle-shaped metal oxide comprises at least one selected from Al, Si, Y, Ti, Zr and Sn.

[0027]

[11] The zirconia sintered body according to any one of [1] to

[10] , wherein the aforementioned needle-shaped metal oxide is selected from at least one of Al, Si, Ti and Sn.

[0028]

[12] The zirconia sintered body according to any one of [1] to

[11] , wherein the aforementioned needle-shaped metal oxide comprises at least one selected from Al and Ti.

[0029]

[13] The zirconia sintered body according to any one of [1] to

[12] , wherein the aforementioned needle-shaped metal oxide comprises TiO2.

[0030] Invention Effects

[0031] According to the present invention, a zirconia sintered body with high strength and machinability is provided. Furthermore, according to the present invention, a machinable zirconia sintered body is provided, which offers selectivity in crown shape due to the ability to freely choose the shape of the machinable zirconia sintered body. Attached Figure Description

[0032] Figure 1These are scanning electron microscope images of the needle-shaped metal oxides used in Examples 1 and 2.

[0033] Figure 2 These are scanning electron microscope images of the metal oxides used in Comparative Example 1. Detailed Implementation

[0034] As one embodiment of the present invention, a zirconia shaped body is included, comprising zirconia, a stabilizer capable of inhibiting the zirconia phase transformation, a sintering aid, and a needle-like metal oxide. By using this zirconia shaped body, a zirconia sintered body that balances strength and processability can be obtained. Hereinafter, as an embodiment of the present invention, the zirconia sintered body will be described first. The present invention relates to a zirconia sintered body comprising zirconia, a stabilizer capable of inhibiting the zirconia phase transformation (hereinafter sometimes referred to as "stabilizer"), a sintering aid, and a needle-like metal oxide. The present invention is not limited to the following description. A zirconia sintered body refers to a substance, for example, in which zirconia particles (powder) are in a sintered state. The relative density of the zirconia sintered body is preferably 99.5% or higher. The relative density can be calculated as the ratio of the measured density, measured by the Archimedes method, to the theoretical density. Relative density refers to the value obtained by dividing the density d1 of the sintered body (which is formed by filling particles into a specific mold and using pressure to create a specific shape) by the theoretical density d2 of zirconium oxide (which contains no internal voids). It should be noted that in this invention, the upper and lower limits of various numerical ranges (content of each component, various elements (average fiber diameter, average fiber length, aspect ratio, etc.) and various physical properties (three-point bending strength, Vickers hardness, Mohs hardness, breaking toughness, etc.)) can be appropriately combined.

[0035] [Zirconium oxide sintered body]

[0036] The average grain size of the zirconia sintered body of the present invention is not particularly limited, but from the viewpoint of balancing processability and strength, it is preferably 1 μm to 10 μm. When the average grain size of the zirconia sintered body is less than 1 μm, the processability decreases. In addition, when the average grain size of the zirconia sintered body is 10 μm or more, the strength decreases. From the perspective of obtaining a zirconia sintered body that balances strength and processability, the average grain size of the zirconia sintered body is preferably 1 μm or more, more preferably 1.5 μm or more, and even more preferably 2 μm or more. In addition, the average grain size of the zirconia sintered body is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. It should be noted that the average grain size of the zirconia sintered body can be determined by taking a scanning electron microscope (SEM) image of the surface of the zirconia sintered body and selecting 100 arbitrary particles present in the image, and averaging their respective circular equivalent diameters (the diameter of a circle of the same area).

[0037] The zirconia sintered body of the present invention contains a stabilizer. Examples of stabilizers include, for instance, calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y₂O₃), cerium oxide (CeO₂), scandium oxide (Sc₂O₃), lanthanum oxide (La₂O₃), erbium oxide (Er₂O₃), and praseodymium oxide (Pr₆O₃). 11 Oxides such as samarium oxide (Sm₂O₃), europium oxide (Eu₂O₃), and thulium oxide (Tm₂O₃) are preferred, with yttrium oxide being the most suitable from the viewpoint of strength and light transmittance. The content of this stabilizer is preferably 0.1–18 mol%, more preferably 1–15 mol%, and even more preferably 2–10 mol%. The stabilizer content refers to the ratio (mol%) of the number of moles of stabilizer relative to the total number of moles of zirconium oxide and stabilizer. The stabilizer content in the zirconia sintered body can be determined by, for example, inductively coupled plasma (ICP) luminescence spectrophotometry or fluorescence X-ray analysis.

[0038] As a suitable embodiment, a zirconia sintered body containing yttrium oxide as a stabilizer and having a yttrium oxide content of 2.5 to 10 mol% can be cited. When the yttrium oxide content in the zirconia sintered body is less than 2.5 mol%, the crystalline phase becomes monoclinic, and a dense sintered body cannot be obtained. Furthermore, when the yttrium oxide content in the zirconia sintered body exceeds 10 mol%, the strength decreases. From the viewpoint of obtaining a dense zirconia sintered body with excellent strength, the yttrium oxide content in the zirconia sintered body is preferably 2.5 mol% or more, more preferably 3.5 mol% or more, and even more preferably 4.5 mol% or more, from the viewpoint of excellent light transmittance. Additionally, the yttrium oxide content in the zirconia sintered body is preferably 10 mol% or less, more preferably 8.5 mol% or less, and even more preferably 7.0 mol% or less, from the viewpoint of excellent strength. In embodiments where strength is of greater importance, it can be 6.5 mol% or less. It should be noted that the yttrium oxide content in the zirconia sintered body refers to the ratio (mol%) of the number of moles of yttrium oxide to the total number of moles of zirconia and yttrium oxide.

