Zirconia composite sintered body

Abstract

The present invention provides a zirconia composite sintered body which has suitable strength for dental use, which has excellent mechanical workability in a sintered body state, and which has excellent aesthetic properties. The present invention relates to a zirconia composite sintered body comprising: zirconia; a stabilizer which is capable of suppressing a phase transition of the zirconia; and Nb2O5 and / or Ta2O5, said zirconia composite sintered body comprising a plurality of layers which differ in terms of the content of at least one component from among the stabilizer, the Nb2O5, and the Ta2O5, with respect to the total amount, in moles, of the zirconia, the stabilizer, the Nb2O5 and the Ta2O5.

Description

Zirconia composite sintered body

[0001] The present invention relates to a zirconia composite sintered body. More specifically, the present invention relates to a zirconia composite sintered body that has strength suitable for dental use, excellent machinability in a sintered state, and excellent aesthetics.

[0002] Ceramics made from metal oxides have been widely used industrially, and zirconia sintered bodies are particularly used as dental materials for dental prostheses and other applications due to their high strength and aesthetic appeal.

[0003] Zirconia sintered bodies have excellent strength, so when used as dental materials for prostheses and other applications, problems such as breakage rarely occur. Zirconia sintered bodies also have high translucency and are less likely to discolor in the oral cavity, resulting in excellent aesthetics. On the other hand, once fully sintered, they have high hardness, making them almost impossible to process with dental processing machines. For example, machining a cubic zirconia sintered body to obtain a zirconia sintered body with a shape that matches the shape of a patient's teeth results in significant wear of metal processing tools, and requires an enormous amount of time to produce even a single dental prosthesis.

[0004] For these reasons, when using zirconia sintered bodies for dental material applications, they are usually not fully sintered, but rather a calcined body in a semi-sintered state that is easy to process is processed into the shape of the desired dental prosthesis, and then further sintered to produce a sintered body processed into the shape of the intended dental prosthesis. After that, the sintered body is subjected to slight adjustment processing so that the sintered body having the shape of the dental prosthesis fits comfortably in the patient's oral cavity when placed in the dental clinic. In recent years, when processing the calcined body into the shape of the desired dental prosthesis, machining using a CAD / CAM system is used, which can obtain a shape that matches the patient's tooth treatment site, and calcined bodies (mill blanks) for CAD / CAM systems are widely used.

[0005] As described above, when a zirconia sintered body is used as a dental material, due to the problems inherent in sintering zirconia, extensive machining is avoided after the sintering, and the processing of the sintered body is limited to fine adjustments when the sintered body is fitted into the oral cavity of a patient at a dental clinic. In other words, measures are taken in dental material applications that take into account the gradual changes in physical properties that occur as zirconia sinters.

[0006] Furthermore, dental treatment generally involves many steps, such as acquiring information about the shape of the patient's oral cavity, such as information about the dentition, taking into consideration the unique circumstances resulting from the physical properties of the zirconia sintered body described above; machining a calcined body (mill blank) into the shape of the desired dental prosthesis using a CAD / CAM system based on the acquired information; sintering the calcined body having the shape of the desired dental prosthesis to obtain a sintered body; and making slight adjustments to the sintered body so that it fits comfortably in the patient's oral cavity when worn at a dental clinic.

[0007] Under these circumstances, a calcined body has been proposed that can shorten the process of firing the calcined body to obtain a sintered body (for example, Patent Document 1).

[0008] Patent Document 1 discloses a calcined zirconia body that contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, in which the zirconia has a predominant monoclinic crystal system and that has a plurality of layers with different stabilizer contents relative to the total moles of zirconia and the stabilizer.

[0009] However, in dental treatment using a dental prosthesis made of zirconia sintered body, it is difficult to complete all of the above steps in a single visit to the dental clinic. Therefore, even for treatment of a single tooth, multiple visits to the dental clinic are required, and the treatment period from start to completion often takes more than one month.

[0010] On the other hand, patients prefer to visit the hospital as few times as possible in order to reduce the time it takes for new artificial teeth to be fitted after treatment and to reduce the burden of visiting the hospital, and the need to complete treatment in a short period of time is increasing every year.

[0011] If it were possible to perform extensive machining on the zirconia sintered body, the process of machining the calcined body once and then producing the sintered body by sintering would become unnecessary. After obtaining information on the shape of the patient's oral cavity, the unprocessed sintered body could be machined into the shape of the desired dental prosthesis using a CAD / CAM system based on that information, and the prosthesis could be fitted into the patient's oral cavity and fine-tuned, allowing dental treatment to be completed in one day.

[0012] Furthermore, when dental prostheses are used, dental treatment can be completed in one day if materials other than zirconia, such as lithium disilicate glass ceramics and feldspar-based glass ceramics, are used. However, in the case of zirconia sintered bodies, there are specific circumstances resulting from the physical properties of the zirconia sintered bodies, making it very difficult to achieve this.

[0013] As described above, zirconia is in high demand in terms of strength and aesthetics. Accordingly, in response to the increasing need for shortening the treatment period, new zirconia sintered bodies have been proposed that have excellent machinability in the sintered state and can be machined from a prismatic or disc-shaped mill blank into the shape of a desired dental prosthesis, unlike conventional zirconia materials that are machined from a calcined body and then fired to obtain a sintered body (e.g., Patent Documents 2 and 3).

[0014] Patent Document 2 discloses a processable zirconia, which is a sintered body formed to contain a tetragonal zirconia composite powder containing 79.8 to 92 mol% ZrO2, 4.5 to 10.2 mol% YO3, 3.5 to 7.5 mol% Nb2O5 or 5.5 to 10.0 mol% Ta2O5, and a TiO2 nanopowder whose mass ratio to the zirconia composite powder is more than 0 mass% and 2.5 mass% or less, and a method for producing the same.

[0015] Furthermore, Patent Document 3 discloses a machinable zirconia composite sintered body using a raw material containing 78 to 95 mol % ZrO, 2.5 to 10 mol % YO, 2 to 8 mol % NbO and / or 3 to 10 mol % TaO, in which the ZrO has a monoclinic main crystal phase, and a method for producing the same.

[0016] International Publication No. 2020 / 138316 Japanese Patent Application Laid-Open No. 2015-127294 International Publication No. 2021 / 132644

[0017] In Patent Document 1, a highly transparent layer and an opaque layer are reproduced by laminating zirconia powders with different yttria contents, but sintering is required after machining, which increases the treatment time for patients and leaves room for improvement from the perspective of shortening the treatment time. Furthermore, the zirconia sintered bodies disclosed in Patent Documents 2 and 3 can be machined in the sintered state, but there is no mention of lamination, resulting in the incisal edge and the cervical portion having the same transparency. The present inventors have found that there is room for further improvement in order to maintain the machinability in the sintered state while achieving an appearance closer to natural teeth even when used very closely with a person.

[0018] Furthermore, when the composition is changed to reduce the hardness of the material in order to improve machinability, there is a problem that the strength of the material is reduced. Therefore, it has been difficult to provide a zirconia sintered body that has excellent strength, excellent machinability in the sintered state, and further, different translucencies between the incisal edge and the cervical part, allowing the production of a dental prosthesis with an appearance closer to that of a natural tooth.

[0019] An object of the present invention is to provide a zirconia composite sintered body that has strength suitable for dental use, is excellent in machinability in the sintered state, and has excellent aesthetic properties.

[0020] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the problems can be solved by forming a zirconia composite sintered body containing zirconia, a stabilizer capable of suppressing a phase transition of zirconia, and at least one of NbO and TaO, and having a plurality of layers in which the content of at least one of the stabilizer, NbO, or TaO differs relative to the total mol of zirconia, the stabilizer, NbO, and TaO. Based on this finding, the present inventors have conducted further research and have completed the present invention.

[0021] That is, the present invention encompasses the following: [1] A zirconia composite sintered body containing zirconia, a stabilizer capable of suppressing a phase transition of zirconia, and at least one of Nb2O5 and Ta2O5, and having a plurality of layers having different contents of at least one of the stabilizer, Nb2O5, or Ta2O5 relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5. [2] The zirconia composite sintered body according to [1], wherein the plurality of layers have different contents of Nb2O5 or Ta2O5. [3] The zirconia composite sintered body according to [2], wherein, on a straight line extending in a first direction from one end of the zirconia composite sintered body to the other end, the increase / decrease trend of the Nb2O5 or Ta2O5 content relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5 does not change from the one end to the other end. [4] The zirconia composite sintered body according to [3], wherein the stabilizer is yttria. [5] The zirconia composite sintered body according to [4], wherein the layer including one end has an Nb2O5 or Ta2O5 content of 2 mol% or more and 12 mol% or less, and the layer including the other end has an Nb2O5 or Ta2O5 content of 1 mol% or more and 10 mol% or less, relative to the total mol of zirconia, yttria, Nb2O5, and Ta2O5. [6] The zirconia composite sintered body according to [1], wherein the plurality of layers have different stabilizer contents. [7] The zirconia composite sintered body according to [6], wherein the content of the stabilizer does not change relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5 from one end to the other end of the zirconia composite sintered body on a straight line extending in a first direction from one end to the other end of the zirconia composite sintered body. [8] The zirconia composite sintered body according to [7], wherein the stabilizer is yttria. [9] The zirconia composite sintered body according to [8], wherein the yttria content of the layer including the one end is 1 mol% or more and 8 mol% or less, and the yttria content of the layer including the other end is 2 mol% or more and 9 mol% or less, relative to the total mol of zirconia, yttria, Nb2O5, and Ta2O5.

[10] The zirconia composite sintered body according to any one of [1] to [9], wherein at least one of the plurality of layers further contains an element or ion derived from a capping agent.

[11] The zirconia composite sintered body according to

[10] , wherein the content of the element or ion derived from the capping agent is more than 0 mol% and not more than 5 mol%, relative to 100 mol% of the total of zirconia, the stabilizer, Nb2O5, and Ta2O5.

[12] The zirconia composite sintered body according to

[10] or

[11] , wherein the element or ion derived from the capping agent is an element or ion thereof belonging to Periods 2 to 7 of the periodic table and having a first ionization energy smaller than that of Group 18 elements in the same period, and / or an element or ion thereof having a high electron affinity.

[13] The zirconia composite sintered body according to

[10] or

[11] , wherein the element or ion derived from the capping agent contains at least one element or ion thereof selected from the group consisting of Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl, and F.

[14] The zirconia composite sintered body according to

[10] or

[11] , wherein the element or ion derived from the capping agent contains at least one element or ion thereof selected from the group consisting of Li, Na, K, Rb, Cs, and Fr.

