Zirconia layered body

Abstract

There is provided a layered body that has gradations in translucency and color allowing the layered body to give an impression similar to that of natural teeth and with which the chipping of the surface layer (layer closer to the incisal edge of the dental restoration) can be reduced. The layered body comprises a surface layer containing zirconia containing at least one stabilizing element and a composition-gradient layer composed of two or more unit layers. The unit layers each contain at least one coloring element and zirconia containing at least one stabilizing element, and the composition-gradient layer is constructed as a result of the unit layers being stacked in such a manner that the amount of the stabilizing element in the zirconia containing at least one stabilizing element contained in the composition-gradient layer remains unchanged or decreases from the surface layer toward the surface of the layered body opposite the surface layer. The amount of the stabilizing element in the zirconia containing at least one stabilizing element contained in the surface layer is smaller than the amount of the stabilizing element in the zirconia containing at least one stabilizing element contained in a first composition-gradient layer (21), which is one of the unit layers constituting the composition-gradient layer and is adjacent to the surface layer. The most suitable drawing: FIG. 1

Description

Zirconia laminate

[0001] The present disclosure relates to compositions having layers of zirconia laminated thereto, and further to zirconia laminates.

[0002] Zirconia (ZrO ２ The sintered body of zirconia is manufactured by molding, calcining, and sintering raw material powder, which mainly contains zirconia. The raw material powder undergoes thermal shrinkage and densification through heat treatments such as sintering and calcining, but the behavior during heat treatment varies depending on the characteristics of the raw material powder, especially its 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 a sintered body consisting of laminates with different color tones can be obtained by adjusting the composition and thermal shrinkage behavior of raw material powders by coating them with a dopant and then molding the resultant. Patent Document 2 discloses that a sintered body consisting of laminates with different color tones can be obtained by applying vibrations that form boundary layers where the powders in the upper and lower layers are mixed, and then molding the laminates.

[0005] 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 provide a texture different from that of natural teeth, which has a texture due to variations in translucency.

[0006] Therefore, there is a demand for a zirconia laminate having gradation in translucency and color tone that can give an impression similar to that of natural teeth.Patent Document 3 discloses a dental prosthetic component having gradation in translucency and color tone, in which zirconia composition layers containing different amounts of yttria are laminated between adjacent layers.

[0007] US Patent Application Publication No. 2016 / 0157971 US Patent Application Publication No. 2014 / 0328746 US Patent Application Publication No. 2013 / 0221554

[0008] Conventional laminates made of zirconia composition layers used as dental prosthetic components have a structure in which layers with different compositions are laminated so that the color tone and transmittance gradually change from the back layer (the layer corresponding to the cervical part of the tooth) to the surface layer (the layer corresponding to the incisal edge) in order to give an impression similar to that of natural teeth. However, when layers with different compositions are laminated so that the color tone and transmittance gradually change, the surface layer (the layer on the incisal edge side of the denture) has high transmittance but low mechanical strength, which is a problem in that it is not possible to suppress the occurrence of chipping.

[0009] An object of the present disclosure is to provide at least one of a laminate, a precursor thereof, or a manufacturing method thereof, which has translucency and color gradation that can give an impression similar to that of natural teeth when viewed visually and can suppress chipping of the surface layer (layer on the incisal edge side of the denture).From another viewpoint, an object of the present disclosure is to provide at least one of a laminate, a precursor thereof, or a manufacturing method thereof that is suitable as a dental prosthetic component.

[0010] The present inventors have found that the above-mentioned problems can be solved by specifying the relationship between the content of a stabilizing element for zirconia in a surface layer and a layer adjacent to the surface layer, and have completed the invention according to the present disclosure. That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows.

[0011] [1] A laminate having a surface layer containing zirconia containing a stabilizing element and a compositionally graded layer composed of two or more unit layers, each of which contains zirconia containing a stabilizing element and a coloring element, wherein the compositionally graded layer is formed by stacking the unit layers such that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the compositionally graded layer does not vary or decreases from the surface layer side toward the surface side of the laminate opposite the surface layer, wherein the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface layer is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first compositionally graded layer, which is a unit layer adjacent to the surface layer among the unit layers constituting the compositionally graded layer. [2] The laminate according to [1], wherein the surface layer further contains a coloring element. [3] The laminate according to [1] or [2], wherein the content of the stabilizing element in the zirconia containing a stabilizing element contained in the surface layer is 2.5 mol% or more and 6.0 mol% or less. [4] The laminate according to any one of [1] to [3], wherein the difference between the stabilizing element content of the surface layer and the stabilizing element content of the first composition gradient layer is 0.2 mol% or more. [5] The laminate according to any one of [1] to [4], wherein the stabilizing element content of the zirconia containing the stabilizing element contained in the first composition gradient layer is 2.5 mol% or more and 6.0 mol% or less. [6] The laminate according to any one of [1] to [5], wherein the stabilizing element is one or more 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). [7] The laminate according to any one of [1] to [6], wherein the coloring element is at least one of a transition metal element and a lanthanoid rare earth element. [8] The laminate according to any one of [1] to [7], wherein the content of the coloring element is 0.01% by mass or more and 1.0% by mass or less. [9] The laminate according to any one of [1] to [8], wherein the warpage measured using a thickness gauge in accordance with JIS B 7524: 2008 is 1.0 mm or less.

[10] The laminate according to any one of [1] to [9], wherein the laminate is a sintered body.

[11] The laminate according to

[10] , wherein the surface layer has a three-point bending strength of 700 MPa or more as measured by a method in accordance with JIS R 1601.

[12] The laminate according to any one of [1] to [9], wherein the laminate is a calcined body.

[13] A method for producing a laminate according to any one of [1] to

[11] , comprising: a surface powder composition layer containing zirconia containing a stabilizing element; and a compositionally gradient powder composition layer composed of two or more unit powder composition layers, each of which contains zirconia containing a stabilizing element and a coloring element; the compositionally gradient powder composition layer is formed by stacking the unit powder composition layers such that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the compositionally gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact, opposite to the surface powder composition layer; and the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface powder composition layer is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first compositionally gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the compositionally gradient powder composition layer, the method comprising: sintering a compact at 1200°C or more and 1600°C or less.

[14] A process of calcining a compact at 800°C or more and less than 1200°C to obtain a calcined body, the compact having a surface powder composition layer containing zirconia containing a stabilizing element and a composition gradient powder composition layer composed of two or more unit powder composition layers, each of the unit powder composition layers containing zirconia containing a stabilizing element and a coloring element, the composition gradient powder composition layer being constructed by stacking the unit powder composition layers so that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the composition gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact opposite to the surface powder composition layer, the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface powder composition layer being smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first composition gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the composition gradient powder composition layer, and The method for producing a laminate according to any one of [1] to

[11] , further comprising a step of sintering the calcined body at 1200°C or higher and 1600°C or lower.