[0039] The zirconia sintered body of the present invention includes a sintering aid. Examples of sintering aids include niobium pentoxide (Nb₂O₅) and tantalum pentoxide (Ta₂O₅), with niobium pentoxide being preferred from the viewpoint of balancing strength and processability when combined with stabilizers and needle-like metal oxides. As a suitable embodiment, a zirconia sintered body is provided in which the sintering aid includes niobium pentoxide, and the content of niobium pentoxide is 5 to 15 parts by mass relative to 100 parts by mass of the total of zirconia and stabilizer. When the content of niobium pentoxide in the zirconia sintered body is less than 5 parts by mass relative to 100 parts by mass of the total of zirconia and stabilizer, the processability decreases. Furthermore, when the content of niobium pentoxide in the zirconia sintered body exceeds 15 parts by mass relative to 100 parts by mass of the total of zirconia and stabilizer, the crystal phase changes to a monoclinic system, and a dense sintered body cannot be obtained. From the perspective of obtaining a dense zirconia sintered body with excellent processability, the content of niobium pentoxide in the zirconia sintered body is preferably 5 parts by mass or more, more preferably 6.5 parts by mass or more, and even more preferably 8 parts by mass or more. In addition, the content of niobium pentoxide in the zirconia sintered body is preferably 15 parts by mass or less, more preferably 13.5 parts by mass or less, and even more preferably 12 parts by mass or less.

[0040] The zirconia sintered body of the present invention comprises needle-shaped metal oxides. By including needle-shaped metal oxides in the zirconia sintered body, the processability of the sintered body can be maintained and the strength improved when combined with stabilizers and sintering aids (suitably niobium pentoxide). The type of needle-shaped metal oxide is not particularly limited; one or more types can be used. The needle-shaped metal oxides have the following properties: Figure 1The structure is visible in the image. It should be noted that in this invention, the aspect ratio refers to the ratio d:D of the minor axis (d) to the major axis (D). Hereinafter, the major axis (D) of the needle-like metal oxide will be defined as the average fiber length, and the minor axis (d) as the average fiber diameter. The average fiber length and average fiber diameter can be calculated from SEM-based images using an image analysis device. Alternatively, the average fiber length and average fiber diameter can also be calculated using a laser diffraction particle size distribution measuring device.

[0041] The aspect ratio (average fiber diameter: average fiber length) of the needle-like metal oxide is not particularly limited, but from the viewpoint that it can maintain the processability of the sintered body and further improve its strength when combined with a stabilizer and a sintering aid (suitably niobium pentoxide), it is preferably 1:3 or more, more preferably 1:5 or more, and even more preferably 1:10 or more. Furthermore, from the viewpoint that it can maintain the processability of the sintered body and further improve its strength when combined with a stabilizer and a sintering aid (suitably niobium pentoxide), the aspect ratio of the needle-like metal oxide is preferably 1:55 or less, more preferably 1:45 or less, and even more preferably 1:35 or less.

[0042] The average fiber length of the needle-like metal oxide is preferably 0.5 μm or more, more preferably 0.75 μm or more, and even more preferably 1 μm, from the viewpoint that it can maintain the processability of the sintered body and further improve its strength when combined with a stabilizer and a sintering aid (suitably niobium pentoxide). Furthermore, the average fiber length of the needle-like metal oxide is preferably 15 μm or less, more preferably 13.5 μm or less, and even more preferably 12 μm or less, from the viewpoint that it can maintain the processability of the sintered body and further improve its strength when combined with a stabilizer and a sintering aid (suitably niobium pentoxide).

[0043] The average fiber diameter of the needle-like metal oxide is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.05 μm, from the viewpoint that it can maintain the processability of the sintered body and further improve its strength when combined with a stabilizer and a sintering aid (suitably niobium pentoxide). Furthermore, the average fiber diameter of the needle-like metal oxide is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less, from the viewpoint that it can maintain the processability of the sintered body and further improve its strength when combined with a stabilizer and a sintering aid (suitably niobium pentoxide).

[0044] As for the needle-like metal oxide, there is no particular limitation as long as it is an inorganic metal oxide with a needle-like structure, and examples include needle-like metal oxides such as Al, Si, Y, Ti, Zr, and Sn. These needle-like metal oxides may contain only one metal element or two or more metal elements. For example, the needle-like metal oxide may be a composite oxide containing two or more of the aforementioned metal elements. In addition, the zirconia sintered body of the present invention can use a combination of needle-like metal oxides and metal oxides having shapes other than needle-like. From the perspective of more significantly exerting the effects of the present invention, the metal elements constituting these needle-like metal oxides are preferably Al, Si, Ti, and Sn, more preferably Al and Ti, and even more preferably Ti. Examples of needle-like metal oxides include TiO2 and Al2O3. Commercially available products can also be used as needle-like metal oxides. Examples of commercially available products include needle-like titanium dioxide such as FTL-100, FTL-200, and FTL-300 (manufactured by Ishihara Sangyo Co., Ltd.); and needle-like alumina fillers such as the CerasurBMI series.

