The calcined and sintered frameworks of zirconia.

Abstract

Invention details;

Description

Zirconia calcined and sintered bodies

[0001] The present disclosure relates to a zirconia laminate, that is, a calcined zirconia body and a sintered zirconia body.

[0002] Zirconia (ZrO ２ ) sintered bodies are manufactured by molding, calcining, and sintering raw material powders that mainly contain zirconia. The raw material powders undergo thermal shrinkage and densification through heat treatments such as sintering and calcining, but their behavior during heat treatment varies depending on the characteristics of the raw material powders, particularly their composition.

[0003] Zirconia accounts for the majority of the raw material powder. Nevertheless, even when raw material powders differ only by less than 0.1% by mass in additive content, the thermal shrinkage behavior of the two powders is significantly different. When a molded body formed by stacking raw material powders with such slight differences in composition is heat-treated, defects such as partial peeling of layers or distortion occur. The above-mentioned defects occur even when the same zirconia is used and additives are added. In order to heat-treat the molded body without these defects, special adjustments and treatments have been required (e.g., Patent Documents 1 and 2).

[0004] Patent Document 1 discloses that by adjusting the composition and thermal shrinkage behavior of raw material powders by coating them with dopants and then molding them, a sintered body consisting of laminates with no distortion and different color tones can be obtained. Patent Document 2 also discloses that by applying vibrations that form boundary layers where upper and lower layers of powder are mixed, a sintered body consisting of laminates with layers containing different amounts of coloring elements and with varying color tones can be obtained by laminating and molding the resulting material. However, the laminates disclosed in Patent Documents 1 and 2 have the same composition of zirconia, which accounts for the majority of the raw material powder, and these laminates also have the same texture, which is mainly due to the translucency of zirconia. Therefore, they have a different texture compared to natural teeth, which have a texture due to variations in translucency.

[0005] Therefore, there is a demand for a zirconia laminate having translucency and color gradation that can give an impression similar to that of natural teeth.Patent Document 3 discloses a laminate formed by laminating a plurality of zirconia composition layers having different chemical compositions.

[0006] US Patent Application Publication No. 2016 / 0157971 US Patent Application Publication No. 2014 / 0328746 US Patent Application Publication No. 2015 / 0173869

[0007] In Patent Document 3, layers with gradually varying amounts of yttrium or coloring elements are stacked from the bottom layer to the top layer so that the color tone and transmittance gradually change. However, when layers with different compositions are stacked so that the color tone and transmittance gradually change, the compositions of the bottom layer and the top layer differ significantly, which results in significantly different shrinkage rates between the bottom layer and the top layer. When such a molded body with a large difference in shrinkage rate between the bottom layer and the top layer is heat-treated, a calcined body or sintered body is obtained that is significantly warped toward the side with the larger shrinkage rate.

[0008] Therefore, an object of the present disclosure is to provide at least one of a zirconia calcined body and sintered body that has gradation in translucency and color tone and that can give an impression similar to that of natural teeth when viewed visually, and a calcined body that provides such a sintered body, and that has reduced warping even after heat treatment such as sintering or calcining. Another object of the present disclosure is to provide at least one of a calcined body and a sintered body that are suitable as a dental prosthetic material, and a method for manufacturing the same.

[0009] The present inventors have focused on the relationship between the content of the stabilizing element in the zirconia composition contained in the bottom layer and the content of the stabilizing element in the zirconia composition contained in the top layer, or the relationship between the shrinkage rate of the bottom layer and the shrinkage rate of the top layer, and have found that by controlling these to a specific relationship, it is possible to obtain a sintered body that has reduced warping, and a calcined body that can give such a sintered body, despite having a layered structure that gradually changes translucency and color tone, similar to natural teeth.

[0010] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] A zirconia sintered body, wherein the zirconia contains (i) zirconia containing a stabilizing element, or (ii) zirconia containing zirconia containing a stabilizing element and a coloring element, the sintered body has three or more regions stacked in layers, and adjacent two of the regions have different contents of at least one of the stabilizing element and the coloring element, and the difference between the content of the stabilizing element contained in a first region located at one end of the stacked regions and the content of the stabilizing element contained in a second region located at the other end of the stacked regions is 2.0 mol% or less. [2] The sintered body according to [1], wherein the third region stacked in layers between the first region and the second region includes one or more regions. [3] The sintered body according to [2], wherein the third region includes two or more regions, and at least one of the increase / decrease trends in translucency and color tone does not change along the stacking direction from the first region to the third region or from the second region to the third region. [4] A sintered body of zirconia, wherein the zirconia contains (i) a stabilizing element-containing zirconia or (ii) a zirconia containing a stabilizing element-containing zirconia and a coloring element, the sintered body has three or more regions stacked in layers, and adjacent two of the regions have different contents of at least one of the stabilizing element and the coloring element, and the difference (shrinkage rate difference) between the shrinkage rate of the sintered body of a first region located at one end of the stacked regions and the shrinkage rate of the sintered body of a second region located at the other end of the stacked regions is 0.4% or less. [5] The sintered body according to [4], wherein the third region stacked in layers between the first region and the second region includes one or more regions. [6] The third region includes two or more regions, and the tendency of increase or decrease in at least one of the translucency and color tone does not change along the stacking direction from the first region to the third region, or from the second region to the third region. [5] A sintered body.[7] A calcined body of a zirconia composition, wherein the zirconia composition contains (iii) a stabilizing-element-containing zirconia composition having a necking structure, or (iv) a zirconia composition containing a stabilizing-element-containing zirconia having a necking structure and a coloring element, the calcined body having three or more regions stacked in layers, wherein adjacent two of the regions have different contents of at least one of the stabilizing element and the coloring element, and the difference between the content of the stabilizing element contained in a first region located at one end of the stacked regions and the content of the stabilizing element contained in a second region located at the other end of the stacked regions is 2.0 mol% or less. [8] The calcined body according to [7], wherein a third region stacked in layers between the first region and the second region includes one or more regions. [9] The calcined body according to [8], wherein the third region includes two or more regions, and wherein the tendency of increase or decrease in color tone does not change along the stacking direction from the first region to the third region or from the second region to the third region.

[10] A calcined body of a zirconia composition, wherein the zirconia composition contains (iii) a stabilizing element-containing zirconia composition having a necking structure, or (iv) a zirconia composition containing a stabilizing element-containing zirconia having a necking structure and a coloring element, the calcined body having three or more regions stacked in layers, wherein adjacent two of the regions have different contents of at least one of the stabilizing element and the coloring element, and the difference (shrinkage rate difference) between the contraction rate of a calcined body of a first region located at one end of the stacked regions and the contraction rate of a calcined body of a second region located at the other end of the stacked regions is 0.4% or less.

[11] The calcined body according to

[10] , wherein the third region stacked in layers on the first region and the second region includes one or more regions.

[12] The third region includes two or more regions, and the color tone does not change in the stacking direction from the first region to the third region, or from the second region to the third region.

[11] The calcined body described in.

[13] A method for producing a sintered body according to any one of [1] to [6], comprising a step of sintering a molded body having three or more layers of powder composition made of a zirconia raw material powder containing zirconia containing a stabilizing element and, if a coloring element is contained, also the coloring element, laminated thereon, at 1200°C or more and 1600°C or less.

[14] A method for producing a sintered body according to any one of [1] to [6], comprising a step of calcining a molded body having three or more layers of powder composition made of a zirconia raw material powder containing zirconia containing a stabilizing element and, if a coloring element is contained, also the coloring element, laminated thereon, at 800°C or more and less than 1200°C to obtain a calcined body, and a step of sintering the calcined body at 1200°C or more and 1600°C or less.

[15] A method for producing the calcined body according to any one of [7] to

[12] , comprising a step of calcining a compact at 800°C or higher and lower than 1200°C, wherein the compact is composed of three or more layers of powder composition made of a raw material powder of zirconia containing zirconia containing a stabilizing element and, if a coloring element is contained, the coloring element.

[16] A dental material comprising the sintered body according to any one of [1] to [6].

[17] A dental material comprising the calcined body according to any one of [7] to

[12] .

[0011] According to the present disclosure, it is possible to provide at least one of a zirconia calcined body and a sintered body that have gradations in translucency and color tone and that can give an impression similar to that of natural teeth when viewed visually, and a calcined body that gives such a sintered body, and that has reduced warping even when subjected to heat treatment such as sintering or calcining. Furthermore, it is possible to provide at least one of a calcined body and a sintered body that are suitable as a dental prosthetic component, and a method for manufacturing the same.

[0012] Schematic diagram showing a cross section of a sintered body having a structure in which three zirconia layers are laminated. Schematic diagram showing a cross section of a sintered body having a structure in which four zirconia layers are laminated. Schematic diagram explaining the molding process of uniaxial press molding. Schematic diagram explaining the molding process of CIP treatment. Schematic diagram showing a method for measuring warpage. Schematic diagram showing a method for measuring three-point bending strength. Schematic diagram showing zirconia having a necking structure. Schematic diagram explaining the molding process of uniaxial press molding when producing a laminate in the examples. Schematic diagram explaining the molding process of CIP treatment when producing a laminate in the examples.

[0013] Hereinafter, a zirconia sintered body and a calcined body according to one embodiment of the present disclosure will be described in detail. Note that the following description of the constituent elements is an example for explaining one embodiment of the present disclosure, and the present disclosure is not limited to these details.

[0014] In this specification, the term "laminated body" may include any of a sintered body, a calcined body, and a molded body. For example, the laminate of this embodiment may be a sintered body when used as a dental prosthesis, and a calcined body when used as a precursor thereof. For example, in this embodiment, when the laminate is a sintered body, the sintered body has a structure in which regions consisting of "stabilizing-element-containing zirconia, which is zirconia having a stabilizing element dissolved therein, and zirconia containing a coloring element, if a coloring element is contained" are laminated in layers. When the laminate is a calcined body, the calcined body has a structure in which regions consisting of "stabilizing-element-containing zirconia exhibiting a necking structure, and a zirconia composition containing a coloring element, if a coloring element is contained" are laminated in layers. When the laminate is a molded body, the molded body has a structure in which regions consisting of "a powder composition containing a stabilizing-element-containing zirconia, and a powder composition containing a coloring element, if a coloring element is contained" are laminated in layers. By laminating regions having different contents of at least one of the stabilizing element and the coloring element in layers, it is possible to change the light transmittance and color tone (for example, L ＊ a ＊ b ＊By changing the color tone (color tone according to a color system), it is possible to form a gradation of translucency and color tone. In the present disclosure, the region is defined as being "laminated in layers," which means that a plurality of regions made of zirconia with different compositions due to different contents of stabilizing elements and coloring elements are present in the sintered body or calcined body, and these plurality of regions are present along the lamination direction. In the present disclosure, the "laminated layer" state in which the interfaces between the layers are visible and the lamination state of each layer can be confirmed is not specified. In the sintered body or calcined body of this embodiment, the lamination state of each layer is not required to be visible. Even if there are no visible interfaces, the region as defined in the present disclosure can be said to be "laminated in layers" as long as it can be said that a plurality of regions with different compositions are present along one direction.

[0015] Incidentally, calcined bodies and sintered bodies are obtained by laminating powder composition layers made of zirconia raw material powder containing stabilizing element-containing zirconia and, if a coloring element is contained, also the coloring element to form a molded body, followed by molding the molded body and then calcining or sintering the molded body. The "regions" in the sintered body or calcined body are formed by calcining or sintering each powder composition layer in the molded body. In other words, each "region" in the sintered body or calcined body substantially corresponds to each powder composition layer in the molded body. Therefore, in this specification, when describing the layered structure of a laminate such as a sintered body or calcined body and describing each layer constituting the laminate, the "regions" in the sintered body or calcined body will be appropriately referred to as the "layers" constituting the layered structure of the sintered body or calcined body.

[0016] Furthermore, in this specification, when multiple preferred lower limit values ​​and multiple preferred upper limit values ​​are listed as preferred condition ranges for any requirement, any combination of these lower limit values ​​and upper limit values ​​may be used when interpreting the preferred condition range. For example, when a preferred range of layer thickness is described as having a lower limit of 1 mm or more, more preferably 2 mm or more, and an upper limit of 20 mm or less, more preferably 15 mm or less, preferred embodiments of the layer thickness are, for example, 1 mm or more and 20 mm or less, 1 mm or more and 15 mm or less, 2 mm or more and 2 mm or more and 15 mm or less. The sintered body will be described below.

[0017] (Sintered body) The sintered body according to this embodiment is a zirconia sintered body, wherein the zirconia contains (i) stabilizing element-containing zirconia or (ii) zirconia containing stabilizing element-containing zirconia and a coloring element. The zirconia contains (i) stabilizing element-containing zirconia. The stabilizing element-containing zirconia of (i) may further contain a coloring element, in which case the zirconia contains (ii) stabilizing element-containing zirconia and a coloring element. The sintered body has three or more regions stacked in layers, wherein adjacent two of the regions have different contents of at least one of the stabilizing element and the coloring element, and the difference between the content of the stabilizing element contained in a first region located at one end of the stacked regions and the content of the stabilizing element contained in a second region located at the other end of the stacked regions is 2.0 mol% or less. Another embodiment of the sintered body according to the present invention is a zirconia sintered body, wherein the zirconia contains either (i) zirconia containing a stabilizing element or (ii) zirconia containing zirconia containing a stabilizing element and a coloring element, and the sintered body has three or more regions stacked in layers, wherein adjacent two of the regions have different contents of at least one of the stabilizing element and the coloring element, and the difference (shrinkage difference) between the shrinkage of a first region located at one end of the stacked regions and the shrinkage of a second region located at the other end of the stacked regions is 0.4% or less.

[0018] The sintered body is a laminate comprising a sintered structure. In this embodiment, the sintered structure is a structure primarily composed of zirconia in the later stages of sintering. The sintered body of this embodiment has a zirconia layer composed of zirconia containing a stabilizing element, or, if a coloring element is contained, a zirconia layer composed of zirconia containing a stabilizing element and a coloring element (hereinafter, these zirconia layers are also collectively referred to as "zirconia layers"). The zirconia layer is primarily composed of zirconia crystal particles containing a stabilizing element. Therefore, the sintered body of this embodiment can be regarded as a zirconia layer composed of zirconia crystal particles containing a stabilizing element, or, if a coloring element is contained, as a laminate comprising three or more layers of zirconia composed of zirconia crystal particles containing a stabilizing element and zirconia containing a coloring element. Note that in this specification, the zirconia layer is also referred to as a sintered body layer.