[15] A method for producing a laminate according to any one of [1] to [9] and

[12] , comprising: a step of calcining a compact at 800°C or more and less than 1200°C, the compact having a surface powder composition layer containing zirconia containing a stabilizing element, and a compositionally gradient powder composition layer composed of two or more unit powder composition layers, each of which contains zirconia containing a stabilizing element and a coloring element, the compositionally gradient powder composition layer being constructed by stacking the unit powder composition layers such that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the compositionally gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact on the opposite side from the surface powder composition layer, and the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface powder composition layer is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first compositionally gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the compositionally gradient powder composition layer.

[16] The manufacturing method according to any one of

[13] to

[15] , wherein the surface powder composition layer further contains a coloring element.

[17] The manufacturing method according to any one of

[13] to

[16] , wherein the powder composition contained in the powder composition layer is a granulated powder.

[18] A dental material comprising the laminate according to any one of [1] to

[12] .

[0012] The present disclosure can provide a laminate, a precursor thereof, or a manufacturing method thereof, which can give an impression similar to that of natural teeth, has gradation in translucency and color tone, and can suppress chipping of the surface layer (layer on the incisal edge side of the denture).Furthermore, it can provide at least one of a laminate, a precursor thereof, or a manufacturing method thereof, which is suitable as a dental prosthetic component.

[0013] Schematic diagram showing a cross section of a sintered body having a structure in which two unit zirconia layers are laminated. Schematic diagram showing a cross section of a sintered body having a structure in which four unit zirconia layers are laminated. 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 uniaxial pressing molding process when producing a laminate in the examples. Schematic diagram explaining the CIP processing molding process when producing a laminate in the examples.

[0014] The present disclosure will be described in detail below. Note that the explanation of the components described below is an example for explaining the present disclosure, and the present disclosure is not limited to these contents. Furthermore, the dimensional ratios of the drawings are not limited to the ratios shown in the drawings.

[0015] Furthermore, in this specification, when a preferred condition range for any requirement includes multiple preferred lower limit values ​​and multiple preferred upper limit values, any combination of these lower limit values ​​and upper limit values ​​may be used when interpreting the preferred condition range.

[0016] (Laminate) The laminate of this embodiment has a surface layer containing zirconia containing a stabilizing element, and a compositionally gradient layer composed of two or more unit layers, each of which contains zirconia containing a stabilizing element and a coloring element, and the compositionally gradient layer is composed by stacking the unit layers such that the content of the stabilizing element in the zirconia containing a stabilizing element contained in the compositionally gradient layer does not vary or decreases from the surface layer side toward the surface side opposite the surface layer of the laminate, and the content of the stabilizing element in the zirconia containing a stabilizing element contained in the surface layer is smaller than the content of the stabilizing element in the zirconia containing a stabilizing element contained in the first compositionally gradient layer, which is a unit layer adjacent to the surface layer among the unit layers constituting the compositionally gradient layer.

[0017] The laminate of this embodiment may be one or more selected from the group consisting of a sintered body, a calcined body, and a molded body, and is preferably at least one of a sintered body and a calcined 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. In this embodiment, the phrase "a surface layer containing zirconia containing a stabilizing element, a unit layer containing zirconia containing a stabilizing element and a coloring element, and a compositionally graded zirconia layer composed of two or more unit layers" may be replaced with "a surface zirconia layer containing zirconia containing a stabilizing element, a unit zirconia layer containing zirconia containing a stabilizing element and a coloring element, and a compositionally graded zirconia layer composed of two or more unit zirconia layers" when the laminate is a sintered body. Similarly, in an embodiment in which the laminate is a calcined body, the term "surface zirconia composition layer containing zirconia that contains a stabilizing element and has a necking structure, unit zirconia composition layers containing zirconia that contains a stabilizing element and has a necking structure and a coloring element, and a compositionally gradient zirconia composition layer constituted from two or more unit zirconia composition layers" may be used, and in an embodiment in which the laminate is a molded body, the term "surface powder composition layer made of a powder composition containing zirconia that contains a stabilizing element, unit powder composition layers containing zirconia that contains a stabilizing element and a coloring element and are made of a powder composition, and a compositionally gradient powder composition layer constituted from two or more unit powder composition layers" may be used. Hereinafter, the laminate of the present disclosure will be described with reference to an example of an embodiment in which the laminate is a sintered body.

[0018] (Sintered body) This embodiment is a sintered body having a surface zirconia layer containing zirconia containing a stabilizing element, and a composition-graded zirconia layer constituted by two or more unit zirconia layers, each of which contains zirconia containing a stabilizing element and a coloring element, and the composition-graded zirconia layer is constituted by stacking the unit zirconia layers such that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the composition-graded zirconia layer does not vary or decreases from the surface zirconia layer side toward the surface side of the sintered body opposite the surface zirconia layer, and the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface zirconia layer is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first composition-graded zirconia layer, which is a unit layer adjacent to the surface zirconia layer among the unit zirconia layers constituting the composition-graded zirconia layer.

[0019] The sintered body of this embodiment is a composition having a multilayer structure, a so-called laminate, and is a laminate consisting of a sintered structure. In this embodiment, the sintered structure is a structure mainly consisting of zirconia in the later stage of sintering. The sintered body of this embodiment has a surface zirconia layer containing zirconia containing a stabilizing element, and unit zirconia layers containing zirconia containing a stabilizing element and a coloring element. The composition-graded zirconia layer is composed of two or more unit zirconia layers. The surface zirconia layer may contain a coloring element. The surface zirconia layer and the unit zirconia layer are mainly composed of zirconia crystal particles containing a stabilizing element. Therefore, the sintered body of this embodiment can also be considered a laminate having three or more layers containing zirconia consisting of zirconia crystal particles containing a stabilizing element and, if a coloring element is contained, the coloring element.

[0020] <Laminated Structure> Fig. 1 is a schematic diagram showing an example of the structure of the sintered body of this embodiment, and schematically shows a cross section of a sintered body (100) having a surface zirconia layer (10) and a compositionally graded zirconia layer (20) composed of two or more unit zirconia layers (two unit zirconia layers in Fig. 1). The compositionally graded zirconia layer (20) includes a first compositionally graded zirconia layer (21) which is a unit zirconia layer adjacent to the surface zirconia layer (10), and a second compositionally graded zirconia layer (22) which is a unit zirconia layer located on the surface of the sintered body (100) opposite to the surface zirconia layer (10). In the laminated body (100) of this embodiment, the surface zirconia layer (10) is provided on one side of the first compositionally graded zirconia layer (21), and the second compositionally graded zirconia layer (22) which is a unit zirconia layer is provided on the other side of the first compositionally graded zirconia layer (21). In FIG. 1 , the direction in which the layers are stacked (the direction from the composition-gradient zirconia layer toward the surface zirconia layer; hereinafter also referred to as the “stacking direction”) is shown in the Y-axis direction, and the direction in which each layer extends (hereinafter also referred to as the “horizontal direction”) is shown in the X-axis direction.

