Dental workpiece and method for producing same

Abstract

The present invention provides a dental workpiece in which appearance defects in a product are suppressed and which has excellent machinability in a state of a sintered body. The present invention pertains to a dental workpiece comprising a polycrystalline ceramic, wherein the polycrystalline ceramic is a laminate provided with two or more layers having different contents of a capping agent-derived element or ion, and the laminate is provided with a layer (W) in which the content of the capping agent-derived element or ion is less than 0.15 mol% relative to a total of 100 mol% of the components constituting the polycrystalline ceramic.

Description

Dental workpiece and method for manufacturing the same

[0001] The present invention relates to a dental workpiece and a method for manufacturing the same. More specifically, the present invention relates to a dental workpiece that is excellent in strength and light transmittance, and has excellent processability in the sintered state, and a method for manufacturing the same.

[0002] Ceramics made from metal oxides have been widely used industrially. Among them, zirconia sintered bodies are used in dental materials such as dental prosthetics due to their high strength and aesthetic properties.

[0003] Zirconia sintered bodies have excellent strength, so when used in dental materials such as prosthetics, problems such as breakage rarely occur. In addition, zirconia sintered bodies have high translucency and do not easily stain in the oral cavity, making them aesthetically pleasing. On the other hand, once the sintered body is fully sintered, it has high hardness, making it almost impossible to process with dental processing machines. For example, if a cubic zirconia sintered body is machined to obtain a zirconia sintered body that matches the shape of a patient's tooth, the wear of metal processing tools becomes extremely large, and it takes an enormous amount of time to manufacture even just one dental prosthesis.

[0004] For these reasons, when zirconia sintered bodies are used for dental materials, they are usually not fully sintered, but rather a partially sintered body that is easier to process. This is done by first processing the calcined body into the desired shape of the dental prosthesis, and then further sintering it to produce a sintered body that has been processed into the shape of the target dental prosthesis. Subsequently, the sintered body undergoes minor adjustments to ensure that it fits comfortably in the patient's mouth when placed in the dental clinic. In recent years, when processing calcined bodies into the desired shape of the dental prosthesis, machining using CAD / CAM systems is used to obtain shapes that match the teeth of the patient's treatment area, and calcined bodies (mill blanks) for CAD / CAM systems are widely used.

[0005] As described above, when using zirconia sintered bodies for dental material applications, due to the unique problems in zirconia sintering, major machining after sintering is avoided, and processing of the sintered body is limited to minor adjustments performed in the dental clinic when it is placed in the patient's mouth. In other words, dental material applications are being handled in accordance with the gradual changes in physical properties caused by zirconia sintering.

[0006] Furthermore, in dental treatment, taking into account the unique circumstances arising from the physical properties of the zirconia sintered body described above, treatment is generally carried out through many steps, including: acquiring information on the patient's oral cavity shape, such as tooth alignment information; machining a calcined body (mill blank) into the desired shape of the dental prosthesis using a CAD / CAM system based on the acquired information; sintering the calcined body having the desired shape of the dental prosthesis to obtain a sintered body; and making minor adjustments to the sintered body at the dental clinic so that it fits comfortably without discomfort when placed in the patient's oral cavity.

[0007] Thus, in dental treatment using zirconia sintered dental prostheses, it is difficult to complete all of the above steps in a single visit to the dentist. Therefore, even for the treatment of a single tooth, multiple visits to the dental clinic are often required, and the treatment period from start to finish often takes more than a month.

[0008] On the other hand, from the patient's perspective, it is desirable to have as few hospital visits as possible to reduce the time until new artificial teeth are fitted after treatment and to alleviate the burden of hospital visits. The need to complete treatment in a short time is increasing year by year.

[0009] If significant machining is possible in the zirconia sintered state, the process of machining the material in a calcined state and then manufacturing the sintered body through sintering becomes unnecessary. Instead, after obtaining information on the shape of the patient's oral cavity, it becomes possible to machine the unprocessed sintered body into the desired shape of the dental prosthesis using a CAD / CAM system based on that information, fit it into the patient's mouth, perform fine adjustments, and complete the dental treatment in a single day.

[0010] Furthermore, while it is possible to complete dental treatment in a single day using dental prostheses with materials other than zirconia, such as lithium disilicate glass ceramics and feldspar-based glass ceramics, achieving this in the case of zirconia sintered bodies presents unique challenges due to the physical properties of the sintered body, making it highly difficult to achieve.

[0011] As described above, zirconia is in high demand due to its strength and aesthetic properties, and in response to the growing need for shorter treatment periods, sintered zirconia bodies have been proposed that are highly machinable in their sintered state and can be processed from prismatic or disc-shaped mill blanks into the desired shape of dental prostheses (for example, Patent Documents 1 and 2).

[0012] For example, Patent Document 1 discloses a processable zirconia and a method for producing the same, which is a sintered body formed to include a tetragonal zirconia composite powder containing 79.8 to 92 mol% ZrO2 and 4.5 to 10.2 mol% Y2O3 and 3.5 to 7.5 mol% Nb2O5 or 5.5 to 10.0 mol% Ta2O5, and TiO2 nanopowder having a mass ratio of more than 0 mass% and 2.5 mass% or less to the zirconia composite powder.

[0013] Furthermore, Patent Document 2 discloses a machinable zirconia composition and a method for producing the same, using raw materials comprising 78 to 95 mol% ZrO2, 2.5 to 10 mol% Y2O3, 2 to 8 mol% Nb2O5 and / or 3 to 10 mol% Ta2O5, wherein the main crystalline phase of ZrO2 is monoclinic.

[0014] Furthermore, as an improved invention, a zirconia sintered body containing elements or ions derived from a capping agent has been proposed, which exhibits particularly excellent machinability in the sintered state and can be processed from a prismatic or disc-shaped mill blank into the desired shape of a dental prosthesis (for example, Patent Document 3).

[0015] Japanese Patent Publication No. 2015-127294, International Publication No. 2021 / 132644, International Publication No. 2023 / 234397

[0016] However, in Patent Document 3, when a molded body or calcined body is placed on a high-purity alumina sheath and fired at a predetermined heating temperature to obtain a sintered body, elements or ions derived from the capping agent react with the alumina sheath, resulting in white spots appearing on the contact surface of the resulting zirconia sintered body, or cracks appearing in the resulting zirconia sintered body, thus impairing the appearance of the product.

[0017] The present invention aims to provide a dental workpiece that suppresses defects in the appearance of the product and exhibits excellent machinability in its sintered state.

[0018] The present inventors conducted extensive research to solve the above problems and found that the above problems can be solved by providing a dental workpiece made of polycrystalline ceramic, wherein the polycrystalline ceramic is a laminate comprising two or more layers with different content rates of elements or ions derived from the capping agent, and the laminate includes a layer (W) in which the content rate of elements or ions derived from the capping agent is less than 0.15 mol% of the total 100 mol% of each component constituting the polycrystalline ceramic. Based on this finding, the inventors furthered their research and completed the present invention.

[0019] In other words, the present invention encompasses the following inventions: [1] A dental workpiece made of polycrystalline ceramic, wherein the polycrystalline ceramic is a laminate comprising two or more layers having different content rates of elements or ions derived from a capping agent, and the laminate comprises a layer (W) in which the content rate of elements or ions derived from the capping agent is less than 0.15 mol% with respect to a total of 100 mol% of the total content of each component constituting the polycrystalline ceramic. [2] The dental workpiece according to [1], wherein the polycrystalline ceramic comprises zirconia and a stabilizer capable of suppressing the phase transition of zirconia. [3] The dental workpiece according to [2], wherein the polycrystalline ceramic further comprises Nb2O5 and / or Ta2O5. [4] The dental workpiece according to any one of [1] to [3], wherein the thickness of the layer (W) is 7.0 mm or less. [5] The dental workpiece according to any one of [2] to [4], wherein the stabilizer capable of suppressing the phase transition of zirconia is yttria. [6] A dental workpiece according to any one of [1] to [5], wherein the layer (W) is arranged as the outermost layer. [7] A dental workpiece according to any one of [1] to [6], for use as a dental prosthesis. [8] A method for manufacturing a dental workpiece according to any one of [1] to [5], comprising the steps of laminating a raw material composition for a layer (W) in which the content of elements or ions derived from a capping agent is less than 0.15 mol% with respect to 100 mol% of the total of each component constituting the polycrystalline ceramic, and a raw material composition for a layer in which the content of elements or ions derived from a capping agent is different from that of the layer (W), to produce a molded body having a laminated structure, and sintering the molded body to obtain a laminate, wherein the laminate is a dental workpiece made of polycrystalline ceramic. [9] A method for manufacturing a dental workpiece according to [8], wherein the maximum sintering temperature in the step of sintering the molded body to obtain a laminate is 1300 to 1680°C.

[10] A method for producing a dental workpiece according to [8] or [9], wherein the polycrystalline ceramic comprises zirconia and a stabilizer capable of suppressing the phase transition of zirconia.

[0020] According to the present invention, it is possible to provide a dental workpiece that suppresses defects in the appearance of the product and exhibits excellent machinability in the sintered state.

[0021] The dental workpiece of the present invention is a dental workpiece made of polycrystalline ceramic, wherein the polycrystalline ceramic is a laminate comprising two or more layers with different content rates of elements or ions derived from the capping agent, and the laminate comprises a layer (W) (hereinafter also simply referred to as "layer (W)") in which the content rate of elements or ions derived from the capping agent is less than 0.15 mol% with respect to 100 mol% of the total of each component constituting the polycrystalline ceramic.

[0022] In this specification, "polycrystalline ceramic" means a ceramic that can consist of a large number of crystalline particles as observed by SEM or the like. In this specification, "total of each component" means, for example, 100 mol% of the total of ZrO2, HfO2, and a stabilizer capable of suppressing the phase transition of zirconia when the dental workpiece is composed of a zirconia-based composite oxide, and 100 mol% of the total of ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, NbO5, and Ta2O5 when the zirconia-based composite oxide further contains Nb2O5 and / or Ta2O5. In this specification, machining includes cutting and grinding. Furthermore, machining may be either wet or dry, and is not particularly limited. In this specification, "molded body" means a body that has not reached either a semi-sintered state (calcined state) or a sintered state. In other words, a molded body is distinguished from a calcined body and a sintered body in that it is unfired after being molded. In this specification, "calcined body" means a material that can be a precursor (intermediate product) of a sintered body, in which the particles are necking (adhered) to each other and are not completely sintered. In this specification, "sintered body" means a sintered state in which metal oxide (e.g., zirconia, alumina) particles (powder) have been completely sintered. In this specification, "in the air" means under standard atmospheric pressure (1 atm). In this specification, the upper and lower limits of the numerical range (content of each component, values ​​calculated from each component, and each physical property, etc.) can be combined as appropriate.