[0045] The content of needle-like metal oxides in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of needle-like metal oxides, etc. From the viewpoint of strength, it is preferable to be more than 0 parts by mass relative to 100 parts by mass of the total of zirconia and stabilizer, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more. In addition, the content of needle-like metal oxides in the zirconia sintered body is preferably 10 parts by mass or less relative to 100 parts by mass of the total of zirconia and stabilizer, more preferably 6 parts by mass or less, and even more preferably 3 parts by mass or less. By making this content above or below the above-mentioned lower limit and below the above-mentioned upper limit, the strength can be improved.

[0046] The zirconia sintered body of the present invention may contain a fluorescent agent. By including a fluorescent agent in the zirconia sintered body, it acquires fluorescence. The type of fluorescent agent is not particularly limited; one or more fluorescent agents capable of emitting fluorescence using light of any wavelength may be used. Examples of such fluorescent agents include those containing a metal element. Examples of such metal elements include, for example, Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain only one of these metal elements or may contain two or more. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred from the perspective of more significantly exerting the effects of the present invention, and Bi and Eu are more preferred. Examples of fluorescent agents used in manufacturing the zirconia sintered body of the present invention include, for example, oxides, hydroxides, acetates, and nitrates of the aforementioned metal elements. In addition, fluorescent agents can be Y₂SiO₅:Ce, Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, yttrium oxide:Eu, YAG:Ce, ZnGa₂O₄:Zn, BaMgAl10 O 17 Eu et al.

[0047] The content of fluorescent agent in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of fluorescent agent and the intended use of the zirconia sintered body. From the viewpoint of preferably using it as a dental restoration, the content is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, relative to the mass of zirconia contained in the zirconia sintered body and calculated based on the oxide content of the metal element contained in the fluorescent agent. In addition, the content of fluorescent agent in the zirconia sintered body is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. By making this content above the lower limit, the fluorescence is comparable to that of natural human teeth. Furthermore, by making this content below the upper limit, the reduction in light transmittance and intensity can be suppressed.

[0048] The zirconia sintered body of the present invention may contain a colorant. By including a colorant in the zirconia sintered body, a colored zirconia sintered body is formed. The type of colorant is not particularly limited; known pigments commonly used for coloring ceramics, known dental liquid colorants, etc., can be used. Examples of colorants include colorants containing metallic elements, specifically oxides, composite oxides, and salts containing metallic elements such as iron, vanadium, praseodymium, arsenic, chromium, nickel, and manganese. Alternatively, commercially available colorants may be used. Commercially available products may include, for example, Colour Liquid Prettau (registered trademark) manufactured by Zirkonzahn (Italy). The zirconia sintered body may contain one colorant or two or more colorants.

[0049] The content of colorant in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of colorant and the intended use of the zirconia sintered body. From the viewpoint of preferably using it as a dental restoration, the content is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, relative to the mass of zirconia contained in the zirconia sintered body and calculated based on the oxide content of the metal element contained in the colorant. In addition, the content of colorant in the zirconia sintered body is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, can be 0.1% by mass or less, and further can be 0.05% by mass or less.

[0050] The zirconia sintered body of the present invention may contain a light transmittance modifier. Specific examples of light transmittance modifiers include, for instance, alumina, titanium dioxide, silicon dioxide, zircon, lithium silicate, and lithium disilicate. However, metal oxides with needle-like structures are excluded as light transmittance modifiers. The zirconia sintered body may contain one or more light transmittance modifiers.

[0051] The content of the light transmittance modifier in the zirconia sintered body is not particularly limited, and can be appropriately adjusted according to the type of light transmittance modifier and the intended use of the zirconia sintered body. From the viewpoint that it is preferred to be used as a dental patch, the content is preferably 0.1% by mass or less relative to the mass of zirconia contained in the zirconia sintered body.

[0052] The zirconia sintered body of the present invention is obtained by sintering a shaped body of zirconia powder. The average primary particle size of the zirconia particles contained in the zirconia powder is not particularly limited, but from the viewpoint of processability and strength of the sintered body, it is preferably 0.07 μm to 0.25 μm. When the average primary particle size of the zirconia particles is less than 0.07 μm, the processability of the sintered body decreases. Furthermore, when the average primary particle size of the zirconia particles exceeds 0.25 μm, the strength of the sintered body decreases. From the perspective of obtaining a zirconia sintered body that balances processability and strength, the average primary particle size of the zirconia particles is preferably 0.07 μm or more, more preferably 0.1 μm or more. Furthermore, the primary particle size of the zirconia particles is preferably 0.25 μm or less, more preferably 0.2 μm or less. The average primary particle size of the zirconia particles can be determined by measurement using laser diffraction scattering. Specifically, the laser diffraction scattering method can be performed using, for example, a laser diffraction particle size distribution measuring device (SALD-2300: manufactured by Shimadzu Corporation), with a 0.2% sodium hexametaphosphate aqueous solution used as the dispersion medium, and the measurement is performed on a volume basis.

[0053] The method for preparing the zirconia particles of the present invention is not particularly limited, and can employ, for example, a decomposition process to achieve micronization by pulverizing coarse particles, or a stacking process to synthesize atoms and ions through nucleation and growth. Among these, the stacking process is preferred in order to obtain high-purity fine zirconia particles.

[0054] The decomposition process can be carried out by pulverization, for example, using a ball mill or bead mill. In this case, it is preferable to use pulverizing media with very small particle sizes, for example, media with a particle size of 100 μm or less. Furthermore, it is preferable to classify the zirconium oxide particles after pulverization.