[0021] Among the unit zirconia layers constituting the sintered body, adjacent layers may have the same or different stabilizing element contents, but preferably different stabilizing element contents. By having a structure in which zirconia layers containing zirconia with different stabilizing element contents are stacked, the sintered body becomes a stack in which a color change in the stacking direction based on the synergistic effect of the difference in stabilizing element content, translucency, etc. can be visually recognized.

[0022] Furthermore, the composition-graded zirconia layer is constructed by stacking the unit zirconia layers so that the content of the stabilizing element in the zirconia containing a stabilizing element contained in the composition-graded zirconia layer does not vary or decreases from the surface zirconia layer side toward the surface side of the sintered body opposite the surface zirconia layer (in the direction opposite to the Y direction in FIG. 1 , i.e., in the direction opposite to the stacking direction). Preferably, the composition-graded zirconia layer is constructed by stacking the unit zirconia layers so that the content of the stabilizing element in the zirconia containing a stabilizing element decreases toward the back surface side. This allows a color gradation to be formed in the sintered body based on the synergistic effect of the difference in the stabilizing element content and translucency. Furthermore, the content of the stabilizing element in the zirconia containing a stabilizing element contained in the surface zirconia layer is smaller than the content of the stabilizing element in the zirconia containing a stabilizing element contained in the first composition-graded zirconia layer.

[0023] Generally, increasing the content of stabilizing elements in the zirconia layer increases the translucency of the zirconia layer but decreases its mechanical strength. Conventional sintered bodies with translucency and color tone gradation increase the translucency by increasing the content of stabilizing elements in the zirconia in the surface layer (the layer on the incisal edge side of the denture). As a result, the mechanical strength of the surface layer (the layer on the incisal edge side of the denture) of the conventional sintered body is low, and chipping cannot be suppressed. However, in the sintered body of the present embodiment, the content of stabilizing elements in the zirconia containing the stabilizing elements in the surface zirconia layer is lower than the content of stabilizing elements in the zirconia containing the stabilizing elements in the first composition-graded zirconia layer. In other words, the sintered body of the present embodiment has a lower content of stabilizing elements in the zirconia in the surface layer (the layer on the incisal edge side of the denture) compared to conventional sintered bodies. Therefore, the sintered body of the present embodiment has a high mechanical strength in the surface layer (the layer on the incisal edge side of the denture) and can suppress chipping.

[0024] 1 shows a state in which the layers are in contact with each other via an interface. However, the sintered body of the present embodiment may be in a state in which the layers are stacked and sintered, and may be stacked without any visible interface, and the interface between the layers is not limited to a linear one.

[0025] The sintered body of this embodiment may have a structure in which three or more, or even four or more, unit zirconia layers are laminated. By increasing the number of unit zirconia layers, the sintered body becomes a laminate in which subtle changes in texture can be visually recognized. In order to achieve a texture more similar to that of natural teeth, the sintered body of this embodiment may, for example, have a structure in which three to ten, further three to six, further four to seven, or further four to six unit zirconia layers are laminated.

[0026] The compositionally-graded zirconia layer may have a unit zirconia layer (hereinafter also referred to as a "compositionally-graded intermediate zirconia layer") other than the first and second compositionally-graded zirconia layers between the first and second compositionally-graded zirconia layers, or may include a plurality of unit zirconia layers as the compositionally-graded intermediate zirconia layer. When the compositionally-graded intermediate zirconia layer is provided (the first unit zirconia layer stacked adjacent to the first compositionally-graded zirconia layer in the compositionally-graded intermediate zirconia layer is also referred to as the "third compositionally-graded zirconia layer," and the second or subsequent unit zirconia layers stacked from the third compositionally-graded zirconia layer toward the back surface are also referred to as the "fourth compositionally-graded zirconia layer," the "fifth compositionally-graded zirconia layer," etc.), the compositionally-graded intermediate zirconia layer has a structure in which the unit zirconia layers are stacked such that the content of the stabilizing element does not vary or decreases toward the opposite side to the stacking direction. That is, the content of the stabilizing element does not vary or decreases in the order of the third, fourth, and fifth composition-graded zirconia layers. From the viewpoint of making the color tone change based on the synergistic effect of the difference in the content of the stabilizing element, translucency, etc. more easily visible, it is preferable that the composition-graded intermediate zirconia layer has a structure in which unit zirconia layers are stacked so that the content of the stabilizing element decreases toward the opposite side to the stacking direction.

[0027] The sintered body of this embodiment having a compositionally graded intermediate zirconia layer will be described below with reference to FIG.

[0028] Fig. 2 is a schematic diagram showing an example of the structure of the sintered body of this embodiment, and shows a cross section of a sintered body (100) having a surface zirconia layer (10) and a compositionally-graded zirconia layer (20) composed of four unit zirconia layers. The sintered body shown in Fig. 2 has a structure in which, in addition to the surface zirconia layer, first compositionally-graded zirconia layer (21), and second compositionally-graded zirconia layer (22) described above, a third compositionally-graded zirconia layer (23a) and a fourth compositionally-graded zirconia layer (23b) which are compositionally-graded intermediate zirconia layers (23) are laminated. In the sintered body (100) of this embodiment, the content of the stabilizing element in the zirconia does not change or decreases in the order of the first compositionally graded zirconia layer (21), the third compositionally graded zirconia layer (23a), the fourth compositionally graded zirconia layer (23b), and the second compositionally graded zirconia layer (22), and the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface zirconia layer (10) is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in the first compositionally graded zirconia layer (21). The compositions of the surface zirconia layer and the compositionally graded zirconia layer will be described below.

[0029] <Composition of Zirconia Layer> As described above, the surface zirconia layer and the unit zirconia layer are layers containing zirconia as a main component (hereinafter also referred to as "zirconia layer"), and the zirconia is zirconia containing a stabilizing element (hereinafter also referred to as "stabilizing element-containing zirconia"). The sintered body and each zirconia layer of this embodiment contain not only stabilizing element-containing zirconia 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 as the

[0030] 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.

[0031] <<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 a stabilizing element that does not contain an element that has the function of coloring zirconia and has the function of suppressing the phase transition (hereinafter also referred to as a "non-coloring stabilizing element"), and a stabilizing element that contains 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 a non-coloring stabilizing element or a coloring stabilizing element, and preferably contains at least a non-coloring stabilizing element, and is preferably a non-coloring stabilizing element.

[0032] 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).

[0033] Examples of the non-coloring stabilizing element include one or more selected from the group consisting of yttrium, calcium, magnesium, and cerium, preferably at least one of yttrium and cerium, and more preferably yttrium. Examples of the coloring stabilizing element include one or more selected from the group consisting of praseodymium, neodymium, terbium, erbium, and ytterbium, preferably at least one of terbium and erbium, and more preferably erbium.

[0034] The stabilizing element is contained in the zirconia and is dissolved in the zirconia. Preferably, the sintered body of this embodiment does not contain an undissolved stabilizing element, that is, does not contain a stabilizing element that is not dissolved in the zirconia. In this embodiment, "does not contain 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. However, the inclusion of an undissolved stabilizing element is permissible as long as no XRD peaks derived from the stabilizing element are confirmed.