[0023] The reason why the dental workpiece of the present invention has excellent machinability and can suppress defects in the appearance of the product is presumed to be as follows: During firing, layer (W) prevents excessive segregation of elements or ions derived from the capping agent at the contact surface with the alumina sheath, thereby suppressing the reaction between the alumina sheath and elements or ions derived from the capping agent. Furthermore, it is believed that the layers other than layer (W) in the laminate contain elements or ions derived from the capping agent, resulting in excellent machinability.

[0024] The dental workpiece of the present invention refers to a workpiece in which ceramic particles (powder) (e.g., Al2O3 particles, ZrO2 particles) are completely sintered (sintered state). In this specification, the upper and lower limits of the numerical range (content of each component, ratio calculated from each component, value, and physical properties, etc.) can be combined as appropriate. In this specification, machining includes cutting and grinding. Furthermore, machining may be either wet or dry, and is not particularly limited.

[0025] The dental workpiece of the present invention may be either a dental workpiece composed of an alumina-based composite oxide or a dental workpiece composed of a zirconia-based composite oxide (preferably a dental workpiece in which the polycrystalline ceramic constituting the laminate contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizer")), but a dental workpiece composed of a zirconia-based composite oxide is preferred in terms of superior strength. That is, the dental workpiece of the present invention is preferably a zirconia sintered body or an alumina sintered body, and more preferably a zirconia sintered body. Hereinafter, the dental workpiece will be described using as an example a dental workpiece in which the polycrystalline ceramic constituting the laminate contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia.

[0026] In this specification, an element or ion derived from a capping agent (hereinafter also referred to as "capping element or ion") is an element or ion that caps the ends of the bonds of an alumina-based composite oxide or a zirconia-based composite oxide in a dental workpiece (preferably a dental workpiece composed of a zirconia-based composite oxide), thereby weakening the strength of the crystal interface (hereinafter also referred to as "grain boundary") (hereinafter also referred to as "grain boundary strength"). The capping agent can cap a part of the crystal grain boundary. "Capping" means that the target element or ion (capping element or ion) binds to the bond of the alumina-based composite oxide or zirconia-based composite oxide instead of the metal element and exists at the crystal grain boundary. It is presumed that when the capping element or ion exists at the grain boundary in the form of a +1-valent cation or a -1-valent anion, the capping cations or anions repel each other electrostatically, weakening the grain boundary strength.

[0027] In the dental workpiece of the present invention, in the dental workpiece in which the polycrystalline ceramic constituting the laminate contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, the polycrystalline ceramic may not contain Nb₂O₅ and Ta₂O₅. On the other hand, in the dental workpiece in which the polycrystalline ceramic constituting the laminate contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, the polycrystalline ceramic further containing Nb₂O₅ and / or Ta₂O₅ is more excellent in machinability. From this viewpoint, hereinafter, as an embodiment, a dental workpiece in which the polycrystalline ceramic is a laminate having two or more layers with different contents of elements or ions derived from a capping agent, and the laminate contains zirconia, a stabilizer capable of suppressing the phase transition of zirconia, and Nb₂O₅ and / or Ta₂O₅ will be described by way of example.

[0028] In this specification, the content of each component in a dental workpiece can be calculated from the amount of raw materials used. Furthermore, the content (mol%) of elements or ions derived from the capping agent is the external addition rate relative to the total of 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5. Therefore, the content of elements or ions derived from the capping agent in a dental workpiece can be calculated by converting the amount (mass) of raw materials used at the time of addition to mol%. Furthermore, the content (mass%) of the reinforcing agent is the external addition rate relative to the total of 100 mass% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5. Therefore, the content of the reinforcing agent in a dental workpiece can be calculated from the amount (mass) of raw materials used at the time of addition. In this specification, "reinforcing agent" means a material that has the function of improving the mechanical strength of polycrystalline ceramics constituting dental workpieces (for example, polycrystalline ceramics containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia; polycrystalline ceramics composed of alumina-based composite oxides). Furthermore, the content of each component of ZrO2, HfO2, stabilizer, Nb2O5 and Ta2O5, elements or ions derived from the capping agent, and reinforcing agent in dental workpieces can also be measured by, for example, atomic absorption spectrometry (AAS), inductively coupled plasma emission spectrometry (ICP), X-ray fluorescence analysis, etc. For dental workpieces in which the polycrystalline ceramic is composed of alumina-based composite oxides, the calculation can be performed by replacing ZrO2 and HfO2 with Al2O3.

[0029] The reason why the dental workpiece of the present invention exhibits excellent machinability in its sintered state is not entirely clear, but it is presumed to be as follows: In a dental workpiece contained in a polycrystalline ceramic in which ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5 constitute a laminate, the presence of capping elements or ions at the grain boundaries is presumed to reduce the grain boundary strength in the form of +1 valence cations or -1 valence anions, thereby acting in a direction that makes it easier to separate the particles from each other, making it easier to cut and improving machinability. The dental workpiece of the present invention is presumed to have a structure comprising zirconia particles containing ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5, a release component containing a capping element or ion, and, if necessary, an adhesive component containing ZrO2, HfO2, Nb2O5 and / or Ta2O5, and a metal element derived from a reinforcing agent (e.g., Ti). Parts of ZrO2, HfO2, Nb2O5 and / or Ta2O5 are present in both the zirconia particles and the adhesive component. Furthermore, the dental workpiece of the present invention is presumed to have grain boundaries where no release component exists, and a moderate amount of the release component containing the capping element or ion is present at the grain boundaries, thereby enabling an appropriate reduction in grain boundary strength while minimizing the reduction in strength. For example, even when an adhesive component containing a reinforcing agent is present in a dental workpiece, the strength can be increased without suppressing the effect of the release component on reducing the grain boundary strength obtained.

[0030] The capping element or ion becomes a +1-valent cation or a -1-valent anion at the grain boundaries of the dental workpiece and binds to the bonds of the zirconia-based composite oxide. By this binding, the cations or anions repel each other electrostatically, and while maintaining the properties of strength and translucency as the particles constituting the dental workpiece, the grain boundary strength can be weakened, which acts in the direction of improving the machinability. For example, a form in which a +1-valent cation binds to the other bond of an oxygen atom bonded to a metal element (e.g., Zr, Hf, Y, Nb, or Ta) contained in the zirconia-based composite oxide instead of the metal element is conceivable. Also, a form in which a -1-valent anion binds to an OH 2+ bonded to a metal element (e.g., Zr, Hf, Y, Nb, or Ta) contained in the zirconia-based composite oxide is conceivable. Further, a form in which a -1-valent anion binds to a cation derived from a metal element (e.g., Zr, Hf, Y, Nb, or Ta) contained in the zirconia-based composite oxide and bonded to another metal element is conceivable.

[0031] Also, Nb2O5 and / or Ta2O5 act in the direction of coarsening the fine structure and reducing the hardness in the dental workpiece. Therefore, the capping element or ion and Nb2O5 and / or Ta2O5 act together in the direction of improving the machinability. Thus, it is presumed that the capping element or ion and Nb2O5 and / or Ta2O5 act together, and while having the strength required as an artificial tooth, excellent machinability can be imparted, so that the processing time by machining can be shortened. Further, by the above action, it is presumed that the consumption of the processing tool can be suppressed, the number of dental prostheses obtained by continuous machining using one processing tool can be increased, and the specific problems in the continuous machining of the sintered body can be solved.

[0032] In the dental workpiece of the present invention, the capping element or ion acts as a machining property-imparting agent as described above and does not significantly impair the strength and translucency. Therefore, the dental workpiece of the present invention is preferably for dental prostheses.

[0033] The content of capping elements or ions in the layers other than the layer (W) constituting the laminate in the dental workpiece of the present invention is preferably more than 0 mol% and 5 mol% or less, based on 100 mol% of the total of each component (ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5) constituting the layers other than the layer (W). More preferably, it is 0.05 mol% to 3 mol%, even more preferably 0.06 mol% to 2.5 mol%, particularly preferably 0.07 mol% to 1.0 mol%, and most preferably 0.08 mol% to 0.34 mol%. Furthermore, when the capping element or ion contained in the dental workpiece of the present invention is a Group 17 element or ion, it is more preferable that the capping element or ion is 0.2 mol% to 5 mol%, even more preferable that it is 0.3 mol% to 4 mol%, particularly preferable that it is 0.4 mol% to 3.5 mol%, and most preferable that it is 0.5 mol% to 3.0 mol%, from the standpoint of superior machinability and the ability to increase the number of dental prostheses that can be continuously processed with a single processing tool. When the laminate comprises two or more layers in addition to layer (W) (i.e., when the laminate is a laminate of three or more layers comprising layer (W)), the content of the capping element or ion in each layer other than layer (W) constituting the laminate may be the same or different.

[0034] As mentioned above, the capping element or ion should be a +1 valent cation or a -1 valent anion, and it is important that it exists at the grain boundary, as it exhibits appropriate interaction between the charged site and the adsorption site at the grain boundary.

[0035] The content of capping elements or ions contained in the layer (W) constituting the laminate is less than 0.15 mol%, preferably 0.14 mol% or less, more preferably 0.12 mol% or less, even more preferably 0.10 mol% or less, and particularly preferably 0.09 mol% or less, relative to the total of 100 mol% of each component constituting the layer (W) (100 mol% of ZrO2, HfO2, and the stabilizer contained in the layer (W), and if the layer (W) further contains Nb2O5 and / or Ta2O5, 100 mol% of the total of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5). The content of capping elements or ions contained in the layer (W) may be 0 mol%, 0 mol% or more, or greater than 0 mol%, relative to the total of 100 mol%. In other words, the content of capping elements or ions contained in layer (W) is preferably 0 mol% or more and 0.14 mol% or less, more preferably 0 mol% or more and 0.12 mol% or less, even more preferably 0 mol% or more and 0.10 mol% or less, and particularly preferably 0 mol% or more and 0.09 mol% or less. As one embodiment, a dental workpiece is provided in which the content of capping elements or ions contained in layer (W) is 0 mol% or more and less than 0.15 mol%. The laminate is a laminate comprising two or more layers with different content of elements or ions derived from the capping agent, and the content of capping elements or ions in layers other than layer (W) is not limited as long as it is different from the content of capping elements or ions in layer (W), but it is preferable that it is higher than the content of capping elements or ions in layer (W) in terms of superior machinability. When the laminate comprises two or more layers in addition to layer (W) (i.e., when the laminate is a laminate of three or more layers including layer (W)), the content of capping elements or ions in all layers other than layer (W) is preferably higher than the content of capping elements or ions in layer (W) because it offers superior machinability.