[0055] On the other hand, as a deposition process, examples include the following methods: gas-phase thermal decomposition method, which involves vaporizing oxoacid salts or organometallic compounds with high vapor pressure metal ions while thermally decomposing them to precipitate oxides; gas-phase reaction method, which involves synthesis through a gas-phase chemical reaction between a gaseous metal compound with a reactant gas; evaporation concentration method, which involves heating the raw material to vaporize it and then rapidly cooling it in an inert gas at a specified pressure to condense the vapor into particulate particles; melt method, which involves cooling and solidifying the melt into small droplets to produce powder; solvent evaporation method, which involves evaporating the solvent to increase the concentration in the liquid, creating a supersaturated state, and precipitating the solvent; and precipitation method, which involves reacting with a precipitant and hydrolyzing the solute to create a supersaturated state, followed by a nucleation-growth process to precipitate insoluble compounds such as oxides and hydroxides.

[0056] Precipitation methods can be further subdivided into the following methods: homogeneous precipitation, which generates a precipitant in solution through a chemical reaction to eliminate local unevenness in precipitant concentration; coprecipitation, which causes multiple metal ions coexisting in a liquid to precipitate simultaneously by adding a precipitant; hydrolysis, which yields oxides or hydroxides from metal salt solutions, metal alkoxides, or other alcohol solutions through hydrolysis; and solvothermal synthesis, which obtains oxides or hydroxides from high-temperature, high-pressure fluids. Solvothermal synthesis can be further subdivided into the following methods: hydrothermal synthesis, which uses water as a solvent; and supercritical synthesis, which uses supercritical fluids such as water and carbon dioxide as solvents.

[0057] Regarding any deposition process, in order to obtain finer zirconia particles, it is preferable to accelerate the precipitation rate. Furthermore, it is preferable to classify the resulting zirconia particles.

[0058] As a zirconium source in the deposition process, nitrates, acetates, chlorides, alkoxides, etc. can be used. Specifically, zirconium oxychloride, zirconium acetate, zirconium oxynitrate, etc. can be used.

[0059] As a yttrium source, nitrates, acetates, chlorides, alkoxides, etc. can be used. Specifically, yttrium chloride, yttrium acetate, yttrium nitrate, etc. can be used.

[0060] The zirconia sintered body of the present invention can be obtained by sintering a shaped or pre-sintered body of the zirconia powder. The zirconia powder is obtained by drying a slurry containing zirconia particles. The drying method is not particularly limited and can include, for example, spray drying, supercritical drying, freeze drying, hot air drying, and reduced pressure drying. Among these methods, spray drying, supercritical drying, and freeze drying are preferred, more preferably, either spray drying or supercritical drying, and even more preferably, spray drying, to suppress particle aggregation during drying and obtain a denser zirconia sintered body.

[0061] The dispersion medium supplied in the dried slurry containing zirconium oxide particles is not particularly limited. From the viewpoint of uniform dispersion, water or organic solvents can be used as the dispersion medium. From the viewpoint of environmental impact, water is preferred.

[0062] The zirconia sintered body of the present invention is obtained by sintering a zirconia shaped body. This zirconia shaped body can be manufactured by press forming zirconia powder; the specific method of press forming is not particularly limited, and a known press forming machine can be used. Examples of specific press forming methods include uniaxial press forming. Furthermore, to increase the density of the obtained zirconia shaped body, it is preferable to further perform CIP (Cold Isostatic Pressing) treatment after uniaxial press forming.

[0063] The zirconia pre-sintered body of the present invention is obtained by pre-sintering a zirconia shaped body. As a method for manufacturing this zirconia pre-sintered body, a preferred method is one that includes, for example, pre-sintering the zirconia shaped body of the present invention at a temperature of 200°C or higher and less than 1200°C. From the viewpoint of easily obtaining the desired zirconia pre-sintered body, the pre-sintering temperature is preferably 200°C or higher, more preferably 300°C or higher, and even more preferably 500°C or higher. Furthermore, the pre-sintering temperature is preferably 1200°C or lower, more preferably 1150°C or lower, and even more preferably 1100°C or lower. The zirconia pre-sintered body refers to, for example, a semi-sintered body obtained by forming a block of zirconia particles (powder) in a state where they are not completely sintered.

[0064] When pre-firing the zirconia molded body of the present invention, the heating rate is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. Furthermore, the heating rate is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the heating rate to the lower limit or above, productivity is improved. Additionally, by setting the heating rate to the upper limit or below, the volume difference between the interior and exterior of the zirconia molded body can be suppressed. Furthermore, when the zirconia molded body contains organic matter, the rapid decomposition of that organic matter can be suppressed, thereby preventing cracking and damage.

[0065] The zirconia sintered body of the present invention can be not only a sintered body obtained by sintering a zirconia shaped body and the zirconia pre-sintered body of the present invention under normal pressure to no pressure (zirconia primary sintered body), but can also be sintered by HIP (Hot Isostatic Pressing). In addition, the zirconia primary sintered body can be further subjected to HIP treatment.

[0066] Regarding the zirconia sintered body of the present invention, the sintering temperature is not particularly limited when sintering the zirconia shaped body or the zirconia pre-sintered body. However, from the perspective of obtaining a sintered body with good workability and strength, the sintering temperature is preferably 1350°C or higher, more preferably 1450°C or higher, and even more preferably 1500°C or higher. Furthermore, the sintering temperature is preferably 1800°C or lower, more preferably 1700°C or lower, and even more preferably 1650°C or lower.