[0035] The content of the stabilizing element of zirconia contained in the surface zirconia layer (hereinafter also referred to as "stabilizing element content of the surface zirconia layer") is preferably 2.5 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, even more preferably 4 mol% or more, even more preferably 4.3 mol% or more, and even more preferably 4.9 mol% or more. The stabilizing element content of the surface zirconia layer may be 6.0 mol% or less, 5.8 mol% or less, 5.5 mol% or less, or 5.2 mol% or less. Examples of the stabilizing element content of the surface zirconia layer include 2.5 mol% to 6.0 mol%, 3.5 mol% to 5.2 mol%, 3.5 mol% to 6.0 mol%, and 3.5 mol% to less than 5.2 mol%.

[0036] The content of the stabilizing element of zirconia contained in the unit zirconia layer (hereinafter also referred to as "stabilizing element content of the unit zirconia layer") is preferably 2.5 mol% or more, more preferably 3.5 mol% or more, even more preferably 3.7 mol% or more, even more preferably 4.0 mol% or more, even more preferably 4.5 mol% or more, and even more preferably 4.9 mol% or more. The stabilizing element content of the unit zirconia layer may be 6.0 mol% or less, 5.8 mol% or less, 5.5 mol% or less, or 5.2 mol% or less. Examples of the stabilizing element content of the unit zirconia layer include 2.5 mol% to 6.0 mol%, 3.5 mol% to 5.5 mol%, 3.5 mol% to 6.0 mol%, and 3.5 mol% to less than 5.5 mol%.

[0037] The stabilizing element content of the surface zirconia layer is smaller than the stabilizing element content of the zirconia contained in the first composition-graded zirconia layer (hereinafter also referred to as the "stabilizing element content of the first composition-graded zirconia layer"). Specifically, the stabilizing element content of the surface zirconia layer is smaller than that of the first composition-graded zirconia layer, and the difference between the stabilizing element content of the surface zirconia layer and the stabilizing element content of the first composition-graded zirconia layer exceeds 0 mol%, preferably 0.05 mol% or more, more preferably 0.1 mol% or more, even more preferably 0.15 mol% or more, and even more preferably 0.2 mol% or more, or may be 2.5 mol% or less, 1.5 mol% to 1.0 mol% or less, 0.5 mol% or less, or 0.4 mol% or less. Within the above range, a sintered body having a high mechanical strength of the surface zirconia layer and capable of suppressing chipping is easily obtained. The difference between the stabilizing element content of the surface zirconia layer and the stabilizing element content of the first composition-gradient zirconia layer is preferably greater than 0 mol% and not more than 2.5 mol%, 0.05 mol% to 1.5 mol%, 0.1 mol% to 1.0 mol%, 0.15 mol% to 0.5 mol%, or 0.2 mol% to 0.4 mol%.

[0038] The content of the stabilizing element in the first composition-graded zirconia layer may be within the range of the content of the stabilizing element in the unit zirconia layer described above, and may be greater than the content in the surface zirconia layer.

[0039] The content of the stabilizing element of zirconia contained in the second composition-graded zirconia layer (hereinafter also referred to as the "stabilizing element content of the second composition-graded zirconia layer") may be within the range of the stabilizing element content of the unit zirconia layer described above, and is preferably greater than the stabilizing element content of the first composition-graded zirconia layer.

[0040] The content of the stabilizing element for zirconia contained in each layer in the composition-graded intermediate zirconia layer (hereinafter also referred to as the "stabilizing element content of the composition-graded intermediate zirconia layer") is equal to or greater than the minimum value and equal to or less than the maximum value of the content of the stabilizing element for zirconia contained in the first and second composition-graded zirconia layers. Furthermore, the stabilizing element content of the composition-graded intermediate zirconia layer does not vary or decreases from the surface zirconia layer side toward the opposite side of the stacking direction. From the viewpoint of making color tone changes based on the synergistic effects of the difference in stabilizing element content, translucency, and the like more easily visible, it is preferable that the stabilizing element content of the composition-graded intermediate zirconia layer decreases from the surface zirconia layer side toward the surface side opposite the surface zirconia layer of the laminate.

[0041] The sintered body of this embodiment preferably has a structure in which the difference in the content of the stabilizing element between adjacent unit zirconia layers in the composition-graded zirconia layer is 0.1 mol % or more, 0.3 mol % or more, 0.5 mol % or more, or 1.0 mol % or more. Also, the sintered body preferably has a structure in which the difference in the content of the stabilizing element between adjacent unit zirconia layers in the composition-graded zirconia layer is 3.0 mol % or less, 2.5 mol % or less, or 2.0 mol % or less.

[0042] The content of the stabilizing element in the sintered body of this embodiment (the content of the stabilizing element in the entire sintered body) is arbitrary, but is preferably greater than 1.5 mol%, preferably 2.5 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, even more preferably 4.1 mol% or more, and even more preferably 4.2 mol% or more. The content of the stabilizing element in the sintered body (the content of the stabilizing element in the entire sintered body) is arbitrary, but is preferably less than 7.0 mol%, more preferably 6.5 mol% or less, even more preferably 6.0 mol% or less, even more preferably 5.5 mol% or less, even more preferably 5.3 mol% or less, and even more preferably 5.0 mol% or less. These upper and lower limits may be combined in any way. Therefore, the content of the stabilizing element in the sintered body of this embodiment (the content of the stabilizing element in the entire sintered body) can be, for example, more than 1.5 mol% and less than 7.0 mol%, further 2.5 mol% to 6.5 mol%, further 3.0 mol% to 6.0 mol%, or even 3.5 mol% to 5.8 mol%, preferably 4.1 mol% to 5.5 mol%, more preferably 4.2 mol% to 5.3 mol%, and even more preferably 4.2 mol% to 5.0 mol%. The stabilizing element content of the sintered body is calculated using the following formula and varies depending on the thickness of each layer.

[0043] Stabilizing element content of sintered body = (thickness of surface zirconia layer / height of sintered body) × content of stabilizing element in stabilizing element-containing zirconia contained in surface zirconia layer + (thickness of each unit zirconia layer / height of sintered body) × content of stabilizing element in stabilizing element-containing zirconia contained in each unit zirconia layer

[0044] In this embodiment, the content of the stabilizing element is the molar ratio of the stabilizing element in oxide form to the total of zirconia and the stabilizing element in oxide form. ２ O ３ , calcium oxide is CaO, magnesium oxide is MgO, cerium oxide is CeO ２ , praseodymium oxide is Pr ６O １１ , neodymium oxide is Nd ２ O ３ , terbium oxide is Tb ４ O ７ , erbium oxide is Er ２ O ３ and ytterbium oxide is 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.

[0045] <<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, and erbium.

[0046] 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, titanium, and manganese, 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 one of terbium and erbium, and even more preferably at least erbium. Particularly preferred coloring elements include one or more selected from the group consisting of iron, titanium and erbium; cobalt, titanium and erbium; iron and erbium, further cobalt, titanium and erbium, and / or iron and erbium, and further iron and erbium.