[0036] The aforementioned layer (W) is preferably placed as the outermost layer in the laminate, in order to efficiently suppress the reaction of elements or ions derived from the capping agent with the alumina pod.

[0037] The thickness of the layer (W) is preferably 7.0 mm or less, more preferably 4.0 mm or less, from the viewpoint of efficiently suppressing the reaction between the alumina pod and elements or ions derived from the capping agent in the laminate, and having excellent machinability as a whole dental workpiece in the sintered state, and is even more preferably 3.0 mm or less, and particularly preferably 1.0 mm or less, from the viewpoint of superior machinability. Furthermore, the thickness of the layer (W) is preferably 0.01 mm or more, more preferably 0.05 mm or more, and particularly preferably 0.10 mm or more. In other words, the thickness of the layer (W) is preferably 0.01 mm to 7.0 mm, more preferably 0.05 mm to 4.0 mm, even more preferably 0.10 mm to 3.0 mm, and particularly preferably 0.10 mm to 1.0 mm. As described above, the thickness of the layer (W) is not particularly limited as long as it is within a predetermined suitable range, in order to efficiently suppress the reaction between the alumina pod and elements or ions derived from the capping agent and to have excellent machinability in the sintered state, the ratio of the thickness of the layer (W) to the thickness of the other layers (layer (W): layer (W): layer (W)) is preferably 1:1 to 1:1400. Other embodiments of the thickness ratio include 1:1 to 1:700, 1:1 to 1:200, 1:1 to 1:100, 1:1 to 1:80, 1:1 to 1:40, 1:1 to 1:20, or 1:1 to 1:10. In one embodiment, the thickness ratio is preferably in the range of 1:1 to 1:20. In another embodiment, the thickness ratio is preferably in the range of 1:1 to 1:10.

[0038] Preferred capping elements or ions include elements or ions belonging to the 2nd to 7th periods of the periodic table, having a first ionization energy lower than that of the Group 18 elements of the same period, elements or ions with high electron affinity, nitrate ions, hypochlorite ions, chlorite ions, chlorate ions, perchlorate ions, bromate ions, permanganate ions, metaborate ions, and cyanide ions. One embodiment is a dental workpiece in which the elements or ions derived from the capping agent belong to the 2nd to 7th periods of the periodic table, have a first ionization energy lower than that of the Group 18 elements of the same period, and / or elements or ions with high electron affinity.

[0039] Among the elements belonging to the 2nd to 7th periods of the periodic table, those whose first ionization energy is lower than that of the group 18 elements of the same period include Cu, Ag, Li, Na, K, Rb, Cs, Fr, etc., because they are easier to obtain as +1 cations and have superior machinability.

[0040] As elements with high electron affinity, Group 17 elements are preferred because -1 valent anions are more readily obtained and they have superior machinability. Preferred Group 17 elements are At, I, Br, Cl, and F.

[0041] The first ionization energy is the energy required to remove one electron from a neutral atom to ionize it. The first ionization energy can be the same as the first ionization energy described in "Shriver & Atkins Inorganic Chemistry (Vol. 1), 4th Edition, Part I, Fundamentals, 1. Atomic Structure". The first ionization energy can be converted to kJ / mol units using the unit "eV" for the first ionization energy described in "Shriver & Atkins Inorganic Chemistry (Vol. 1), 4th Edition, Appendix 2", with 1 eV = 96.485 kJ / mol. The first ionization energy can also be determined by photoelectron yield spectroscopy (PYS). Electron affinity (EA) is the energy released when an electron is added to a neutral atom. Electron affinity can be measured from the ionization potential by the energy gap difference. The ionization potential is defined as the energy difference between the highest-energy occupied orbital of the compound molecule and the vacuum level, and its value is measured using ultraviolet photoelectron spectroscopy. For the first ionization energy and electron affinity, data stored in the NIST Chemistry WebBook (https: / / webbook.nist.gov / chemistry / ) can be used (select Ionization Energy or Electron Affinity from Ion energetics properties). Since it is sufficient to compare the ease of forming a +1 valence cation or a -1 valence anion with other elements, the measurement method described above can be used as appropriate.

[0042] Examples of capping elements include Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl, and F, with Cu, Ag, Li, Na, K, Rb, Cs, Fr, I, Br, Cl, and F being preferred because they can further improve machinability. In one embodiment, a dental workpiece is provided in which the elements derived from the capping agent include at least one element selected from the group consisting of Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl, and F, and the ion of the element is at least one +1 valent cation or -1 valent anion selected from the group consisting of Cu, Ag, Li, Na, K, Rb, Cs, Fr, I, Br, Cl, and F. In another embodiment, a dental workpiece is provided in which the capping agent-derived elements or ions include at least one element or ion selected from the group consisting of Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl, and F. The capping elements or ions may be used individually or in combination of two or more.

[0043] In the dental workpiece of the present invention, the total content of ZrO2 and HfO2 is 78 to 97.5 mol% of the total of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5 in 100 mol%, and is preferably 79 mol% to 96 mol%, more preferably 80 mol% to 94 mol%, and even more preferably 81 mol% to 93 mol% from the viewpoint of superior light transmittance and strength. The total content of ZrO2 and HfO2 in each layer may be the same or different.

[0044] Examples of stabilizers that can suppress the phase transition of zirconia include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y2O3), cerium oxide (CeO2), scandium oxide (Sc2O3), lanthanum oxide (La2O3), erbium oxide (Er2O3), and praseodymium oxide (Pr2O3, Pr6O3). 11Examples of oxides include samarium oxide (Sm2O3), europium oxide (Eu2O3), thulium oxide (Tm2O3), gallium oxide (Ga2O3), indium oxide (In2O3), and ytterbium oxide (Yb2O3). Y2O3 (yttria) and / or CeO2 are preferred, and Y2O3 (yttria) is more preferred, as they offer superior effects and are particularly aesthetically pleasing. The stabilizer may be used alone or in combination of two or more types.

[0045] As described above, the capping element or ion acts in conjunction with Nb2O5 and / or Ta2O5, and does not impair the effect of the stabilizer; therefore, the stabilizer is not particularly limited and will produce the effects of the present invention.

[0046] In the dental workpiece of the present invention, the content of the stabilizer capable of suppressing the phase transition of zirconia is 1 to 12 mol% in a total of 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5. It is preferably 2 mol% to 10 mol% from the standpoint of easily obtaining sufficient machinability, more preferably 3 mol% to 8 mol% from the standpoint of superior light transmittance and strength, and even more preferably 3.5 mol% to 7.5 mol%. As one embodiment, a dental workpiece is provided in which the stabilizer capable of suppressing the phase transition of zirconia contains Y2O3 and / or CeO2, and the total content of Y2O3 and CeO2 is 2 mol% to 10 mol%. Another embodiment is a dental workpiece in which a stabilizer capable of suppressing the phase transition of zirconia contains Y2O3, and the content of Y2O3 is 2 mol% or more and 10 mol% or less. In any of the embodiments described above, the content of Y2O3 and CeO2 can be appropriately changed within the range described herein. For example, from the viewpoint of superior light transmittance and strength, the total content of Y2O3 and CeO2 may be 2.5 mol% or more and 10 mol% or less, or 3 mol% or more and 9 mol% or less. The content of the stabilizer in each layer may be the same or different.

[0047] In each layer of the laminate constituting the dental workpiece of the present invention, the total content of Nb2O5 and Ta2O5 is 1 to 9 mol% of the total 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5, preferably 1.5 mol% to 8.5 mol%, more preferably 2.5 mol% to 8 mol%, and even more preferably 3 mol% to 7 mol%, from the viewpoint of acting integrally with capping elements or ions and having better machinability. If the total content of Nb2O5 and Ta2O5 is less than 1 mol%, it is difficult to obtain sufficient machinability. Also, if the total content of Nb2O5 and Ta2O5 exceeds 9 mol%, chipping and other defects may occur in the resulting dental workpiece, making it difficult to obtain sufficient physical properties. The total content of Nb2O5 and Ta2O5 in each layer may be the same or different.

[0048] As described above, Nb2O5 and Ta2O5 act to coarseen the microstructure and reduce hardness, and in conjunction with capping elements or ions, they can impart superior machinability. Furthermore, through interaction with other components added to dental workpieces (e.g., TiO2, Al2O3) and the application of HIP, they can maximize sinter density and ensure the aesthetics of natural teeth.

[0049] The content of each component ZrO2, HfO2, stabilizer, Nb2O5, and Ta2O5 as described above is the proportion relative to the total of ZrO2, HfO2, stabilizer, Nb2O5, and Ta2O5 in 100 mol%, and the total of ZrO2, HfO2, stabilizer, Nb2O5, and Ta2O5 does not exceed 100 mol%. For example, if the raw material composition contains Nb2O5 but does not contain Ta2O5, the content of each component ZrO2, HfO2, stabilizer, and Nb2O5 means the proportion of each component relative to the total of ZrO2, HfO2, stabilizer, and Nb2O5 in 100 mol%.

[0050] Furthermore, when the content of the stabilizer is A mol%, and the total content of Nb2O5 and Ta2O5 is B mol%, the A / B ratio is preferably 0.9 to 3, more preferably 0.95 to 2, from the viewpoint of machinability. This ratio enhances the effect of the capping element or ion acting together with Nb2O5 and / or Ta2O5, providing better machinability, suppressing wear on the machining tool, and increasing the number of dental prostheses that can be obtained by continuous machining using a single machining tool. Therefore, it is even more preferable that the ratio be 1 to 1.6.