[0019] <Laminated Structure> A sintered body having a structure in which three zirconia layers (sintered body layers) are laminated will be described below. FIG. 1 is a schematic diagram showing an example of the laminated structure of the sintered body of this embodiment. FIG. 1 shows a cross section of a sintered body (100) having a structure in which three zirconia layers are laminated. Each of the three layers in FIG. 1 corresponds to each "region" described in the present disclosure. In FIG. 1, the lamination direction is indicated in the Y-axis direction, and the direction in which each layer extends (hereinafter also referred to as the "horizontal direction") is indicated in the X-axis direction. The sintered body (100) has a first zirconia layer (hereinafter also referred to as the "first layer") (11), a second zirconia layer (hereinafter also referred to as the "second layer") (12), and a third zirconia layer (hereinafter also referred to as the "third layer") (13), and has a structure in which the first layer (11), the third layer (13), and the second layer (12) are laminated in this order. Each layer (region) designated as the first layer (11), the third layer (13), and the second layer (12) has the same zirconia composition, but the zirconia composition between adjacent layers is different. Each of the first layer (11), the third layer (13), and the second layer (12) may further contain a coloring element in addition to stabilizing element-containing zirconia. The coloring element may be contained in all three layers, the first layer (11), the third layer (13), and the second layer (12), or only in some of the layers. When the first layer (11), the third layer (13), and the second layer (12) do not contain a coloring element, each of the layers (regions) designated as the first layer (11), the third layer (13), and the second layer (12) has a different content of the stabilizing element from the adjacent layer (region). When a coloring element is contained in all or part of the first layer (11), the third layer (13), and the second layer (12), each layer (each region) indicated as the first layer (11), the third layer (13), and the second layer (12) differs from the adjacent layer (adjacent region) in the content of at least one of the stabilizing element and the coloring element.

[0020] The sintered body of this embodiment will be specifically described below using Fig. 1, taking as an example a case where coloring elements are contained in the three zirconia layers shown in Fig. 1. The sintered body (100) comprises a first zirconia layer (first layer) (11) containing a stabilizing element-containing zirconia and a coloring element, a second zirconia layer (second layer) (12) containing a stabilizing element-containing zirconia and a coloring element, and a third zirconia layer (third layer) (13) containing a stabilizing element-containing zirconia and a coloring element, and has a structure in which the first layer (11), the third layer (13), and the second layer (12) are laminated in this order. Each layer (region) designated as the first layer (11), the third layer (13), and the second layer (12) has the same zirconia composition. Therefore, along the X direction in FIG. 1, no change in light transmittance or color tone due to a difference in the content of at least one of the stabilizing element and the coloring element is observed.

[0021] On the other hand, the zirconia compositions of adjacent layers (regions) designated as the first layer (11), third layer (13), and second layer (12) are different. In other words, the content of at least one of the stabilizing element and the coloring element differs between adjacent layers (regions). "Adjacent layers have different zirconia compositions" refers to, for example, cases where the content of the stabilizing element remains the same between adjacent layers and only the content of the coloring element differs, cases where the content of the coloring element remains the same between adjacent layers and only the content of the stabilizing element differs, or cases where the content of the stabilizing element and the content of the coloring element differ between adjacent layers. Using the example of Figure 1, the content of at least one of the stabilizing element and the coloring element contained in the zirconia layer of the third layer (13) is different from the content of at least one of the stabilizing element and the coloring element contained in the zirconia layer of the adjacent first layer (11), and is also different from the content of at least one of the stabilizing element and the coloring element contained in the zirconia layer of the adjacent second layer (12). Each layer (region) designated as the first layer (11), the third layer (13), and the second layer (12) differs from its adjacent layer (region) in the content of at least one of the stabilizing element and the coloring element, but to obtain the desired light transmittance and color tone change, it is preferable that the contents of the stabilizing element and the coloring element differ from those of the adjacent layer (region). That is, it is preferable that the contents of the stabilizing element and the coloring element contained in the zirconia layer of the third layer (13) differ from those of the stabilizing element and the coloring element contained in the zirconia layer of the adjacent first layer (11), and also differ from those of the stabilizing element and the coloring element contained in the zirconia layer of the adjacent second layer (12).

[0022] By forming a structure in which zirconia layers containing zirconia with different contents of at least one of a stabilizing element and a coloring element are stacked between adjacent layers, a sintered body can be formed in which changes in translucency and color tone based on the difference in the contents of the stabilizing element and the coloring element can be visually recognized along the Y direction in Figure 1. Note that the sintered body (100) in Figure 1 shows a state in which the first layer and the third layer, or the third layer and the second layer, are in contact via an interface. However, the sintered body of this embodiment may be stacked without a visible interface, and further, the interface between the layers is not limited to being linear.

[0023] The sintered body of this embodiment may have a structure in which three or more zirconia layers containing stabilizing element-containing zirconia and, if a coloring element is included, the coloring element are laminated. It may also have a structure in which four or more, or even five or more, zirconia layers are laminated. By increasing the number of layers, the sintered body becomes a laminate in which subtle changes in texture can be visually recognized. To achieve a texture more similar to that of natural teeth, the sintered body of this embodiment may have a structure in which three to ten, even three to six, even four to seven, or even four to six zirconia layers are laminated. A zirconia layer other than the first and second layers (hereinafter also referred to as an "intermediate layer") may be present between the first and second layers, and the sintered body of this embodiment may include multiple intermediate layers. In other words, the third region (intermediate layer) laminated between the first and second regions may include not only one region but also two or more regions. The order of stacking the intermediate layers is arbitrary. However, for example, when multiple intermediate layers are provided (the intermediate layer adjacent to the first layer is referred to as the "third layer," and the second or higher intermediate layers are also referred to as the "fourth layer," "fifth layer," etc., in the stacking direction from the intermediate layer adjacent to the third layer), the sintered body of this embodiment preferably has a structure in which the zirconia layers are stacked so that the change in the content of at least one of the stabilizing element and the coloring element in the stacking direction is constant, i.e., the zirconia layers are stacked so that the content increases (or decreases). In this embodiment, the structure in which the intermediate layer is sandwiched between the first and second layers means a structure in which the intermediate layer is located between the first and second layers in the stacking direction. An example in which the first, third, and second layers are stacked in this order is as explained using FIG. 1. A case in which the intermediate layer has multiple layers will be explained below using FIG. 2. In this embodiment, the numbers 1, 2, 3, etc. are assigned for the convenience of explanation, and the permutation of the stacking order and the stacking state are not limited to those shown in Figures 1 and 2.

[0024] FIG. 2 is a schematic diagram showing another example of the structure of the sintered body of this embodiment. FIG. 2 shows a cross section of a sintered body (200) having a structure in which four zirconia layers are stacked. The sintered body (200) has a structure in which, in addition to a first layer (21) and a second layer (22), intermediate layers, a third layer (23) and a fourth layer (24), are stacked. Each of the first layer (21), the third layer (23), the fourth layer (24), and the second layer (22) (each region) may further contain a coloring element in addition to the stabilizing element-containing zirconia. The coloring element may be contained in all four layers, i.e., the first layer (21), the third layer (23), the fourth layer (24), and the second layer (22), or may be contained in only some of these layers. When the first layer (21), the third layer (23), the fourth layer (24), and the second layer (22) do not contain a coloring element, the layers (regions) designated as the first layer (21), the third layer (23), the fourth layer (24), and the second layer (22) differ from the adjacent layers (regions) in the content of the stabilizing element. When the first layer (21), the third layer (23), the fourth layer (24), and the second layer (22) all or partly contain a coloring element, the layers (regions) designated as the first layer (21), the third layer (23), the fourth layer (24), and the second layer (22) differ from the adjacent layers (regions) in the content of at least one of the stabilizing element and the coloring element.

[0025] The following description will be given taking as an example a sintered body in which coloring elements are contained in the four zirconia layers shown in Figure 2. The sintered body (200) comprises a first zirconia layer (first layer) (21) containing stabilizing element-containing zirconia and a coloring element, a second zirconia layer (second layer) (22) containing stabilizing element-containing zirconia and a coloring element, a third zirconia layer (third layer) (23) containing stabilizing element-containing zirconia and a coloring element, and a fourth zirconia layer (fourth layer) (24) containing stabilizing element-containing zirconia and a coloring element, and has a structure in which the first layer (21), the third layer (23), the fourth layer (24), and the second layer (22) are laminated in this order. Among the layers (regions) designated as the first layer (21), third layer (23), fourth layer (24), and second layer (22), adjacent layers (regions) have different zirconia compositions. That is, the contents of at least one of the stabilizing elements and coloring elements differ between adjacent layers (regions). The contents of at least one of the stabilizing elements and coloring elements contained in the zirconia layer of the third layer (23) are different from the contents of at least one of the stabilizing elements and coloring elements contained in the zirconia layer of the adjacent first layer (21), and are also different from the contents of at least one of the stabilizing elements and coloring elements contained in the zirconia layer of the adjacent fourth layer (24). The contents of at least one of the stabilizing elements and coloring elements contained in the zirconia layer of the adjacent third layer (23) are also different from the contents of at least one of the stabilizing elements and coloring elements contained in the zirconia layer of the adjacent second layer (22). Each layer (each region) represented by the first layer (21), the third layer (23), the fourth layer (24), and the second layer (22) differs from its adjacent layer (adjacent region) in the content of at least one of the stabilizing element and the coloring element, but in order to obtain a desired change in light transmittance and color tone, it is preferable that the contents of the stabilizing element and the coloring element differ from its adjacent layer (adjacent region).That is, the contents of the stabilizing elements and coloring elements contained in the zirconia layer of the third layer (23) are different from the contents of the stabilizing elements and coloring elements contained in the zirconia layer of the adjacent first layer (21), and are preferably different from the contents of the stabilizing elements and coloring elements contained in the zirconia layer of the adjacent fourth layer (24). Furthermore, the contents of the stabilizing elements and coloring elements contained in the zirconia layer of the fourth layer (24) are different from the contents of the stabilizing elements and coloring elements contained in the zirconia layer of the adjacent third layer (23), and are preferably different from the contents of the stabilizing elements and coloring elements contained in the zirconia layer of the adjacent second layer (22).

[0026] When the third region (intermediate layer) includes two or more regions, the zirconia layers are preferably stacked so that the increase / decrease trends of at least one of the translucency and color tone do not change along the stacking direction. In other words, when the third region (intermediate layer) includes multiple zirconia layers, such as a fourth layer and a fifth layer, the zirconia layers are preferably stacked so that the increase / decrease trends of at least one of the translucency and color tone do not change along the stacking direction. In particular, a structure in which the zirconia layers are stacked so that the content of at least one of the stabilizing element and the coloring element changes uniformly along the stacking direction is preferred. This allows for a gradation of translucency and color tone to be formed based on the difference in the content of at least one of the stabilizing element and the coloring element. However, in the present disclosure, as described in the sections "<First Form>" and "Second Form>" under "Features of the Laminated Structure" below, the amount of stabilizing element or the shrinkage rate of the layer located at one end of the stacked layers (i.e., one region that is the uppermost or lowermost layer in the stacking direction) is similar to the layer located at the other end (i.e., the other region that is the uppermost or lowermost layer in the stacking direction). Therefore, in the present disclosure, in a sintered body having four or more stacked zirconia layers, the layer located at one end or the layer located at the other end may exhibit an increase / decrease trend in at least one of the translucency and color tone along the stacking direction that is opposite to the increase / decrease trend of the other layers. However, this disclosure also includes such a configuration. More specifically, such a configuration can be described as (a) or (b) below. (a) When the third region includes two or more regions, the composition of the layers can be such that the increase / decrease trend in at least one of the translucency and color tone does not change along the stacking direction from the first region to the third region. That is, in FIG. 2, the composition of the layers can be such that the increase / decrease trend in at least one of the translucency and color tone does not change from the first layer (21) (corresponding to the first region) to the third layer (23) and fourth layer (24) (corresponding to the third region), which are intermediate layers. This allows for a gradation of translucency and color tone similar to that of natural teeth. A second layer (corresponding to the second region) 22 is laminated on the fourth layer 24. The second layer 22 has a stabilizing element content close to that of the first layer or a shrinkage rate close to that of the first layer.By stacking the second layer (22) having a stabilizing element content and / or shrinkage rate similar to those of the first layer, the increase / decrease in at least one of the translucency and color tone exhibited from the first layer (21) to the fourth layer (24) may be reversed in some cases. However, in such cases, when processing into a dental product shape such as a crown, the crown shape can be processed within the layering range where the desired gradation is formed. (b) When the third region includes two or more regions, the composition of the layers can be such that the increase / decrease trend in at least one of the translucency and color tone does not change along the stacking direction from the second region to the third region. In other words, in Figure 2, the composition of the layers can be such that the increase / decrease trend in at least one of the translucency and color tone does not change from the second layer (22) (corresponding to the second region) to the fourth layer (24) and the third layer (23) (corresponding to the third region), which are intermediate layers. This allows for the formation of a gradation in translucency and color tone similar to that of natural teeth. The first layer (21) (corresponding to the first region) is laminated under the third layer (23). The first layer (21) has a stabilizing element content close to that of the second layer or a shrinkage rate close to that of the second layer. Therefore, by laminating the first layer (21) having a stabilizing element content and / or shrinkage rate close to that of the second layer, the increase / decrease in at least one of the translucency and color tone exhibited from the second layer (22) to the third layer (23) may reverse in some cases. However, in such a case, when processing into the shape of a dental product such as a dental crown, adjustments may be made so that the dental crown shape is processed within the layering range where the desired gradation is formed.

[0027] <Characteristics of Laminated Structure> Preferred embodiments of the sintered body of the present disclosure include a sintered body described in the following form (A) and a sintered body described in the following form (B).

[0028] <<Configuration (A)>> In the sintered body of this embodiment, the difference between the content of the stabilizing element contained in the first region located at one end of the stacked regions and the content of the stabilizing element contained in the second region located at the other end is 2.0 mol% or less. Configuration (A) will be described with reference to FIG. 1 . Along the Y-axis direction (stacking direction) in FIG. 1 , the contents of the stabilizing element contained in the first region located at one end (e.g., the first layer (11)) and the second region located at the other end (e.g., the second layer (12)) are set to similar values ​​(specifically, 2.0 mol% or less). This balances the difference in shrinkage rate between the first layer and the second layer in the stacking direction of the sintered body, thereby suppressing warpage of the sintered body. As a result, the sintered body of this embodiment has translucency and color gradation similar to those of natural teeth, while suppressing warpage and resulting in a sintered body with minimal deformation. In this embodiment, only the relationship between the first region (e.g., the first layer (11)) located at one end and the second region (e.g., the second layer (12)) located at the other end is specified. However, by adjusting the shrinkage rates of the regions (layers) located at both ends, warpage of the sintered body can be effectively suppressed. Therefore, a zirconia layer having any composition can be laminated on each intermediate layer disposed between the first layer (11) and the second layer (12). In the sintered body of this embodiment, the difference between the content of the stabilizing element contained in the first region and the content of the stabilizing element contained in the second region is 2.0 mol% or less, and preferably 1.8 mol% or less, 1.5 mol% or less, or 0.8 mol% or less. The difference between the content of the stabilizing element contained in the first region and the content of the stabilizing element contained in the second region is preferably small, and may be, for example, 0 mol% or more, more than 0 mol%, 0.1 mol% or more, or 0.3 mol% or more. The difference may be 0 mol% or more and 2.0 mol% or less, 0 mol% or more and 1.5 mol% or less, more than 0 mol% and 1.8 mol% or less, or more than 0 mol% and 1.5 mol% or less.

[0029] In this embodiment, the content of the stabilizing element in each region (each layer) is the molar ratio of the stabilizing element converted into an oxide to the total of zirconia and the stabilizing element converted into an oxide. ２ O ３ , calcium is CaO, magnesium is MgO, cerium is CeO ２ , praseodymium Pr ６ O １１ , neodymium is Nd ２ O ３ , terbium is Tb ４ O ７ , erbium is Er ２ O ３ and ytterbium as Yb ２ O ３ For example, when yttrium and erbium are contained as stabilizing elements, the content (mol%) of the stabilizing elements is (Y ２ O ３ + Er ２ O ３ ) / (ZrO ２ +Y ２ O ３ + Er ２ O ３ ) x 100.