[0047] The type and content of the coloring elements contained in the surface zirconia layer and the unit zirconia layer are not particularly limited, and may be appropriately selected taking into consideration the gradation of color tone of each layer, etc.

[0048] The content of the coloring element in the sintered body of this embodiment, expressed as the mass ratio of the coloring element, calculated as an oxide, relative to the mass of the sintered body of this embodiment, has a lower limit of more than 0 mass%, preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and even more preferably 0.04 mass% or more, and an upper limit of 1.5 mass% or less, preferably 1.0 mass% or less, more preferably 0.8 mass% or less, and even more preferably 0.3 mass% or less. Any combination of these upper and lower limits is acceptable. Therefore, the content of the coloring element in the sintered body of this embodiment, expressed as the mass ratio of the coloring element, calculated as an oxide, relative to the mass of the sintered body of this embodiment, may be, for example, more than 0 mass% to 1.5 mass% or less, preferably 0.01 mass% to 1.0 mass%, more preferably 0.03 mass% to 0.8 mass%, and even more preferably 0.04 mass% to 0.3 mass%. 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 elements 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 Pr ６ O １１ , neodymium oxide is Nd ２ O ３ , terbium oxide is Tb ４ O ７ , erbium oxide is Er ２ O ３ , ytterbium oxide is Yb ２ O ３ , iron oxide is Fe ２ O ３ , cobalt oxide is Co ３ O ４ , nickel oxide is NiO, manganese oxide is Mn ３ O ４, and titanium oxide is TiO ２ This can be done as follows.

[0049] The surface zirconia layer may contain a coloring element. The content of the coloring element contained in the surface zirconia layer, expressed as an oxide-equivalent mass ratio relative to the mass of the sintered body of this embodiment, is such that the lower limit is greater than 0 mass%, preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and even more preferably 0.04 mass% or more, and the upper limit is 2 mass% or less, preferably 1.2 mass% or less, more preferably 0.8 mass% or less, and even more preferably 0.3 mass% or less. Any combination of these upper and lower limits is acceptable. Therefore, the content of the coloring element contained in the surface zirconia layer, expressed as an oxide-equivalent mass ratio relative to the mass of the sintered body of this embodiment, is, for example, greater than 0 mass% and 2 mass% or less, preferably 0.01 mass% or more and 1.2 mass% or less, more preferably 0.03 mass% or more and 0.8 mass% or less, and even more preferably 0.04 mass% or more and 0.3 mass% or less. The content of the coloring element contained in the unit zirconia layer, expressed as the mass ratio of the coloring element, calculated as an oxide, relative to the mass of the sintered body of this embodiment, is preferably greater than 0 mass%, preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and even more preferably 0.04 mass% or more, and the upper limit is preferably 2 mass% or less, preferably 1.2 mass% or less, more preferably 0.8 mass% or less, and even more preferably 0.3 mass% or less. Any combination of these upper and lower limits is acceptable. Therefore, the content of the coloring element contained in the unit zirconia layer, expressed as the mass ratio of the coloring element, calculated as an oxide, relative to the mass of the sintered body of this embodiment, is preferably greater than 0 mass% and 2 mass% or less, preferably 0.01 mass% to 1.2 mass%, more preferably 0.03 mass% to 0.8 mass%, and even more preferably 0.04 mass% to 0.3 mass%.

[0050] In the sintered body of this embodiment, the difference in the content of the coloring element between adjacent zirconia layers is preferably 0% by mass or more, more preferably 0.002% by mass or more, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, even more preferably 0.015% by mass or more, and even more preferably 0.02% by mass or more. The greater the difference in the content of the coloring element, the greater the difference in color tone between the zirconia layers tends to be, but warping may also be greater. If the difference in the content of the coloring element between adjacent unit layers is less than 1% by mass, 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 unit layers is preferably 0% by mass or more but less than 1% by mass, 0.002% by mass or more but 0.8% by mass or less, or 0.005% by mass or more but 0.5% by mass or less, and it is preferable that the difference in the content of the coloring element between all adjacent unit layers satisfy this range.

[0051] The sintered body of this embodiment may contain alumina, preferably at least one zirconia layer contains alumina, and more preferably the surface zirconia layer and the compositionally graded zirconia layer contain alumina. When the sintered body of this embodiment contains alumina, the alumina content, expressed as a ratio of the mass of alumina to the mass of the sintered body, may be 0 mass% or more, such as 0 mass% to 0.15 mass%, further 0 mass% to 0.10 mass%, or even 0 mass% to 0.07 mass%. When alumina is contained, for example, the lower limit of the alumina content is greater than 0 mass%, preferably 0.005 mass% or more, more preferably 0.01 mass% or more, and the upper limit of the alumina content is 0.15 mass% or less, preferably 0.10 mass% or less, and more preferably 0.07 mass% or less. These upper and lower limits may be in any combination. Therefore, the alumina content is, for example, more than 0 mass% and 0.15 mass% or less, preferably 0.005 mass% or more and 0.10 mass% or less, and more preferably 0.01 mass% or more and 0.07 mass% or less.

[0052] The alumina content of the zirconia layer may be within the same range as described above. The alumina content of the zirconia layer may affect the thermal shrinkage behavior during the calcination step. The alumina content of the zirconia layer is arbitrary, and the zirconia layers may have different alumina contents, but it is preferable that the alumina contents are equal. When the alumina contents of the zirconia layers are different, 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, further 0.1 mass% or less, or even 0.01 mass% or less. Any combination of these upper and lower limits may be used. Therefore, the difference in alumina content between adjacent zirconia layers can be, for example, more than 0 mass% and 0.15 mass% or less, further more than 0 mass% and 0.1 mass% or less, further more than 0 mass% and 0.01 mass% or less, and further more than 0.05 mass% and 0.01 mass% or less. For example, alumina (Al ２ O ３ In the case of a zirconia layer comprising zirconia containing yttrium as a non-coloring stabilizing element and erbium as a coloring stabilizing element, the alumina content is {Al ２ O ３ / (ZrO ２ +Y ２ O ３ + Er ２ O ３ +Al ２ O ３ )}×100 (mass %).

[0053] 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.

[0054] 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.

[0055] 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

[0056] The obtained XRD pattern is smoothed and background removed, and then profile-fitted using a split pseudo-Voigt function to determine the ratio of tetragonal to cubic crystals (the ratio of integrated peak intensities), and the crystalline phase with the highest ratio is 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).

[0057] <Characteristics of the sintered body and each zirconia layer (each sintered body layer) constituting the sintered body> The sintered body (100) shown in Figures 1 and 2 shows each layer 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, or any one of the layers may be thick. From the viewpoint of achieving a texture similar to that of natural teeth, the thickness of the surface zirconia layer is preferably thinner than the thickness of the composition-graded zirconia layer, and is further preferably thinner than the thickness of the unit zirconia layers constituting the composition-graded zirconia layer.