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

[14] , wherein, when the content of the stabilizer is A mol % and the total content of Nb2O5 and Ta2O5 is B mol %, the ratio A / B of at least one of the plurality of layers satisfies 0.9 to 3.

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

[15] , wherein at least one of the plurality of layers further contains a zirconia toughener, and the content of the zirconia toughener is more than 0 mass% and not more than 6.0 mass%, relative to 100 mass% of the total of zirconia, the stabilizer, Nb2O5, and Ta2O5.

[17] The zirconia composite sintered body according to

[16] , wherein the zirconia toughener contains TiO2 and / or Al2O3.

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

[17] , wherein the zirconia composite sintered body has an average crystal grain size of 0.5 to 5.0 μm.

[0022] According to the present invention, a zirconia composite sintered body having strength suitable for dental use, excellent machinability in a sintered state, and excellent aesthetics can be provided. Furthermore, according to the present invention, not only is the translucency excellent, but also the translucency of the incisal edge and the cervical portion of the dental prosthesis obtained after machining is different, and the gradation of translucency allows the dental prosthesis to have an appearance closer to that of natural teeth, so that aesthetics similar to those of natural teeth can be obtained even when the other person is very close (for example, about 45 cm).

[0023] The zirconia composite sintered body of the present invention contains zirconia, a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizer"), and at least one of NbO and TaO, and has a plurality of layers having different contents of at least one of the stabilizer, NbO, and TaO relative to the total mol of zirconia, the stabilizer, NbO, and TaO.

[0024] As used herein, the term "molded body" refers to a body that has not yet 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 a body that has not yet been sintered after being formed into a molded body. As used herein, a "zirconia composite calcined body" refers to a body in a semi-sintered state in which raw material powders such as zirconia are necked (adhered) together and are not completely sintered. As used herein, a "zirconia composite sintered body" refers to a body in a sintered state in which raw material powders such as zirconia are completely sintered. In a zirconia composite sintered body, raw material powders such as zirconia solidify or dissolve together during sintering, increasing the relative density and densifying the body. As used herein, "zirconia" refers to zirconium(IV) oxide (ZrO), containing a trace amount (0.5% by mass to 3% by mass) of HfO relative to the amount of ZrO. Because HfO2 is difficult to separate, terms such as "zirconia" and "zirconia powder" refer to ZrO2 and HfO2. Also, powders in which a stabilizer is dissolved in zirconia are included in the term "zirconia powder." As used herein, "in the atmosphere" refers to a state under standard atmospheric pressure (1 atm). As used herein, "zirconia strengthening agent" refers to a component that functions to improve the mechanical strength of a zirconia composite sintered compact. As used herein, the content of each component in a zirconia composite sintered compact can be calculated from the amount of raw material charged. As used herein, machining includes cutting and grinding. Furthermore, machining may be either wet or dry, and is not particularly limited. In this specification, the upper and lower limits of numerical ranges (temperature ranges, content rates of each component, crystal system abundance rates, components, etc., values ​​calculated from these, and physical property values, etc.) can be appropriately combined.

[0025] In this specification, "the content of at least one of the stabilizer, NbO, or TaO differs" means that the difference in content of at least one of the stabilizer, NbO, or TaO between the layers is 0.05 mol% or more, preferably 0.08 mol% or more, more preferably 0.09 mol% or more, even more preferably 0.10 mol% or more, and particularly preferably 0.11 mol% or more. Also, the difference in content of at least one of the stabilizer, NbO, or TaO between the layers is preferably 3.0 mol% or less, more preferably 2.8 mol% or less, even more preferably 2.5 mol% or less, and particularly preferably 2.0 mol% or less.

[0026] The zirconia composite sintered body of the present invention has a laminated structure in which all layers contain zirconia, a stabilizer capable of suppressing a phase transition of zirconia, and at least one of NbO and TaO, and the laminated structure has a plurality of layers in which the content of at least one of the stabilizer, NbO, and TaO differs relative to the total mol of zirconia, the stabilizer, NbO, and TaO. In this specification, the phrase "the content of a certain component is different with respect to the total mol of zirconia, the stabilizer, NbO, and TaO" means that when the total mol of zirconia, the stabilizer, NbO, and TaO in a specific layer is calculated and the total mol of zirconia, the stabilizer, NbO, and TaO in another specific layer is calculated, the content of a certain component (at least one of the stabilizer, NbO, or TaO) between the specific layer and the other specific layer is different.

[0027] Furthermore, the reason why the zirconia composite sintered body of the present invention has excellent machinability in a sintered state while maintaining strength is not clear, but it is presumed that this is achieved by improving fracture toughness (IF method) by additionally adding at least one of Nb2O5 and Ta2O5 to zirconia to which a conventional stabilizer has been added, and by minimizing hardness by coarsening the microstructure.

[0028] The reason why the zirconia composite sintered body of the present invention has aesthetic properties similar to those of natural teeth is believed to be as follows: In a sintered body containing at least one of NbO or TaO in addition to the stabilizer, the sintered body has multiple layers with different contents of at least one of the stabilizer, NbO, or TaO relative to the total moles of zirconia, the stabilizer, NbO, and TaO. This results in the layer corresponding to the incisal edge having larger crystal grains than at least the layer corresponding to the cervical region, resulting in high translucency, while the layer corresponding to the cervical region has smaller crystal grains than at least the incisal edge, resulting in lower translucency. As a result, the dental prosthesis obtained after machining is believed to have translucency equivalent to or greater than that of natural teeth, while achieving a sufficient translucency gradation compared to natural teeth.

[0029] The zirconia composite sintered body of the present invention has a laminated structure in which all layers contain zirconia, a stabilizer, and at least one of NbO and TaO. By varying any one of (1) the content of at least one of NbO and TaO relative to the content of the stabilizer, (2) the content of the stabilizer relative to the content of NbO, or (3) the content of the stabilizer relative to the content of TaO between layers, the zirconia composite sintered body can have the above-mentioned properties of being machinable in a sintered state, having excellent strength, and being able to provide a dental prosthesis having an appearance that is similar to that of natural teeth.

[0030] In this specification, the description of the zirconia composite sintered body of the present invention is applicable to all embodiments unless otherwise specified. Furthermore, the description of each component and its content is applicable to all layers in the laminate structure unless otherwise specified.

[0031] In the zirconia composite sintered body of the present invention, the zirconia content is preferably 78 to 97.5 mol % relative to a total of 100 mol % of zirconia, the stabilizer, NbO, and TaO. From the viewpoint of achieving better translucency and strength, the zirconia content is more preferably 79 mol % or more and 96 mol % or less, even more preferably 80 mol % or more and 94 mol % or less, and particularly preferably 81 mol % or more and 93 mol % or less.

[0032] In the zirconia composite sintered body of the present invention, examples of stabilizers capable of suppressing the phase transition of zirconia include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (YO), cerium oxide (CeO), scandium oxide (ScO), lanthanum oxide (LaO), erbium oxide (ErO), praseodymium oxide (PrO, PrO) and the like. 11 Examples of oxides that can be used include oxides such as samarium oxide (SmO), europium oxide (EuO), thulium oxide (TmO), gallium oxide (GaO), indium oxide (InO), and ytterbium oxide (YbO), with yttria and / or CeO being preferred because, when combined with other components including at least one of NbO or TaO, they provide excellent machinability and strength in the sintered state and excellent aesthetics in that the prosthesis obtained after machining is closer to natural teeth. The stabilizers may be used alone or in combination of two or more.

[0033] In the zirconia composite sintered body of the present invention, the content of the stabilizer is preferably 1 to 12 mol% relative to a total of 100 mol% of zirconia, the stabilizer, NbO, and TaO. From the viewpoint of easily obtaining sufficient machinability, the content is more preferably 2 mol% to 10 mol%. From the viewpoint of more excellent translucency and strength, the content is even more preferably 3 mol% to 8.0 mol%, even more preferably 3.5 mol% to 7.5 mol%, particularly preferably 3.8 mol% to 7.0 mol%, and most preferably 4.0 mol% to 6.5 mol%.

[0034] In the zirconia composite sintered body of the present invention, the content of Nb2O5 or Ta2O5 is preferably 1 to 9 mol%, more preferably 1.5 mol% to 8.5 mol%, based on a total of 100 mol% of zirconia, the stabilizer, Nb2O5, and Ta2O5. From the viewpoint of superior machinability, it is even more preferably 2.5 mol% to 8.0 mol%, even more preferably 2.7 mol% to 7.0 mol%, particularly preferably 2.8 mol% to 6.0 mol%, and most preferably 3.0 mol% to 5.5 mol%. If the content of Nb2O5 or Ta2O5 is within the above range, sufficient machinability can be obtained while suppressing the occurrence of defects such as chipping.

[0035] In all layers of the laminated structure of the zirconia composite sintered body, the contents of zirconia, stabilizer, Nb2O5 and Ta2O5 are within the above ranges.

[0036] The number of layers in the laminated structure of the zirconia composite sintered body of the present invention is not particularly limited, and may be 2 to 10 layers, 3 to 6 layers, or 4 to 5 layers. In one preferred embodiment, the number of layers in the laminated structure of the zirconia composite sintered body is 3 to 5 layers.

[0037] In the laminated structure of the zirconia composite sintered body of the present invention, when the laminated structure has n layers (n is preferably an integer of 3 or more and 10 or less), the translucency ΔL of the first layer (the layer corresponding to the cutting edge) * (W-B) and the translucency ΔL in the nth layer (layer corresponding to the cervical region) * The difference from (W-B) is preferably 1.2 or more, more preferably 1.5 or more, in order to obtain an appearance closer to that of natural teeth, and is even more preferably 1.8 or more, particularly preferably 2.0 or more, in order to obtain aesthetics similar to that of natural teeth even when the patient is very close to the patient (for example, about 45 cm). * (W-B) and the translucency ΔL in the nth layer (layer corresponding to the cervical region) *The difference from (W−B) is preferably 6.0 or less, more preferably 5.5 or less, even more preferably 5.0 or less, and particularly preferably 4.5 or less, in order to obtain an appearance closer to that of natural teeth. * The method for measuring (WB) is as described in the Examples below.

[0038] Preferred embodiments of the zirconia composite sintered body of the present invention will be described below.

[0039] A preferred embodiment (hereinafter, this embodiment may also be referred to as "first embodiment") includes a zirconia composite sintered body containing zirconia, a stabilizer capable of suppressing a phase transition of zirconia, and at least one of NbO and TaO, and including a plurality of layers having different contents of NbO or TaO relative to the total mol of zirconia, the stabilizer, NbO, and TaO.

[0040] In the layered structure of the zirconia composite sintered body according to the first embodiment, the tendency of increasing or decreasing the content of Nb2O5 or Ta2O5 may be changed as long as a dental prosthesis having an appearance closer to that of a natural tooth can be obtained.