[0051] One embodiment of the present invention is a dental workpiece made of polycrystalline ceramic, wherein the polycrystalline ceramic is a laminate comprising two or more layers with different content rates of elements or ions derived from the capping agent, each layer constituting the laminate contains ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5, in each layer, of a total of 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5, the total content rate of ZrO2 and HfO2 is 78 to 97.5 mol%, the content rate of the stabilizer is 1 to 12 mol%, and the total content rate of Nb2O5 and Ta2O5 is 1 to 9 mol%, and the laminate comprises a layer (W) in which the content rate of elements or ions derived from the capping agent is less than 0.15 mol% of a total of 100 mol% of the components constituting the polycrystalline ceramic. An example of a dental workpiece is one in which the content of elements or ions derived from the capping agent in layers other than the layer (W) constituting the laminate is 0.15 mol% or more with respect to the total of 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5 constituting the polycrystalline ceramic, the stabilizer contains Y2O3 and / or CeO2, and when the content of the stabilizer is A mol% and the total content of Nb2O5 and Ta2O5 is B mol%, the ratio of A / B is 0.9 or more and 3 or less.

[0052] One embodiment of the present invention is a dental workpiece comprising ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, Nb2O5 and / or Ta2O5, a capping element or ion, and a reinforcing agent. In a dental workpiece containing ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5, the reinforcing agent acts integrally with the capping element or ion, improving the strength of the sintered body while maintaining workability.

[0053] In dental workpieces containing reinforcing agents, as described above, the total content of ZrO2 and HfO2, the type and content of the stabilizer, the total content of Nb2O5 and Ta2O5, the type and content of the capping element or ion, and the A / B ratio can be appropriately changed.

[0054] In a dental workpiece in which each layer constituting the laminate contains a reinforcing agent, the content of the reinforcing agent is preferably more than 0% by mass and 6.0% by mass or less, based on 100% by mass of the total of ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, Nb2O5, and Ta2O5. More preferably, it is 0.01% by mass or more and 5.5% by mass or less, and even more preferably, 0.5% by mass or more and 5.0% by mass or less, from the viewpoint that it acts as a whole when combined with a capping element or ion and has superior strength. The content of the reinforcing agent in each layer may be the same or different.

[0055] Examples of the reinforcing agent include TiO2 and Al2O3. The reinforcing agent may be used alone or in combination of two or more. The reinforcing agent can be selected according to the type of polycrystalline ceramic constituting the laminate. In dental workpieces in which the polycrystalline ceramic is composed of alumina-based composite oxides, the reinforcing agent is preferably TiO2.

[0056] One embodiment is a dental workpiece containing a reinforcing agent, wherein the reinforcing agent contains TiO2 and the TiO2 content is 0.6 to 4.5% by mass.

[0057] One embodiment is a dental workpiece made of polycrystalline ceramic, wherein the polycrystalline ceramic is a laminate comprising two or more layers with different content rates of elements or ions derived from the capping agent, the laminate comprises a layer (W) in which the content rate of elements or ions derived from the capping agent is less than 0.15 mol% with respect to 100 mol% of the total of each component constituting the polycrystalline ceramic, each layer constituting the laminate contains ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, Nb2O5 and / or Ta2O5, and a reinforcing agent, in each layer, of the total 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5, the total content rate of ZrO2 and HfO2 is 78 to 97.5 mol%, the content rate of the stabilizer is 1 to 12 mol%, and the total content rate of Nb2O5 and Ta2O5 is 1 to 9 mol%. A dental workpiece is provided in which each of the aforementioned layers further contains a capping element or ion, the stabilizer contains Y2O3 and / or CeO2, the reinforcing agent contains TiO2 with a TiO2 content of 0.6 to 4.5% by mass, the content of the capping element or ion in the layers other than the layer (W) constituting the laminate is greater than 0 mol% and less than or equal to 5 mol% with respect to a total of 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5, and when the content of the stabilizer is A mol% and the total content of Nb2O5 and Ta2O5 is B mol%, the ratio of A / B is 0.9 or more and less than or equal to 3.

[0058] The average crystalline particle diameter of the dental workpiece of the present invention is preferably 0.5 to 5.0 μm, more preferably 0.5 to 4.5 μm, and even more preferably 1.0 to 4.0 μm, from the viewpoint of superior machinability, strength, and light transmittance. The method for measuring the average crystalline particle diameter is as described in the examples below. The average crystalline particle diameter can be measured by adjusting the number of particles in the method described in the examples so that the number of particles contained in one field of view of the SEM image is approximately 50, 100, 200, 500, or 1000.

[0059] The density of dental workpieces is 5.5 g / cm³ because higher density results in fewer internal voids, reduced light scattering, improved light transmission, and increased strength. 3 Preferably, it is 5.7 g / cm³ or more. 3 It is more preferable that the value be greater than or equal to 5.9 g / cm³. 3 It is even more preferable that the above conditions are met. It is particularly preferable that the dental workpiece contains virtually no voids. The density of the dental workpiece can be calculated as (mass of dental workpiece) / (volume of dental workpiece). The shape of the dental workpiece is not particularly limited, but examples include prismatic and disc-shaped.

[0060] Other embodiments include a method for manufacturing a dental workpiece, which includes the steps of laminating a raw material composition for a layer (W) in which the content of elements or ions derived from the capping agent is less than 0.15 mol% with respect to the total 100 mol% of each component constituting the polycrystalline ceramic, and a raw material composition for a layer in which the content of elements or ions derived from the capping agent is different from that of the layer (W), to produce a molded body having a laminated structure, and sintering the molded body to obtain a laminate, wherein the laminate is a dental workpiece made of polycrystalline ceramic.

[0061] In the method for manufacturing a dental workpiece of the present invention, it is preferable that the polycrystalline ceramic contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia.

[0062] The following description will use as an example a method for manufacturing a dental workpiece, in which the polycrystalline ceramic is a laminate comprising two or more layers with different concentrations of elements or ions derived from the capping agent, and the laminate is a dental workpiece containing zirconia, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5.

[0063] Another embodiment of the present invention is a dental workpiece made of polycrystalline ceramic, wherein the polycrystalline ceramic is a laminate comprising two or more layers with different content rates of elements or ions derived from a capping agent, the laminate comprises a layer (W) in which the content rate of elements or ions derived from the capping agent is less than 0.15 mol% with respect to 100 mol% of the total amount of each component constituting the polycrystalline ceramic, each layer constituting the laminate contains ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5, and the method for manufacturing a dental workpiece includes a step of laminating a raw material composition for layer (W) and raw material compositions for each layer other than layer (W) (layers with different content rates of elements or ions derived from the capping agent from layer (W)) to produce a molded body having a laminated structure, wherein the molded body is a dental workpiece made of polycrystalline ceramic.

[0064] In the method for manufacturing the dental workpiece, in each layer, it is preferable that the total content of ZrO2 and HfO2 is 78 to 97.5 mol% of the total 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5. It is preferable that the content of the stabilizer is 1 to 12 mol%. It is preferable that the total content of Nb2O5 and Ta2O5 is 1 to 9 mol%.

[0065] When the polycrystalline ceramic constituting the laminate is a dental workpiece containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, the raw material composition used to manufacture each layer other than layer (W) in the laminate preferably contains ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, Nb2O5 and / or Ta2O5, and a capping agent. The content of each component in each layer is as described above. The raw material composition used to manufacture layer (W) in the laminate contains ZrO2, HfO2, a stabilizer capable of suppressing the phase transition of zirconia, Nb2O5 and / or Ta2O5, and a capping agent in an amount of less than 0.15 mol% per 100 mol% of the total amount of each component constituting layer (W). The content of each component in layer (W) is as described above. The raw material composition for the dental workpiece may be in a dry state, or it may contain a liquid or be contained in a liquid. The raw material composition may be in the form of, for example, powder, granules or granulated material, paste, slurry, etc. A molded body having a laminated structure can be produced by laminating the raw material compositions for each layer other than layer (W) with the raw material composition for layer (W). The method of laminating the raw material compositions is not particularly limited, and known methods and apparatus (molds, etc.) can be used.

[0066] The raw material composition contains a capping agent so that the resulting dental workpiece contains capping elements or ions. The capping agent is not particularly limited as long as it is a compound that can become a monovalent ion (+1 valent cation or -1 valent anion) in a solvent containing water, and examples include hydroxides, salts, halides (fluorides, chlorides, bromides, iodides), cyanides, etc., that contain elements or ions derived from the capping agent. Each capping agent may be used alone or two or more may be used in combination. If multiple layers other than layer (W) are included, the type and content of the capping elements or ions in the raw material composition for each layer other than layer (W) may be the same or different. The type and content of the capping elements or ions in the raw material composition for each layer other than layer (W) and the type of capping elements or ions in the raw material composition for layer (W) may be the same or different.

[0067] Examples of hydroxides containing capping elements or ions include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide. Examples of salts containing capping elements or ions include carbonates, bicarbonates, nitrates, hypochlorites, chlorites, chlorates, perchlorates, bromates, permanganates, metaborates, sulfides, and cyanides.

[0068] Examples of carbonates containing capping elements or ions include lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, francium carbonate, and cesium carbonate. Examples of bicarbonates containing capping elements or ions include lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, francium bicarbonate, and cesium bicarbonate. Examples of nitrates containing capping elements or ions include calcium nitrate, strontium nitrate, iron(II) nitrate, iron(III) nitrate, cobalt(II) nitrate, magnesium nitrate, gallium nitrate, yttrium(III) nitrate, lanthanum(III) nitrate, praseodymium nitrate, neodymium(III) nitrate, manganese(II) nitrate, europium nitrate, copper(II) nitrate, thorium nitrate, aluminum nitrate, nickel(II) nitrate, chromium(III) nitrate, titanium(IV) nitrate, zirconium nitrate(IV) hydrate (ZrO(NO3)2・xH2O), cerium(III) nitrate, tin nitrate, bismuth(III) nitrate, scandium(III) nitrate, indium(III) nitrate, and hafnium(IV) nitrate. Examples of hypochlorites containing capping elements or ions include sodium hypochlorite and calcium hypochlorite. Examples of chlorites containing capping elements or ions include sodium chlorite, potassium chlorite, lithium chlorite, calcium chlorite, magnesium chlorite, barium chlorite, copper(II) chlorite, copper(III) chlorite, silver chlorite, and nickel chlorite. Examples of chlorates containing capping elements or ions include calcium chlorate, barium chlorate, cobalt chlorate, nickel chlorate, magnesium chlorate, zinc chlorate, and copper chlorate. Examples of perchlorates containing capping elements or ions include iron(III) perchlorate, barium perchlorate, calcium perchlorate, cobalt perchlorate, nickel perchlorate, magnesium perchlorate, beryllium perchlorate, aluminum perchlorate, and cerium perchlorate. Examples of bromates containing capping elements or ions include neodymium bromate, lanthanum bromate, and praseodymium bromate.Examples of permanganates containing capping elements or ions include calcium permanganate (VII), potassium permanganate (VII), and sodium permanganate (VII). Examples of metaborates containing capping elements or ions include sodium metaborate and barium metaborate. Examples of sulfide salts containing capping elements or ions include copper(I) sulfide. Examples of cyanide salts containing capping elements or ions include barium cyanide, sodium cyanide, potassium cyanide, and calcium cyanide.