[0067] Regarding the zirconia sintered body of the present invention, the heating rate is not particularly limited when sintering the zirconia molded body and the zirconia pre-sintered body, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. Furthermore, the heating rate is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the heating rate to the lower limit or above, productivity is improved. Furthermore, by setting the heating rate to the upper limit or below, the volume difference between the interior and exterior of the zirconia molded body and the zirconia pre-sintered body can be suppressed. Additionally, in the case where the zirconia molded body contains organic matter, the rapid decomposition of the organic matter can be suppressed, and cracking and damage can be prevented.

[0068] Regarding the zirconia sintered body of the present invention, the sintering time is not particularly limited when sintering the zirconia shaped body or the zirconia pre-sintered body. From the perspective of obtaining a zirconia sintered body with good productivity and high efficiency and stability, the sintering time is preferably 5 minutes or more, more preferably 8 minutes or more, and even more preferably 10 minutes or more. Furthermore, the sintering time is preferably 10 hours or less, more preferably 7 hours or less, and even more preferably 5 hours or less.

[0069] Regarding the zirconia sintered body of the present invention, the HIP temperature is not particularly limited when performing HIP treatment on the zirconia shaped body, the zirconia pre-sintered body, and the zirconia one-time sintered body. However, from the perspective of obtaining a dense sintered body with high strength, the HIP temperature is preferably 1000°C or higher, more preferably 1200°C or higher, and even more preferably 1300°C or higher. Furthermore, the HIP temperature is preferably 1700°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower.

[0070] Regarding the zirconia sintered body of the present invention, the heating rate is not particularly limited when performing HIP treatment on the zirconia molded body, the zirconia pre-sintered body, and the zirconia primary sintered body, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. Furthermore, the heating rate is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the heating rate to the lower limit or above, productivity is improved. Furthermore, by setting the heating rate to the upper limit or below, the volume difference between the interior and exterior of the zirconia molded body, the zirconia pre-sintered body, and the zirconia primary sintered body can be suppressed. Additionally, in the case where the zirconia molded body contains organic matter, the rapid decomposition of the organic matter can be suppressed, thereby suppressing cracking and damage.

[0071] Regarding the zirconia sintered body of the present invention, the HIP pressure is not particularly limited when performing HIP treatment on the zirconia shaped body, the zirconia pre-sintered body, and the zirconia one-time sintered body. However, from the perspective of obtaining a dense sintered body with high strength, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. Furthermore, the HIP pressure is preferably 200 MPa or less, more preferably 185 MPa or less, and even more preferably 170 MPa or less.

[0072] Regarding the zirconia sintered body of the present invention, the HIP time is not particularly limited when performing HIP treatment on the zirconia shaped body, the zirconia pre-sintered body, and the zirconia one-time sintered body. However, from the perspective of obtaining a dense sintered body with high strength, the HIP time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Furthermore, the HIP time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0073] Regarding the zirconia sintered body of the present invention, when performing HIP treatment on the zirconia shaped body, when sintering the zirconia pre-sintered body, and when performing HIP treatment on the zirconia primary sintered body, the pressure medium is not particularly limited. From the viewpoint of minimizing the impact on zirconia, the pressure medium is selected from at least one of oxygen and inactive gases (e.g., nitrogen, argon, etc.).

[0074] The zirconia sintered body of the present invention exhibits excellent strength. The three-point flexural strength of the zirconia sintered body of the present invention is preferably 500 MPa or more, more preferably 530 MPa or more, and even more preferably 540 MPa or more. By giving the zirconia sintered body of the present invention this three-point flexural strength, breakage and bending in the oral cavity can be suppressed when used, for example, as a dental restoration. There is no particular upper limit to this three-point flexural strength; for example, it can be set to 2000 MPa or less, and further, to 1500 MPa or less. It should be noted that the three-point flexural strength of the zirconia sintered body can be measured according to ISO 6872:2015.

[0075] The zirconia sintered body of the present invention preferably has high light transmittance. Light transmittance can be measured using ΔL... * (WB) was used for evaluation. Specifically, regarding light transmittance, the ΔL of the zirconia sintered body of the present invention at a diameter of 14 mm and a thickness of 1.2 mm was... * (WB) is preferably 6 or more, more preferably 8 or more, and even more preferably 10 or more.

[0076] ΔL * (WB) refers to the lightness (L) against a white background. * ) and brightness (L) against a black background * The difference is 1.5%. Specifically, it refers to the difference between L and L against a white background. * Value (JIS Z 8781-4:2013 Colorimetry - Part 4: CIE 1976 L*a*b* color space) and L against a black background * The difference in values. The white background refers to the white portion of the occlusion rate test paper described in Section 1, Part 4 of JIS K 5600-4-1:1999, and the black background refers to the black portion of the aforementioned occlusion rate test paper. By making this ΔL... * (WB) Within the range described above, a zirconia sintered body with high light transmittance is obtained. This ΔL * There is no specific upper limit for (WB), for example, below 30; from an aesthetic point of view, it could be further set below 25. It should be noted that the ΔL of the zirconia sintered body is [not specified] when the diameter is 14 mm and the thickness is 1.2 mm. * (WB) measurements can be performed using a spectrophotometer. After applying a contact liquid to the surface of the sample, measurements are taken using, for example, a dental colorimetric device (“Crystaleye CE100-CE / JP”, with a seven-band LED light source and analysis software “Crystaleye” (manufactured by Olympus Corporation)). As the contact liquid, a contact liquid with a refractive index nD of 1.60, measured using a wavelength of 589 nm (sodium D-rays), can be used.