[0030] <<Mode (B)>> In the sintered body of this embodiment, the difference (shrinkage rate difference) between the shrinkage rate of the sintered body in a first region located at one end of the stacked regions and the shrinkage rate of the sintered body in a second region located at the other end is 0.4% or less.

[0031] The embodiment (B) will be described with reference to FIG. 1 . The shrinkage rates of the sintered body of a first region (e.g., the first layer (11)) located at one end along the Y-axis direction (stacking direction) in FIG. 1 and a second region (e.g., the second layer (12)) located at the other end are set to similar values ​​(specifically, 0.4% or less). This balances the difference in shrinkage rates between the first and second layers in the stacking direction of the sintered body, thereby suppressing warpage of the sintered body. As a result, the sintered body of this embodiment has translucency and color gradation similar to those of natural teeth, while suppressing warpage and resulting in a sintered body with little deformation. In this embodiment, only the relationship between the first region (e.g., the first layer (11)) located at one end and the second region (e.g., the second layer (12)) located at the other end is specified. However, by adjusting the shrinkage rates of the regions (layers) located at both ends, warpage of the sintered body can be effectively suppressed. Therefore, for each layer of the intermediate layer disposed between the first layer (11) and the second layer (12), a zirconia layer of any composition can be laminated. In the sintered body of this embodiment, the difference between the shrinkage rate of the sintered body in the first region and the shrinkage rate of the sintered body in the second region is 0.4% or less, and preferably 0.36% or less, 0.3% or less, or 0.2% or less. The difference between the shrinkage rate of the sintered body in the first region and the shrinkage rate of the sintered body in the second region is preferably small, and may be, for example, 0% or more, more than 0%, 0.01% or more, or 0.02% or more. The difference may be 0% or more and 0.4% or less, more than 0% and 0.36% or less, 0.0.01% or more and 0.2% or less, or 0.02% or more and 0.2% or less.

[0032] <<<<Method for Measuring Shrinkage Rate>>> The shrinkage rates of a first region (e.g., first layer (11)) located at one end and a second region (e.g., second layer (12)) located at the other end are determined as follows. A zirconia raw material powder having the same composition as the first layer (11) and the second layer (12) is filled into a mold, molded by uniaxial pressing (hereinafter also referred to as "uniaxial pressing"), and then subjected to cold isostatic pressing (hereinafter also referred to as "CIP") to form a powder composition layer, which is a sample for shrinkage rate measurement. The powder composition layer is calcined at 800°C or higher but lower than 1200°C, and then sintered at 1200°C or higher but lower than 1600°C to obtain a zirconia layer. The shrinkage rate of the zirconia layer is determined by the method described in the section "Method for Evaluating Shrinkage Rate" below.

[0033] A sample for measuring shrinkage may be prepared under the following conditions: [Sample for measuring shrinkage] Mold diameter: Φ25 mm Powder mass: 4 g Molding pressure: Uniaxial press molding: 49 MPa + CIP treatment: 196 MPa Molding process: Powder to be evaluated is placed in the mold → leveled → uniaxial press molding → CIP treatment

[0034] In the above sample production, a schematic diagram of the uniaxial press molding process is shown in Figure 3, and a schematic diagram of the CIP process is shown in Figure 4. Figure 3 shows the process of (a) putting powder (31) into a mold (32), (b) leveling the powder, and (c) compressing the powder through uniaxial press molding (33). Figure 4 shows the process of placing the uniaxially pressed powder (41) into a high-pressure vessel, filling the vessel with a solvent (42) such as water, and isotropically compressing the powder using water pressure (CIP process).

[0035] The obtained sample for shrinkage measurement is calcined under the following conditions, and then sintered. [Calcining / Sintering Conditions] Calcination is performed at 800°C or higher and lower than 1200°C, and sintering is performed at 1200°C or higher and 1600°C or lower. More detailed conditions can be selected as appropriate. Preferably, in the present disclosure, calcination and subsequent sintering are performed under the following conditions: Calcination: From room temperature to 300°C at 15°C / hour, held at 300°C for 5 hours, from 300°C to 700°C at 15°C / hour, held at 700°C for 1 hour, from 700°C to 1000°C at 50°C / hour, held at 1000°C for 2 hours, and then cooled in the furnace. Sintering: From room temperature to 1500°C at 100°C / hour, held at 1500°C for 2 hours, and then cooled in the furnace.

[0036] The shrinkage rate is measured for the sintered sample for shrinkage rate measurement obtained as described above. [Method for evaluating shrinkage rate] The diameter of the sintered sample for shrinkage rate measurement (hereinafter also referred to as "sample diameter") is measured using a vernier caliper. The sample diameter can be determined by measuring the diameter of each sample for shrinkage rate measurement at four points using the vernier caliper, and taking the average of the measured values ​​as the sample diameter. The shrinkage rate is calculated using the following formula (1): Shrinkage rate (%) = (mold diameter: Φ25 mm - sample diameter) / mold diameter: Φ25 mm x 100 (1) For example, if the sample diameter is 24 mm, the shrinkage rate is (25 - 24) / 25 x 100 = 4%.

[0037] <Composition of Zirconia Layer> The sintered body of this embodiment is composed of a zirconia layer containing zirconia containing a stabilizing element, and, if a coloring element is contained, the coloring element. The zirconia layer is a layer containing zirconia as a main component, and the zirconia is zirconia containing a stabilizing element. The sintered body and zirconia layer (sintered body layer) of this embodiment contain not only the stabilizing element zirconia and the coloring element, but also hafnia (HfO ２ The content of hafnia as an inevitable impurity varies greatly depending on the raw material ore and the manufacturing method, but can be, for example, 2.0 mass % or less. In this embodiment, values ​​related to the composition, such as the content and density, are calculated by assuming that hafnia is replaced with zirconia (ZrO ２ ) can be considered for calculation.

[0038] In the sintered body of this embodiment, the zirconia is preferably zirconia obtained by heat-treating a zirconia sol and then sintering the zirconia, more preferably zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of a zirconium compound and then sintering the zirconia, and even more preferably zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of zirconium oxychloride and then sintering the zirconia. The zirconia contained in the zirconia layer may be sintered zirconia, i.e., zirconia crystal particles.

[0039] <<Stabilizing Element>> The stabilizing element may be any element that has the function of suppressing the phase transition of zirconia. Examples of the stabilizing element include at least one of an element that does not have the function of coloring zirconia but has the function of suppressing the phase transition (hereinafter also referred to as a "non-coloring stabilizing element") and an element that has the function of coloring zirconia and has the function of suppressing the phase transition (hereinafter also referred to as a "coloring stabilizing element"). The stabilizing element may be either a non-coloring stabilizing element or a coloring stabilizing element, and preferably contains at least a non-coloring stabilizing element. Specific examples of the stabilizing element include one or more elements selected from the group consisting of yttrium (Y), calcium (Ca), magnesium (Mg), cerium (Ce), praseodymium (Pr), neodymium (Nd), terbium (Tb), erbium (Er), and ytterbium (Yb). Examples of the non-coloring stabilizing element include one or more elements selected from the group consisting of yttrium, calcium, magnesium, and cerium. At least one of yttrium and cerium is preferred, and yttrium is more preferred. Examples of the color stabilizing element include one or more selected from the group consisting of praseodymium, neodymium, terbium, erbium, and ytterbium, and at least one of terbium and erbium is preferred. Preferred stabilizing elements include one or more selected from the group consisting of yttrium, terbium, and erbium, such as yttrium, terbium, and erbium, or at least one of terbium and erbium and yttrium, or erbium and yttrium, or yttrium. The stabilizing element is contained in zirconia and is in a solid solution state in zirconia. Furthermore, it is preferred that the sintered body of this embodiment does not contain an undissolved stabilizing element, that is, does not contain a stabilizing element that is not solid-dissolved in zirconia. In this embodiment, "not containing an undissolved stabilizing element" means that no XRD peaks derived from the stabilizing element are confirmed in the XRD measurement and XRD pattern analysis described below, and it is acceptable to contain an undissolved stabilizing element to the extent that no XRD peaks derived from the stabilizing element are confirmed.

[0040] In the sintered body of this embodiment, the content of the stabilizing element in the stabilizing-element-containing zirconia contained in each layer (corresponding to each region) can be, for example, a lower limit of 1.5 mol% or more, 2.5 mol% or more, 3.0 mol% or more, 3.5 mol% or more, or 4.0 mol% or more, and an upper limit of 7.0 mol% or less, 6.0 mol% or less, or 5.0 mol% or less. Any combination of these upper and lower limits is acceptable. Therefore, the content of the stabilizing element in the stabilizing-element-containing zirconia contained in each layer (corresponding to each region) of this embodiment can be, for example, 1.5 mol% or more and 7.0 mol% or less, 2.5 mol% or more and 6.0 mol% or less, or 3.0 mol% or more and 6.0 mol% or less.

[0041] For example, taking the sintered body of FIG. 1 as an example, the content of the stabilizing element in the stabilizing-element-containing zirconia contained in the first layer (corresponding to the first region) (11) and the second layer (corresponding to the second region) (12) is preferably, for example, 1.5 mol% or more or 2.5 mol% or more as the lower limit, and preferably 6.0 mol% or less or 5.5 mol% or less as the upper limit. Any combination of these upper and lower limits is acceptable. Therefore, the content of the stabilizing element in the stabilizing-element-containing zirconia contained in the first layer (corresponding to the first region) (11) and the second layer (corresponding to the second region) (12) of this embodiment may be 1.5 mol% or more and 6.0 mol% or less, or 2.5 mol% or more and 5.5 mol% or less. In the sintered body of FIG. 1 , the content of the stabilizing element in the stabilizing-element-containing zirconia contained in the third layer (corresponding to the third region) (13) is, for example, preferably 2.5 mol% or more or 3.0 mol% or more as the lower limit, and preferably 7.0 mol% or less or 6.0 mol% or less as the upper limit. Any combination of these upper and lower limits is acceptable. Therefore, the content of the stabilizing element in the stabilizing-element-containing zirconia contained in the third layer (corresponding to the third region) (13) of this embodiment may be 2.5 mol% or more and 7.0 mol% or less, or 3.0 mol% or more and 6.0 mol% or less. In FIG. 1 , the difference in the content of the stabilizing element between adjacent layers is preferably 0.01 mol% or more, or even 0.2 mol% or more, or even 0.3 mol% or more, or even 0.5 mol% or more, or even 0.7 mol% or more, or even 1.0 mol% or more, or even 1.2 mol% or more. The greater the difference in the stabilizing element content, the greater the difference in translucency between the zirconia layers tends to be, but warping may also increase. If the difference in the stabilizing element content between adjacent layers is less than 2.5 mol%, further 2.0 mol% or less, or even 1.7 mol% or less, the change in translucency of the sintered body is likely to be equivalent to that of natural teeth. Examples of the difference in the stabilizing element content between adjacent layers include 0.01 mol% or more and less than 2.5 mol%, 0.2 mol% or more and 2.0 mol% or less, 0.3 mol% or more and 1.7 mol% or less, or even 0.5 mol% or more and 1.7 mol% or less.

[0042] Taking the sintered body of FIG. 2 as an example, the content of the stabilizing element in the stabilizing-element-containing zirconia contained in the first layer (corresponding to the first region) (21) and the second layer (corresponding to the second region) (22) is preferably, for example, 1.5 mol % or more or 2.5 mol % or more in lower limit, and 7.0 mol % or less or 6.0 mol % or less in upper limit. Any combination of these upper and lower limits is acceptable. Therefore, the content of the stabilizing element in the stabilizing-element-containing zirconia contained in the first layer (corresponding to the first region) (21) and the second layer (corresponding to the second region) (22) of this embodiment is preferably 1.5 mol % or more and 7.0 mol % or less, or 2.5 mol % or more and 6.0 mol % or less. The stabilizing element content of the stabilizing element-containing zirconia contained in the intermediate layers, i.e., the third layer (corresponding to the third region) (23) and the fourth layer (corresponding to the third region) (24) in the sintered body of FIG. 2 , is preferably, for example, 2.0 mol% or more or 2.5 mol% or more as the lower limit, and 6.0 mol% or less or 5.5 mol% or less as the upper limit. Any combination of these upper and lower limits is acceptable. Therefore, the stabilizing element content of the stabilizing element-containing zirconia contained in the third layer (corresponding to the third region) (23) and the fourth layer (corresponding to the third region) (24) of this embodiment is preferably 2.0 mol% or more and 6.0 mol% or less, or 2.5 mol% or more and 5.5 mol% or less. In Figure 2, the difference in the content of the stabilizing element between adjacent layers is preferably 0.01 mol% or more, further 0.2 mol% or more, further 0.3 mol% or more, further 0.5 mol% or more, further 0.7 mol% or more, further 1.0 mol% or more, or further 1.2 mol% or more. As the difference in the content of the stabilizing element increases, the difference in translucency between the zirconia layers tends to increase, but warping may also increase. If the difference in the content of the stabilizing element between adjacent layers is 2.5 mol% or less, less than 2.5 mol%, further 2.0 mol% or less, or further 1.7 mol% or less, the change in translucency of the sintered body is likely to be equivalent to that of natural teeth.The difference in the content of the stabilizing element between adjacent layers can be, for example, 0.01 mol% or more and 2.5 mol% or less, 0.01 mol% or more and less than 2.5 mol%, 0.2 mol% or more and 2.0 mol% or less, 0.3 mol% or more and 1.7 mol% or less, or even 0.5 mol% or more and 1.7 mol% or less, or 1.2 mol% or more and 1.7 mol% or less.

[0043] The stabilizing element content of the sintered body is calculated using the following formula, and varies depending on the thickness of each zirconia layer: stabilizing element content of sintered body = (thickness of first layer / height of sintered body) × stabilizing element content of first layer + (thickness of second layer / height of sintered body) × stabilizing element content of second layer + ... + (thickness of nth layer / height of sintered body) × stabilizing element content of nth layer In this embodiment, the stabilizing element content is the molar ratio of the stabilizing element to the total of zirconia and the stabilizing element, as described above. In calculating the stabilizing element content, the content of each stabilizing element may be calculated in terms of the oxide described above.