[0058] The thickness ratio of the surface zirconia layer to the compositionally graded zirconia layer is not particularly limited, but is preferably 1:1 to 1:50, more preferably 1:1 to 1:30, and even more preferably 1:2 to 1:20, in terms of the thickness of the surface zirconia layer:the thickness of the compositionally graded zirconia layer.

[0059] The shape of the sintered body of this embodiment may be any shape, including at least one selected from the group consisting of spherical, elliptical, discoid, cylindrical, cubic, rectangular, and polyhedral shapes, shapes suitable for dental materials including dental prosthetic materials such as crowns, bridges, onlays, and onlays, and any other shape depending on the intended use. Note that in this embodiment, the term "spherical" may include shapes similar to a true sphere other than a true sphere, such as an approximately spherical shape, and the term "polyhedral" may include shapes similar to a polyhedron, such as an approximately polyhedral shape, in addition to a polyhedron.

[0060] The dimensions of the sintered body of this embodiment are arbitrary, and examples thereof 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 arbitrary, but examples thereof include a thickness of 4 mm to 40 mm, and further, a thickness of 5 mm to 30 mm.

[0061] <<Warpage and Deformation of Sintered Body>> The warpage in this embodiment is a value measured using a thickness gauge (hereinafter simply referred to as "gauge") in accordance with JIS B 7524:2008. The warpage of the sintered body of this embodiment is preferably 1.0 mm or less, more preferably 0.3 mm or less, even more preferably 0.2 mm or less, even more preferably 0.1 mm or less, and particularly preferably 0.05 mm or less. It is preferable that the sintered body has no warpage (warpage of 0 mm), but the sintered body of this embodiment may have warpage that cannot be measured with a gauge (warpage of 0 mm or more). For example, the sintered body of this embodiment may have warpage exceeding 0 mm, or even 0.01 mm or more. The warpage is preferably 0.06 mm or less, even 0.05 mm or less, or even less than the measurement limit (less than 0.03 mm). The warpage of the sintered body of this embodiment can be, for example, less than the measurement limit, 0 mm or more and 0.06 mm or less, 0 mm or more and 0.05 mm or less, or 0 mm or more and less than 0.03 mm.

[0062] 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 (laminate) is placed in contact with a horizontal plate. FIG. 3 is a schematic diagram showing a method for measuring warpage. The sintered body (300) shows a cross section of a disk-shaped sample, and shows the sintered body warped in the stacking direction (Y-axis direction). For ease of explanation, FIG. 3 exaggerates the warpage of the sintered body (300). As shown in FIG. 3, when measuring warpage, the sintered body (300) is placed so that the convex portion of the uneven sintered body (300) is in contact with the horizontal plate (31). This forms a gap between the surface where the sintered body (300) and the horizontal plate (31) come into contact (hereinafter also referred to as the "bottom surface") and the horizontal plate (31). The gauge is inserted into the gap, and the maximum thickness of the gauge that can be inserted is used to measure warpage. In Figure 3, the gauge (32A) is located below the bottom surface of the sintered body (300) and can be inserted into the gap, while the gauge (32B) is not located below the bottom surface of the sintered body (300) and cannot be inserted into the gap. The gauges (32A) and (32B) in Figure 3 differ from each other in thickness by one step (e.g., 0.01 mm), and the warpage of the sintered body (300) is the thickness of the gauge (32A). For ease of explanation, Figure 3 shows both gauges (32A) and (32B) inserted, but warpage can be measured by inserting the gauges into the gap in order from thinnest to thickest (e.g., after measurement using the gauge (32A), it can be removed and then measured using the thicker gauge (32B)).

[0063] The sintered body of this embodiment preferably has a warpage (hereinafter also referred to as "deformation amount") relative to the dimensions of the sintered body of 1.0 or less, more preferably 0.5 or less, even more preferably 0.2 or less, and even more preferably 0.15 or less. The deformation amount can be, for example, 0 or more, further 0.01 or more, or further 0.05 or more.

[0064] The amount of deformation can be calculated using the following formula: Deformation = (Warpage: mm) / (Dimensions of sintered body: mm) × 100 The dimensions of the sintered body are the size of the sintered body in a direction perpendicular to the direction of warpage. Since the sintered body (300) in FIG. 3 is aligned along the stacking direction (Y-axis direction), the dimensions of the sintered body (300) are the size (33) 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 such as a vernier caliper or a micrometer. 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 calculated by using a vernier caliper to measure the diameter of the upper end and the diameter of the lower end at four points each, calculating the average of the diameters of the upper end and the lower end, and using the average of the calculated values ​​as the dimensions of the laminate.

[0065] In this embodiment, the warpage and deformation are preferably measured using a disk-shaped sample, and more preferably using a disk-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 is 0.2 / 105 × 100 = 0.19.

[0066] <<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 Above, 5.9g / cm ３ or more than 6.0 g / cm ３ The upper limit of the density is 6.3 g / cm ３ or less than 6.1 g / cm ３ The density of the calcined body is, for example, 5.7 g / cm or less. Any combination of these upper and lower limits is acceptable. ３ 6.3g / cm or more ３ 5.9 g / cm or less ３ 6.1g / cm or more ３ or less, or 6.0 g / cm ３ 6.1g / cm or more ３The 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.

[0067] <<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 is L ＊ a ＊ b ＊ Lightness L indicated by the color system ＊ The lower limit of the lightness L ＊ The upper limit of hue a is 90 or less, preferably 85 or less. ＊ The lower limit of hue a is -5 or more, preferably -3 or more, ＊ The upper limit of hue b is 5 or less, preferably 3 or less, ＊ The lower limit of hue b is 0 or more, preferably 3 or more, ＊ The upper limit of the hue a is 25 or less, preferably 20 or less. Any combination of these upper and lower limits is acceptable. Therefore, the color tone of the sintered body of this embodiment or each zirconia layer (each sintered body layer) is, for example, 60 or more and 90 or less, preferably 65 or more and 85 or less, and the hue a ＊ is -5 or more and 5 or less, preferably -3 or more and 3 or less, and hue b ＊ is, for example, from 0 to 25, preferably from 3 to 20. When the color tone is in this range, the sintered body exhibits a color tone similar to that of natural teeth.

[0068] Since the sintered body of this embodiment has a change in color tone, the saturation C of each zirconia layer ＊ 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 saturation C of adjacent unit zirconia layers in the composition-graded zirconia layer is calculated by＊ The absolute value of the difference (△C ＊ ) is 0.1 or more, further 0.3 or more, further 1.0 or more, further 1.5 or more, and the absolute value (ΔC ＊ ) is 15.0 or less, further 10.0 or less, further 5.0 or less, or further 3.0 or less. Any combination of these upper and lower limits is acceptable. Therefore, in the sintered body of this embodiment, the saturation C ＊ The absolute value of the difference (△C ＊ ) can be, for example, 0.1 or more and 15.0 or less, further 0.3 or more and 10.0 or less, further 1.0 or more and 5.0 or less, or further 1.5 or more and 3.0 or less. ＊ When the lightness L of adjacent unit zirconia 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 preferably 0.1 or more, more preferably 0.5 or more, and is preferably 15.0 or less, more preferably 10.0 or less.