[0041] In the first embodiment, for example, a zirconia composite sintered body in which the difference in content of NbO or TaO between adjacent layers is 0.08 mol% or more and 3.0 mol% or less can be used, since a dental prosthesis having an appearance closer to that of natural teeth can be obtained by gradation of translucency.

[0042] In the first embodiment, a zirconia composite sintered body is more preferred in that, on a straight line extending in a first direction from one end of the zirconia composite sintered body to the other end, the increase / decrease trend of the NbO or TaO content relative to the total mol of zirconia, the stabilizer, NbO, and TaO does not change from the one end to the other end. In this specification, the "one end" may be the incisal end side, the "layer including the one end" may be the layer on the incisal end side, the "other end" may be the cervical side, and the "layer including the other end" may be the layer on the cervical side. In the first embodiment, a zirconia composite sintered body in which the decreasing trend of the content of NbO or TaO relative to the total mol of zirconia, the stabilizer, NbO, and TaO does not change from one end to the other is more preferred, in that not only is it excellent in translucency, but also the transparency of the incisal edge and the cervical part of the dental prosthesis obtained after machining is different, making it easy to obtain a gradation of translucency, and making it easy to obtain a dental prosthesis with an appearance closer to that of natural teeth.

[0043] Furthermore, in the first embodiment, in view of being able to obtain a dental prosthesis having superior strength and machinability in a sintered state, and having an appearance closer to that of natural teeth due to the gradation of translucency, a zirconia composite sintered body in which the content of Nb2O5 or Ta2O5 in the layer including one end is 2 mol% or more and 12 mol% or less, and the content of Nb2O5 or Ta2O5 in the layer including the other end is 1 mol% or more and 10 mol% or less, relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5, is more preferred; a zirconia composite sintered body in which the content of Nb2O5 or Ta2O5 in the layer including one end is 2 mol% or more and 8 mol% or less, and the content of Nb2O5 or Ta2O5 in the layer including the other end is 1 mol% or more and 6 mol% or less is even more preferred; A zirconia composite sintered body in which the Nb2O5 or Ta2O5 content of the layer including the one end is 2.5 mol% or more and 6 mol% or less, and the Nb2O5 or Ta2O5 content of the layer including the other end is 1.5 mol% or more and 5 mol% or less is particularly preferred. Furthermore, by having the Nb2O5 or Ta2O5 content of the layer including the other end within this range, the crystal grains in the zirconia composite sintered body can be made smaller, and the translucency of the layer including the other end, which corresponds to the tooth cervical region, can be reduced so that the resulting dental prosthesis has an appearance closer to that of a natural tooth.

[0044] Another preferred embodiment (hereinafter, this embodiment may also be referred to as "second embodiment") is a zirconia composite sintered body that contains zirconia, a stabilizer capable of suppressing a phase transition of zirconia, and at least one of NbO and TaO, and has a plurality of layers with different stabilizer contents relative to the total mol of zirconia, the stabilizer, NbO, and TaO.

[0045] In the layered structure of the zirconia composite sintered body according to the second embodiment, the tendency of increasing or decreasing the content of the stabilizer may be changed as long as a dental prosthesis having an appearance closer to that of a natural tooth can be obtained.

[0046] In the second embodiment, for example, a zirconia composite sintered body in which the difference in stabilizer content between adjacent layers is 0.08 mol% or more and 3.0 mol% or less can be mentioned, because a dental prosthesis with an appearance closer to that of natural teeth can be obtained by the gradation of translucency.

[0047] In the second embodiment, a zirconia composite sintered body in which the content of the stabilizer does not change from one end to the other end of the zirconia composite sintered body in a first direction relative to the total mol of zirconia, the stabilizer, NbO, and TaO on a straight line extending from one end to the other end of the zirconia composite sintered body in a first direction is more preferred, because the gradation of translucency allows a dental prosthesis with an appearance closer to that of natural teeth to be obtained. In the second embodiment, a zirconia composite sintered body in which the content of the stabilizer does not change from one end to the other end of the zirconia composite sintered body in a first direction relative to the total mol of zirconia, the stabilizer, NbO, and TaO, is more preferred, because the gradation of translucency allows a dental prosthesis with an appearance closer to that of natural teeth to be obtained, because the incisal edge and the cervical portion of the dental prosthesis obtained after machining have different translucencies, and the gradation of translucency allows a dental prosthesis with an appearance closer to that of natural teeth to be obtained.

[0048] Furthermore, in the second embodiment, in view of obtaining a dental prosthesis having superior strength and machinability in a sintered body state, and having an appearance closer to that of natural teeth due to the gradation of translucency, a zirconia composite sintered body is more preferably one in which the content of the stabilizer (preferably yttria) in the layer including one end is 1 mol% or more and 8 mol% or less, and the content of the stabilizer (preferably yttria) in the layer including the other end is 2 mol% or more and 9 mol% or less, relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5; and a zirconia composite sintered body is even more preferably one in which the content of the stabilizer (preferably yttria) in the layer including one end is 2 mol% or more and 8 mol% or less, and the content of the stabilizer (preferably yttria) in the layer including the other end is 3 mol% or more and 9 mol% or less, A zirconia composite sintered body is particularly preferred in which the content of the stabilizer (preferably yttria) in the layer including the one end is 3 mol% to 7.5 mol%, and the content of the stabilizer (preferably yttria) in the layer including the other end is 4 mol% to 8.5 mol%. Furthermore, when the stabilizer in the layer including the other end is yttria, within the above-mentioned yttria content range, a conventional yttria-stabilized zirconia sintered body increases its translucency as the yttria content increases. However, in a zirconia composite sintered body containing at least one of NbO or TaO, the crystal grains in the zirconia composite sintered body can be made smaller, and the translucency of the layer including the other end, which corresponds to the cervical region of the tooth, can be reduced so that the resulting dental prosthesis has an appearance closer to that of a natural tooth.

[0049] In addition, in any embodiment of the present invention, the zirconia composite sintered body preferably further contains elements or ions derived from a capping agent in at least one layer of the laminated structure, in order to improve machinability in a sintered body state, and all layers may contain elements or ions derived from a capping agent.

[0050] In this specification, an element or ion derived from a capping agent (hereinafter also referred to as "capping element or ion") refers to an element or ion that caps the ends of bonds of a zirconia-based composite oxide in a zirconia composite sintered body composed of a zirconia-based composite oxide, thereby weakening the strength (hereinafter also referred to as "grain boundary strength") of the crystal interface (hereinafter also referred to as "grain boundary"). The capping agent can cap at least a portion of the crystal grain boundary. "Capping" refers to the presence of a target element or ion (capping element or ion) at the crystal grain boundary, bonding to the bonds of the zirconia-based composite oxide in place of the metal element. It is presumed that the presence of the capping element or ion at the grain boundary in the form of a +1-valent cation or a -1-valent anion causes electrostatic repulsion between the capped cations or anions, thereby weakening the grain boundary strength.

[0051] The contents of zirconia, stabilizer, NbO, and TaO in the zirconia composite sintered body can also be measured by, for example, inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis, etc. The content (mol%) of the element or ion derived from the capping agent is the external addition rate relative to 100 mol% of the total of zirconia, the stabilizer, NbO, and TaO. Therefore, the content of the element or ion derived from the capping agent in the zirconia composite sintered body can be calculated by converting the amount (mass) of the raw materials used for addition into mol%. The content (mass%) of the zirconia strengthener is the external addition rate relative to 100 mol% of the total of zirconia, the stabilizer, NbO, and TaO. Therefore, the content of the zirconia strengthener in the zirconia composite sintered body can be calculated from the amount (mass) of the raw materials used for addition.

[0052] The reason why the zirconia composite sintered body of the present invention has strength and translucency suitable for dental use and high machinability, and therefore can be machined in the sintered state, is unclear, but is presumed to be as follows: In a zirconia composite sintered body containing zirconia, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5, the presence of capping elements or ions at the grain boundaries is presumed to cause the capping elements or ions to reduce the grain boundary strength in the form of +1-valent cations or -1-valent anions, thereby acting in a direction that makes it easier for particles to peel off, making it easier to cut, and improving machinability.

[0053] The capping element or ion becomes a +1-valent cation or a -1-valent anion at the grain boundary of the zirconia composite sintered body and bonds to a bond possessed by the zirconia composite oxide. This bond causes electrostatic repulsion between the cations or anions, weakening the grain boundary strength while maintaining the strength and translucency properties of the particles constituting the zirconia composite sintered body, and acting in the direction of improving machinability. For example, a +1-valent cation may bond 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 composite oxide in place of the metal element. Alternatively, a -1-valent anion may bond to an OH2 bonded to a metal element (e.g., Zr, Hf, Y, Nb, or Ta) contained in the zirconia composite oxide. + Furthermore, a form in which a −1-valent anion is bonded to a cation derived from a metal element (for example, Zr, Hf, Y, Nb, or Ta) contained in the zirconia-based composite oxide and bonded to another metal element is also conceivable.

[0054] Furthermore, since Nb2O5 and / or Ta2O5 act to coarsen the microstructure and reduce hardness in the zirconia composite sintered body, the capping element or ion and Nb2O5 and / or Ta2O5 act together to further improve machinability. Therefore, the capping element or ion and Nb2O5 and / or Ta2O5 act together to further enhance excellent machinability while maintaining the strength required for artificial teeth, thereby shortening the machining time and suppressing wear of the machining tool, thereby increasing the number of dental prostheses that can be obtained by continuous machining using a single machining tool.

[0055] In the zirconia composite sintered body of the present invention, the capping element or ion further improves the machinability and acts as a free cutting aid as described above, without significantly impairing the strength and translucency.

[0056] When at least one of the multiple layers constituting the zirconia composite sintered body of the present invention is a layer further containing elements or ions derived from a capping agent, the content of the capping elements or ions contained in the layer is preferably more than 0 mol% and not more than 5 mol%, and from the viewpoints of providing better machinability in the sintered body state and further increasing the number of dental prostheses that can be continuously machined with a single machining tool, the content is more preferably 0.05 mol% or more and 3 mol% or less, even more preferably 0.06 mol% or more and 2.5 mol% or less, particularly preferably 0.07 mol% or more and 1.0 mol% or less, and most preferably 0.08 mol% or more and 0.34 mol% or less. Furthermore, when the capping element or ion contained in the zirconia composite sintered body of the present invention is a Group 17 element or ion, the capping element or ion is more preferably 0.2 mol% or more and 5 mol% or less, even more preferably 0.3 mol% or more and 4 mol% or less, particularly preferably 0.4 mol% or more and 3.5 mol% or less, and most preferably 0.5 mol% or more and 3.0 mol% or less, in order to provide better machinability in the sintered body state and to further increase the number of dental prostheses that can be continuously machined with one machining tool.