[0044] <<Coloring Element>> The coloring element in this embodiment is an element that has the function of coloring zirconia. Specific examples of the coloring element include at least one of a transition metal element and a lanthanoid rare earth element, preferably at least one selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), titanium (Ti), praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd), terbium (Tb), erbium (Er), and ytterbium (Yb), more preferably at least one selected from the group consisting of iron, cobalt, manganese, titanium, praseodymium, gadolinium, terbium, and erbium, and even more preferably at least one selected from the group consisting of iron, cobalt, titanium, terbium, and erbium. The coloring element contained in the sintered body of this embodiment may be at least one of a coloring element contained in an oxide state (hereinafter also referred to as an "oxide coloring element") and a coloring element contained in a solid solution state in zirconia, such as a color stabilizing element. Preferred oxide coloring elements include one or more selected from the group consisting of iron, cobalt, nickel, manganese, and titanium, and more preferably one or more selected from the group consisting of iron, cobalt, and titanium. The sintered body of this embodiment may contain two or more coloring elements, for example, two to five, or even three to four, coloring elements. The sintered body of this embodiment preferably contains at least a color stabilizing element, more preferably at least terbium or erbium, and even more preferably at least terbium and erbium. The type and content of the coloring element contained in each zirconia layer may be appropriately selected taking into account the shrinkage rate of each layer, etc. The content of the coloring element in the sintered body of this embodiment, expressed as the mass ratio of the coloring element converted to an oxide relative to the mass of the sintered body of this embodiment, has a lower limit exceeding 0 mass%, preferably 0.01 mass% or more, 0.03 mass% or more, or 0.04 mass% or more, and an upper limit of 2.0 mass% or less, 0.8 mass% or less, or 0.3 mass% or less. Any combination of these upper and lower limits is possible.Therefore, the content of the coloring element in the sintered body of this embodiment, expressed as the mass ratio of the coloring element converted to an oxide relative to the mass of the sintered body of this embodiment, can be, for example, more than 0 mass% to 2.0 mass% or less, 0.01 mass% to 1.2 mass% or less, 0.03 mass% to 0.8 mass% or less, or 0.04 mass% to 0.3 mass% or less. For example, when yttrium (a non-coloring stabilizing element) and erbium (a coloring stabilizing element) are contained as stabilizing elements, and alumina and cobalt (oxide coloring elements) are also contained, the content (mass%) of the coloring element is (Co. ３ O ４ + Er ２ O ３ ) / (ZrO ２ +Y ２ O ３ + Er ２ O ３ +Co ３ O ４ +Al ２ O ３ ) × 100. The oxide equivalent of the coloring element is praseodymium, ６ O １１ , neodymium is Nd ２ O ３ , terbium is Tb ４ O ７ , erbium is Er ２ O ３ and ytterbium as Yb ２ O ３ , iron as Fe ２ O ３ , Cobalt ３ O ４ , nickel is NiO, manganese is Mn ３ O ４ and titanium as TiO ２ This can be done as follows.

[0045] The content of the coloring element in the sintered body layer of this embodiment is, for example, the mass ratio of the coloring element, calculated as an oxide, relative to the mass of the sintered body of this embodiment. The lower limit is preferably greater than 0 mass%, and is 0.01 mass% or more, 0.03 mass% or more, or 0.04 mass% or more. The upper limit is preferably 2.0 mass% or less, 1.2 mass% or less, 0.8 mass% or less, or 0.3 mass% or less. Any combination of these upper and lower limits is acceptable. Therefore, the mass ratio of the coloring element, calculated as an oxide, relative to the mass of the sintered body of this embodiment may be greater than 0 mass% to 2.0 mass% or less, 0.01 mass% to 1.2 mass%, 0.03 mass% to 0.8 mass% or less, or 0.04 mass% to 0.3 mass%. For example, taking the sintered body of FIG. 1 as an example, the content of the coloring element in the coloring element-containing zirconia contained in the first layer (corresponding to the first region) (11) and the second layer (corresponding to the second region) (12) can have a lower limit of 0.01 mass % or more, 0.05 mass % or more, or 0.1 mass % or more, and an upper limit of 2.0 mass % or less or 1.2 mass % or less. These upper and lower limits may be in any combination. Therefore, the content of the coloring element in the coloring element-containing zirconia contained in the first layer (corresponding to the first region) (11) and the second layer (corresponding to the second region) (12) of this embodiment can be 0.01 mass % or more and 2.0 mass % or less, or 0.05 mass % or more and 1.2 mass % or less. In the sintered body of FIG. 1 , the content of the coloring element in the coloring element-containing zirconia contained in the third layer (corresponding to the third region) (13) is, for example, preferably 0.001 mass% or more or 0.1 mass% or more as a lower limit, and more preferably 2.0 mass% or less or 1.2 mass% or less as an upper limit. Any combination of these upper and lower limits is acceptable. Therefore, the content of the coloring element in the coloring element-containing zirconia contained in the third layer (corresponding to the third region) (13) of this embodiment may be 0.001 mass% or more and 2.0 mass% or less, or 0.1 mass% or more and 1.2 mass% or less. In FIG. 1 , the difference in the content of the coloring element between adjacent layers is preferably 0.002 mass% or more, 0.005 mass% or more, 0.01 mass% or more, 0.015 mass% or more, or 0.02 mass% or more.The greater the difference in coloring element content, the greater the difference in color tone between the zirconia layers tends to be, but warping may also increase. If the difference in the coloring element content between adjacent layers is 1% by mass or less, further 0.8% by mass or less, or even 0.5% by mass or less, the color change of the sintered body is likely to be similar to that of natural teeth. The difference in the coloring element content between adjacent layers is preferably 0.002% by mass or more and 1% by mass or less, 0.005% by mass or more and 0.8% by mass or less, 0.01% by mass or more and 0.5% by mass or less, 0.015% by mass or more and 0.5% by mass or less, or 0.02% by mass or more and 0.5% by mass or less.

[0046] Taking the sintered body of FIG. 2 as an example, the content of the coloring element in the coloring element-containing zirconia contained in the first layer (corresponding to the first region) (21) and the second layer (corresponding to the second region) (22) is, for example, preferably 0.01 mass% or more, 0.05 mass% or more, or 0.1 mass% or more, and preferably 2.0 mass% or less or 1.2 mass% or less. Any combination of these upper and lower limits is acceptable. Therefore, the content of the coloring element in the coloring element-containing zirconia contained in the first layer (corresponding to the first region) (21) and the second layer (corresponding to the second region) (22) of this embodiment may be 0.01 mass% or more and 2.0 mass% or less, or 0.05 mass% or more and 1.2 mass% or less. The coloring element content of the coloring element-containing zirconia contained in the intermediate layers, i.e., the third layer (corresponding to the third region) (23) and the fourth layer (corresponding to the third region) (24) in the sintered body of FIG. 2 , is preferably 0.001% by mass or more or 0.1% by mass or more, and preferably 2.0% by mass or less or 1.2% by mass or less. Any combination of these upper and lower limits is acceptable. Therefore, the coloring element content of the coloring element-containing zirconia contained in the third layer (corresponding to the third region) (23) and the fourth layer (corresponding to the third region) (24) of this embodiment may be 0.001% by mass or more and 2.0% by mass or less, or 0.1% by mass or more and 1.2% by mass or less. In Figure 2, the difference in the content of the coloring element between adjacent layers is preferably 0.001% by mass or more, 0.002% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more. As the difference in the content of the coloring element increases, the difference in color tone between the zirconia layers tends to increase, but warping may also increase. If the difference in the content of the coloring element between adjacent layers is 1% by mass or less, further 0.8% by mass or less, or even 0.5% by mass or less, the color change of the sintered body is likely to be similar to that of natural teeth. The difference in the content of the coloring element between adjacent layers is preferably 0.002% by mass or more to 1% by mass or less, 0.005% by mass or more to 0.8% by mass or less, 0.01% by mass or more to 0.5% by mass or less, 0.015% by mass or more to 0.5% by mass or less, or 0.02% by mass or more to 0.5% by mass or less.

[0047] The sintered body of this embodiment may contain alumina, and preferably at least one zirconia layer contains alumina. The alumina content of the sintered body of this embodiment may be 0% by mass or more, expressed as a ratio of the mass of alumina to the mass of the sintered body, and may be 0% by mass or more and 0.15% by mass or less, further 0% by mass or more and 0.10% by mass or less, or even 0% by mass or more and 0.07% by mass or less. When alumina is contained, for example, the lower limit of the alumina content is greater than 0% by mass, preferably 0.005% by mass or more or 0.01% by mass or more, and the upper limit of the alumina content is 0.15% by mass or less, 0.10% by mass or less, or 0.07% by mass or less. These upper and lower limits may be in any combination. Therefore, the alumina content may be, for example, greater than 0% by mass and 0.15% by mass or less, 0.005% by mass or more and 0.10% by mass or less, or 0.01% by mass or more and 0.07% by mass or less. The alumina content of each zirconia layer may be within the same range as described above. The alumina content of each zirconia layer may affect the thermal shrinkage behavior during the calcination step. The alumina content of each zirconia layer is arbitrary, and although the alumina contents of the zirconia layers may differ, it is preferable that the alumina contents are equal. When the alumina contents of the zirconia layers differ from each other, for example, the lower limit of the difference in alumina content between adjacent zirconia layers may be greater than 0 mass% or even 0.005 mass% or more, and the upper limit of the difference in alumina content between adjacent zirconia layers may be 0.15 mass% or less, 0.1 mass% or less, 0.03 mass% or less, or 0.01 mass% or less. These upper and lower limits may be in any combination. Therefore, the difference in alumina content between adjacent zirconia layers may be greater than 0 mass% but not more than 0.15 mass%, greater than 0 mass% but not more than 0.1 mass%, greater than 0 mass% but not more than 0.03 mass%, or 0.005 mass% or more but not more than 0.01 mass%. For example, alumina (Al ２ O ３ ) and the non-coloring stabilizing element is yttrium (Y ２ O ３ ) and the color stabilizing element is erbium (Er ２ O ３In the case of a zirconia layer made of zirconia in which the alumina content is {Al ２ O ３ / (ZrO ２ +Y ２ O ３ + Er ２ O ３ +Al ２ O ３ )}×100 (mass %). The sintered body of this embodiment is substantially composed of silica (SiO ２ It is preferable that the silica content is below the detection limit.

[0048] The sintered body of this embodiment preferably includes at least a zirconia layer containing zirconia having at least one of a tetragonal (T phase) and a cubic (C phase) crystal phase, more preferably includes at least a zirconia layer containing zirconia having a tetragonal crystal phase as the main phase, and even more preferably includes a zirconia layer containing zirconia having a tetragonal crystal phase as the main phase and a zirconia layer containing zirconia having a cubic crystal phase as the main phase. Note that the "main phase" in this embodiment refers to the crystal phase with the highest abundance (proportion of peak integrated intensity) among the zirconia crystal phases. The abundance can be determined from the XRD pattern of the sintered body surface. The following conditions can be exemplified as measurement conditions for the XRD pattern of the sintered body surface. Radiation source: CuKα radiation (λ=1.541862 Å) Measurement mode: Continuous scan Scan speed: 4° / min Measurement range: 2θ=26° to 33° Acceleration voltage / current: 40 mA / 40 kV Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185 mm The obtained XRD pattern is smoothed and background removed, and profile fitted using a split pseudo-Voigt function to determine the proportion of tetragonal and cubic crystals (proportion of integrated peak intensity), and the crystal phase with the highest proportion can be determined as the main phase. Measurement and fitting of the XRD pattern can be performed using a general-purpose powder X-ray diffractometer (e.g., Ultima IV, manufactured by RIGAKU Corporation) and an analysis program attached to the X-ray diffractometer (e.g., integrated powder X-ray analysis software PDXL Ver. 2.2, manufactured by RIGAKU Corporation).

[0049] <Characteristics of the sintered body and each zirconia layer (each sintered body layer) constituting the sintered body> The sintered body (100) in FIG. 1 shows the first layer, the third layer, and the second layer as having approximately the same thickness. However, in the sintered body of this embodiment, the thickness of each layer (hereinafter also referred to as "layer thickness") may be different, and any of the first to third layers may have a thicker layer thickness. For example, the lower limit of the layer thickness of the first to third layers may be 1 mm or more, further 2 mm or more, or even 3 mm or more, and the upper limit of the layer thickness may be 20 mm or less, further 15 mm or less, or even 10 mm or less. Any combination of these upper and lower limits may be used. Therefore, the layer thickness of the first to third layers may be, for example, 1 mm or more and 20 mm or less, further 2 mm or more and 15 mm or less, or even 3 mm or more and 10 mm or less. More specifically, in the sintered body of Fig. 1, the thickness of the first layer is preferably 0.5 mm to 10 mm, the thickness of the second layer is preferably 0.5 mm to 10 mm, and the thickness of the third layer is preferably 1 mm to 20 mm. Also, in the sintered body of Fig. 2, the thickness of the first layer is preferably 0.5 mm to 10 mm, and the thickness of the second layer is preferably 0.5 mm to 10 mm. The thickness of each layer in the intermediate layer is preferably 1 mm to 10 mm.

[0050] The shape of the sintered body of this embodiment may be any shape depending on the purpose, including at least one selected from the group consisting of spherical, elliptical, discoid, cylindrical, cubic, rectangular, and polyhedral shapes, shapes suitable for dental materials such as dental prosthetic materials for crowns, bridges, onlays, and onlays, and any other shape depending on the intended use. In this embodiment, "spherical" includes shapes similar to a perfect sphere other than a perfect sphere, such as an approximately spherical shape, and "polyhedral" includes shapes similar to a polyhedron, such as an approximately polyhedral shape, in addition to a polyhedron. The dimensions of the sintered body of this embodiment are arbitrary, and examples include a length of 10 mm to 120 mm, a width of 12 mm to 120 mm, and a height of 6 mm to 40 mm. The thickness of the sintered body of this embodiment in the stacking direction, i.e., the height of the sintered body, is also arbitrary, but may be, for example, 4 mm to 40 mm, or even 5 mm to 30 mm.

[0051] <<Warpage and Deformation of Sintered Body>> The sintered body of this embodiment preferably has a warpage (hereinafter simply referred to as "warpage") of 1.0 mm or less, as measured using a thickness gauge (hereinafter simply referred to as "gauge") in accordance with JIS B 7524:2008. A sintered body having a structure including three or more zirconia layers warps in the stacking direction (or the opposite direction to the stacking direction) upon sintering. When such a sintered body is placed on a horizontal plate, a gap is formed between the sintered body and the horizontal plate. The warpage in this embodiment is a value measured using a gauge. The warpage of the sintered body of this embodiment is preferably 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, or 0.05 mm or less. Preferably, the sintered body has no warpage (warpage of 0 mm), but the sintered body of this embodiment may have a warpage that cannot be measured with a gauge (warpage of 0 mm or more). The sintered body of this embodiment may have a warpage of more than 0 mm, or even 0.01 mm or more, for example. The warpage is preferably 0.06 mm or less, more preferably 0.05 mm or less, and even less than the measurement limit (less than 0.03 mm). The warpage can be measured by the maximum thickness of a gauge that can be inserted into a gap formed when the convex portion of the sintered body is placed in contact with a horizontal plate. The warpage of the sintered body of this embodiment may be 0 mm or more and 0.3 mm or less, 0 mm or more and 0.05 mm or less, 0 mm or more and less than 0.03 mm, or more than 0 mm and less than 0.03 mm.