[0077] The zirconia sintered body of the present invention exhibits excellent workability. The workability of the zirconia sintered body of the present invention is determined, for example, by hardness. The method for measuring the hardness of the zirconia sintered body of the present invention is not particularly limited, and can be performed using, for example, a 10-stage Mohs hardness tester. The Mohs hardness of the zirconia sintered body of the present invention is preferably 9.5 or less, more preferably 8.5 or less. By giving the zirconia sintered body of the present invention this Mohs hardness, it exhibits good workability. From the viewpoint of suppressing damage to dental restorations in the oral cavity, this Mohs hardness is preferably 3.5 or more, more preferably 4.5 or more.

[0078] The zirconia sintered body of the present invention exhibits excellent workability. The workability of the zirconia sintered body of the present invention can be determined, for example, by Vickers hardness. The Vickers hardness of the zirconia sintered body of the present invention can be measured using a Vickers hardness tester. The Vickers hardness of the zirconia sintered body of the present invention is preferably 1200 HV or less, more preferably 1050 HV or less, and even more preferably 950 HV or less. By giving the zirconia sintered body of the present invention this Vickers hardness, it exhibits good workability. From the viewpoint of suppressing damage to dental restorations in the oral cavity, this Vickers hardness is preferably 150 HV or more, more preferably 300 HV or more, and even more preferably 500 HV or more. It should be noted that the Vickers hardness of the zirconia sintered body can be measured according to JIS Z 2244:2009. The Vickers hardness can be calculated using, for example, a micro / macro Vickers hardness tester (trade name "FALCON 509FA", manufactured by Innovatest Japan), with a load of 5 kgf held for 30 seconds. For example, the average value can be set as n = 10.

[0079] The zirconia sintered body of the present invention exhibits excellent workability. The workability of the zirconia sintered body of the present invention can also be determined, for example, by its fracture toughness value. The method for determining the fracture toughness value of the zirconia sintered body of the present invention is not particularly limited, and can be determined, for example, by the indentation-fracture method (IF method). The fracture toughness value of the zirconia sintered body of the present invention is preferably 5 MPa·m. 1 / 2 The above is preferred, with 6 MPa·m 1 / 2 The above is further preferred to be 7 MPa·m 1 / 2 The above describes how the zirconia sintered body of the present invention exhibits better processability by possessing this fracture toughness value. There is no particular upper limit to this fracture toughness value; for example, it can be set to 10 MPa·m. 1 / 2 Therefore, it can be set to 15 MPa·m 1 / 2 That concludes the above. It should be noted that the failure toughness value of zirconia sintered bodies can be determined according to JIS R 1607:2015.

[0080] The zirconia sintered body of the present invention can be machined into a crown shape using a dental computer-aided design / manufacturing unit. The machining method for dental restorations using the dental computer-aided design / manufacturing unit can be selected from, for example, dry cutting, wet cutting, and wet grinding. From the viewpoint of machining efficiency, wet grinding is preferred for the zirconia sintered body of the present invention. Regarding the machining of the zirconia sintered body of the present invention, commercially available dental computer-aided design / manufacturing units can be used without any limitations, such as CEREC MC XL (manufactured by Dentsply Sirona), CEREC Primemill (manufactured by Dentsply Sirona), and DWX-42W (manufactured by Roland DG).

[0081] Applications of zirconia sintered bodies

[0082] The shape of the zirconia sintered body of the present invention is not limited, and it can be disc-shaped, prismatic, or other shapes. Due to its excellent machinability, the shape can be selected according to the application, and the selectivity for tooth crown shapes is excellent. The applications of the zirconia sintered body of the present invention are not particularly limited. The zirconia sintered body of the present invention offers a high selectivity for tooth crown shapes and has high strength, and can be machined; therefore, it is particularly suitable as a dental material such as dental restorations.

[0083] Example

[0084] The present invention will now be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples, etc. It should be noted that the oxides of the materials used in each example and comparative example and the methods for measuring their properties are as follows.

[0085] [Needle-shaped metal oxides]

[0086] • Needle-shaped metal oxide T1: Needle-shaped TiO2, average fiber length: 1.68 μm, average fiber diameter: 0.13 μm, aspect ratio (average fiber diameter : average fiber length) = 1 : 13

[0087] • Needle-shaped metal oxide T2: Needle-shaped TiO2, average fiber length: 10.47 μm, average fiber diameter: 0.5 μm, aspect ratio (average fiber diameter : average fiber length) = 1 : 21

[0088] • Needle-shaped metal oxide T3: Needle-shaped Al2O3, average fiber length: 2.5 μm, average fiber diameter: 0.1 μm, aspect ratio (average fiber diameter : average fiber length) = 1 : 25

[0089] [Metal oxides other than needle-shaped metal oxides]

[0090] • Granular metal oxide X1: Granular TiO2, average particle size: 0.3~1.0μm

[0091] [Average crystal grain size]

[0092] The average grain size in the zirconia sintered body was determined as follows: For the zirconia sintered bodies obtained in each embodiment and comparative example, the surface was photographed using a scanning electron microscope (trade name "VE-9800", manufactured by Keyence), and 100 arbitrary particles present in the photographed image were selected and the average value of their respective circular equivalent diameters (the diameter of a circle of the same area) was determined.