[0057] Furthermore, the capping element or ion content may be the same or different in all layers of the laminate structure of the zirconia composite sintered body containing the capping element or ion. In this specification, "different capping element or ion contents" means that, when the external addition rate of zirconia, the stabilizer, NbO, and TaO in a specific layer is calculated relative to a total of 100 mol%, and the external addition rate of zirconia, the stabilizer, NbO, and TaO in another specific layer is calculated relative to a total of 100 mol%, the capping element or ion content between the specific layer and the other specific layer is different. In this specification, when "different capping element or ion contents" are used, the difference in the capping element or ion content between the layers is 0.01 mol% or more, preferably 0.02 mol% or more, more preferably 0.03 mol% or more, even more preferably 0.04 mol% or more, and particularly preferably 0.05 mol% or more. The difference in content of the capping element or ion between layers is preferably 3.0 mol % or less, more preferably 2.0 mol % or less, even more preferably 1.0 mol % or less, and particularly preferably 0.5 mol % or less.

[0058] Furthermore, one preferred embodiment is a zirconia composite sintered body that contains zirconia, a stabilizer, at least one of NbO and TaO, and a capping element or ion, and has a plurality of layers with different contents of NbO or TaO relative to the total mol of zirconia, the stabilizer, NbO, and TaO, wherein, on a straight line extending in a first direction from one end of the zirconia composite sintered body to the other end, the increase / decrease trend of the NbO or TaO content relative to the total mol of zirconia, the stabilizer, NbO, and TaO does not change from the one end to the other end, and the content of the capping element or ion differs in each layer, and the increase / decrease trend of the capping element or ion content does not change from the one end to the other end. Furthermore, in terms of superior machinability in the sintered state, examples of suitable zirconia composite sintered bodies include those in which the capping element or ion content increases or decreases in the opposite direction to the NbO or TaO content. Specific examples include those in which the NbO or TaO content decreases while the capping element or ion content increases; and those in which the NbO or TaO content increases while the capping element or ion content decreases. In terms of particularly superior machinability in the sintered state, preferred are those in which the NbO or TaO content decreases while the capping element or ion content increases. In the preferred embodiment, the gradation of translucency allows the production of dental prostheses with an appearance closer to that of natural teeth, and the sintered body has superior machinability.

[0059] Another preferred embodiment is a zirconia composite sintered body that contains zirconia, a stabilizer, at least one of NbO and TaO, and a capping element or ion, and has a plurality of layers with different contents of the stabilizer relative to the total mol of zirconia, the stabilizer, NbO, and TaO, wherein, on a straight line extending in a first direction from one end of the zirconia composite sintered body to the other end, the increase / decrease trend of the stabilizer content relative to the total mol of zirconia, the stabilizer, NbO, and TaO does not change from the one end to the other end, and the content of the capping element or ion differs in each layer, and the increase / decrease trend of the capping element or ion content does not change from the one end to the other end. Furthermore, in terms of superior machinability in the sintered state, examples of zirconia composite sintered bodies include those in which the capping element or ion content increases or decreases in the same direction as the stabilizer content. Specific examples include zirconia composite sintered bodies in which the capping element or ion content decreases while the stabilizer content decreases; and zirconia composite sintered bodies in which the capping element or ion content increases while the stabilizer content increases. In terms of particularly superior machinability in the sintered state, preferred are zirconia composite sintered bodies in which the capping element or ion content increases while the stabilizer content increases. In the preferred embodiment, a dental prosthesis with an appearance closer to that of natural teeth can be obtained due to the gradation of translucency, and the machinability in the sintered state is superior.

[0060] As described above, it is important that the capping element or ion is a +1-valent cation or a −1-valent anion and is present at the grain boundary in order to exhibit appropriate interaction between the charged site at the grain boundary and the adsorption site.

[0061] The capping element or ion is preferably an element or ion thereof belonging to Periods 2 to 7 of the periodic table and having a smaller first ionization energy than Group 18 elements of the same period, an element or ion thereof having a high electron affinity, nitrate ion, hypochlorite ion, chlorite ion, chlorate ion, perchlorate ion, bromate ion, permanganate ion, metaborate ion, or cyanide ion. A preferred embodiment includes a zirconia composite sintered body in which the element or ion thereof derived from the capping agent is an element or ion thereof belonging to Periods 2 to 7 of the periodic table and having a smaller first ionization energy than Group 18 elements of the same period, and / or an element or ion thereof having a high electron affinity.

[0062] Suitable examples of elements belonging to Periods 2 to 7 of the periodic table and having a first ionization energy smaller than that of Group 18 elements in the same period include Cu, Ag, Li, Na, K, Rb, Cs, and Fr, from the viewpoints that +1-valent cations can be more easily obtained and that the machinability in the sintered body state is superior.

[0063] As elements with high electron affinity, Group 17 elements are preferred, since −1-valent anions are more easily obtained and the sintered body has better machinability. Preferred Group 17 elements are At, I, Br, Cl, and F.

[0064] The first ionization energy is the energy required to remove one electron from a neutral atom and ionize it. This can be the same as the first ionization energy described in "Schreiber-Atkins Inorganic Chemistry (Vol. 1), 4th Edition, Part I, Fundamentals, 1. Atomic Structure." The first ionization energy can be converted to units of "KJ / mol" using the unit "eV" described in "Schreiber-Atkins Inorganic Chemistry (Vol. 1), 4th Edition, Appendix 2," where 1 eV = 96.485 KJ / mol. The first ionization energy can also be determined using 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 by the difference in the energy gap from the ionization potential. The ionization potential is defined as the energy difference between the highest-energy occupied orbital of a compound's molecules and the vacuum level, and its value is measured using ultraviolet photoelectron spectroscopy. The first ionization energy and electron affinity may be determined using data stored in the NIST Chemistry WebBook (https: / / webbook.nist.gov / chemistry / ) (select "Ionization Energy" or "Electron Affinity" from "Ion energetics properties"). The first ionization energy and electron affinity are sufficient if they allow comparison of the likelihood of an element becoming a +1-valent cation or a -1-valent anion with other elements to be compared, and therefore the measurement methods described above can be used as appropriate.

[0065] Specific examples of the capping element include Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl, and F, and from the viewpoint of further improving machinability, Cu, Ag, Li, Na, K, Rb, Cs, Fr, I, Br, Cl, and F are preferred. In a preferred embodiment, the element derived from the capping agent includes 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, and the zirconia composite sintered body is mentioned. In another preferred embodiment, the zirconia composite sintered body may include a zirconia composite sintered body in which the element or ion derived from the capping agent contains at least one element or ion thereof selected from the group consisting of Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl, and F. The capping element or ion may be used alone or in combination of two or more.

[0066] As described above, the capping element or ion and NbO and / or TaO act together without impairing the effect of the stabilizer, so the stabilizer is not particularly limited and the effects of the present invention can be achieved.

[0067] As described above, NbO and TaO act to coarsen the microstructure and reduce hardness, and act together with the capping elements or ions to impart excellent machinability. In addition, they can maximize the sintered density through interaction with other components (e.g., TiO, AlO) added to the zirconia composite sintered body and application of HIP, thereby ensuring the aesthetics of natural teeth.

[0068] The content of each of the above-mentioned components, zirconia, stabilizer, NbO, and TaO, is a percentage relative to a total of 100 mol% of zirconia, stabilizer, NbO, and TaO, and the total of zirconia, stabilizer, NbO, and TaO does not exceed 100 mol%. For example, if the raw material composition contains NbO but does not contain TaO, the content of each of the components, zirconia, stabilizer, and NbO means a content percentage relative to a total of 100 mol% of zirconia, stabilizer, and NbO.

[0069] 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 in at least one of the plurality of layers is preferably 0.9 to 3 inclusive, more preferably 0.95 to 2 inclusive, from the viewpoint of machinability. Furthermore, it is even more preferably 1.0 to 1.7 inclusive, from the viewpoint of providing better machinability, suppressing wear of the processing tool, and further increasing the number of dental prostheses obtained by continuous processing using a single processing tool. In a preferred embodiment, from the viewpoint of machinability, it is preferable that at least the layer on the cutting edge side of the plurality of layers constituting the zirconia composite sintered body of the present invention satisfies the A / B ratio. In any of the above-mentioned embodiments, when a layer having an A / B ratio within the above range further contains an element or ion derived from a capping agent, the combined effect of the capping element or ion and Nb2O5 and / or Ta2O5 is enhanced, resulting in better machinability in the sintered body state.

[0070] In a preferred embodiment of the present invention, the laminated structure includes a laminated structure containing zirconia, a stabilizer, and at least one of Nb2O5 and Ta2O5 in all layers, and the laminated structure includes a plurality of layers having different contents of at least one of the stabilizer, Nb2O5, or Ta2O5 relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5, and all layers have a zirconia content of 78 to 97.5 mol%, a stabilizer content of 1 to 12 mol%, and a total content of Nb2O5 and Ta2O5 of 1 to 9 mol%, with the total of zirconia, the stabilizer, Nb2O5, and Ta2O5 being 100 mol%, and further includes a capping element or ion, and the stabilizer includes Y2O3 and / or CeO2, The content of the capping element or ion is more than 0 mol % and 5 mol % or less relative to 100 mol % of the total of zirconia, 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 A / B is 0.9 or more and 3 or less.

[0071] In one embodiment of the present invention, from the viewpoint of superior strength, a zirconia composite sintered body is provided, which contains zirconia, the stabilizer, and at least one of NbO or TaO, and has multiple layers with different contents of at least one of the stabilizer, NbO, or TaO relative to the total moles of zirconia, the stabilizer, NbO, and TaO, and further includes a zirconia strengthener in at least one layer of the laminate structure in addition to zirconia, the stabilizer, NbO and / or TaO, and capping elements or ions. Another example of a zirconia composite sintered body, from the viewpoint of particularly superior strength, is one in which the zirconia strengthener is contained in all layers of the laminate structure. In a zirconia composite sintered body containing zirconia, the stabilizer, and NbO and / or TaO, the zirconia strengthener acts integrally with the capping elements or ions to improve the strength of the sintered body.

[0072] In the case of a zirconia composite sintered body containing a zirconia strengthening agent, as described above, the zirconia content, the type and content of the stabilizer, the total content of NbO and TaO, the type and content of the capping element or ion, and the A / B ratio can be appropriately changed.