[0069] Examples of fluorides containing capping elements or ions include lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, cesium fluoride, francium fluoride, beryllium fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, barium fluoride, scandium (III) fluoride, yttrium (III) fluoride, lanthanum (III) fluoride, cerium (III) fluoride, and neodymium (I) fluoride. Examples include (II) titanium fluoride (III), titanium fluoride (IV), zirconium fluoride (IV), hafnium fluoride (IV), tantalum fluoride (V), manganese fluoride (II), manganese fluoride (III), iron fluoride (II), iron fluoride (III), copper fluoride (II), zinc fluoride (II), aluminum fluoride, chromium fluoride (III), bismuth fluoride (III), indium fluoride (III), tin fluoride (II), etc.

[0070] Examples of chlorides containing capping elements or ions include zirconium oxychloride, lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, francium chloride, beryllium chloride, magnesium chloride, calcium chloride, strontium chloride, barium chloride, scandium(III) chloride, yttrium(III) chloride, lanthanum(III) chloride, cerium(III) chloride, praseodymium chloride, neodymium(III) chloride, samarium chloride, europium chloride, titanium(III) chloride, titanium(IV) chloride, zirconium(IV) chloride, hafnium(IV) chloride, tantalum(V) chloride, manganese chloride, iron(II) chloride, iron(III) chloride, cobalt(II) chloride, nickel(II) chloride, copper(I) chloride, copper(II) chloride, zinc(II) chloride, aluminum chloride, gallium chloride, bismuth(III) chloride, indium(I) chloride, indium(III) chloride, tin(II) chloride, and others.

[0071] Examples of bromides containing capping elements or ions include lithium bromide, sodium bromide, potassium bromide, rubidium bromide, cesium bromide, francium bromide, beryllium bromide, magnesium bromide, calcium bromide, strontium bromide, barium bromide, scandium(III) bromide, yttrium(III) bromide, cerium(III) bromide, neodymium(III) bromide, titanium(IV) bromide, zirconium(IV) bromide, tantalum(V) bromide, manganese(II) bromide, iron(II) bromide, iron(III) bromide, cobalt(II) bromide, nickel(II) bromide, copper(I) bromide, copper(II) bromide, zinc(II) bromide, chromium(III) bromide, bismuth(III) bromide, vanadium(III) bromide, indium(III) bromide, and tin bromide.

[0072] Examples of iodides containing capping elements or ions include lithium iodide, sodium iodide, potassium iodide, rubidium iodide, cesium iodide, francium iodide, beryllium iodide, calcium iodide, magnesium iodide, strontium iodide, barium iodide, scandium(III) iodide, yttrium(III) iodide, lanthanum(III) iodide, cerium(III) iodide, neodymium(III) iodide, and titanium(IV) iodide. Examples of iodides include zirconium iodide (IV), hafnium iodide (IV), tantalum iodide (V), manganese iodide (II), iron iodide (II), iron iodide (III), cobalt iodide (II), nickel iodide (II), copper iodide (I), zinc iodide (II), aluminum iodide, chromium iodide (III), vanadium iodide (II), bismuth iodide (III), indium iodide (III), tin iodide (II), and tin iodide (IV).

[0073] For ZrO2 and HfO2, commercially available zirconia powder can be used. Examples of commercially available products include zirconia powder (product name "Zpex®" (Y2O3 content: 3 mol%), "Zpex® 4" (Y2O3 content: 4 mol%), "Zpex® Smile® (registered trademark) (Y2O3 content: 5.5 mol%), TZ-3Y (Y2O3 content: 3 mol%), TZ-3YS (Y2O3 content: 3 mol%), TZ-4YS (Y2O3 content: 4 mol%), TZ-6Y (Y2O3 content: 6 mol%), TZ-6YS (Y2O3 content: 6 mol%), TZ-8YS (Y2O3 content: 8 mol%), TZ-10YS (Y2O3 content: 10 mol%), TZ-3Y-E (Y2O3 content: 3 mol%) Examples include "TZ-3YS-E" (Y2O3 content: 3 mol%), "TZ-3YB-E" (Y2O3 content: 3 mol%), "TZ-3YSB-E" (Y2O3 content: 3 mol%), "TZ-3YB" (Y2O3 content: 3 mol%), "TZ-3YSB" (Y2O3 content: 3 mol%), "TZ-3Y20AB" (Y2O3 content: 3 mol%), "TZ-8YSB" (Y2O3 content: 8 mol%), and "TZ-0" (Y2O3 content: 0 mol%); all manufactured by Tosoh Corporation. The aforementioned commercially available zirconia powders also contain HfO2. Commercially available products that also contain Y2O3 can also be used. As for the zirconia powder, the raw material composition of the present invention may also use zirconia powder in which Y2O3 is uniformly dispersed and solid-solved, such as the commercially available TZ series (which includes "TZ" in part of the product name).

[0074] There are no particular restrictions on the method for producing zirconia powder. For example, known methods such as a breakdown process, which involves pulverizing coarse particles to produce fine powder, and a building-up process, which involves synthesizing zirconia powder from atoms or ions through nucleation and growth processes, can be employed.

[0075] The type of zirconia powder in the raw material composition is not particularly limited. If the zirconia powder contains ZrO2 and HfO2 and does not contain a stabilizer, or if the content of the stabilizer is increased as needed, stabilizer particles can be added separately. The stabilizer particles are not particularly limited, as long as they can adjust the stabilizer content in the dental workpiece to the predetermined range described above. For example, commercially available stabilizer particles may be used, or commercially available powder may be pulverized in a known grinding and mixing device (such as a ball mill) before use.

[0076] The stabilizer can be either a stabilizer that is not solid-soluble in ZrO2 and HfO2, or a stabilizer that is solid-soluble in ZrO2 and HfO2. In one embodiment, a method for producing a dental workpiece is provided in which the stabilizer (preferably Y2O3) in the raw material composition is a stabilizer that is not solid-soluble in ZrO2 and HfO2, as this contributes to the easy acquisition of the desired dental workpiece. The presence of a stabilizer that is not solid-soluble in zirconia can be confirmed, for example, by an X-ray diffraction (XRD) pattern.

[0077] If peaks originating from stabilizers are detected in the XRD pattern of the raw material composition or molded product, it means that there are stabilizers in the raw material composition or molded product that are not solid-dissolved in ZrO2 and HfO2. If the entire amount of stabilizer is solid-dissolved in ZrO2 and HfO2, then generally no peaks originating from stabilizers will be detected in the XRD pattern. However, depending on conditions such as the crystalline state of the stabilizer, it is possible that the stabilizer is not solid-dissolved in ZrO2 and HfO2 even if no stabilizer peaks are present in the XRD pattern.

[0078] The case where the stabilizer includes a stabilizer that is not solid-soluble in ZrO2 and HfO2 will be explained below, using yttria as an example of the stabilizer.

[0079] In the raw material composition or molded article of the present invention, the abundance of yttria that is not dissolved in ZrO2 and HfO2 (hereinafter sometimes referred to as "undissolved yttria") is fy can be calculated based on the following mathematical formula (1). f y = I 29 / (I 28 + I 29 + I 30 ) × 100 (1) (In the formula, f y represents the ratio (%) of un-dissolved yttria. In XRD measurement, I 28 represents the peak area intensity near 2θ = 28° where the main peak of the monoclinic system appears, I 29 represents the peak area intensity near 2θ = 29° where the main peak of yttria appears, and I 30 represents the peak area intensity near 2θ = 30° where the main peak of the tetragonal or cubic system appears.)

[0080] Also, when using a stabilizer other than yttria in combination, by substituting the peak of the other stabilizer instead of I 29 , it can also be applied to calculate the undissolved existence rate of the stabilizer other than yttria.

[0081] The existence rate f y of un-dissolved yttria is preferably greater than 0% from the viewpoint that the target dental workpiece can be easily obtained, more preferably 1% or more, further preferably 2% or more, and particularly preferably 3% or more. The upper limit of the existence rate f y of un-dissolved yttria may be, for example, 25% or less, but preferably depends on the yttria content in the raw material composition or the molded body. In one embodiment, the existence rate f y of un-dissolved yttria is preferably more than 0% and 25% or less, more preferably 2% or more and 25% or less, and further preferably 3% or more and 25% or less. When a plurality of each layer other than the layer (W) is included, the existence rate f y of un-dissolved yttria in the raw material composition for each layer other than the layer (W) may be the same or different. The existence rate f y of un-dissolved yttria in the raw material composition for each layer other than the layer (W) and the existence rate f y of un-dissolved yttria in the raw material composition for the layer (W) may be the same or different.

[0082] For example, when the yttria content in the raw material composition for each layer other than layer (W), and in the raw material composition for layer (W) or the molded article is 3 mol% or more and 8 mol% or less, the following applies. When the yttria content is 3 mol% or more and less than 4.5 mol%, f y It can be 15% or less. When the yttria content is 4.5 mol% or more and less than 5.8 mol%, f y It can be 20% or less. When the yttria content is 5.8 mol% or more and 8 mol% or less, f y This can be set to 25% or less.

[0083] For example, when the yttria content is 3 mol% or more and less than 4.5 mol%, f y It is preferable that the content is 2% or more, more preferably 3% or more, even more preferably 4% or more, and particularly preferably 5% or more. When the yttria content is 4.5 mol% or more and less than 5.8 mol%, f y It is preferable that the content is 3% or more, more preferably 4% or more, even more preferably 5% or more, even more preferably 6% or more, and particularly preferably 7% or more. When the yttria content is 5.8 mol% or more and 8 mol% or less, f y It is preferably 4% or more, more preferably 5% or more, even more preferably 6% or more, even more preferably 7% or more, and particularly preferably 8% or more.