[0093] [Light transmittance ΔL] * (WB)]

[0094] Light transmittance ΔL * (WB) L was measured using a dental colorimeter (“Crystaleye CE100-CE / JP”, seven-band LED light source, manufactured by Olympus) and analysis software “Crystaleye” (manufactured by Olympus). * a * b * The L value of chromaticity (color space) in the color system (JIS Z 8781-4:2013) * The value was calculated (n=1). A zirconia sintered body with a diameter of 14 mm and a thickness of 1.2 mm was used in the measurement. The L value was measured with the sintered body sample background set to white. * The value is set to the first L. * Value, for measuring the first L * For the same sample after the value was obtained, the L value was measured with the sample background set to black. * The value is set to the second L. * Value, will the first L * Value minus the second L * The obtained value is set as a numerical value representing light transmittance. A contact liquid with a refractive index nD of 1.60 is coated on the test surface of the sample. The white background refers to the white portion of the opacity test paper described in Section 1, Part 4 of JIS K 5600-4-1:1999, and the black background refers to the black portion of the aforementioned opacity test paper.

[0095] Mohs hardness

[0096] Mohs hardness is measured using a Mohs hardness tester (manufactured by Tokyo-Science).

[0097] Vickers hardness

[0098] Vickers hardness was measured using a micro / macro Vickers hardness tester (trade name "FALCON 509FA", manufactured by Innovatest Japan) according to JIS Z 2244:2009 with a load of 5 kgf held for 30 seconds.

[0099] [Break Toughness Value]

[0100] The breaking toughness value was determined using a micro / macro Vickers hardness tester (trade name "FALCON 509FA", manufactured by Innovatest Japan) in accordance with JIS R 1607:2015.

[0101] Three-point bending strength

[0102] The three-point bending strength was determined as follows: For a zirconia sintered body with a width of 14 mm × length of 14 mm × thickness of 14 mm, the test was conducted using a universal testing machine AGS-X (manufactured by Shimadzu Corporation) according to ISO 6872:2015, under the conditions of a distance between support points of 30 mm and a crosshead speed of 0.5 mm / min (average value of n = 3).

[0103] [Grinding volume]

[0104] Grinding volume refers to the amount of material removed from a sintered zirconia body (14mm in length × 14mm in width × 14mm in thickness) from the start of machining until the machining device automatically stops due to the inability to continue machining. The dental computer-aided design / manufacturing unit uses a DWX-42W (manufactured by Roland DG) to machine the sintered body using wet grinding. The milling rods used in the machining unit are the ZGB2-125D (manufactured by Roland DG) for rough grinding and the ZGB2-50D (manufactured by Roland DG) for finish grinding.

[0105] [Grinding Time]

[0106] Regarding grinding time, the time from the start of processing in the above grinding volume measurement to the continuous cutting of the block, the wear of the milling bar, and the automatic stopping of the processing device due to increased processing load is measured.

[0107] [Examples 1-5 and Comparative Example 1]

[0108] First, a mixture of zirconium oxide, yttrium oxide, niobium pentoxide, and needle-like or granular metal oxides was prepared as described in Table 1. Next, this mixture was added to water to form a slurry, which was then wet-milled using a ball mill until the average primary particle size of the zirconium oxide particles reached 0.13 μm. The pulverized slurry was then dried using a spray dryer to obtain zirconium oxide powder. Using the obtained zirconium oxide powder, the powder was subjected to a spray drying process at 300 kg / cm³. 2 The zirconia sintered body is pressurized to obtain a zirconia sintered body with a diameter of 14 mm and a thickness of 1.2 mm, a zirconia sintered body with a width of 4 mm, a length of 16 mm, and a thickness of 1.2 mm, and a zirconia sintered body with a width of 14 mm, a length of 14 mm, and a thickness of 14 mm. Then, it is pressurized at 1700 kg / cm². 2 Further CIP treatment was performed to obtain zirconia shaped bodies. The resulting zirconia shaped bodies were sintered at 1550°C for 120 minutes, and then subjected to HIP treatment at 1450°C for 60 minutes under conditions of 150 MPa (using gas Ar:O2 = 80:20), thereby producing the zirconia sintered bodies described in Examples 1-5 and Comparative Example 1. The results are shown in Table 1. The SEM observation results of the needle-like metal oxide T1 used in Examples 1 and 2 are shown in... Figure 1 The results of SEM observation of the granular metal oxide X1 used in Comparative Example 1 are shown below. Figure 2 .

[0109] [Comparative Example 2]

[0110] First, a mixture of zirconium oxide and yttrium oxide was prepared as described in Table 1. Next, this mixture was added to water to form a slurry, which was then wet-milled using a ball mill until the average primary particle size of the zirconium oxide particles reached 0.13 μm. Then, the pulverized slurry was dried using a spray dryer to obtain zirconium oxide powder. Using the obtained zirconium oxide powder, the powder was subjected to a spray drying process at 300 kg / cm³. 2 The zirconia sintered body is pressurized to obtain a zirconia sintered body with a diameter of 14 mm and a thickness of 1.2 mm, a zirconia sintered body with a width of 4 mm, a length of 16 mm, and a thickness of 1.2 mm, and a zirconia sintered body with a width of 14 mm, a length of 14 mm, and a thickness of 14 mm. Then, it is pressurized at 1700 kg / cm². 2 Further CIP treatment was performed to obtain a zirconia shaped body. The obtained zirconia shaped body was sintered at a sintering temperature of 1500℃ for 120 minutes to produce a zirconia sintered body. The results are shown in Table 1.