[0073] When at least one of the multiple layers constituting the zirconia composite sintered body is a layer containing a zirconia reinforcement, the content of the zirconia reinforcement contained in the layer is preferably more than 0 mass% and not more than 6.0 mass%, relative to 100 mass% of the total of zirconia, the stabilizer, NbO, and TaO. In view of the fact that the zirconia reinforcement acts as a unit when combined with a capping element or ion and provides superior strength, the content is more preferably 0.01 mass% or more and 5.5 mass% or less, and even more preferably 0.5 mass% or more and 5.0 mass% or less.

[0074] Examples of zirconia strengthening agents include TiO2 and Al2O3. The zirconia strengthening agents may be used singly or in combination. The content of the zirconia strengthening agent may be the same or different in all layers. In this specification, the phrase "different contents of zirconia strengthening agent" means that, when the external addition rate of zirconia, the stabilizer, Nb2O5, and Ta2O5 in a specific layer is calculated relative to a total of 100 mass% of zirconia, the stabilizer, Nb2O5, and Ta2O5 in another specific layer, the content of the zirconia strengthening agent between the specific layer and the other specific layer is different. In this specification, when the "zirconia toughening agent content is different," the difference in zirconia toughening agent content between the layers is 0.05% by mass or more, preferably 0.08% by mass or more, more preferably 0.09% by mass or more, even more preferably 0.10% by mass or more, and particularly preferably 0.11% by mass or more. Also, the difference in zirconia toughening agent content between the layers is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, even more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less.

[0075] In one preferred embodiment, the zirconia composite sintered body includes a zirconia reinforcer containing TiO2, and the TiO2 content is 0.6 to 4.5 mass% relative to 100 mass% of the total of zirconia, the stabilizer, Nb2O5, and Ta2O5.

[0076] In one preferred embodiment, the ceramic ceramic material contains zirconia, a stabilizer, at least one of Nb2O5 and Ta2O5, and a capping element or ion, and has a plurality of layers with different contents of at least one of the stabilizer, Nb2O5, or Ta2O5 relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5, and in a total of 100 mol% of zirconia, the stabilizer, Nb2O5, and Ta2O5, the content of zirconia is 78 to 97.5 mol%, the content of the stabilizer is 1 to 12 mol%, the total content of Nb2O5 and Ta2O5 is 1 to 9 mol%, and the stabilizer contains Y2O3 and / or CeO2, The zirconia reinforcement agent contains TiO2, the content of TiO2 is 0.6 to 4.5 mass% relative to a total of 100 mass% of zirconia, the stabilizer, Nb2O5, and Ta2O5, the content of the capping element or ion is more than 0 mol% and 5 mol% or less relative to a total of 100 mol% of zirconia, 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 A / B is 0.9 or more and 3 or less.

[0077] The average crystal grain size of the zirconia composite sintered body 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 translucency. The method for measuring the average crystal grain size is as described in the Examples below. The average crystal grain size can be measured by adjusting the number of particles in one field of view of an SEM photograph by the method described in the Examples, so that the number of particles contained in one field of view of an SEM photograph is approximately 50, 100, 200, 500, or 1,000.

[0078] The density of the zirconia composite sintered body is set to 5.5 g / cm because the higher the density, the fewer internal voids there are, the less light scattering occurs, and the more translucency and strength are improved. 3 It is preferable that the density is 5.7 g / cm or more. 3 More preferably, it is 5.9 g / cm or more. 3 It is more preferable that the zirconia composite sintered body is substantially free of voids. The density of the composite sintered body can be calculated by dividing the mass of the composite sintered body by the volume of the composite sintered body.

[0079] The method for producing a zirconia composite sintered body of the present invention includes, for example, a step of preparing a compact using a raw material composition and a step of sintering the compact, wherein the compact has a laminated structure containing zirconia, a stabilizer, and at least one of Nb2O5 or Ta2O5 in all layers, and the laminated structure has multiple layers with different contents of at least one of the stabilizer, Nb2O5, or Ta2O5 relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5. When producing the compact, a raw material composition containing zirconia, a stabilizer, and at least one of Nb2O5 or Ta2O5, with the contents of the components adjusted so that the contents of the stabilizer, Nb2O5, or Ta2O5 are different, can be used to obtain a compact having a desired laminated structure.

[0080] The raw material composition for the zirconia composite sintered body contains zirconia, a stabilizer capable of suppressing the phase transition of zirconia, NbO and / or TaO, and, if necessary, a capping agent. The inclusion of a capping agent in the raw material composition can further significantly improve the machinability achieved by adding at least one of NbO and TaO. The raw material composition for the zirconia composite sintered body may be in a dry state, or may contain or be contained in a liquid. The raw material composition may be in the form of, for example, powder, granules, agglomerates, paste, slurry, etc.

[0081] In an embodiment in which the resulting zirconia composite sintered body contains a capping element or ion, the raw material composition contains a capping agent. The capping agent is not particularly limited as long as it is a compound that can become a monovalent ion (a +1-valent cation or a -1-valent anion) in a solvent containing water, and examples thereof include hydroxides, salts, halides (fluorides, chlorides, bromides, iodides), cyanides, etc., containing an element or ion derived from the capping agent. Each of the capping agents may be used alone, or two or more may be used in combination.

[0082] Examples of hydroxides containing capping elements or ions include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, francium hydroxide, etc. Examples of salts containing capping elements or ions include carbonates, bicarbonates, nitrates, hypochlorites, chlorites, chlorates, perchlorates, bromates, permanganates, metaborates, sulfide salts, and cyanide salts.

[0083] Examples of carbonates containing capping elements or ions include lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, francium carbonate, cesium carbonate, etc. Examples of bicarbonates containing capping elements or ions include lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, francium bicarbonate, cesium bicarbonate, etc. 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, zirconium oxynitrate (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.

[0084] 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, neodymium (I) fluoride, and 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, tin fluoride, and the like.

[0085] 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, and tin (II) chloride.

[0086] 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.

[0087] 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, titanium (IV) iodide, ), zirconium iodide (IV), hafnium iodide (IV), tantalum iodide (V), manganese iodide (II), iron iodide (II), iron (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, and tin iodide (IV).

[0088] Regarding zirconia, commercially available zirconia powder can be used. Examples of commercially available zirconia powder include zirconia powder (trade name "Zpex (registered trademark)" (Y2O3 content: 3 mol%), "Zpex (registered trademark) 4" (Y2O3 content: 4 mol%), and "Zpex (registered trademark) Smile (registered trademark)" (YO content: 5.5 mol%), "TZ-3Y" (YO content: 3 mol%), "TZ-3YS" (YO content: 3 mol%), "TZ-4YS" (YO content: 4 mol%), "TZ-6Y" (YO content: 6 mol%), "TZ-6YS" (YO content: 6 mol%), "TZ-8YS" (YO content: 8 mol%), "TZ-10YS" (YO content: 10 mol%), and "TZ-3Y-E" (YO content: 3 mol%) Examples include "TZ-3YS-E" (YO content: 3 mol%), "TZ-3YB-E" (YO content: 3 mol%), "TZ-3YSB-E" (YO content: 3 mol%), "TZ-3YB" (YO content: 3 mol%), "TZ-3YSB" (YO content: 3 mol%), "TZ-3Y20AB" (YO content: 3 mol%), "TZ-8YSB" (YO content: 8 mol%), and "TZ-0" (YO content: 0 mol%); all manufactured by Tosoh Corporation. The commercially available zirconia powder also contains HfO. Commercially available products that also contain YO can be used. As the zirconia powder, a zirconia powder in which Y2O3 is uniformly dispersed and solid-solved, such as the commercially available TZ series (product names including "TZ"), can be used in the raw material composition of the present invention.

[0089] There are no particular limitations on the method for producing the zirconia powder, and known methods such as a breakdown process in which coarse particles are pulverized to produce fine powder, or a building-up process in which zirconia is synthesized from atoms or ions through a nucleation and growth process can be used.

[0090] The type of zirconia powder in the raw material composition is not particularly limited. When the zirconia powder contains zirconia but no stabilizer, or when the stabilizer content 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 zirconia composite sintered body to the above-mentioned predetermined range. For example, a commercially available product may be used as the stabilizer particles, or a commercially available powder may be crushed using a known crushing and mixing device (such as a ball mill) before use.

[0091] The stabilizer may be either a stabilizer that is not solid-dissolved in zirconia or a stabilizer that is solid-dissolved in zirconia. In a preferred embodiment, a method for producing a zirconia composite sintered body includes a stabilizer (preferably YO) that is not solid-dissolved in zirconia in the raw material composition, because this is one factor that makes it easy to obtain the desired zirconia composite sintered body. The fact that the stabilizer includes one that is not solid-dissolved in zirconia can be confirmed, for example, by an X-ray diffraction (XRD) pattern.

[0092] When a peak attributable to the stabilizer is confirmed in the XRD pattern of the raw material composition or the molded body, it means that the stabilizer is present in the raw material composition or the molded body without being solid-dissolved in zirconia. When the entire amount of the stabilizer is solid-dissolved in zirconia, basically, no peak attributable to the stabilizer is confirmed in the XRD pattern. However, depending on conditions such as the crystalline state of the stabilizer, even if no stabilizer peak is present in the XRD pattern, the stabilizer may not be solid-dissolved in zirconia.

[0093] A case where the stabilizer contains a stabilizer that is not solid-dissolved in zirconia will be described below, taking as an example a case where the stabilizer is yttria.

[0094] In the raw material composition or the molded body of the present invention, the abundance rate f of yttria that is not dissolved in zirconia (hereinafter sometimes referred to as "undissolved yttria") is ycan be calculated based on the following formula (1): y =I 29 / (I 28 +I 29 +I 30 )×100 (1) (where f y represents the proportion (%) of undissolved yttria, and in the XRD measurement, I 28 represents the integrated intensity of the peak at around 2θ = 28° where the main peak of the monoclinic system appears, and I 29 represents the area intensity of the peak at 2θ=29° where the main peak of yttria appears, and I 30 represents the area intensity of the peak near 2θ = 30° where the main peak of the tetragonal or cubic crystal system appears.)

[0095] When a stabilizer other than yttria is used in combination, I 29 By substituting the peak of another stabilizer in place of yttria, the formula can also be applied to calculate the undissolved fraction of stabilizers other than yttria.

[0096] Undissolved yttria abundance f y From the viewpoint that the desired zirconia composite sintered body can be easily obtained, the content f of undissolved yttria is preferably greater than 0%, more preferably 1% or more, even more preferably 2% or more, and particularly preferably 3% or more. y The upper limit may be, for example, 25% or less, but preferably depends on the content of yttria in the raw material composition or the compact.

[0097] For example, when the content of yttria in the raw material composition or the molded article of the present invention is 3 mol % or more and 8 mol % or less, the following applies: When the content of yttria is 3 mol % or more and less than 4.5 mol %, f y When the yttria content is 4.5 mol % or more and less than 5.8 mol %, f y When the content of yttria is 5.8 mol % or more and 8 mol % or less, f y can be 25% or less.