[0052] FIG. 5 is a schematic diagram illustrating a method for measuring warpage. The sintered body (500) shows a cross section of a disk-shaped sample, warped in the stacking direction (Y-axis direction). For ease of explanation, FIG. 5 emphasizes the warpage of the sintered body (500). As shown in FIG. 5, when measuring warpage, the sintered body (500) is positioned so that the convex portions of the uneven sintered body (500) are in contact with the horizontal plate (51). This creates a gap between the contact surface (hereinafter referred to as the "bottom surface") between the sintered body (500) and the horizontal plate (51) and the horizontal plate (51). A gauge is inserted into the gap, and the maximum thickness of the gauge that can be inserted is used to measure warpage. In FIG. 5, the gauge (52A) is positioned below the bottom surface of the sintered body (500) and is inserted into the gap. Meanwhile, the gauge (52B) is not positioned below the bottom surface of the sintered body (500) and is not inserted into the gap. The gauges (52A) and (52B) in Fig. 5 are gauges differing in thickness by one step (for example, 0.01 mm), and the warpage of the sintered body (500) corresponds to the thickness of the gauge (52A). For ease of explanation, Fig. 5 shows both the gauges (52A) and (52B) inserted, but the warpage can be measured by inserting the gauges into the gaps in order from the thinnest gauge (for example, after measurement using the gauge (52A), it can be removed and then measurement can be performed using the thicker gauge (52B)).

[0053] The sintered body of this embodiment preferably has a warpage (hereinafter also referred to as "deformation") relative to the dimensions of the sintered body of 1.0 or less, 0.5 or less, 0.2 or less, or 0.15 or less. The deformation amount can be, for example, 0 or more, 0.01 or more, or even 0.05 or more. The deformation amount may be 0 or more to 1.0 or less, 0 or more to 0.15 or less, 0.01 or more to 1.0 or less, or 0.05 or more to 0.15 or less. The deformation amount can be calculated using the following formula (2): Deformation amount = (warpage: mm) / (sintered body dimensions: mm) × 100 (2) The dimensions of the sintered body are the size of the sintered body in a direction perpendicular to the warpage direction. Since the sintered body (500) in FIG. 5 is aligned along the stacking direction (Y-axis direction), the dimensions of the sintered body (500) are the size (53) of the sintered body in the horizontal direction (X-axis direction) perpendicular to the stacking direction. The dimensions can be measured using a known measurement method using a vernier caliper, micrometer, or the like. For example, in the case of a disc-shaped or cylindrical laminate, the dimensions of the sintered body refer to the diameter of the sintered body. In the case of a disc-shaped or cylindrical laminate, the dimensions of the sintered body can be measured using a vernier caliper. For example, the diameter of the top end and the diameter of the bottom end are measured at four points each, the average of the top and bottom end diameters is calculated, and the average of the calculated values ​​is used as the dimensions of the laminate. In this embodiment, the warpage and deformation amount are preferably measured using a disc-shaped sample, and more preferably using a disc-shaped sample with a diameter of 5 mm to 120 mm. For example, if the diameter of the sintered body is 105 mm and the warpage is 0.2 mm, the deformation amount is 0.2 / 105 × 100 = 0.19.

[0054] <<Density of Sintered Body>> The sintered body of this embodiment has a density of 5.7 g / cm3 or less, as measured by a method according to JIS R 1634. ３ or more than 5.9 g / cm ３ or more, and the upper limit of the density is 6.3 g / cm ３ or less than 6.1 g / cm ３ The density of the sintered body of this embodiment can be, for example, 5.7 g / cm or less. Any combination of these upper and lower limits is acceptable. ３ 6.3g / cm or more ３Preferably, it is 5.9 g / cm or less. ３ 6.1g / cm or more ３ The density in this range corresponds to a relative density of 99% or more, and is a density that results in a so-called dense sintered body having practical strength.

[0055] <<Color Tone of Sintered Body or Sintered Body Layer>> The color tone of the sintered body or each zirconia layer (each sintered body layer) of this embodiment may be, for example, L ＊ a ＊ b ＊ The color tone of the sintered body of this embodiment or each zirconia layer (each sintered body layer) can be evaluated by the color tone according to a color system. ＊ a ＊ b ＊ Lightness L indicated by the color system ＊ The lower limit of the lightness L ＊ The upper limit of hue a is 80 or less or 70 or less, ＊ The lower limit of hue a is -5 or more or -3 or more, ＊ The upper limit of the hue b is 15 or less or 10 or less, and ＊ The lower limit of hue b is 0 or more or 3 or more, ＊ The upper limit value of the zirconia layer (each sintered body layer) may be 45 or less or 35 or less. Any combination of these upper limit values ​​and lower limit values ​​is acceptable. Therefore, the color tone of the sintered body of this embodiment or each zirconia layer (each sintered body layer) is L ＊ a ＊ b ＊ Lightness L indicated by the color system ＊ is 50 or more and 80 or less, or 55 or more and 70 or less, and hue a ＊ is -5 or more and 15 or less, or -3 or more and 10 or less, and hue b ＊ is, for example, from 0 to 45, or from 3 to 35. When the color tone is in this range, the sintered body exhibits a color tone similar to that of natural teeth.

[0056] Since the sintered body of this embodiment has a change in color tone, the saturation C ＊ It is preferable that the saturation C ＊ is an index of vividness, and L ＊ a＊ b ＊ Hue a shown in the color system ＊ and b ＊ From C ＊ = {(a ＊ ) ２ +(b ＊ ) ２} ０．５ The chroma between adjacent layers, C ＊ The absolute value of the difference (△C ＊ ) is 0.1 or more, 0.3 or more, 1.0 or more, or 1.5 or more, and the absolute value (ΔC ＊ ) may be 20.0 or less, 15.0 or less, 10.0 or less, or 5.0 or less. Any combination of these upper and lower limits may be used. Therefore, in the sintered body of this embodiment, the chroma C ＊ The absolute value of the difference (△C ＊ ) can be, for example, 0.1 or more and 20.0 or less, 0.3 or more and 15.0 or less, 1.0 or more and 10.0 or less, or 1.5 or more and 5.0 or less. ＊ When the lightness L between adjacent layers is in this range, the laminate can be visually recognized as having a gradation of vividness similar to that of natural teeth. ＊ The absolute value of the difference (ΔL ＊ ) is 1.0 or more, further 1.5 or more, and the absolute value (ΔL ＊ ) is preferably 30.0 or less, and more preferably 15.0 or less. Any combination of these upper and lower limits is acceptable. Therefore, the sintered body of this embodiment has a lightness L ＊ The absolute value of the difference (ΔL ＊ ) is, for example, 1.0 or more and 30.0 or less, and further 1.5 or more and 15.0 or less. ＊ , a ＊ and b ＊ ) and C ＊ can be determined using a colorimetric color difference meter (for example, ZE6000, manufactured by Nippon Denshoku Industries Co., Ltd.) equipped with an illumination / light-receiving optical system conforming to the geometric condition c of JIS Z 8722. ＊Specific measurement conditions for the method of placing a zero calibration box on the measurement sample (so-called black background measurement) include the following conditions: The color tone of the sintered body of this embodiment can be measured by cutting out any part of the sintered body horizontally and processing it to a sample thickness of 2.8±0.1 mm. Light source: D65 light source Viewing angle: 2° Measurement method: SCI

[0057] <<Transmittance of Sintered Body or Sintered Body Layer>> The sintered body of this embodiment preferably includes at least a translucent zirconia layer. Furthermore, it is preferable that the sintered body has at least a zirconia layer having a total luminous transmittance (hereinafter simply referred to as "total luminous transmittance") of 15% or more, 20% or more, 30% or more, 32% or more, or 35% or more relative to CIE standard illuminant D65 at a sample thickness of 1.0±0.1 mm, and an upper limit of 50% or less, 45% or less, or 42% or less. Any combination of these upper and lower limits is acceptable. Therefore, the sintered body of this embodiment preferably has a zirconia layer having a total luminous transmittance of, for example, 15% or more and 50% or less, further 20% or more and 45% or less, or even 32% or more and 42% or less. The sintered body of this embodiment absorbs different wavelengths of light depending on its color. Therefore, the total luminous transmittance for light containing different wavelengths, such as CIE standard illuminant D65, is suitable as an indicator of translucency. In the sintered body of this embodiment, the lower limit of the difference in total light transmittance between adjacently stacked zirconia layers is preferably 1% or more or 1.5% or more, and the upper limit of the difference in total light transmittance is preferably 10% or less or 5% or less. Any combination of these upper and lower limits may be used. Therefore, in the sintered body of this embodiment, the difference in total light transmittance between adjacently stacked zirconia layers is preferably, for example, 1% or more and 10% or less, or 1.5% or more and 5% or less.

[0058] The total luminous transmittance can be measured by a method conforming to JIS K 7361, using CIE standard illuminant D65 as incident light, and can be determined as the transmittance value obtained by adding up the diffuse transmittance and linear transmittance for the incident light. A sample is cut out horizontally from any location of the sintered body, and the cut out sample is adjusted to a thickness of 1.0±0.1 mm and a surface roughness (Ra)≦0.02 μm. The sample is irradiated with light from the CIE standard illuminant D65 using a general turbidity meter (e.g., NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.), and the transmitted light is collected using an integrating sphere to measure the transmittance (diffuse transmittance and linear transmittance) of the sample, which can be used as the total luminous transmittance.

[0059] <<Three-point bending strength of sintered body layer>> The three-point bending strength of each zirconia layer (each sintered body layer) in the sintered body of this embodiment, measured by a method conforming to JIS R 1601, is preferably 500 MPa or more, 550 MPa or more, or 600 MPa or more. The three-point bending strength can be, for example, less than 1200 MPa, or even 1160 MPa or less. Preferred three-point bending strengths are 500 MPa or less and 1200 MPa or less, 550 MPa or more and 1160 MPa or less, or 600 MPa or more and 1160 MPa or less. FIG. 6 is a schematic diagram showing how the three-point bending strength of the zirconia layer (sintered body layer) (600) is measured. In FIG. 6, the Y-axis direction represents the stacking direction, and the X-axis direction represents the horizontal direction. The measurement sample used for measuring the three-point bending strength is a rectangular parallelepiped sintered body prepared with the thickness as the stacking direction and the width and length as the horizontal directions. As shown in Fig. 6, the three-point bending strength may be measured by applying a load (61) perpendicular to the length of the measurement sample (600). The measurement sample may be positioned so that the load (61) is applied to the middle of the support distance (62). The three-point bending strength is measured using a columnar sintered body having a support distance of 30 mm, a width of 4 mm, and a thickness of 3 mm as the measurement sample, and the crosshead speed is 0.5 mm / min. The average value of 10 measurements may be used as the three-point bending strength of the zirconia layer (sintered body layer) according to this embodiment.

[0060] Next, the calcined body will be described below, focusing on the differences from the sintered body described above.

[0061] (Calcined Body) The calcined body according to this embodiment is a calcined body of a zirconia composition, wherein the zirconia composition contains (iii) a stabilizing element-containing zirconia composition having a necking structure, or (iv) a zirconia composition containing stabilizing element-containing zirconia having a necking structure and a coloring element. The calcined body has three or more regions stacked in layers, and adjacent two of the regions have different contents of at least one of the stabilizing element and the coloring element, and the difference between the content of the stabilizing element contained in a first region located at one end of the stacked regions and the content of the stabilizing element contained in a second region located at the other end of the stacked regions is 2.0 mol% or less. Another form of the calcined body according to this embodiment is a calcined body of a zirconia composition, wherein the zirconia composition contains (iii) a stabilizing element-containing zirconia composition having a necking structure, or (iv) a zirconia composition containing stabilizing element-containing zirconia having a necking structure and a coloring element. The calcined body has three or more regions stacked in layers, and two adjacent regions among the regions have different contents of at least one of a stabilizing element and a coloring element, and the difference (shrinkage rate difference) between the shrinkage rate of the calcined body of a first region located at one end of the stacked regions and the shrinkage rate of the calcined body of a second region located at the other end is 0.4% or less.

[0062] The calcined body is a laminate consisting of a structure having a necking structure, i.e., so-called calcined particles. The calcined body can be processed as needed and used as a precursor to a sintered body, and is also called a pre-sintered body, soft sintered body, or semi-sintered body. The necking structure is a structure possessed by zirconia heat-treated below the sintering temperature, in which zirconia particles are chemically adhered to each other. As shown in FIG. 7 , the zirconia (71) contained in the zirconia composition layer of the calcined body is a structure in which the particle shape of zirconia in the powder composition can be partially confirmed. In this embodiment, the structure having the necking structure is a structure consisting of zirconia in the early stage of sintering. This is different from the sintered structure, i.e., a structure consisting of zirconia crystal particles in the later stage of sintering. Therefore, the calcined body of this embodiment can also be considered a laminate including three or more zirconia composition layers each including zirconia particles having a necking structure of zirconia containing a stabilizing element, or, if a coloring element is included, a zirconia composition layer containing zirconia particles having a necking structure of zirconia containing a stabilizing element and a coloring element. Instead of a zirconia layer, the calcined body includes a zirconia composition layer including zirconia containing a stabilizing element and having a necking structure, or, if a coloring element is included, a zirconia composition layer including zirconia containing a stabilizing element and having a necking structure and a coloring element (hereinafter, these zirconia composition layers are also referred to simply as "zirconia composition layer" or "composition layer"). It has a structure equivalent to the laminate structure shown in FIG. 1 or FIG. 2. In the calcined body, the stabilizing element and the coloring element may be in a solid solution state in zirconia or in the form of an oxide or a precursor thereof. In this specification, the zirconia composition layer is also referred to as a calcined body layer.

[0063] <Characteristics of Layered Structure> Preferred embodiments of the calcined body of the present disclosure include the calcined body described in the following form (C) and the calcined body described in the following form (D).

[0064] <<Configuration (C)>> In the calcined body of this embodiment, the difference between the content of the stabilizing element contained in the first region located at one end of the stacked regions and the content of the stabilizing element contained in the second region located at the other end is 2.0 mol% or less. Configuration (C) will be described with reference to FIG. 1 . Along the Y-axis direction (stacking direction) in FIG. 1 , the contents of the stabilizing element contained in the first region located at one end (e.g., the first layer (11)) and the second region located at the other end (e.g., the second layer (12)) are set to similar values ​​(specifically, 2.0 mol% or less). This allows for a balance between the shrinkage rates of the first and second layers in the stacking direction Y of the calcined body, thereby suppressing warpage of the calcined body. As a result, the calcined body of this embodiment has reduced warpage and minimal deformation. Such a calcined body can effectively form a sintered body with reduced warpage and minimal deformation while exhibiting translucency and color gradation similar to those of natural teeth when visually observed. In this embodiment, only the relationship between the first region (e.g., the first layer (11)) located at one end and the second region (e.g., the second layer (12)) located at the other end is specified. However, by adjusting the shrinkage rates of the regions (layers) located at both ends, warping of the calcined body can be effectively suppressed. Therefore, a zirconia composition layer having any composition can be laminated on each intermediate layer disposed between the first layer (11) and the second layer (12). In the calcined body of this embodiment, the difference between the content of the stabilizing element contained in the first region and the content of the stabilizing element contained in the second region is 2.0 mol% or less, preferably 1.8 mol% or less, more preferably 1.5 mol% or less, and even more preferably 0.8 mol% or less. The difference between the content of the stabilizing element contained in the first region and the content of the stabilizing element contained in the second region is preferably small, and may be, for example, 0 mol% or more, more than 0 mol%, 0.1 mol% or more, or 0.3 mol% or more. The difference between the content of the stabilizing element contained in the first region and the content of the stabilizing element contained in the second region can be, for example, 0 mol% or more and 2.0 mol% or less, more than 0 mol% and 1.8 mol% or less, 0.1 mol% or more and 1.5 mol% or less, or 0.3 mol% or more and 0.8 mol% or less.