[0084] In the raw material composition or molded article of the present invention, it is not necessary for all of the stabilizer to be solid-dissolved in ZrO2 and HfO2. In this invention, solid-dissolution of the stabilizer means, for example, that the elements (atoms) contained in the stabilizer are solid-dissolved in ZrO2 and HfO2.

[0085] The Nb2O5 and / or Ta2O5 added to the raw material composition of the present invention is not particularly limited, as long as the content of Nb2O5 and / or Ta2O5 in the dental workpiece can be adjusted to the predetermined range described above. The Nb2O5 and / or Ta2O5 is not particularly limited, and for example, commercially available products may be used, or commercially available powder may be pulverized in a known grinding and mixing device (such as a ball mill) before use.

[0086] Examples of the process for preparing the raw material composition include a method in which each of the raw materials of the raw material composition (ZrO2, HfO2, a stabilizer, Nb2O5 and / or Ta2O5, a capping agent (for example, a compound that can become a monovalent ion in a solvent containing water), and a reinforcing agent as needed) is wet-mixed in a solvent containing water to obtain the raw material composition.

[0087] The method for wet mixing each of the above raw materials in a solvent containing water is not particularly limited. For example, each raw material may be wet-ground and mixed using a known grinding and mixing device (such as a ball mill) to form a slurry, and then the slurry may be dried and granulated to produce a granular raw material composition.

[0088] In the wet mixing process, additives such as binders, plasticizers, dispersants, emulsifiers, defoamers, pH adjusters, and lubricants may be further included. Each additive may be used individually or in combination of two or more.

[0089] The binder may be added after a primary powder consisting of a mixture of ZrO2, HfO2, Y2O3, Nb2O5 and / or Ta2O5 and a capping agent is added to water to form a slurry, and then the slurry is pulverized.

[0090] The binder is not particularly limited, and known binders can be used. Examples of binders include polyvinyl alcohol-based binders, acrylic-based binders, wax-based binders (such as paraffin wax), methylcellulose, carboxymethylcellulose, polyvinyl butyral, polymethyl methacrylate, ethylcellulose, polyethylene, polypropylene, ethylene vinyl acetate copolymer, polystyrene, atactic polypropylene, methacrylic resin, and the like.

[0091] Examples of plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutylphthalic acid.

[0092] Examples of dispersants include ammonium polycarboxylate (such as triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic ester copolymer, polyacrylic acid, bentonite, carboxymethylcellulose, anionic surfactants (such as polyoxyethylene alkyl ether phosphates like polyoxyethylene lauryl ether phosphate), nonionic surfactants, oleic glycerides, amine salt type surfactants, oligosaccharide alcohols, and stearic acid.

[0093] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitan derivatives.

[0094] Examples of defoaming agents include alcohol, polyether, silicone, and wax.

[0095] Examples of pH adjusting agents include ammonia and ammonium salts (including ammonium hydroxide such as tetramethylammonium hydroxide).

[0096] Examples of lubricants include polyoxyethylene alkyl ethers and waxes.

[0097] The solvent used for wet mixing is not particularly limited as long as it contains water, and an organic solvent may be used, a mixed solvent of water and an organic solvent may be used, or water may be used alone. Examples of organic solvents include ketone solvents such as acetone and ethyl methyl ketone; and alcohol solvents such as ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, glycerin, diglycerin, polyglycerin, propylene glycol, dipropylene glycol, polypropylene glycol, ethylene glycol, diethylene glycol, polyethylene glycol, polyethylene glycol monomethyl ether, 1,2-pentadiol, 1,2-hexanediol, and 1,2-octanediol.

[0098] In the case where the laminate is a dental workpiece containing zirconia, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5, in one embodiment, the raw material composition for each layer other than layer (W) may contain ZrO2, Y2O3, Nb2O5, Ta2O5, a capping agent (in a different concentration than layer (W)), and may further contain other components other than the reinforcing agent (hereinafter also referred to as "other components") as needed, insofar as the effects of the present invention are achieved. In the above embodiment, the raw material composition for layer (W) may contain ZrO2, Y2O3, Nb2O5, Ta2O5, and the aforementioned capping agent in an amount of less than 0.15 mol%, and may further contain other components other than the reinforcing agent (hereinafter also referred to as "other components") as needed, insofar as the effects of the present invention are achieved. In the above embodiment, the raw material composition for layer (W) may not contain the capping agent (concentration of 0 mol%). Examples of the other components mentioned above include colorants (pigments and composite pigments), fluorescent agents, SiO2, etc. Each of the other components may be used individually or in combination of two or more.

[0099] Examples of the pigment include oxides of at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, NiO, Cr2O3, etc.), with a preference for oxides of at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb, and a preference for oxides of at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb. However, Y2O3 and CeO2 may be excluded from the pigment.

[0100] Examples of the aforementioned composite pigments include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, and (Co,Zn)Al2O4.

[0101] Examples of the fluorescent agents include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 Examples include the EU.

[0102] Next, the obtained raw material compositions (raw material compositions for each layer other than layer (W), and the raw material composition for layer (W)) are laminated to produce a molded body. These raw material compositions can be molded to produce a molded body having a laminated structure. The molding method is not particularly limited, and known methods (for example, press molding, etc.) can be used.

[0103] In the production of a zirconia molded article having a laminated structure by a method that includes a step of press molding a raw material composition, there are no particular restrictions on the specific method of press molding, and it can be carried out using a known press molding machine. Specific methods of press molding include, for example, a uniaxial press.

[0104] The press pressure is set to an optimal value as appropriate depending on the desired size of the molded body, open porosity, biaxial bending strength, and particle size of the raw material powder, and is usually between 5 MPa and 1000 MPa. By increasing the press pressure during molding in the above manufacturing method, the pores of the resulting molded body are filled more effectively, allowing for a lower open porosity and increasing the density of the molded body. Furthermore, to increase the density of the resulting zirconia molded body, a cold isostatic pressing (CIP) treatment may be applied after uniaxial pressing.

[0105] Next, the obtained molded body is sintered to obtain a laminate. The laminate is a dental workpiece made of polycrystalline ceramic. The sintering temperature (maximum sintering temperature) for sintering the molded body to obtain the dental workpiece is preferably 1300°C or higher, more preferably 1350°C or higher, even more preferably 1400°C or higher, even more preferably 1450°C or higher, and particularly preferably 1500°C or higher. Furthermore, the sintering temperature is preferably 1680°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower. In the method for manufacturing a dental workpiece of the present invention, the maximum sintering temperature in the step of sintering a molded body having a laminated structure to obtain a laminate is preferably 1300 to 1680°C, more preferably 1400 to 1650°C, and even more preferably 1450 to 1600°C. The maximum sintering temperature is preferably the temperature in air.

[0106] The holding time (anchoring time) at the maximum sintering temperature is preferably 30 hours or less, more preferably 20 hours or less, even more preferably 10 hours or less, even more preferably 5 hours or less, particularly preferably 3 hours or less, and most preferably 2 hours or less, depending on the temperature. Furthermore, the holding time can also be 25 minutes or less, 20 minutes or less, or 15 minutes or less. Also, the holding time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. That is, the holding time is preferably 1 minute or more and 30 hours or less, more preferably 5 minutes or more and 10 hours or less, even more preferably 10 minutes or more and 5 hours or less, most preferably 10 minutes or more and 2 hours or less, and can also be 10 minutes or more and 25 minutes or less. According to the manufacturing method of the present invention, dental workpieces with excellent bending strength, light transmittance, and machinability can be produced depending on the content of the stabilizer. Furthermore, the sintering time may be shortened as long as the effects of the present invention are obtained. By shortening the sintering time, production efficiency can be increased and energy costs can be reduced.

[0107] In the method for manufacturing dental workpieces of the present invention, when sintering the molded body, 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. That is, the heating rate when sintering the molded body is preferably 0.1°C / min or more and 50°C / min or less, more preferably 0.2°C / min or more and 30°C / min or less, and even more preferably 0.5°C / min or more and 20°C / min or less. Productivity is improved when the heating rate is above the above lower limit.

[0108] A general-purpose furnace for dental zirconia can be used in the process of sintering the molded body. Commercially available furnaces for dental zirconia may also be used. Examples of commercially available furnaces include Noritake Katana (registered trademark) F-1, F-1N, and F-2 (all manufactured by SK Medical Electronics Co., Ltd.).

[0109] Furthermore, the process of sintering the molded body preferably includes a step of hot isostatic pressing (HIP) treatment in addition to sintering at the maximum sintering temperature mentioned above. HIP treatment can further improve the light transmittance and strength of the dental workpiece.

[0110] In the following, the sintered body obtained by sintering at the above-mentioned maximum sintering temperature will be referred to as the "primary sintered body," and the sintered body after HIP treatment will be referred to as the "HIP-treated sintered body."

[0111] HIP treatment can be performed using a known hot isohydraulic press (HIP) apparatus.

[0112] The temperature for HIP treatment is not particularly limited, but it is preferably 1200°C or higher, more preferably 1300°C or higher, and even more preferably 1400°C or higher, as this allows for the production of high-strength, dense dental workpieces. Furthermore, the temperature for HIP treatment is preferably 1700°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower. In other words, the temperature for HIP treatment is preferably 1200°C to 1700°C, more preferably 1300°C to 1650°C, and even more preferably 1400°C to 1600°C.

[0113] In the method for manufacturing dental workpieces of the present invention, when the primary sintered body is subjected to HIP treatment, the pressure of the HIP treatment is not particularly limited, and a dense sintered body with high strength can be obtained. Therefore, the pressure of the HIP treatment is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. Furthermore, there is no particular upper limit to the pressure of the HIP treatment, but it can be, for example, 400 MPa or less, 300 MPa or less, or even 200 MPa or less.

[0114] In the method for manufacturing dental workpieces of the present invention, when the primary sintered body is subjected to HIP treatment, 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. That is, the heating rate when the primary sintered body is subjected to HIP treatment is preferably 0.1°C / min or more and 50°C / min or less, more preferably 0.2°C / min or more and 30°C / min or less, and even more preferably 0.5°C / min or more and 20°C / min or less. Productivity is improved when the heating rate is above the above lower limit.

[0115] In the method for manufacturing dental workpieces of the present invention, when the primary sintered body is subjected to HIP treatment, the HIP treatment time is not particularly limited, and a dense dental workpiece with high strength can be obtained. Therefore, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Furthermore, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less. In other words, the HIP treatment time is preferably 5 minutes or more and 10 hours or less, more preferably 10 minutes or more and 6 hours or less, and even more preferably 30 minutes or more and 3 hours or less.