[0098] For example, when the content of yttria is 3 mol% or more and less than 4.5 mol%, f y is preferably 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 is preferably 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 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.

[0099] In the raw material composition or the molded article of the present invention, the stabilizer does not have to be entirely dissolved in zirconia. In the present invention, the stabilizer being dissolved in solid solution means, for example, that an element (atom) contained in the stabilizer is dissolved in solid solution in zirconia.

[0100] The NbO and / or TaO added to the raw material composition of the present invention is not particularly limited as long as the content of NbO and / or TaO contained in the zirconia composite sintered body can be adjusted to the above-mentioned range. The NbO and / or TaO are not particularly limited, and for example, commercially available products may be used, or the powder of the commercially available product may be crushed in a known crushing and mixing device (such as a ball mill) before use.

[0101] Examples of the step of preparing the raw material composition include a method of wet-mixing the raw materials of the raw material composition (zirconia, a stabilizer, NbO and / or TaO, if necessary, a capping agent (e.g., a compound that can become a monovalent ion in a solvent containing water), and if necessary, a zirconia strengthening agent) in a solvent containing water to obtain the raw material composition.

[0102] The method for wet-mixing the raw materials in a solvent containing water is not particularly limited. For example, the raw materials may be wet-pulverized and mixed in a known pulverizing and mixing device (such as a ball mill) to form a slurry, and then the slurry may be dried and granulated to prepare a granular raw material composition.

[0103] In the wet mixing step, additives such as a binder, a plasticizer, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, a lubricant, etc. may be further contained. Each of the additives may be used alone or in combination of two or more.

[0104] The binder may be added to a slurry obtained by adding a primary powder consisting of a mixture of zirconia, Y2O3, Nb2O5 and / or Ta2O5, and optionally a capping agent, to water, and then milling the slurry.

[0105] The binder is not particularly limited, and known binders can be used, such as polyvinyl alcohol binders, acrylic binders, wax binders (paraffin wax, etc.), methyl cellulose, carboxymethyl cellulose, polyvinyl butyral, polymethyl methacrylate, ethyl cellulose, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, atactic polypropylene, and methacrylic resins.

[0106] Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0107] Examples of dispersants include ammonium polycarboxylate (e.g., triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (e.g., polyoxyethylene alkyl ether phosphate esters such as polyoxyethylene lauryl ether phosphate esters), nonionic surfactants, olein glyceride, amine salt surfactants, oligosaccharide alcohols, and stearic acid.

[0108] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitan derivatives.

[0109] Examples of the antifoaming agent include alcohol, polyether, silicone, and wax.

[0110] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide).

[0111] Examples of the lubricant include polyoxyethylene alkyl ether and wax.

[0112] The solvent used in the wet mixing is not particularly limited as long as it contains water, and an organic solvent, a mixed solvent of water and an organic solvent, or water alone may be used. Examples of the organic solvent 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-pentanediol, 1,2-hexanediol, and 1,2-octanediol.

[0113] The raw material composition for the zirconia composite sintered body used in the present invention may contain other components in addition to zirconia, YO, NbO, TaO, and, if necessary, a capping agent and a zirconia reinforcement, as long as the effects of the present invention are achieved. Examples of such other components include colorants (pigments and composite pigments), fluorescent agents, and SiO. Each of the other components may be used alone, or two or more may be used in combination.

[0114] Examples of the pigment include an oxide 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.), preferably an oxide 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 more preferably an oxide 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, YO and CeO may be excluded from the pigment.

[0115] Examples of the composite pigment include (Zr, V) O 2 , Fe(Fe, Cr) 2 O 4 , (Ni, Co, Fe)(Fe, Cr) 2 O 4 .ZrSiO 4 , and (Co, Zn)Al 2 O 4 .

[0116] Examples of the fluorescent agent include Y2SiO5:Ce, Y2SiO5:Tb, (Y, Gd, Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 : Eu, etc.

[0117] Next, the obtained raw material composition is molded to produce a molded body. The molding method is not particularly limited, and known methods (for example, press molding) can be used.

[0118] When a zirconia molded body is produced by a method including a step of press-molding a raw material composition, the specific method of press-molding is not particularly limited, and the press-molding can be carried out using a known press-molding machine. Specific examples of the press-molding method include uniaxial pressing.

[0119] The pressing pressure in the press molding is set to an optimum value depending on the size, open porosity, biaxial bending strength, and particle size of the raw material powder of the target molded body, and is usually 5 MPa to 1000 MPa. By increasing the pressing pressure during molding in the above-mentioned production method, the pores of the obtained molded body are more fully filled, the open porosity can be set lower, and the density of the molded body can be increased. Furthermore, in order to increase the density of the obtained zirconia molded body, a cold isostatic pressing (CIP) treatment may be further performed after uniaxial pressing.

[0120] Next, the obtained compact is sintered to obtain a zirconia composite sintered body. The sintering temperature (maximum sintering temperature) at which the compact is sintered to obtain the zirconia composite sintered body is, for example, 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. The sintering temperature is, for example, preferably 1680°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower. The method for producing a zirconia composite sintered body of the present invention preferably includes a step of sintering the compact at a maximum sintering temperature of 1300 to 1680°C. The maximum sintering temperature is preferably a temperature in the atmosphere.

[0121] The holding time (holding time) at the maximum sintering temperature varies depending on the temperature, but 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. Furthermore, the holding time can be 25 minutes or less, 20 minutes or less, or 15 minutes or less. The holding time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. According to the manufacturing method of the present invention, a zirconia composite sintered body having excellent bending strength, translucency, and machinability in the sintered state can be produced depending on the stabilizer content. 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 improved and energy costs can be reduced.

[0122] In the method for producing a zirconia composite sintered body of the present invention, the heating rate during sintering of the molded body 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. The heating rate is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the heating rate at or above the lower limit, productivity is improved.

[0123] A common dental zirconia firing furnace can be used in the step of sintering the green body. Commercially available dental zirconia firing furnaces may be used. Examples of commercially available dental zirconia firing furnaces include Noritake Katana (registered trademark) F-1, F-1N, and F-2 (all manufactured by SK Medical Electronics Co., Ltd.).

[0124] Furthermore, the step of sintering the compact preferably includes a step of hot isostatic pressing (HIP) treatment in addition to sintering at the maximum sintering temperature. The HIP treatment can further improve the translucency and strength of the zirconia composite sintered body.

[0125] Hereinafter, the sintered body obtained by sintering at the maximum sintering temperature will be referred to as a "primary sintered body," and the sintered body after HIP treatment will be referred to as a "HIP-treated sintered body."

[0126] The HIP treatment can be carried out using a known hot isostatic press (HIP) device.

[0127] The temperature of the HIP treatment is not particularly limited, but since a dense zirconia composite sintered body with high strength can be obtained, the HIP temperature is preferably 1200° C. or higher, more preferably 1300° C. or higher, and even more preferably 1400° C. or higher. The HIP temperature is also preferably 1700° C. or lower, more preferably 1650° C. or lower, and even more preferably 1600° C. or lower.

[0128] In the method for producing a zirconia composite sintered body of the present invention, the HIP pressure when the primary sintered body is subjected to HIP treatment is not particularly limited, and since a dense sintered body with high strength can be obtained, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. In addition, the upper limit of the HIP pressure is not particularly limited, but can be, for example, 400 MPa or less, 300 MPa or less, or even 200 MPa or less.

[0129] In the method for producing a zirconia composite sintered body 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. The heating rate is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the heating rate at or above the lower limit, productivity is improved.

[0130] In the method for producing a zirconia composite sintered body of the present invention, when the primary sintered body is subjected to HIP treatment, the HIP time is not particularly limited, and since a dense zirconia composite sintered body with high strength can be obtained, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Moreover, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0131] In the method for producing a zirconia composite sintered body 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 low influence on zirconia, at least one pressure medium selected from the group consisting of oxygen gas, oxygen mixed gas, air, and inert gas (e.g., nitrogen gas, argon gas, etc.) can be selected as the pressure medium. When the primary sintered body is HIP treated in an oxygen mixed gas atmosphere, the oxygen concentration is not particularly limited, but can be, for example, more than 0% to 20% or less. When an oxygen mixed gas is used, at least one inert gas (e.g., nitrogen gas, argon gas, etc.) can be selected as the gas other than oxygen.

[0132] In the method for producing a zirconia composite sintered body of the present invention, if the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as "tempering treatment") in air or an oxygen-rich atmosphere at 1650°C or less after the HIP treatment step. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-rich atmosphere. 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 more than 21% and less than or equal to 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.

[0133] In the method for producing a zirconia composite sintered body of the present invention, the translucency can be adjusted by appropriately adjusting the various conditions in the HIP treatment described above. For example, the translucency can be intentionally reduced by lowering the heat treatment temperature. Therefore, the desired translucency can be adjusted in each layer by adjusting the various conditions in the HIP treatment in addition to adjusting the components, such as reducing the translucency in the layer corresponding to the cervical region and increasing the translucency in the layer corresponding to the incisal edge.

[0134] The zirconia composite sintered body of the present invention is not particularly limited as long as it exhibits the effects of the present invention, and may be a primary sintered body, a HIP-treated sintered body, or a sintered body after tempering. A preferred embodiment is a zirconia composite sintered body that is a sintered body after tempering.

[0135] The temperature of the heat treatment in the air or in an oxygen-excess atmosphere can be appropriately changed depending on the aesthetics of the zirconia composite sintered body (e.g., the shade of a dental prosthesis). In a preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1650°C or less, more preferably 1600°C or less, and even more preferably 1550°C or less, from the viewpoint of the aesthetics of the zirconia composite sintered body. In another preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1400°C or less, more preferably 1300°C or less, and even more preferably 1200°C or less, from the viewpoint of the aesthetics of the zirconia composite sintered body. Furthermore, in any embodiment, the temperature of the heat treatment is preferably 500°C or more, more preferably 600°C or more, and even more preferably 700°C or more.

[0136] A general dental zirconia firing furnace can be used for the tempering treatment. Commercially available dental zirconia firing furnaces may be used. Examples of commercially available dental zirconia firing furnaces include Noritake Katana (registered trademark) F-1, F-1N, and F-2 (all manufactured by SK Medical Electronics Co., Ltd.).

[0137] The zirconia composite sintered body of the present invention has excellent machinability despite being a sintered body, and therefore does not need to be machined in the form of a mill blank of a semi-sintered composite calcined body and then sintered to form a sintered body. On the other hand, a method for producing a zirconia composite sintered body may also be a method in which a molded body obtained from the raw material composition is calcined to produce a semi-sintered composite calcined body, and the unprocessed composite calcined body is then machined to form a sintered body.