[0069] Color tone (L ＊ , a ＊ and b ＊ ) and C ＊ can be determined using a spectrophotometer equipped with an illumination and light-receiving optical system conforming to the geometric condition c of JIS Z 8722, and using values ​​measured by the SCI method. An example of a spectrophotometer is the CM-700d manufactured by Konica Minolta. To measure the color tone of the sintered body or sintered body layer of this embodiment, a measurement sample can be obtained by cutting out any part of the sintered body in the horizontal direction and processing it into a disk shape with a diameter of 20 mm, a thickness of 1.0±0.1 mm, and a surface roughness (Ra) of ≦0.02 μm. ＊ Specific measurement conditions for the method of placing a measurement sample on a black board (so-called black back measurement) include the following: Light source: D65 light source Viewing angle: 10° Measurement method: SCI

[0070] <<Transmittance of Sintered Body or Sintered Body Layer>> The sintered body of this embodiment preferably includes at least a zirconia layer having a translucent appearance. Furthermore, it is preferable to have at least a zirconia layer having a total luminous transmittance (hereinafter also simply referred to as "total luminous transmittance") of preferably 15% or more, more preferably 20% or more, and even more preferably 23% or more, relative to CIE Standard Illuminant D65 at a sample thickness of 1.0±0.1 mm. It is also preferable to have a zirconia layer having a total luminous transmittance of preferably 60% or less, more preferably 55% or less, and even more preferably 50% 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.

[0071] In the sintered body of this embodiment, the difference in total light transmittance between adjacent zirconia layers (each sintered body layer) is preferably 1% or more, more preferably 1.5% or more, and more preferably 10% or less, more preferably 5% or less.

[0072] The total light transmittance of the sintered body of this embodiment may be measured by cutting out any portion of the sintered body in the horizontal direction and processing it to a thickness of 1.0±0.1 mm to prepare a measurement sample.

[0073] 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 having a thickness of 1.0±0.1 mm and a surface roughness (Ra)≦0.02 μm is used as a measurement specimen, and light from the CIE standard illuminant D65 is irradiated onto the sample using a general turbidity meter (e.g., NDH4000, manufactured by NIPPON DENSOKU). 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.

[0074] <<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 in accordance with JIS R 1601, is preferably 500 MPa or more, more preferably 550 MPa or more, more preferably 600 MPa or more, and even more preferably 800 MPa or more. The three-point bending strength can be, for example, less than 1300 MPa, or even 1200 MPa or less, and is preferably 500 MPa or more and less than 1300 MPa, or 800 MPa or more and 1200 MPa or less. The three-point bending strength of the surface zirconia layer (sintered body layer), measured by a method in accordance with JIS R 1601, is preferably 700 MPa or more, more preferably 750 MPa or more, and even more preferably 800 MPa or more. If the three-point bending strength of the surface zirconia layer (sintered body layer) is 700 MPa or more, chipping can be sufficiently suppressed. To suppress chipping, the surface zirconia layer has a higher three-point bending strength than the first composition-graded zirconia layer, and the difference is preferably 50 MPa or more, 100 MPa or more, or 150 MPa or more. The difference in three-point bending strength between the surface zirconia layer and the first composition-graded zirconia layer can be any value as long as it does not impair aesthetics, but it should be 500 MPa or less, or even 300 MPa or less.

[0075] FIG. 4 is a schematic diagram showing the measurement of the three-point bending strength of a zirconia layer (sintered body layer) (400). In FIG. 4, the Y-axis direction represents the stacking direction, and the X-axis direction represents the horizontal direction. The measurement sample used for the three-point bending strength measurement is a rectangular parallelepiped sintered body manufactured with the thickness as the stacking direction and the width and length as the horizontal directions. As shown in FIG. 4, the three-point bending strength may be measured by applying a load (41) perpendicular to the length of the measurement sample (400). The measurement sample may be positioned so that the load (41) is applied to the middle of the support distance (42). The three-point bending strength measurement uses a columnar sintered body with a support distance of 30 mm, a width of 4 mm, and a thickness of 3 mm as the measurement sample. The crosshead speed is 0.5 mm / min, and the average value of 10 measurements may be used to determine the three-point bending strength of the zirconia layer (sintered body layer) according to this embodiment.

[0076] Next, referring to an embodiment in which the laminate is a calcined body, the main points that differ from the above-mentioned sintered body will be described.

[0077] (Calcined body) The calcined body of this embodiment is a calcined body having a surface zirconia composition layer containing zirconia that contains a stabilizing element and has a necking structure, and a composition-graded zirconia composition layer constituted by two or more unit zirconia composition layers, each of which contains zirconia that contains a stabilizing element and has a necking structure, and a coloring element, and the composition-graded zirconia composition layer is constituted by stacking the unit zirconia composition layers such that the content of the stabilizing element in the zirconia that contains the stabilizing element contained in the composition-graded zirconia composition layer does not vary or decreases from the surface zirconia composition layer side toward the surface side of the calcined body opposite to the surface zirconia composition layer, The calcined body has a stabilizing element content of zirconia containing a stabilizing element contained in the surface zirconia composition layer that is smaller than the stabilizing element content of zirconia containing a stabilizing element contained in a first composition-graded zirconia composition layer, which is a unit zirconia composition layer adjacent to the surface zirconia composition layer among the unit zirconia composition layers that constitute the composition-graded zirconia composition layer.

[0078] The calcined body is a composition having a multilayer structure, i.e., a laminate, and is a laminate consisting of a structure having a necking structure, i.e., calcined particles. The calcined body can be processed as necessary and used as a precursor of a sintered body, and is also called a pre-sintered body, a soft sintered body, or a semi-sintered body.

[0079] The necking structure is a structure possessed by zirconia heat-treated below the sintering temperature, and is a structure in which zirconia particles are chemically adhered to each other. As shown in FIG. 5 , the zirconia (51) contained in the surface zirconia composition layer and the unit zirconia composition layer (hereinafter also referred to as the "zirconia composition layer") of the calcined body shows a part of the particle shape of zirconia in the powder composition. 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 as a laminate having three or more layers, each layer containing zirconia consisting of zirconia particles having a necking structure of zirconia containing a stabilizing element and a layer containing the coloring element, if a coloring element is included.

[0080] The calcined body has a zirconia composition layer (hereinafter also referred to as "composition layer") containing zirconia having a necking structure and a coloring element, if any, instead of a zirconia layer, and has a structure equivalent to the laminate structure described for the sintered body. In the calcined body, the stabilizing element and the coloring element may be in a state of solid solution in zirconia, or in a state of an oxide or a precursor thereof.

[0081] <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 has been heat-treated at a temperature lower than the sintering temperature, more preferably in a state where zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of a zirconium compound has been heat-treated at a temperature lower than 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 has been heat-treated at a temperature lower than the sintering temperature.