[0065] <<Form (D)>> In the calcined body of this embodiment, the difference (shrinkage rate difference) between the shrinkage rate of the calcined body of a first region located at one end of the stacked regions and the shrinkage rate of the calcined body of a second region located at the other end is 0.4% or less.

[0066] The embodiment (D) will be explained with reference to FIG. 1 . In this embodiment, the shrinkage rates of the calcined body of a first region (e.g., the first layer (11)) located at one end along the Y-axis direction (stacking direction) in FIG. 1 and a second region (e.g., the second layer (12)) located at the other end are set to similar values ​​(specifically, 0.4% or less). This balances the difference in shrinkage rates between the first layer and the second layer in the stacking direction Y of the calcined body, thereby suppressing warpage of the calcined body. As a result, the calcined body of this embodiment has reduced warpage and less deformation. This calcined body can effectively form a sintered body with reduced warpage and less deformation, while having translucency and color gradation similar to those of natural teeth when visually observed. In the present disclosure, only the relationship between the first region (e.g., the first layer (11)) located at one end and the second region (e.g., the second layer (12)) located at the other end is specified. However, by adjusting the shrinkage rates of the regions (layers) located at both ends, warping of the calcined body can be effectively suppressed. Therefore, for each layer of the intermediate layer disposed between the first layer (11) and the second layer (12), a zirconia composition layer having any composition can be laminated. In the calcined body of this embodiment, the difference between the shrinkage rate of the calcined body of the first region and the shrinkage rate of the calcined body of the second region is preferably 0.4% or less, 0.36% or less, 0.3% or less, or 0.2% or less. The difference between the shrinkage rate of the calcined body of the first region and the shrinkage rate of the calcined body of the second region is preferably small, and may be, for example, 0% or more, more than 0%, 0.01% or more, or 0.02% or more. The difference between the shrinkage rate of the calcined body of the first region and the shrinkage rate of the calcined body of the second region may be 0% or more and 0.4% or less, more than 0% and 0.36% or less, 0.01% or more and 0.3% or less, or 0.02% or more and 0.2% or less.

[0067] <<<Method for Measuring Shrinkage Rate>>> The shrinkage rates of a first region (e.g., the first layer (11)) located at one end and a second region (e.g., the second layer (12)) located at the other end are determined as follows. A zirconia raw material powder having the same composition as the first layer (11) and the second layer (12) is filled into a mold, and uniaxially press-molded and then subjected to CIP treatment to form a powder composition layer, which is a sample for shrinkage rate measurement. The powder composition layer is calcined at 800°C or higher and lower than 1200°C to obtain a zirconia composition layer. The shrinkage rate of the zirconia composition layer is determined by the method described in [Method for Evaluating Shrinkage Rate] in the section <<Form (B)>> of the sintered body above. Note that when determining the shrinkage rate of the calcined body, the method for preparing the sample for shrinkage rate measurement and the calcination conditions are as described above.

[0068] <Composition of Zirconia Composition Layer> The zirconia contained in the calcined body is preferably in a state where zirconia obtained by heat-treating a zirconia sol is heat-treated at a temperature below the sintering temperature, more preferably in a state where zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of a zirconium compound is heat-treated at a temperature below the sintering temperature, and even more preferably in a state where zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of zirconium oxychloride is heat-treated at a temperature below the sintering temperature. The content of the stabilizing element in the stabilizing element-containing zirconia contained in the first composition layer (corresponding to the first region), the content of the stabilizing element in the stabilizing element-containing zirconia contained in the second composition layer (corresponding to the second region), and the content of the stabilizing element in the stabilizing element-containing zirconia contained in the third composition layer or the intermediate layer composition layer (corresponding to the third region) may be the same as the stabilizing element content of the first layer, second layer, and third layer (intermediate layer) described above, respectively. The content of the stabilizing element in each composition layer in the calcined body is arbitrary, but may be the same as that of the sintered body layer of the present embodiment described above. The calcined body more preferably includes at least a zirconia composition layer containing zirconia having a tetragonal or cubic crystal as a main phase.

[0069] <Characteristics of the calcined body and each zirconia composition layer (each calcined body layer) constituting the calcined body> The calcined body preferably has a warpage of 1.0 mm or less, 0.5 mm or less, 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, or 0.05 mm or less. The calcined body preferably has no warpage (warpage of 0 mm), but may have a warpage that cannot be measured with a gauge (warpage of 0 mm or more). The calcined body may have a warpage of more than 0 mm, or even 0.01 mm or more. The warpage is preferably 0.06 mm or less, further preferably 0.05 mm or less, or even below the measurement limit (less than 0.03 mm). The warpage of the calcined body may be 0 mm or more and 0.3 mm or less, 0 mm or more and 0.05 mm or less, 0 mm or more and less than 0.03 mm, or more than 0 mm and less than 0.03 mm. The calcined body preferably has a deformation amount of 1.0 or less, 0.5 or less, 0.2 or less, or 0.15 or less. The deformation amount can be, for example, 0 or more, 0.01 or more, or even 0.05 or more. The deformation amount may be 0 to 1.0, 0 to 0.15, 0.01 to 1.0, or 0.05 to 0.15.

[0070] The calcined body has a density lower limit of 2.4 g / cm ３ or more than 3.1 g / cm ３ The upper limit of the density is 3.7 g / cm ３ or less than 3.5 g / cm ３ The upper and lower limits may be in any combination. Therefore, the density of the calcined body is 2.4 g / cm ３ 3.7g / cm or more ３ Preferably, it is 3.1 g / cm or less. ３ 3.5g / cm or more ３ Examples of the density range are as follows. This range of density corresponds to a relative density of 40% to 60%. The calcined body may be a laminate having strength suitable for processing such as CAD / CAM processing. The density of the calcined body is determined from the mass determined by mass measurement and the volume determined by dimensional measurement. The color tone of the zirconia composition layer contained in the calcined body may be different from that of the sintered body (sintered body layer) obtained by sintering it.

[0071] The calcined body and each composition layer (each calcined body layer) are opaque and have a total light transmittance of 0%, but when measurement error is taken into consideration, the total light transmittance can be, for example, 0% or more and 0.2% or less. The calcined body and each composition layer (each calcined body layer) only need to have a strength that makes it difficult for defects to occur during processing such as CAD / CAM or cutting, and for example, a Vickers hardness of 25 HV to 150 HV (= kgf / mm ２ ) or less, or 30 HV to 130 HV. The Vickers hardness can be measured using a common Vickers tester (for example, Q30A, manufactured by Qness) equipped with a diamond square pyramidal indenter. The measurement is performed by statically pressing the indenter into the surface of the test sample, and visually measuring the diagonal length of the indentation mark formed on the surface of the test sample. Using the obtained diagonal length, the Vickers hardness can be calculated from the following formula: Hv = F / {d ２ / 2 sin(α / 2)} In the above formula, Hv is Vickers hardness (HV), F is the measurement load (1 kgf), d is the diagonal length of the indentation mark (mm), and α is the facing angle of the indenter (136°). The following conditions can be used to measure Vickers hardness. Measurement sample: Disc-shaped with a thickness of 2.0±0.5 mm Measurement load: 1 kgf Prior to measurement, the measurement sample can be prepared by cutting out any location of the calcined body horizontally, and polishing the measurement surface with #800 waterproof abrasive paper to remove irregularities exceeding 0.1 mm, as a pretreatment.

[0072] The laminate of this embodiment can be used for known zirconia applications such as decorative members, structural materials, and optical materials. However, when the laminate is a sintered body, it can be suitably used as a dental material for dentures, such as crowns and bridges, and a dental material containing the sintered body of this embodiment can be used. Furthermore, when the laminate is a calcined body, it can be suitably used as a precursor for dental materials for dentures, such as crowns and bridges, and can be used as dental prosthetic materials such as blanks, discs, blocks, and mill blanks, and their precursors. Laminates of the sintered body or calcined body of this embodiment can be used as dental materials. Next, the manufacturing methods for each laminate of this embodiment (specifically, sintered body, calcined body, and molded body) will be described below.

[0073] (Methods for Producing Sintered Body and Calcined Body) A method for producing a sintered body according to this embodiment is as follows. It is a method for producing a sintered body, comprising a step of sintering a molded body, in which three or more layers of powder composition made of a zirconia raw material powder containing stabilizing element-containing zirconia and, if a coloring element is contained, also the coloring element, at 1200°C or more and 1600°C or less, stacked. Another method for producing a sintered body according to this embodiment is as follows. It is a method for producing a sintered body, comprising a step of calcining a molded body, in which three or more layers of powder composition made of a zirconia raw material powder containing stabilizing element-containing zirconia and, if a coloring element is contained, also the coloring element, stacked, at 800°C or more and less than 1200°C, to obtain a calcined body, and a step of sintering the calcined body at 1200°C or more and 1600°C or less.

[0074] The method for producing the calcined body of this embodiment is as follows: The method for producing the calcined body includes a step of calcining a compact at 800°C or higher and lower than 1200°C, in which three or more powder composition layers made of zirconia raw material powder containing zirconia containing a stabilizing element and, if a coloring element is contained, the coloring element are laminated.

[0075] The method for producing a molded body to produce the sintered body or the calcined body is as follows: This method includes a step of producing a molded body by stacking three or more powder composition layers made of zirconia raw material powder containing zirconia containing a stabilizing element and, if a coloring element is contained, the coloring element. In this specification, the powder composition layers are also referred to as molded body layers.

[0076] The molded body used in the manufacturing method of this embodiment is mainly different from the sintered body described above in the following points: The molded body used in the manufacturing method of this embodiment is formed by laminating three or more powder composition layers made of raw material powder of zirconia containing a stabilizing element, or, when a coloring element is contained, powder composition layers made of raw material powder of zirconia containing a stabilizing element and a coloring element.

[0077] The molded body is a laminate formed by stacking powder composition layers, and can be used as a precursor for a calcined body or a sintered body. Instead of a zirconia layer, the molded body has a powder composition layer made of a powder composition of stabilizing element-containing zirconia, or, if a coloring element is contained, a powder composition layer made of a powder composition containing stabilizing element-containing zirconia and a coloring element (hereinafter, these powder composition layers are collectively referred to as "powder layers"). It has a structure equivalent to the laminate structure shown in FIG. 1 or FIG. 2. Therefore, the molded body can also be considered a laminate having three or more layers containing zirconia powder containing a stabilizing element. In the molded body, the stabilizing element and the coloring element may be in a solid solution state with zirconia, or in the form of an oxide or a precursor thereof. Examples of precursors include one or more selected from the group consisting of sulfides, chlorides, nitrates, sulfates, hydroxides, and oxyhydroxides, and further one or more selected from the group consisting of chlorides, hydroxides, and oxyhydroxides. Furthermore, it is preferable that the coloring element contains at least an oxide.

[0078] The zirconia contained in the powder layer is preferably zirconia obtained by heat-treating a zirconia sol, more preferably zirconia obtained by hydrolysis of a zirconium compound and heat-treated, and even more preferably zirconia obtained by hydrolysis of zirconium oxychloride and heat-treated.

[0079] The zirconia contained in the powder layer is preferably zirconia powder. The zirconia powder preferably has a lower limit of an average particle size of 0.3 μm or more or 0.4 μm or more, and an upper limit of the average particle size of 0.7 μm or less or 0.5 μm or less. Any combination of these upper and lower limits is acceptable. Therefore, the average particle size of the zirconia powder is preferably, for example, 0.3 μm or more and 0.7 μm or less, or 0.4 μm or more and 0.5 μm or less.

[0080] The zirconia powder has a BET specific surface area of ​​7.5 m ２ / g or more 15m ２ / g or less. If the BET specific surface area is less than this range, the sintering rate becomes too slow, while if the BET specific surface area exceeds this range, the sintering rate becomes too fast. In either case, densification becomes difficult in atmospheric sintering, particularly in air sintering. Even when sintering with a high heating rate is applied, densification tends to be promoted, so the lower limit of the BET specific surface area is set to 8 m ２ / g or more, 9m ２ / g or more, or 9.5m ２ / g or more, and the upper limit of the BET specific surface area is 15 m ２ / g or less, 13m ２ / g or less, or 11m ２ / g or less. Any combination of these upper and lower limits is acceptable. Therefore, the BET specific surface area of ​​the zirconia powder is preferably, for example, 8 m ２ / g or more 15m ２ / g or less, 9m ２ / g or more 13m ２ / g or less, or 9.5m ２ / g or more 11m ２ / g or less. In this embodiment, the BET specific surface area is the BET specific surface area measured in accordance with JIS R 1626, and may be measured by the BET 5-point method using a carrier gas method in which nitrogen is used as the adsorption gas. Specific measurement conditions for the BET specific surface area include, for example, the following conditions.

[0081] [BET specific surface area measurement conditions] Adsorption medium: N ２ Adsorption temperature: -196°C Pretreatment conditions: Degassing treatment in air at 250°C for 1 hour or more The BET specific surface area can be measured using a common device (for example, Tristar II 3020, manufactured by Shimadzu Corporation).

[0082] The coloring element contained in the powder layer is preferably at least one of a mixture with zirconia powder and a solid solution in zirconia, and may be a mixture of the coloring element powder and zirconia powder.

[0083] The molded body may contain a binder. By including a binder, the shape retention of the molded body is improved. The binder contained in the molded body can be a known binder used in molding ceramics, and is preferably an organic binder. The organic binder is at least one selected from the group consisting of polyvinyl alcohol, polyvinyl butyrate, wax, and acrylic resin, preferably at least one of polyvinyl alcohol and acrylic resin, and more preferably an acrylic resin. In this embodiment, the acrylic resin is a polymer containing at least one of an acrylic acid ester and a methacrylic acid ester. Specific examples of the acrylic resin include at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid, acrylic acid copolymers, and methacrylic acid copolymers, as well as derivatives thereof. Specific examples of the acrylic resin binder include acrylic resins used for ceramic powders, and at least one selected from the group consisting of AS-1100, AS-1800, and AS-2000 (all product names, manufactured by Toagosei Co., Ltd.).

[0084] The contents of the stabilizing elements in the stabilizing-element-containing zirconia contained in the first powder layer, the second powder layer, and the third powder layer may be the same as the contents of the stabilizing elements in the first layer, the second layer, and the third layer (intermediate layer) described above, respectively. The contents of the stabilizing elements and coloring elements in each powder layer in the compact are arbitrary, but may be the same as those in the sintered body of the present embodiment described above.

[0085] When each powder layer contains a binder, from the viewpoint of suppressing defects during molding, the binder content of each powder layer preferably has a lower limit of 1.5 mass% or more, 1.5 mass% or more, 2.0 mass% or more, or 2.5 mass% or more, and an upper limit of 8.0 mass% or less, 6.0 mass% or less, or 5.5 mass% or less. Any combination of these upper and lower limits is acceptable. Therefore, the binder content of each powder layer is preferably, for example, 1.5 mass% or more and 8.0 mass% or less, 2.0 mass% or more and 6.0 mass% or less, or 2.5 mass% or more and 5.5 mass% or less. The binder content is the mass ratio of the binder to the mass of the powder composition in the powder layer excluding the binder ({binder / (powder composition-binder)} x 100). In producing the powder composition, the total mass of the components of the powder composition other than the binder (for example, the stabilizing element, zirconia, and alumina converted into oxides) is determined, and then the mass ratio of the desired binder relative to this is determined to produce the powder composition.