[0138] As another embodiment, there is mentioned a method for producing a zirconia composite sintered body, which includes the steps of: preparing a molded body using the raw material composition; calcining the obtained molded body to obtain a zirconia composite calcined body (calcining step); and sintering the zirconia composite calcined body.

[0139] In order to ensure blocking, the firing temperature (calcination temperature) in the calcination step is, for example, preferably 800°C or higher, more preferably 900°C or higher, and even more preferably 950°C or higher. The calcination temperature is, for example, preferably 1200°C or lower, more preferably 1150°C or lower, and even more preferably 1100°C or lower. The calcination temperature is preferably, for example, 800°C to 1200°C. At such a calcination temperature, it is believed that the dissolution of the stabilizer does not progress significantly in the calcination step.

[0140] The density of the zirconia composite calcined body is 2.7 g / cm 3 The density of the zirconia composite calcined body is preferably 4.0 g / cm 3 Preferably, 3.8 g / cm or less 3 More preferably, 3.6 g / cm 3 The following is more preferable. When the density is within this range, processing can be easily performed. The density of the composite calcined body can be calculated, for example, by dividing the mass of the composite calcined body by the volume of the composite calcined body.

[0141] The three-point bending strength of the zirconia composite 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 piece measuring 5 mm thick, 10 mm wide, and 50 mm long, in accordance with ISO 6872:2015, except for the size of the test piece. The test piece's face and C-face (the surface where the corners of the test piece are chamfered at a 45° angle) are surface-finished in the longitudinal direction with #600 sandpaper. The test piece is positioned so that the widest surface faces vertically (the load direction). In the bending test, the span is 30 mm, and the crosshead speed is 1.0 mm / min.

[0142] The step of sintering the zirconia composite calcined body can be carried out by the same method and under the same conditions (temperature, pressure, etc.) as in the step of sintering the molded body described above. Therefore, in the embodiment of the production method using the zirconia composite calcined body, the "molded body" can be read as the "composite calcined body."

[0143] The zirconia composite sintered body of the present invention has excellent strength. The biaxial bending strength of the zirconia composite sintered body 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. When the zirconia composite sintered body of the present invention has such a biaxial bending strength, it 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 the biaxial bending strength can be, for example, 1200 MPa or less, or even 1000 MPa or less. The biaxial bending strength of the zirconia composite sintered body can be measured in accordance with ISO 6872:2015.

[0144] The zirconia composite sintered body of the present invention preferably has high translucency. * Specifically, the translucency can be evaluated by measuring the ΔL (W−B) of a sample having a diameter of 15 mm and a thickness of 1.2 mm in each layer constituting the laminated structure of the zirconia composite sintered body of the present invention. * (W−B) is preferably 10 or more, more preferably 11 or more, even more preferably 12 or more, and particularly preferably 13 or more. * By ensuring that (W-B) is within the above range and by providing a plurality of layers with different contents of at least one of the stabilizer, Nb2O5, and Ta2O5, a gradation in translucency between the layers can be obtained, and by achieving a gradation in translucency that is sufficient compared to natural teeth, a highly aesthetic zirconia composite sintered body that is closer to natural teeth can be obtained.

[0145] ΔL *(W-B) refers to the difference between the lightness (first L* value) of the same sample on a white background and the lightness (second L* value) of the same sample on a black background. Specifically, it refers to the difference between the L* value on a white background (JIS Z 8781-4:2013 Colorimetry - Part 4: CIE 1976 L*a*b* color space) and the L* value on a black background. The white background refers to the white portion of the hiding power test paper described in JIS K 5600-4-1:1999, Part 4, Section 1, and the black background refers to the black portion of the hiding power test paper.

[0146] ΔL * There is no particular upper limit to (WB), but it may be, for example, 25 or less, and from the viewpoint of aesthetics, even 20 or less.

[0147] The ΔL* of a zirconia composite sintered body having a diameter of 15 mm and a thickness of 1.2 mm can be measured using a spectrophotometer, for example, a dental colorimeter (Crystal Eye CE100-CE / JP, 7-band LED light source, analysis software Crystal Eye (manufactured by Olympus Corporation)).

[0148] Dental prostheses manufactured using the zirconia composite sintered body of the present invention include, for example, crown restorations such as inlays, onlays, veneers, crowns, core-integrated crowns, and bridges, as well as abutments, dental posts, dentures, denture bases, and implant components (fixtures and abutments). 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 Inc. and the Katana (registered trademark) system manufactured by Kuraray Noritake Dental Co., Ltd.

[0149] The zirconia composite sintered body of the present invention can also be used for applications other than dental applications, and is particularly suitable for zirconia components that require irregular or complex shapes and strength. Compared to sintered bodies produced solely by existing manufacturing methods (e.g., injection molding, CIP, slip casting, or 3D printing), the zirconia composite sintered body of the present invention can be processed as is. Therefore, for example, it is economical when the desired zirconia component can be obtained in a short time. For complex-shaped components that are difficult to produce using conventional manufacturing methods, it is possible to obtain zirconia components that maintain high strength by eliminating the need to mechanically fit multiple components. Furthermore, since the sintered body can be processed as is, a sintering process is not required when dimensional precision is required, and uneven firing shrinkage is eliminated, resulting in highly accurate zirconia components. Specifically, it can be used as a method for producing jewelry, engine and interior components for mobility such as aircraft and automobiles, display panel frames, building components, electrical appliance components, household goods components, and toy parts. The zirconia component may also be fitted with a different material to form a composite component.

[0150] The present invention includes embodiments in which all or part of the above-described configurations and embodiments are combined in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved.

[0151] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples in any way, and many modifications within the technical scope of the present invention are possible by those skilled in the art.

[0152] In the following examples and comparative examples, the average particle size refers to the average primary particle size, which can be determined by a laser diffraction / scattering method. Specifically, using a laser diffraction / scattering particle size distribution analyzer (Partica LA-950, manufactured by Horiba, Ltd.), a slurry diluted with water is irradiated with ultrasonic waves for 30 minutes, and then the volumetric measurement can be performed while applying ultrasonic waves.

[0153] [Examples 1 to 11 and Comparative Examples 1 and 2] Measurement samples for each of the Examples and Comparative Examples were prepared through the steps of preparing a granular raw material composition, preparing a compact, and preparing a zirconia composite sintered body (preparing a primary sintered body, HIP treatment, and tempering treatment).

[0154] [Preparation of Granular Raw Material Composition] To prepare the granular raw material compositions of each Example and Comparative Example, commercially available ZrO powder, YO powder, NbO powder, TaO powder, capping agent, and TiO powder were mixed so that the content of each component in the sintered zirconia composite sintered body would be the composition shown in Tables 1 and 2. Water was added to prepare a slurry, which was then wet-pulverized and mixed in a ball mill until the average particle size was 0.13 μm or less. A binder was added to the pulverized slurry, which was then dried in a spray dryer to prepare a granular raw material composition (hereinafter also simply referred to as the "raw material composition"). This was used to manufacture the molded body described below. The average particle size was measured on a volume basis using a laser diffraction / scattering particle size distribution analyzer (Partica LA-950: manufactured by Horiba, Ltd.) by irradiating the water-diluted slurry with ultrasound for 30 minutes, followed by ultrasonic irradiation.

[0155] [Preparation of Molded Body] For each Example and Comparative Example, pellet-shaped compacts and block-shaped compacts were prepared as follows to obtain zirconia composite sintered body samples for evaluating translucency and strength and for evaluating processability. For the pellet-shaped compacts, 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 zirconia composite sintered body after sintering would be 1.2 mm. Next, the raw material composition was press-molded using a uniaxial press at a surface pressure of 200 MPa to prepare pellet-shaped compacts.

[0156] For the block-shaped compact, the raw material compositions were filled into a mold having an inner dimension of 19 mm x 18 mm in the order shown in Tables 1 and 2 so that the height of the zirconia composite sintered body after sintering would be 14.5 mm. The amount of each layer filled was made uniform. Next, the raw material composition was press-molded using a uniaxial press at a surface pressure of 200 MPa for 90 seconds to produce a laminated compact.

[0157] [Preparation of primary sintered body] The pellet-shaped and block-shaped compacts obtained were subjected to sintering in the atmosphere for 2 hours at the maximum sintering temperature shown in Tables 1 and 2 using a sintering furnace "Noritake Katana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd., to obtain pellet-shaped and block-shaped zirconia composite sintered body (primary sintered body) samples.

[0158] [Preparation of HIP-treated sintered body] The obtained pellet-shaped and block-shaped zirconia composite sintered bodies (primary sintered bodies) were subjected to a HIP apparatus "O2-Dr. HIP" manufactured by Kobe Steel, Ltd., in an argon atmosphere at 150 MPa and at the HIP temperatures shown in Tables 1 and 2 for 2 hours, thereby obtaining pellet-shaped and block-shaped zirconia composite sintered body (HIP-treated sintered body) samples.

[0159] [Preparation of zirconia composite sintered body (tempered sintered body)] The obtained pellet-shaped and block-shaped zirconia composite sintered body (HIP-treated sintered body) was subjected to heating at 700°C for 60 hours in a Noritake Katana (registered trademark) F-1 firing furnace manufactured by SK Medical Electronics Co., Ltd., to obtain pellet-shaped and block-shaped zirconia composite sintered body (tempered sintered body) samples. The pellet-shaped samples had a diameter of 15 mm and a thickness of 1.2 mm, and the block-shaped samples had a width of 15.7 mm, a length of 16.5 mm, and a height of 14.5 mm.

[0160] The content of each component of the zirconia composite sintered body in Tables 1 and 2 is a value calculated from the amount of raw material charged. The content (mol%) of a capping element or ion (e.g., Na) in Tables 1 and 2 is the external addition rate relative to a total of 100 mol% of zirconia, the stabilizer (yttria), NbO, and TaO. The content (mol%) of each of zirconia, the stabilizer, NbO, and TaO in Tables 1 and 2 is the content of each component relative to a total of 100 mol% of zirconia, the stabilizer, NbO, and TaO. The content (mass%) of TiO in Tables 1 and 2 is the external addition rate relative to a total of 100 mol% of zirconia, the stabilizer, NbO, and TaO. In Tables 1 and 2, A / B represents the ratio of A to B when the content of Y2O3 is A mol % and the total content of Nb2O5 and Ta2O5 is B mol %.