[0116] In the method for manufacturing dental workpieces of the present invention, when the primary sintered body is subjected to HIP treatment, the pressure medium is not particularly limited, and from the viewpoint of minimizing the impact on zirconia, at least one can be selected from the group consisting of oxygen gas, oxygen mixed gas, air, and inert gas (e.g., nitrogen gas, argon gas, etc.). When the primary sintered body is subjected to HIP treatment under an oxygen mixed gas atmosphere, the oxygen concentration is not particularly limited, but can be, for example, greater than 0% and 20% or less. When using an oxygen mixed gas, at least one inert gas (e.g., nitrogen gas, argon gas, etc.) can be selected as the gas other than oxygen.

[0117] In the method for manufacturing dental workpieces of the present invention, if the HIP treatment is performed in a reducing atmosphere, such as by using an inert gas, blackening may occur due to oxygen deficiencies. In such cases, in order to remove the blackening, it is preferable to include a step of heat treatment at 1650°C or lower in air or an oxygen-rich atmosphere (hereinafter also referred to as "tempering treatment") after the HIP treatment step, and it is more preferable to perform the heat treatment in an oxygen-rich atmosphere from the viewpoint of efficient heat treatment. An "oxygen-rich atmosphere" means that the oxygen concentration is higher than that of air. The oxygen-rich atmosphere is not particularly limited as long as the oxygen concentration is between 21% and 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.

[0118] The dental workpiece of the present invention is not particularly limited as long as it achieves the effects of the present invention, and may be a primary sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment. One embodiment is a dental workpiece that is a sintered body after tempering treatment.

[0119] Depending on the aesthetics of the dental workpiece (e.g., the shade of the dental prosthesis), the temperature of the heat treatment in air or an oxygen-rich atmosphere can be appropriately changed. In one embodiment, from the viewpoint of the aesthetics of the dental workpiece, the temperature of the heat treatment in air or an oxygen-rich atmosphere is preferably 1650°C or lower, more preferably 1600°C or lower, and even more preferably 1550°C or lower. In another embodiment, from the viewpoint of the aesthetics of the dental workpiece, the temperature of the heat treatment in air or an oxygen-rich atmosphere is preferably 1400°C or lower, more preferably 1300°C or lower, and even more preferably 1200°C or lower. Furthermore, in all embodiments, the temperature of the heat treatment is preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher. That is, the temperature of the heat treatment is preferably 500°C or higher and 1650°C or lower, more preferably 600°C or higher and 1600°C or lower, and even more preferably 700°C or higher and 1550°C or lower.

[0120] For the tempering process, a general-purpose furnace for dental zirconia can be used. Commercially available furnaces for dental zirconia may also be used. Examples of commercially available furnaces include Noritake Katana (registered trademark) F-1, F-1N, and F-2 (all manufactured by SK Medical Electronics Co., Ltd.).

[0121] The dental workpiece of the present invention, despite being a sintered body, exhibits excellent machinability. Therefore, unlike conventional methods, there is no need for a manufacturing process in which the workpiece is machined in a semi-sintered state as a mill blank, and then sintered to form a sintered body. For this reason, in the manufacturing method of dental prostheses, it is preferable that no further heat treatment is required after machining to the desired shape.

[0122] On the other hand, as a method for manufacturing dental workpieces, a molded body obtained using the raw material composition may be calcined to produce a semi-sintered calcined body, and the unprocessed calcined body may be machined to produce a sintered body. Another embodiment of a method for manufacturing dental workpieces includes the steps of: producing a molded body using the raw material composition; calcining the obtained molded body to obtain a zirconia calcined body (calcination step); and sintering the zirconia calcined body.

[0123] In the calcination process, the calcination temperature (calcination temperature) is preferably 800°C or higher, more preferably 900°C or higher, and even more preferably 950°C or higher, in order to ensure block formation. Furthermore, the calcination temperature is preferably 1200°C or lower, more preferably 1150°C or lower, and even more preferably 1100°C or lower. For example, the calcination temperature is preferably between 800°C and 1200°C, and more preferably between 900°C and 1150°C. At such calcination temperatures, it is considered that the solid solution of the stabilizer does not progress significantly during the calcination process.

[0124] The zirconia calcined body of the present invention refers to a state in which the ZrO2 particles are necked (bonded) to each other, and the ZrO2 particles (powder) are not completely sintered (semi-sintered state).

[0125] The density of the calcined zirconia is 2.7 g / cm³. 3 The above is preferable. Furthermore, the density of the zirconia calcined material is 4.0 g / cm³. 3 The following is preferable: 3.8 g / cm³ 3 The following is more preferable: 3.6 g / cm³ 3 The following is even more preferable: the density of the zirconia calcined body is 2.7 to 4.0 g / cm³. 3 Preferably, 2.7 to 3.6 g / cm³ 3 This is more preferable. When the density is within this range, processing can be easily performed. The density of the calcined material can be calculated, for example, as (mass of calcined material) / (volume of calcined material).

[0126] Furthermore, the three-point bending strength of the zirconia calcined body is preferably 15 to 70 MPa, more preferably 18 to 60 MPa, and even more preferably 20 to 50 MPa. The bending strength can be measured using a test specimen measuring 5 mm thick x 10 mm wide x 50 mm long, in accordance with ISO 6872:2015 except for the size of the test specimen. The surface and chamfer (the surface where the corner of the test specimen is chamfered at a 45° angle) of the test specimen are finished in the longitudinal direction with 600-grit sandpaper. The test specimen is positioned so that its widest surface faces the vertical direction (direction of load). In the bending test measurement, the span is 30 mm and the crosshead speed is 1.0 mm / min.

[0127] The process of sintering the zirconia calcined body can be carried out using the same method and conditions (temperature, pressure, etc.) as the process of sintering the molded body described above. Therefore, in the embodiment of the manufacturing method using the zirconia calcined body, "molded body" can be read as "calcined body".

[0128] The dental workpiece of the present invention exhibits excellent strength. The biaxial bending strength of the dental workpiece of the present invention is preferably 300 MPa or more, more preferably 350 MPa or more, even more preferably 400 MPa or more, even more preferably 450 MPa or more, and particularly preferably 500 MPa or more. Having such biaxial bending strength in the dental workpiece of the present invention can suppress fracture in the oral cavity when used, for example, as a dental prosthesis. There is no particular upper limit to the biaxial bending strength, but it can be, for example, 1200 MPa or less, and even 1000 MPa or less. The biaxial bending strength of the dental workpiece can be measured in accordance with ISO 6872:2015.

[0129] The dental workpiece of the present invention preferably has high light transmittance. Light transmittance can be evaluated by ΔL*. Specifically, regarding light transmittance, the dental workpiece of the present invention preferably has a ΔL* of 10 or more at a diameter of 15 mm and a thickness of 1.2 mm, more preferably 12 or more, even more preferably 13 or more, and particularly preferably 14 or more. By having ΔL* within the above range, a dental workpiece with high light transmittance can be obtained.

[0130] ΔL* represents the difference between the brightness (first L* value) on a white background and the brightness (second L* value) on a black background for the same sample. Specifically, it represents the difference between the L* value on a white background (JIS Z 8781-4:2013 Colorimetry - Part IV: CIE 1976 L*a*b* color space) and the L* value on a black background. The white background refers to the white area of ​​the opacity test paper described in Section 1 of Part IV of JIS K 5600-4-1:1999, and the black background refers to the black area of ​​the opacity test paper.

[0131] There is no particular upper limit to ΔL*, but in one embodiment it is 25 or less, and in another embodiment it can be 20 or less from the viewpoint of aesthetics. Specifically, in the dental workpiece of the present invention, the range of ΔL* for a diameter of 15 mm and a thickness of 1.2 mm is at least one embodiment selected from 10 to 25, 12 to 25, 14 to 25, or 14 to 20.

[0132] Furthermore, the ΔL* of a dental workpiece with a diameter of 15 mm and a thickness of 1.2 mm can be measured using a spectrophotometer. For example, it can be measured using a dental colorimeter ("Crystal Eye CE100-CE / JP", 7-band LED light source, analysis software "Crystal Eye" (manufactured by Olympus Corporation)).

[0133] Dental prostheses manufactured using the dental workpiece of the present invention include, for example, crown restorations such as inlays, onlays, veneers, crowns, core-integrated crowns, and bridges, as well as abutment teeth, dental posts, dentures, denture bases, and implant components (fixtures, abutments). Furthermore, machining is preferably performed using, for example, a commercially available dental CAD / CAM system. Examples of such CAD / CAM systems include the "CEREC system" manufactured by Dentsply Sirona Dental Systems Co., Ltd. and the "Katana® system" manufactured by Kuraray Noritake Dental Co., Ltd.

[0134] Furthermore, the dental workpiece of the present invention can be used for applications other than dental use, and is particularly suitable for zirconia members that require irregular or complex shapes and strength. Compared to sintered bodies manufactured using only existing manufacturing methods (injection molding, CIP, slip casting, or 3D printing, etc.), the dental workpiece of the present invention can be processed directly as a sintered body. Therefore, for example, it is economical when the desired zirconia member can be obtained in a short time, and in the case of complex-shaped parts that are difficult to manufacture by conventional manufacturing methods, it eliminates the need to obtain multiple members by mechanical fitting, making it possible to obtain a zirconia member that maintains high strength. Moreover, since the sintered body can be processed directly, the sintering process is unnecessary when dimensional accuracy is required, and uneven firing shrinkage is eliminated, resulting in a zirconia member with high accuracy. Specifically, it can be used as a method for manufacturing parts for jewelry, engine and interior parts for mobility such as aircraft and automobiles, frame materials for display panels, building materials, electrical appliance parts, household goods parts, and toy parts. In addition, this zirconia member may be fitted with a different material to be used as a composite member.

[0135] The present invention includes various combinations of all or part of the above configurations, within the scope of the technical idea of ​​the present invention, insofar as they achieve the effects of the present invention. References to “one embodiment / aspect” or “embodiment / aspect” in this specification mean that certain features, structures, or characteristics described in relation to that embodiment / aspect are included in at least one embodiment / aspect of this disclosure. Uses of the phrases “one embodiment / aspect” or “another embodiment / aspect” in various parts of this specification do not necessarily refer to the same embodiment / aspect, nor are separate or alternative embodiments / aspects mutually exclusive with other embodiments / aspects. Furthermore, various features are described that are shown in some embodiments / aspects but not in others. Similarly, various requirements are described that are required in some embodiments / aspects but not in others. Embodiments and aspects are, in some cases, interchangeable.