[0086] From the viewpoint of operability, the powder composition contained in the powder layer is preferably a powder in which zirconia powder, if a coloring element is contained, and the coloring element, if a binder is contained, are granulated (hereinafter also referred to as "granulated powder"). Granulated powder granulated into granules by spray drying or the like (hereinafter also referred to as "powder granules") is more preferable. The particle size of the granulated powder is arbitrary, but the average agglomerate diameter (hereinafter also referred to as "average granule diameter") can be exemplified by a lower limit of 1 μm or more or 5 μm or more, and an upper limit of 150 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Any combination of these upper and lower limits is acceptable. Therefore, the particle size of the granulated powder can be exemplified by an average agglomerate diameter of 1 μm or more to 150 μm or less, 1 μm or more to 100 μm or less, 5 μm or more to 50 μm or less, or 5 μm or more to 30 μm or less. In another embodiment, 20 μm or more to 50 μm or less can be exemplified. In this embodiment, the average agglomerate diameter is the diameter corresponding to 50% of the cumulative total in the volume particle size distribution measurement. The volume particle size distribution is a value that can be measured using a general-purpose device (e.g., MT3100II, manufactured by Microtrac-Bell Co., Ltd.) and is the volume diameter of particles that are approximately spherical. As a pretreatment, prior to the measurement, the granulated powder is sieved through a sieve with 125 μm openings, and the granulated powder that passed through the sieve is measured.

[0087] The molded body preferably includes at least a powder layer containing zirconia having a tetragonal or cubic crystal as a main phase.

[0088] The molded article preferably has a warpage of 1.0 mm or less, 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, or 0.05 mm or less. The molded article preferably has no warpage (warpage of 0 mm), but may have a warpage that cannot be measured with a gauge (warpage of 0 mm or more). The molded article may have a warpage of more than 0 mm, or even 0.01 mm or more. The warpage is preferably 0.06 mm or less, further 0.05 mm or less, or even below the measurement limit (less than 0.03 mm). The warpage of the molded article may be 0 mm or more and 0.06 mm or less, 0 mm or more and 0.05 mm or less, 0 mm or more and less than 0.03 mm, or more than 0 mm and less than 0.03 mm. The molded article preferably has a deformation amount of 1.0 or less, 0.5 or less, 0.2 or less, or 0.15 or less. The deformation amount may be 0 or more, further 0.01 or more, or even 0.05 or more. The deformation amount may be 0 or more and 1.0 or less, 0 or more and 0.15 or less, 0.01 or more and 1.0 or less, or 0.05 or more and 0.2 or less.

[0089] The molded body has a density lower limit of 2.4 g / cm ３ or more than 3.1 g / cm ３ The upper limit of the density is 3.7 g / cm ３ or less than 3.5 g / cm ３ The density of the compact can be, for example, 2.4 g / cm or less. Any combination of these upper and lower limits is acceptable. ３ 3.7g / cm or more ３ or less, or 3.1 g / cm ３ 3.5g / cm or more ３ Examples of the density are as follows. This range of density corresponds to a relative density of 40% to 60%. Note that the density of the compact may be approximately the same as the density of the calcined body. The density of the compact can be determined from the mass determined by mass measurement and the volume determined by dimensional measurement.

[0090] The color tone of the zirconia powder composition layer (green body layer) contained in the green body may be different from that of the sintered body (sintered body layer) obtained by sintering the green body, or the color tone may not change. The green body and each powder layer are opaque and have a total light transmittance of 0%, but when taking measurement error into consideration, the total light transmittance can be, for example, 0% or more and 0.2% or less.

[0091] The molded body only needs to have a strength sufficient to prevent cracking or chipping when subjected to calcination or sintering.

[0092] The compact is obtained by layering and molding powder compositions. Each powder composition is obtained by mixing zirconia powder and, if a binder is included, the binder in any desired ratio using a known method. Molding is preferably performed by pressure molding. For example, a powder composition having a composition corresponding to the bottom layer is filled into a mold to form the bottom layer. Then, a powder composition having a composition corresponding to the layer adjacent to the bottom layer is filled on top of the bottom layer. To obtain a compact having a structure in which three or more powder layers are stacked, a similar operation can be repeated to stack the required powder compositions. After filling with a powder composition having a composition corresponding to the top layer, the preform is obtained by uniaxial pressing at an arbitrary pressure, and this is then subjected to CIP processing to obtain the compact. During stacking, vibration to form a mixed layer between the layers, such as vibration using a vibrator, is not required. Uniaxial pressing is preferably performed after filling with a powder composition having a composition corresponding to the top layer; it is preferable not to apply pressure before filling with a powder composition having a composition corresponding to the top layer.

[0093] The molding pressure of the uniaxial pressing is preferably 15 MPa or more and 200 MPa or less, and more preferably 18 MPa or more and 100 MPa or less. In the uniaxial pressing, warpage of the molded body tends to be suppressed as the molding pressure increases. The molding pressure of the CIP treatment can be 98 MPa or more and 392 MPa or less.

[0094] The compact is treated at a temperature below the sintering temperature to form a calcined compact. Known methods can be used for the calcination method and conditions. The holding temperature during calcination (hereinafter also referred to as "calcination temperature") can have a lower limit of 800°C or higher, 900°C or higher, or 950°C or higher, and an upper limit of less than 1200°C, 1150°C or lower, or 1100°C or lower. Any combination of these upper and lower limits is acceptable. Therefore, the calcination temperature can be, for example, 800°C or higher but lower than 1200°C, preferably 900°C or higher but lower than 1150°C, and more preferably 950°C or higher but lower than 1100°C. The holding time at the calcination temperature (hereinafter also referred to as "calcination time") can be appropriately set depending on the size of the compact to be subjected to calcination and the characteristics of the calcination furnace. The lower limit is preferably 0.5 hours or higher, more preferably 0.5 hours or higher, and the upper limit is preferably 5 hours or lower, more preferably 3 hours or lower. Any combination of these upper and lower limits is acceptable. Therefore, the calcination time is, for example, 0.5 hours to 5 hours, or 0.5 hours to 3 hours. The temperature may be increased in multiple stages, with the temperature increase rate and the holding time at the increased temperature. For example, the calcination may be performed under the following conditions: from room temperature to 300°C at 15°C / hour, holding at 300°C for 5 hours, from 300°C to 700°C at 15°C / hour, holding at 700°C for 1 hour, from 700°C to 1000°C at 50°C / hour, and holding at 1000°C for 2 hours. The atmosphere in the calcination step (hereinafter also referred to as the "calcination atmosphere") is preferably an atmosphere other than a reducing atmosphere, more preferably at least one of an oxygen atmosphere and an air atmosphere, and even more preferably an air atmosphere.

[0095] In the manufacturing method of this embodiment, either a green body or a calcined body (hereinafter, collectively referred to as "green body, etc.") is treated at 1200°C or higher and 1600°C or lower. This converts the green body, etc., into a sintered body. Prior to sintering, the green body, etc., may be processed into any desired shape. Known sintering methods and sintering conditions can be used. Examples of sintering methods include at least one selected from the group consisting of atmospheric sintering, HIP treatment, SPS, and vacuum sintering. Because this is a commonly used industrial sintering method, atmospheric sintering is preferred, and atmospheric sintering in an air atmosphere is more preferred. The sintering method is preferably atmospheric sintering alone, and more preferably, pressure sintering after atmospheric sintering is not performed. This allows the sintered body to be obtained as an atmospheric sintered body. In this embodiment, atmospheric sintering refers to a sintering method in which the material to be sintered is sintered simply by heating it without applying an external force.

[0096] The holding temperature during sintering (hereinafter also referred to as "sintering temperature") has a lower limit of 1200°C or higher, preferably 1300°C or higher, 1400°C or higher, 1430°C or higher, or 1480°C or higher, and an upper limit of 1650°C or lower, preferably 1580°C or lower, 1560°C or lower, 1560°C or lower, or 1560°C or lower. Any combination of these upper and lower limits may be used. Therefore, the sintering temperature is, for example, 1200°C or higher and 1650°C or lower, 1300°C or higher and 1580°C or lower, 1400°C or higher and 1560°C or lower, 1430°C or higher and 1560°C or lower, or 1480°C or higher and 1560°C or lower. In another embodiment, the sintering temperature is 1450°C or higher and 1650°C or lower, preferably 1500°C or higher and 1650°C or lower, more preferably 1550°C or higher and 1650°C or lower. The heating rate to the sintering temperature may have a lower limit of 50°C / hour or more, such as 100°C / hour or more or 150°C / hour or more, and an upper limit of 800°C / hour or less or 700°C / hour or less. Any combination of these upper and lower limits is acceptable. Therefore, the heating rate to the sintering temperature may be, for example, 50°C / hour or more and 800°C / hour or less, 100°C / hour or more and 800°C / hour or less, 150°C / hour or more and 800°C / hour or less, or 150°C / hour or more and 700°C / hour or less. The holding time at the sintering temperature (hereinafter also referred to as "sintering time") varies depending on the sintering temperature, the size of the molded body, etc., and the characteristics of the sintering furnace, but preferably has a lower limit of 1 hour or more and an upper limit of 5 hours or less, 3 hours or less, or 2 hours or less. Any combination of these upper and lower limits is acceptable. Therefore, the sintering time may be, for example, 1 hour or more and 5 hours or less, more preferably 1 hour or more and 3 hours or less, and even more preferably 1 hour or more and 2 hours or less. For example, sintering may be performed under conditions such as increasing the temperature from room temperature to 1500°C at 100°C / hour and holding at 1500°C for 2 hours. The sintering atmosphere (hereinafter also referred to as "sintering atmosphere") is preferably an atmosphere other than a reducing atmosphere, more preferably at least one of an oxygen atmosphere and an air atmosphere, and even more preferably an air atmosphere. An air atmosphere is, for example, composed mainly of nitrogen and oxygen, with an oxygen concentration of approximately 18 to 23% by volume. Preferred sintering conditions in the sintering step include atmospheric sintering in an air atmosphere.

[0097] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples in any way.

[0098] (BET Specific Surface Area) The BET specific surface area was measured using an automatic specific surface area measuring device (device name: Tristar II 3020, manufactured by Shimadzu Corporation) by the BET 5-point method in accordance with JIS R 1626. The measurement conditions were as follows: Adsorption medium: N ２ Adsorption temperature: -196°C Pretreatment conditions: Degassing in air at 250°C for 1 hour or more

[0099] (Average Granule Particle Size) The average granule particle size was measured by particle size distribution measurement by laser diffraction / scattering method using a Microtrac particle size distribution analyzer (device name: MT3100II, manufactured by Microtrac Bell). The measurement conditions were as follows: Light source: semiconductor laser (wavelength: 780 nm) Voltage: 3 mW Refractive index of zirconia: 2.17 Calculation mode: MT3000 As a pretreatment prior to measurement, the granulated powder was sieved through a sieve with 125 μm openings, and the granulated powder that passed through the sieve was measured.

[0100] (Warpage and Deformation Amount) A disk-shaped compact, calcined body, or sintered body was used as a measurement sample, and the amount of deformation of each was calculated using the following formula (3): Deformation Amount = (Warpage: mm) / (Dimensions: mm) × 100 (3)

[0101] The method for determining the deformation amount will be explained in more detail. The conditions for producing the laminate are as follows: [Laminate] Mold diameter: Φ110 mm Powder mass: 470 g (total mass of laminated powder) Molding pressure: Uniaxial press molding: 49 MPa + CIP treatment: 196 MPa Molding process: Load raw material powder to form the first layer into the mold → leveling → Load raw material powder to form the second layer into the mold → leveling → (repeated) → uniaxial press molding → CIP treatment

[0102] In the production of the laminate, a schematic diagram of the uniaxial press molding process is shown in Figure 8, and a schematic diagram of the CIP process is shown in Figure 9. Figure 8 shows the steps of (a) pouring a powder composition (81) into a mold (82), (b) leveling the powder composition, (c) (forming the second layer in the same way, and repeating thereafter), and (d) uniaxial press molding (83) to pressurize the powder composition. Figure 9 shows the uniaxially pressed powder (laminate) (91) placed in a high-pressure vessel, which is filled with a solvent (92), and isotropically pressing the powder (CIP process).

[0103] A molded body for measuring warpage and deformation was obtained through CIP treatment. The molded body was subjected to calcination under the following conditions to obtain a calcined body for measuring warpage and deformation. The molded body was subjected to calcination and sintering under the following conditions to obtain a sintered body for measuring warpage and deformation. [Calibration and sintering conditions] Calcination: From room temperature to 300°C at 15°C / hour, held at 300°C for 5 hours, from 300°C to 700°C at 15°C / hour, held at 700°C for 1 hour, from 700°C to 1000°C at 50°C / hour, held at 1000°C for 2 hours, and then cooled in the furnace. Sintering: From room temperature to 1500°C at 100°C / hour, held at 1500°C for 2 hours, and then cooled in the furnace.

[0104] The warpage of each laminate of the green body, calcined body, and sintered body was measured using the measurement method shown in Figure 5. The test sample was positioned so that its convex portion was in contact with the horizontal plate. A gauge (product name: 75A19, manufactured by Nagai Gauge Manufacturing Co., Ltd.) was inserted into the gap formed between the horizontal plate and the bottom surface to measure the warpage. The gauge, positioned parallel to the horizontal plate, was inserted into the gap formed between the horizontal plate and the bottom surface of the test sample, and the maximum gauge thickness that could be inserted into the gap was measured. This gauge thickness was taken as the warpage. The warpage was measured sequentially in 0.01 mm increments starting from a gauge thickness of 0.03 mm using a single gauge or a combination of gauges. The dimensions of the test sample were measured using a vernier caliper to measure the diameter of the top end and the diameter of the bottom end at four points each, and the average of the top and bottom diameters was calculated.

[0105] (Zirconia Powder A1) Commercially available zirconia powder Zpex Smile (manufactured by TOSOH Corporation) was used as zirconia powder A1.

[0106] Zirconia powder A1 was uniaxially press-molded at a pressure of 49 MPa and subjected to CIP treatment at a pressure of 196 MPa to obtain a powder layer (green body layer) of zirconia powder A1. The obtained powder layer (green body layer) was calcined and sintered under the following conditions to obtain a zirconia layer (sintered body layer). [Calcining and sintering conditions] Calcination: From room temperature to 300°C at 15°C / hour, held at 300°C for 5 hours, from 300°C to 700°C at 15°C / hour, held at 700°C for 1 hour, from 700°C to 1000°C at 50°C / hour, held at 1000°C for 2 hours, then cooled in the furnace. Sintering: From room temperature to 1500°C at 100°C / hour, held at 1500°C for 2 hours, then cooled in the furnace.

[0107] The zirconia layer (sintered body layer) of zirconia powder A1 was measured for three-point bending strength (MPa), total light transmittance (%), and color tone (L ＊ , a ＊ and b ＊ ) was measured.

[0108] <Three-point bending strength (MPa)> The three-point bending strength was measured by the measurement method shown in FIG. 6 as described above.