[0161] [Evaluation of Translucency of Zirconia Composite Sintered Body] Using samples (diameter: approximately 15 mm × thickness: 1.2 mm) of the pellet-shaped zirconia composite sintered body (sintered body after tempering) of each Example and Comparative Example as they were, the translucency was evaluated by the following method (n=3). Using a dental color measurement device "Crystal Eye" (7-band LED light source) manufactured by Olympus Corporation as a measurement device, first, the background (underlay) of the sample was set to white (the side opposite to the measurement device was set to white) and the L*a*b* color space of the L*a*b* color system (JIS Z 8781-4:2013 Colorimetry - Part 4: CIE 1976 L*a*b* color space) was measured. * The value is measured, and the first L * Next, the first L * For the same sample for which the values ​​were measured, the background (underlay) of the sample was black (the side opposite to the measuring device was black with respect to the sample) and the L*a*b* color system was measured. * The value is measured and the second L * In the present invention, the first L * value and the second L * The difference between the first L * value to the second L * The value obtained by subtracting the value of ΔL * It is expressed as (W−B).* A high (W-B) indicates high light transmittance, and a low ΔL* indicates low light transmittance. For the black and white background (underlay) used in measuring chromaticity, the hiding power test paper used in measurements related to paints described in JIS K 5600-4-1:1999 was used. The ΔL of each sample * The arithmetic mean values ​​of (W−B) are shown in Tables 1 and 2.

[0162] [Esthetic Evaluation of Zirconia Composite Sintered Body] The anterior tooth crown-shaped samples used in the later-described [Evaluation of Workability of Zirconia Composite Sintered Body] were visually observed at close range (approximately 10 cm from the sample) (n=3). All three samples were evaluated as "Good" (pass) if they exhibited the same color tone (transparency) as natural teeth. All three samples were evaluated as "Poor" (fail) if they did not exhibit the same color tone (transparency) as natural teeth. Note that, as shown in the workability evaluation results in Table 2, the sintered body of Comparative Example 1 could not be machined. Therefore, in Comparative Example 1, a block-shaped compact was retained at 1000°C for 2 hours, and the calcined body was then processed into the shape of an anterior tooth crown. This was then retained at 1550°C for 2 hours to obtain a crown-shaped sample for use in the aesthetic evaluation.

[0163] [Strength Evaluation of Zirconia Composite Sintered Body] Using samples of the pellet-shaped zirconia composite sintered body (sintered body after tempering treatment) of each Example and Comparative Example as is, the biaxial bending strength was measured in accordance with ISO6872:2015 using a universal testing machine "AGS-X" (manufactured by Shimadzu Corporation) at a crosshead speed of 1.0 mm / min (n=5). The arithmetic mean values ​​are shown in Tables 1 and 2 as measurement results. A strength of 300 MPa or more was considered acceptable.

[0164] [Method for measuring average crystal grain size in sintered body] For the pellet-shaped zirconia composite sintered bodies (sintered bodies after tempering treatment) of each Example and Comparative Example, images of the surface were taken using a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). After the grain boundaries of each crystal grain were noted in the obtained image, the average crystal grain size was calculated by image analysis. The results are shown in Tables 1 and 2 below. To measure the average crystal grain size, image analysis software (product name "Image-Pro Plus", manufactured by Hakuto Co., Ltd.) was used to binarize the captured SEM image, adjust the brightness range so that the grain boundaries were clearly visible, and recognize the particles from the field of view (area). The crystal grain size obtained using Image-Pro Plus is the average length of the line segments connecting the outlines of the crystal grains passing through the center of gravity, measured at intervals of two degrees from the center of gravity. The arithmetic mean value of the crystal grain size of all particles not on the edge of the SEM photograph (three fields of view) of each example and comparative example was used as the average crystal grain size (by number) in the sintered body. "Particles not on the edge of the image" refers to particles excluding particles whose outlines do not fit within the screen of the SEM photograph (particles whose outlines are interrupted at the top, bottom, left, and right boundary lines). The crystal grain size of all particles not on the edge of the image was determined by selecting the option to exclude all particles on all boundary lines in Image-Pro Plus.

[0165] [Evaluation of Workability of Zirconia Composite Sintered Body] Thirty samples of block-shaped zirconia composite sintered body (sintered body after tempering) of each Example and Comparative Example were prepared by attaching a metal jig to a surface measuring 15.7 mm wide x 14.5 mm high, and processed into a general anterior tooth crown shape using a CEREC system "MC-XL" (manufactured by Dentsply Sirona). The processing program used software "inLab (registered trademark) CAM version 20.0.1.203841", manufacturer: IVOCLAR VIVADENT, material name: IPS e. Max CAD, Production Method: Grinding, Block size: C16 were selected, and Step Bur 12 and Cylinder Pointed Bur 12S were used as machining tools.

[0166] [Machining Time] The machining times shown in Tables 1 and 2 are the time required to complete machining of the first sample using a new machining tool under the conditions described in the above [Evaluation of the Machinability of Zirconia Composite Sintered Body]. If an error occurred due to the load during machining or the like and the CEREC system "MC-XL" stopped midway through machining, a new machining tool was installed and machining was resumed. This operation was repeated until one sample was completely machined, and the time required was recorded as the machining time. In Tables 1 and 2, samples that could not be machined at all are marked with an "x" (impossible).

[0167] [Number of Pieces Machined] The number of pieces machined shown in Tables 1 and 2 refers to the number of pieces machined into a front tooth crown shape using a new set of machining tools under the conditions described in the above [Evaluation of Zirconia Composite Sintered Compacts Machinability] without changing the machining tools. A maximum of 30 samples were used for testing. If machining of up to 30 pieces was completed using one machining tool, no additional machining tests were conducted and the test was uniformly rated as "30 or more." Furthermore, if an error occurred due to a machining load or other reason, causing the MC-XL to stop mid-machining before completing machining of the first sample, the tool was replaced with a new one and machining resumed. This process was repeated until one sample was machined, and the number of pieces machined was calculated as the reciprocal of the number of machining tools used. For example, the notation "0.2 pieces" means that five machining tools were used to obtain a sample machined into a front tooth crown shape. The results are shown in Tables 1 and 2 below.

[0168]

[0169]

[0170] The results above confirmed that the zirconia composite sintered body of the present invention has strength suitable for dental use, excellent machinability in the sintered state, sufficient translucency gradation, and excellent aesthetics. Furthermore, in Examples 1 to 11, wear on the processing tool was suppressed, and a significantly large number of dental prostheses could be continuously processed using a single processing tool.

[0171] On the other hand, Comparative Example 1, which did not contain Nb2O5 or Ta2O5, could not be machined at all in the sintered state. Comparative Example 2, which did not have a laminated structure with multiple layers containing different contents of at least one of the stabilizer, Nb2O5, or Ta2O5 components, had high translucency overall, so the transparency of the area corresponding to the cervical region was too high, resulting in poor aesthetics.

[0172] The zirconia composite sintered body of the present invention has strength suitable for dental use, excellent machinability in the sintered state, and excellent aesthetics, and is therefore particularly useful as a dental material for dental prostheses and other dental treatment applications.

Claims

1. A zirconia composite sintered body comprising zirconia, a stabilizer capable of suppressing a phase transition of zirconia, and at least one of Nb2O5 and Ta2O5, and having a plurality of layers having different contents of at least one of the stabilizer, Nb2O5, or Ta2O5 relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5.

2. The zirconia composite sintered body according to claim 1, wherein the plurality of layers are layers having different contents of Nb2O5 or Ta2O5.

3. A zirconia composite sintered body as described in claim 2, wherein, on a straight line extending in a first direction from one end of the zirconia composite sintered body to the other end, there is no change in the increase / decrease tendency of the Nb2O5 or Ta2O5 content relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5 from one end to the other end.

4. The zirconia composite sintered body according to claim 3, wherein said stabilizer is yttria.

5. The zirconia composite sintered body according to claim 4, wherein the Nb2O5 or Ta2O5 content of the layer including said one end is 2 mol% or more and 12 mol% or less, and the Nb2O5 or Ta2O5 content of the layer including said other end is 1 mol% or more and 10 mol% or less, relative to the total mol of zirconia, yttria, Nb2O5, and Ta2O5.

6. The zirconia composite sintered body according to claim 1, wherein the plurality of layers are layers having different contents of the stabilizer.

7. A zirconia composite sintered body as described in claim 6, wherein, on a straight line extending in a first direction from one end of the zirconia composite sintered body to the other end, there is no change in the increase / decrease tendency of the content of the stabilizer relative to the total mol of zirconia, the stabilizer, Nb2O5, and Ta2O5 from one end of the zirconia composite sintered body to the other end.

8. The zirconia composite sintered body according to claim 7, wherein said stabilizer is yttria.

9. The zirconia composite sintered body according to claim 8, wherein the yttria content of the layer including said one end is 1 mol% or more and 8 mol% or less, and the yttria content of the layer including said other end is 2 mol% or more and 9 mol% or less, relative to the total mol of zirconia, yttria, Nb2O5, and Ta2O5.

10. The zirconia composite sintered body according to claim 1 or 2, wherein at least one of the plurality of layers further contains elements or ions derived from a capping agent.

11. The zirconia composite sintered body according to claim 10, wherein the content of elements or ions derived from the capping agent is greater than 0 mol% and not greater than 5 mol%, relative to a total of 100 mol% of zirconia, the stabilizer, Nb2O5, and Ta2O5.

12. The zirconia composite sintered body according to claim 10, wherein the element or ion derived from the capping agent is an element or ion thereof belonging to Periods 2 to 7 of the periodic table and having a smaller first ionization energy than that of a Group 18 element in the same period, and / or an element or ion thereof having a high electron affinity.

13. The zirconia composite sintered body according to claim 10, wherein the element or ion derived from the capping agent comprises at least one element or ion thereof selected from the group consisting of Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl, and F.

14. The zirconia composite sintered body according to claim 10, wherein the element or ion derived from the capping agent includes at least one element or ion thereof selected from the group consisting of Li, Na, K, Rb, Cs, and Fr.

15. A zirconia composite sintered body as described in claim 1 or 2, wherein, when the content of the stabilizer is A mol % and the total content of Nb2O5 and Ta2O5 is B mol %, at least one of the plurality of layers has an A / B ratio of 0.9 or more and 3 or less.

16. A zirconia composite sintered body according to claim 1 or 2, wherein at least one of the plurality of layers further contains a zirconia reinforcement agent, and the content of the zirconia reinforcement agent is more than 0 mass% and not more than 6.0 mass%, relative to 100 mass% of the total of zirconia, the stabilizer, Nb2O5 and Ta2O5.

17. The zirconia composite sintered body according to claim 16, wherein the zirconia reinforcement agent comprises TiO2 and / or Al2O3.

18. A zirconia composite sintered body according to claim 1 or 2, wherein the average crystal grain size of the zirconia composite sintered body is 0.5 to 5.0 μm.