[0136] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples, and many modifications are possible within the scope of the technical idea of ​​the present invention by those with ordinary skill in the art. In the following examples and comparative examples, the average particle diameter is the average primary particle diameter, which can be determined by laser diffraction scattering. Specifically, it can be measured by volume using a laser diffraction particle size distribution analyzer (SALD-2300: manufactured by Shimadzu Corporation) with a 0.2% aqueous sodium hexametaphosphate solution as the dispersion medium.

[0137] [Examples 1-6 and Comparative Examples 1-3] Measurement samples for each example and comparative example were prepared through the processes of preparing a granular raw material composition, preparing a molded body, and preparing a sintered body (preparation of a primary sintered body, HIP treatment, and tempering treatment).

[0138] [Preparation of Granular Raw Material Compositions] To prepare the granular raw material compositions for each example and comparative example, commercially available ZrO2 powder, Y2O3 powder, Nb2O5 powder, capping agent, and TiO2 powder were mixed to the composition shown in Table 1, water was added to prepare a slurry, and the slurry was wet-milled and mixed in a ball mill until the average particle size was 0.13 μm or less. After adding a binder to the pulverized slurry, it was dried with a spray dryer to prepare a granular raw material composition for layer (W) (corresponding to "lower layer" in Table 1) (hereinafter also referred to as "raw material composition for layer (W)") and a granular raw material composition for layers other than layer (W) (corresponding to "upper layer" in Table 1) (hereinafter also referred to as "raw material composition for layers other than layer (W)"), which were used in the production of molded articles described later. The average particle size was measured by volume using a laser diffraction particle size distribution analyzer (SALD-2300: manufactured by Shimadzu Corporation) with a 0.2% sodium hexametaphosphate aqueous solution as the dispersion medium.

[0139] [Preparation of Molded Bodies] For each example and comparative example, pellet-shaped molded bodies and block-shaped molded bodies were prepared as follows in order to obtain sintered body samples for light transmission and strength evaluation and processability evaluation. For the pellet-shaped molded bodies, a cylindrical mold with a diameter of 19 mm was used, and the raw material composition was placed in the mold so that the thickness of the dental workpiece after sintering would be 1.2 mm. Next, the raw material composition was press-molded using a uniaxial press molding machine at a surface pressure of 200 MPa to produce pellet-shaped molded bodies.

[0140] Furthermore, in the case of block-shaped molded bodies, the raw material composition for layer (W) was placed in a mold with inner dimensions of 19 mm x 18 mm, so that the thickness of each layer in the dental workpiece after sintering would be as shown in Table 1. Then, the raw material compositions for layers other than layer (W) were placed on top of the mold and laminated. Next, the laminated raw material compositions were press-molded using a uniaxial press molding machine at a surface pressure of 200 MPa to produce a block-shaped molded body having a laminated structure.

[0141] [Preparation of Primary Sintered Bodies] The obtained pellet-shaped and block-shaped molded bodies were subjected to a firing furnace "Noritake Katana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd., and suspended in air at the maximum sintering temperature listed in Table 1 for 2 hours to obtain pellet-shaped and block-shaped dental workpieces (primary sintered bodies).

[0142] [Preparation of HIP-treated sintered bodies] The obtained pellet-shaped and block-shaped dental workpieces (primary sintered bodies) were subjected to 2 hours of 150 MPa at the HIP treatment temperature shown in Table 1 using the HIP apparatus "O2-Dr.HIP" manufactured by Kobe Steel, Ltd., thereby obtaining samples of pellet-shaped and block-shaped dental workpieces (HIP-treated sintered bodies).

[0143] [Preparation of dental workpieces (sintered bodies after tempering)] The obtained pellet-shaped and block-shaped dental workpieces (HIP-treated sintered bodies) were subjected to a firing furnace "Noritake Katana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd., at 700°C for 60 hours to obtain samples of pellet-shaped and block-shaped dental workpieces (sintered bodies after tempering). The size of the obtained samples was 15 mm in diameter and 1.2 mm in thickness for the pellet shape, and 15.7 mm in width, 16.5 mm in length, and 14.0 mm in thickness for the block shape.

[0144] Note that the content of each component in the sintered body in Table 1 is a value calculated from the amount of raw materials used. The content (mol%) of capping elements or ions in Table 1 is the external addition rate relative to the total of 100 mol% of ZrO2, HfO2, the stabilizer (yttria), Nb2O5, and Ta2O5. The content (mol%) of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5 in Table 1 is the content of each component relative to the total of 100 mol% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5. For ZrO2 and HfO2 only, the total content of ZrO2 and HfO2 is shown. The content (mass%) of TiO2 in Table 1 is the external addition rate relative to the total of 100 mass% of ZrO2, HfO2, the stabilizer, Nb2O5, and Ta2O5.

[0145] [Evaluation of reaction with alumina pod] The block-shaped molded bodies of each example and comparative example obtained in [Preparation of molded body] were placed on alumina pods and fired using the firing furnace "Noritake Katana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd. under the conditions of [Preparation of primary sintered body] described above. The presence or absence of reaction with the alumina pod was evaluated visually in the resulting primary sintered body (n=1). If a reaction occurs with the alumina pod, white spots will appear on the contact surface of the zirconia sintered body, or cracks will occur in the resulting zirconia sintered body, impairing the appearance of the product. The results are shown in Table 1.

[0146] [Processing Time] The processing times shown in Table 1 represent the time required to process the first sample using a new processing tool under the following conditions. If an error occurred due to the load during processing and the CEREC system "MC-XL" stopped midway through processing, a new processing tool was attached and processing was resumed. This operation was repeated until one sample was processed, and the time taken was defined as the processing time. The processing conditions are as follows. For each example and comparative example, a sample of a block-shaped dental workpiece (sintered body after tempering) was prepared with a metal jig bonded to a surface approximately 15.7 mm wide x 14.0 mm thick (n=1), and processed into a typical anterior tooth crown shape using the CEREC system "MC-XL" (manufactured by Dentsply Sirona). The machining program used was the software "inLab® CAM Version 20.0.1.203841," with the following settings: Manufactory: IVOCLAR VIVADENT, Material name: IPS e. max CAD, Production Method: Grinding, Block size: C16. The machining tools used were Step Bur 12 and Cylinder Pointed Bur 12S.

[0147] [Method for measuring the average crystal particle diameter in sintered bodies] Surface images were obtained from the pellet-shaped dental workpieces (sintered bodies after tempering) of each example and comparative example using a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). After marking the grain boundaries of each crystal particle on the obtained image, the average crystal particle diameter was calculated by image analysis. Image analysis software (product name "Image-Pro Plus", manufactured by Hakuto Co., Ltd.) was used to measure the average crystal particle diameter. The captured SEM image was binarized, the brightness range was adjusted so that the grain boundaries were clear, and particles were recognized from the field of view (region). The crystal grain diameter obtained with Image-Pro Plus is calculated by measuring the length of the line segments connecting the outlines passing through the centroid, determined from the outline of the crystal grain, at 2-degree intervals around the centroid, and averaging the results. For each example and comparative example, the average crystal grain diameter of all particles not overlapping the image edges in the SEM images (3 fields of view) was used as the average crystal grain diameter (number-based) in the sintered body. "Particles not overlapping the image edges" refers to particles excluding those whose outlines do not fit within the SEM image frame (particles whose outlines are interrupted at the top, bottom, left, or right boundaries). The crystal grain diameter of all particles not overlapping the image edges was determined in Image-Pro Plus using the option to exclude particles on all boundaries.

[0148] The average particle size of the crystalline particles in the dental workpiece of Example 1 was 2.0 μm.

[0149]

[0150] From the above results, it was confirmed that the dental workpiece of the present invention suppresses defects in the appearance of the product and exhibits excellent machinability in the sintered state. On the other hand, in Comparative Examples 1 and 3, which did not include the lower layer corresponding to layer (W), it was confirmed that the reaction between elements or ions derived from the capping agent and the alumina pod could not be suppressed during firing. Furthermore, in Comparative Example 2, which did not include elements or ions derived from the capping agent, the reduction in processing time was not sufficient.

[0151] The dental workpiece of the present invention exhibits suppressed defects in product appearance and excellent machinability in its sintered state. In particular, it is useful as a dental material for dental prostheses and other dental treatment applications.

Claims

1. A dental workpiece made of polycrystalline ceramic, wherein the polycrystalline ceramic is a laminate comprising two or more layers with different content rates of elements or ions derived from the capping agent, and the laminate comprises a layer (W) in which the content rate of elements or ions derived from the capping agent is less than 0.15 mol% with respect to 100 mol% of the total amount of each component constituting the polycrystalline ceramic.

2. The dental workpiece according to claim 1, wherein the polycrystalline ceramic contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia.

3. The dental workpiece according to claim 2, wherein the polycrystalline ceramic further contains Nb2O5 and / or Ta2O5.

4. The dental workpiece according to claim 1 or 2, wherein the thickness of the layer (W) is 7.0 mm or less.

5. The dental workpiece according to claim 2, wherein the stabilizing agent capable of suppressing the phase transition of the zirconia is yttria.

6. The dental workpiece according to claim 1 or 2, wherein the layer (W) is arranged as the outermost layer.

7. A dental workpiece according to claim 1 or 2, which is for use in dental prostheses.

8. A method for producing a dental workpiece according to claim 1 or 2, comprising the steps of laminating a raw material composition for a layer (W) having an element or ion content derived from a capping agent of less than 0.15 mol% with respect to 100 mol% of the total of each component constituting the polycrystalline ceramic, and a raw material composition for a layer having a different element or ion content derived from a capping agent from the layer (W), to produce a molded body having a laminated structure, and sintering the molded body to obtain a laminate, wherein the laminate is a dental workpiece made of polycrystalline ceramic.

9. The method for manufacturing a dental workpiece according to claim 8, wherein the maximum sintering temperature in the step of sintering the molded body to obtain a laminate is 1300 to 1680°C.

10. The method for producing a dental workpiece according to claim 8, wherein the polycrystalline ceramic contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia.

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