[0109] <Total Light Transmittance (%)> The total light transmittance of the sample was measured according to the method of JIS K 7361. The measurement sample was irradiated with standard light source D65, and the light flux transmitted through the measurement sample was detected using an integrating sphere, thereby measuring the total light transmittance. A general haze meter (device name: Haze Meter NDH4000, manufactured by NIPPON DENSOKU) was used for the measurement. A measurement sample was obtained by cutting out any location of the sintered compact horizontally, and then mirror-polishing both sides of the sample to a thickness of 1.0±0.1 mm and a surface roughness (Ra) of 0.02 μm or less.

[0110] <L ＊ , a ＊ and b ＊The color tone was measured using a colorimeter (device name: ZE6000, manufactured by Nippon Denshoku Industries Co., Ltd.). The measurement conditions are as follows: Color tone and C ＊ The specific measurement conditions were as follows: A zero calibration box was placed above the measurement sample (so-called black background measurement): Light source: D65 light source Viewing angle: 2° Measurement method: SCI The sintered compact sample was prepared by cutting out any part of the sintered compact horizontally, and then mirror-polishing the measurement surface of the sample to a thickness of 2.8±0.1 mm and a surface roughness (Ra) of 0.02 μm or less.

[0111] The evaluation results of the properties of the zirconia layer (sintered body layer) using zirconia powder A1 are shown in Table 1-2.

[0112] (Zirconia Powder A2) A hydrated zirconia sol was obtained by hydrolyzing an aqueous solution of zirconium oxychloride. ２ O ３ The yttrium chloride and erbium concentration were adjusted to 5.05 mol% in terms of Er ２ O ３ Erbium oxide was added to the hydrated zirconia sol to a concentration of 0.15 mol% in terms of iron oxide, and the sol was then dried at 180°C. The dried zirconia sol was calcined at 1160°C for 2 hours, washed with pure water, and dried in air at 110°C. This was mixed with α-alumina, iron oxide as an oxide coloring element, and pure water to form a slurry, which was then processed in a ball mill for 22 hours to obtain a slurry containing a powder of zirconia containing 0.05 mass% alumina and 0.085 mass% iron as an oxide coloring element in terms of iron oxide, with the remainder being 5.05 mol% yttrium and 0.15 mol% erbium. An acrylic acid-based binder was added to the resulting slurry and mixed so that the mass ratio of the binder to the powder mass in the slurry was 3 mass%. The slurry was spray-dried in air at 180°C to obtain zirconia powder A2. The resulting zirconia powder had a BET specific surface area of ​​10.1 m ２ / g and the average granule particle size was 44 μm.

[0113] (Zirconia Powders A3 to A6) Zirconia powders A3 to A6 were obtained in the same manner as zirconia powder A2, except that they were fired at 1,130° C. and that yttrium chloride, erbium oxide α-alumina, and iron oxide were used so as to obtain the compositions shown in Table 1-1. The compositions of zirconia powders A1 to A6 are shown in Table 1-1.

[0114] Zirconia layers (sintered layers) were produced using each of zirconia powders A2 to A6 in the same manner as described above in the section (Zirconia Powder A1), and the properties of the zirconia layers (sintered layers) were evaluated. The evaluation results are shown in Table 1-2.

[0115] (Zirconia Powder B1) Commercially available zirconia powder Zpex4 (manufactured by TOSOH Corporation) was used as zirconia powder B1.

[0116] (Zirconia Powder C1) Commercially available zirconia powder Zpex (manufactured by TOSOH Corporation) was used as zirconia powder C1.

[0117] (Zirconia Powders B2 to B11, C2 to C4) Zirconia powders B2 to B11 and C2 to C4 having the compositions shown in Table 1-1 were prepared in the same manner as for zirconia powder A2, except that the type and content of the stabilizing element and the type and content of the coloring element were changed as shown in Table 1-1.

[0118] (Zirconia Powders B8 to B11) Zirconia powders B8 to B11 were produced in the same manner as zirconia powder A2, except that they were fired at 1125°C and that yttrium chloride, erbium oxide, α-alumina, iron oxide, tricobalt tetroxide, and titanium oxide were used to obtain the compositions shown in Table 1-1. Sintered body layers were also produced using zirconia powders B1 to B11 and C1 to C4, and the properties of the sintered body layers were evaluated. The evaluation results are shown in Table 1-2. Note that ppm in Table 1-2 refers to ppm by mass.

[0119]

[0120]

[0121] (Measurement of shrinkage ratio of layers using each zirconia powder) Using each of the zirconia powders A1 to A6, B1 to B11, and C1 to C4, sample layers of powder layer (green body layer), zirconia composition layer (calcined body layer), and zirconia layer (sintered body layer) were prepared under the following conditions, and their shrinkage ratios were measured. [Sample layer for shrinkage ratio measurement] Mold diameter: Φ25 mm Powder mass: 4 g Molding pressure: uniaxial press molding: 49 MPa + CIP treatment: 196 MPa Molding process: Raw material powder to be evaluated is placed in mold → leveling → uniaxial press molding → CIP treatment

[0122] The sample layer was produced by the molding process shown in FIGS. 3 and 4 as described above. The resulting sample layer of the compact layer made of the powder layer (powder composition layer) was calcined under the following conditions to obtain a sample layer of a zirconia composition layer (calcined body layer). The sample layer of the zirconia composition layer (calcined body layer) was sintered under the following conditions to obtain a sample layer of a zirconia layer (sintered body layer). [Calibration / Sintering Conditions] Calcination: From room temperature to 300°C at 15°C / hour, held at 300°C for 5 hours, from 300°C to 700°C at 15°C / hour, held at 700°C for 1 hour, from 700°C to 1000°C at 50°C / hour, held at 1000°C for 2 hours, then cooled in the furnace. Sintering: From room temperature to 1500°C at 100°C / hour, held at 1500°C for 2 hours, then cooled in the furnace.

[0123] The shrinkage rate was measured for each sample layer obtained as described above. [Method for evaluating shrinkage rate] The diameter of the sample for shrinkage rate measurement (hereinafter also referred to as "sample diameter") was measured using a vernier caliper. The sample diameter was measured using the vernier caliper at four points on each sample for shrinkage rate measurement, and the average of the measured values ​​was taken as the sample diameter. The shrinkage rate was calculated using the following formula (1). Shrinkage rate (%) = {(mold diameter: Φ25 mm - sample diameter) / mold diameter: Φ25 mm} × 100 ... (1)

[0124] Table 2 shows the measurement results of the shrinkage rates of the sample layers, i.e., the powder layer (green body layer), the zirconia composition layer (calcined body layer), and the zirconia layer (sintered body layer), which were produced using the zirconia powders A1 to A6, B1 to B11, and C1 to C4, respectively.

[0125]

[0126] Example 1 (Molded Body) A mold having an inner diameter of 110 mm was filled with zirconia powder A1 in an amount (21 g) such that the calcined body would have a layer thickness of 1 mm, and the mold was then tapped to form the (i)th powder layer (corresponding to the first layer (21) in Figure 2). Zirconia powder A2 in an amount (214 g) such that the calcined body would have a layer thickness of 10 mm was filled on top of the (i)th powder layer, and the mold was then tapped to form the (ii)th powder layer (corresponding to the third layer (23) in Figure 2). Zirconia powder C3 in an amount (214 g) such that the calcined body would have a layer thickness of 10 mm was filled on top of the (ii)th powder layer, and the mold was then tapped to form the (iii)th powder layer (corresponding to the fourth layer (24) in Figure 2). On the (iii)th powder layer, zirconia powder A1 was filled in an amount (21 g) such that the layer thickness of the calcined body would be 1 mm, and then the mold was tapped to form the (iv)th powder layer (corresponding to the second layer (22) in Figure 2). Thereafter, the filled material from the (i)th powder layer to the (iv)th powder layer was subjected to uniaxial pressure pressing at a pressure of 98 MPa. Thereafter, CIP treatment was performed at a pressure of 196 MPa to obtain a stack consisting of four layers, which was used as the compact according to this example. (Calcined Body) The compact was calcined under the following calcination conditions to obtain a stack, which was used as the calcined body according to this example. [Calming conditions] Calcination: From room temperature to 300°C at 15°C / hour, held at 300°C for 5 hours, from 300°C to 700°C at 15°C / hour, held at 700°C for 1 hour, from 700°C to 1000°C at 50°C / hour, held at 1000°C for 2 hours, then cooled in the furnace. (Sintered body) The calcined body was fired under the sintering conditions below to obtain a laminate, which was used as the sintered body of this example. [Sintering conditions] Sintering: From room temperature to 1500°C at 100°C / hour, held at 1500°C for 2 hours, then cooled in the furnace.

[0127] The types of powders used in Example 1, the order in which the powders were layered, and the conditions for Example 1 are shown in Table 3-1, and the evaluation results are shown in Table 3-2-1. The measurement results for the warpage of the sintered body of Example 1 were less than the measurement limit (0.03 mm). Tables 3-2-1 and 3-2-2 are collectively referred to as Table 3-2.

[0128] Examples 2 to 10 Laminates shown in Table 3-1 were produced in the same manner as in Example 1, except that the types of powders used and the layering order of the powders used were changed as shown in Table 3-1. The evaluation results are shown in Table 3-2 below.

[0129]

[0130]

[0131] In Table 3-2, the measurement result of warpage described as "less than 0.03 mm" means the measurement limit of less than 0.03 mm, the description of "less than 0.03 mm" in the molding and calcination column of deformation amount means the measurement limit of less than 0.03 mm, and the description of "less than 0.04 mm" in the sintering column of deformation amount means the measurement limit of less than 0.04 mm.

[0132] Comparative Examples 1 to 7 Laminates shown in Table 4-1 were produced in the same manner as in Example 1, except that the types of powders used and the layering order of the powders used were changed as shown in Table 4-1 below. The evaluation results are shown in Table 4-2 below.

[0133]

[0134]

[0135] As is clear from the results of the Examples, by setting the stabilizing element contents in the first region (e.g., the bottom layer) located at one end of the laminate and the second region (e.g., the top layer) located at the other end to similar values ​​(specifically, 2.0 mol% or less), it is possible to suppress warping of the sintered body and produce a sintered body with little deformation while maintaining translucency and color gradation similar to that of natural teeth. Furthermore, as is clear from the results of the Examples, by setting the shrinkage rates of the sintered body in the first region (e.g., the bottom layer) located at one end of the laminate and the second region (e.g., the top layer) located at the other end to similar values ​​(specifically, 0.4% or less), it is possible to suppress warping of the sintered body and produce a sintered body with little deformation while maintaining translucency and color gradation similar to that of natural teeth. The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2022-024064, filed February 18, 2022, are hereby incorporated by reference.

[0136] 100, 200, 500, 600: Zirconia sintered body 11, 21: First layer 12, 22: Second layer 13, 23: Third layer 24: Fourth layer 31: Powder composition 32: Mold 33: Uniaxial press molding 41: Uniaxially press-molded powder 42: Solvent 51: Horizontal plate 52A, 52B: Thickness gauge 53: Size of sintered body 61: Load 62: Distance between supports 71: Zirconia having a necking structure 81: Powder composition 82: Mold 83: Uniaxial press molding 91: Uniaxially press-molded powder (laminated body) 92: Solvent

Claims

DEPCT671. A sintered body of zirconia where the zirconia consists of (i) zirconia with a stabilizer or (ii) zirconia composed of zirconia with a stabilizer and a coloring agent, the sintered body has three or more regions superimposed in a layered manner, where two adjacent regions among the regions differ in at least one amount of stabilizer and coloring agent, and the difference between the amount of stabilizer in region one end among the superimposed regions and the amount of stabilizer in region two end among the superimposed regions is 2.0% by mol or less.

2. A sintered body according to claim 1 where a third region superimposed between regions one and two in a layered manner includes one or more regions. 3.

4. A sintered frame under claim 2 where the third region includes two or more regions and the tendency of increase or decrease of at least one of the translucencies and tonalities does not change in the overlapping direction from region one to region three or from region two to region three.

5. A sintered frame of zirconia where the zirconia consists of (i) zirconia with a stabilizer or (ii) zirconia consisting of zirconia with a stabilizer and a coloring element, the sintered frame has three or more regions stacked in layers, where two adjacent regions among the regions differ in at least one amount of stabilizer and coloring element, and the difference between the shrinkage ratio of the sintered frame in region one at one end among the stacked regions and the shrinkage ratio of the sintered frame in region two at the other end (the difference in shrinkage ratio) is 0.4% or less. 5.

6. The sintered structure under claim 5, where the third area overlaps between the first and second areas in a layered manner, including one or more areas; and the tendency to increase or decrease of at least one aspect of transparency and tone does not change in the overlapping direction from the first to the third area or from the second to the third area.

8. Calcined body of zirconia composition where the zirconia composition consists of (iii) a zirconia composition with a stabilizer containing a necking structure, or (iv) a zirconia composition consisting of a zirconia composition with a stabilizer containing a necking structure and a coloring element; the calcined body has three or more regions stacked in a layered manner, where two adjacent regions among the regions differ in at least one amount of stabilizer and the amount of coloring element, and the difference between the amount of stabilizer in the first region at one end among the stacked regions and the amount of stabilizer in the second region at the other end is 2.0% by mol or less.

9. Calcined body according to claim 7 where the third region stacked in a layered manner between the first and second regions includes one or more regions.

10. Calcinate scaffold of zirconia composition where the zirconia composition consists of (iii) a zirconia composition with a stabilizer forming a constricted structure or (iv) a zirconia composition with a stabilizer forming a constricted structure and a coloring element, the calcite scaffold has three or more regions stacked in a layered manner, where two adjacent regions among the regions differ in at least one amount of stabilizer and the amount of coloring element, and the difference between the shrinkage ratio of the calcite scaffold in the first region at one end among the stacked regions and the shrinkage ratio of the calcite scaffold in the second region at the other end (difference in shrinkage ratio) is 0.4% or less. 11.

12. Calcined structure under claim 11 where the third region includes two or more overlapping regions and the tendency for color rise or fall does not change in the overlapping direction from region one to region three or from region two to region three.

13. Method for producing any of the sintered structures under claims 1 through 6, assembly method includes: sintering steps at 1,200°C or higher and 1,600°C or lower; greenbody structure which has three or more powder composition layers consisting of zirconia raw material powder with zirconia stabilizers and, if coloring elements are present, those elements are overlapping. 14.The method for producing the sintered frame according to any of the claims 1 through 6, which includes: a calcination step at 800°C or higher and below 1,200°C; a green frame in which three or more powder composition layers consisting of zirconia raw material powder containing zirconia with stabilizing elements and, if coloring elements are present, the coloring elements are layered to obtain the calcined frame; and a sintering step of the calcined frame at 1,200°C or higher and below 1,600°C.

15. A method for the production of calcined frameworks according to any of the claims 7 through 12, a method which includes: a calcination procedure at 800 degrees Celsius or higher and below 1,200 degrees Celsius; a green framework in which three or more powder composition layers are formed, consisting of zirconia raw material powder with zirconia stabilizers and, if there are coloring components, those coloring components are layered.

16. Dental materials incorporating sintered frameworks according to any of the claims 1 through 6. 17.Dental materials incorporating a calcined framework as provided by any of Claims 7 through 12;

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