[0111] [Comparative Example 3]

[0112] The molar ratio of zirconium oxide to yttrium oxide was set to 94.5:5.5, and the sintering temperature was set to 1550°C. Otherwise, a zirconium oxide sintered body was prepared using the same method as in Comparative Example 2.

[0113] [Comparative Example 4]

[0114] Ten parts by mass of niobium pentoxide were added to Comparative Example 2, and a zirconia sintered body was prepared using the same method as Comparative Example 2. Comparative Example 4 failed to maintain its shape after sintering and collapsed; therefore, its strength and other physical properties could not be measured.

[0115] [Comparative Example 5]

[0116] Ten parts by mass of niobium pentoxide were added to Comparative Example 3. Otherwise, a zirconia sintered body was prepared using the same method as Comparative Example 3.

[0117] First, the light transmittance ΔL*(WB) of the zirconia sintered body will be explained. All examples and comparative examples show a good ΔL*(WB) of 7 or higher, and in particular, Examples 1, 2, and 5 and Comparative Examples 1, 3, and 5 show an excellent ΔL*(WB) of 12 or higher.

[0118] Next, the Mohs hardness of the zirconia sintered bodies will be explained. All examples and comparative examples show a good Mohs hardness of 9.5 or less, especially Examples 1, 2, and 5 and Comparative Examples 1 and 5, which show an excellent Mohs hardness of 8.5 or less.

[0119] Next, the Vickers hardness of the zirconia sintered bodies will be explained. Examples 1-5 and Comparative Examples 1 and 5 show good Vickers hardness below 1050 HV, especially Examples 1, 2, and 5 and Comparative Examples 1 and 5 show excellent Vickers hardness below 950 HV. On the other hand, Comparative Examples 2 and 3 show Vickers hardness above 1200 HV, suggesting poor machinability.

[0120] Next, the fracture toughness value of the zirconia sintered body will be explained. Examples 1-5 and Comparative Examples 1 and 5 show a fracture toughness of 5 MPa·m. 1 / 2 The above-mentioned good breaking toughness values, especially those of Examples 1, 2, and 5 and Comparative Examples 1 and 5, show a value of 7 MPa·m. 1 / 2 The above-mentioned excellent fracture toughness values. On the other hand, Comparative Examples 2 and 3 show a fracture toughness of 5 MPa·m. 1 / 2 The following failure toughness values ​​suggest poor processability.

[0121] Next, the three-point bending strength of the zirconia sintered body will be described. Examples 1 to 5 and Comparative Examples 2 and 3 showed good three-point bending strength of 500 MPa or more. On the other hand, Comparative Examples 1 and 5 showed a three-point bending strength of less than 500 MPa, and there was a possibility that dental restorations in the oral cavity might break and bend.

[0122] Next, the grinding volume of the zirconia sintered body will be described. Examples 1 to 5 and Comparative Examples 1 and 5 could be processed. In particular, Examples 1, 2, 5 and Comparative Examples 1 and 5 showed excellent workability. On the other hand, Comparative Examples 2 and 3 were hardly processable.

[0123]

[0124] Industrial Applicability

[0125] The zirconia sintered body of the present invention and the method for manufacturing the zirconia sintered body can be used for various purposes such as dental products such as dental prostheses, optical fiber connection components such as metal collars and sleeves, various tools (such as grinding balls and grinding tools), various components (such as screws, bolts / nuts), various sensors, electronic components, and ornaments (such as watch bands). When the sintered body is used for dental materials, it can be used for, for example, crowns, frameworks, dental crowns, crown bridges, abutments, implants, implant screws, implant fixators, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, veneers, etc.

Claims

1. A zirconia sintered body, comprising zirconia, a stabilizer capable of inhibiting the zirconia phase transformation, a sintering aid, and a needle-like metal oxide, wherein the aforementioned sintering aid comprises niobium pentoxide. The content of niobium pentoxide is 5-15 parts by weight relative to the total of 100 parts by weight of zirconium oxide and stabilizer. The aforementioned needle-shaped metal oxide is TiO2.

2. The zirconia sintered body according to claim 1, wherein, The aforementioned stabilizer includes yttrium oxide. The content of yttrium oxide relative to the total moles of zirconium oxide and yttrium oxide is 2.5~10 mol.

3. The zirconia sintered body according to claim 1 or 2, wherein, The aforementioned needle-shaped metal oxides have an aspect ratio of 1:3 to 1:

55.

4. The zirconia sintered body according to claim 1 or 2, wherein, The content of the aforementioned needle-shaped metal oxide is more than 0 parts by mass and less than 10 parts by mass relative to the total of 100 parts by mass of zirconium oxide and stabilizer.

5. The zirconia sintered body according to claim 1 or 2, wherein the Vickers hardness is below 1050 HV.

6. The zirconia sintered body according to claim 1 or 2, wherein the breaking toughness value is 5 MPa·m. 1 / 2 above.

7. The zirconia sintered body according to claim 1 or 2 has a three-point bending strength of 500 MPa or more.

8. The zirconia sintered body according to claim 1 or 2, wherein the average crystal grain size is 1~10 μm.

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