[0082] The calcined body and each composition layer may contain any amount of stabilizing elements as long as it is the same as that of the sintered body of the present embodiment. The calcined body preferably contains at least a zirconia composition layer containing zirconia having a tetragonal or cubic crystal as a main phase.

[0083] <Characteristics of the calcined body and layers constituting the calcined body> The calcined body preferably has a warpage of 1.0 mm or less, more preferably 0.5 mm or less, even more preferably 0.3 mm or less, even more preferably 0.2 mm or less, even more preferably 0.1 mm or less, and even more preferably 0.05 mm or less. The calcined body preferably has no warpage (warpage of 0 mm), but may have warpage that cannot be measured with a gauge (warpage of 0 mm or more). For example, 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, even 0.05 mm or less, or even less than the measurement limit (less than 0.03 mm).

[0084] The calcined body preferably has a deformation amount of 1.0 or less, more preferably 0.5 or less, still more preferably 0.2 or less, and even more preferably 0.15 or less. The deformation amount can be, for example, 0 or more, further 0.01 or more, or even 0.05 or more.

[0085] The calcined body has a density of 2.4 g / cm ３ More preferably, 3.1 g / cm ３ More preferably, it is 3.7 g / cm or more. ３ Preferably, it is 3.5 g / cm or less. ３ It is more preferable that the density is less than 40%. A density in this range corresponds to a relative density of 40% to 60%. The calcined body may be any laminate having strength suitable for processing such as CAD / CAM processing. The density of the calcined body can be determined from the mass determined by mass measurement and the volume determined by dimensional measurement.

[0086] The color tone of the zirconia composition layer contained in the calcined body may be different from that of the sintered body obtained by sintering the calcined body, or may not change in color. The calcined body and each zirconia composition layer are opaque and have a total light transmittance of 0%, but when measurement error is taken into consideration, the total light transmittance may be, for example, 0% or more and 0.2% or less. The calcined body may have a strength that is low in defects during processing such as CAD / CAM or cutting, and may have a Vickers hardness of, for example, 25 HV to 150 HV (= kgf / mm２ ) or less, or 30 HV to 130 HV. Measurement of Vickers hardness can be performed 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 measurement sample, and visually measuring the diagonal length of the indentation mark formed on the surface of the measurement 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.

[0087] The laminate of this embodiment can be used for known zirconia applications such as decorative members, structural materials, and optical materials, but 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 produced. Furthermore, when the laminate is a calcined body, it can be suitably used as a precursor for dental materials, such as crowns and bridges, and can be used as dental prosthetic materials such as blanks, discs, blocks, and mill blanks, and precursors thereof. Furthermore, a dental material containing the laminate of this embodiment can be produced.

[0088] (Method for manufacturing laminate) Next, a method for manufacturing a laminate of this embodiment will be described. In the embodiment where the laminate is a sintered body, the manufacturing method includes a step of sintering a compact at 1200°C or higher and 1600°C or lower, the compact having a surface powder composition layer containing zirconia containing a stabilizing element and a compositionally gradient powder composition layer composed of two or more unit powder composition layers, each of the unit powder composition layers containing zirconia containing a stabilizing element and a coloring element, the compositionally gradient powder composition layer being configured by stacking each unit powder composition such that the content of the stabilizing element of the zirconia containing a stabilizing element contained in the compositionally gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact opposite to the surface powder composition layer, and the content of the stabilizing element of the zirconia containing a stabilizing element contained in the surface powder composition layer is lower than the content of the stabilizing element of the zirconia containing a stabilizing element contained in a first compositionally gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the compositionally gradient powder composition layer.

[0089] Another manufacturing method of the present embodiment is a method for manufacturing a laminate, the method comprising: calcining a compact at 800°C or more and less than 1200°C to form a calcined body; and sintering the calcined body at 1200°C or more and 1600°C or less; the method comprising: a surface powder composition layer containing zirconia containing a stabilizing element; and a compositionally gradient powder composition layer composed of two or more unit powder composition layers, each of which contains zirconia containing a stabilizing element and a coloring element; the compositionally gradient powder composition layer is constructed by stacking each unit powder composition such that the content of the stabilizing element in the zirconia containing a stabilizing element contained in the compositionally gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact, opposite the surface powder composition layer; and the content of the stabilizing element in the zirconia containing a stabilizing element contained in the surface powder composition layer is smaller than the content of the stabilizing element in the zirconia containing a stabilizing element contained in a first compositionally gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the compositionally gradient powder composition layer.

[0090] Furthermore, still another production method of the present embodiment is a calcined body having a surface zirconia composition layer containing zirconia that contains a stabilizing element and has a necking structure, and a composition-graded zirconia composition layer constituted by two or more unit zirconia composition layers, each of which contains zirconia that contains a stabilizing element and has a necking structure, and a coloring element, and the composition-graded zirconia composition layer is constituted by stacking the unit zirconia composition layers such that the content of the stabilizing element in the zirconia that contains the stabilizing element contained in the composition-graded zirconia composition layer does not vary or decreases from the surface zirconia composition layer side toward the surface side of the calcined body opposite to the surface zirconia composition layer, a calcined body having a stabilizing element content of zirconia containing a stabilizing element contained in a surface zirconia composition layer that is smaller than the stabilizing element content of zirconia containing a stabilizing element contained in a first composition-graded zirconia composition layer, the first composition-graded zirconia composition layer being a unit zirconia composition layer adjacent to the surface zirconia composition layer among the unit zirconia composition layers constituting the composition-graded zirconia composition layer, at 1200°C or higher and 1600°C or lower.

[0091] a surface powder composition layer containing zirconia containing a stabilizing element and a composition gradient powder composition layer composed of two or more unit powder composition layers, each of which contains zirconia containing a stabilizing element and a coloring element; a composition gradient powder composition layer formed by stacking the unit powder composition layers such that the content of the stabilizing element in the zirconia containing a stabilizing element contained in the composition gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact, the surface powder composition layer having a content of the stabilizing element smaller than the content of the stabilizing element in the zirconia containing a stabilizing element contained in a first composition gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the composition gradient powder composition layer;

[0092] (Molded body) The molded body used in the manufacturing method of this embodiment will be described below in terms of the main differences from the sintered body and calcined body described above. The molded body used in the manufacturing method of this embodiment has a surface powder composition layer containing zirconia containing a stabilizing element, and a compositionally gradient powder composition layer composed of two or more unit powder composition layers, each of which contains zirconia containing a stabilizing element and a coloring element, and the compositionally gradient powder composition layer is formed by stacking each unit powder composition layer such that the content of the stabilizing element in the zirconia containing a stabilizing element contained in the compositionally gradient powder composition layer does not change or decreases from the surface powder composition layer side toward the surface powder composition side of the molded body opposite the surface powder composition layer, and the content of the stabilizing element in the zirconia containing a stabilizing element contained in the surface powder composition layer is smaller than the content of the stabilizing element in the zirconia containing a stabilizing element contained in the first compositionally gradient powder composition layer, which is the unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the compositionally gradient powder composition layer.

[0093] The molded body is a composition having a multilayer structure, a so-called laminate, and is a laminate made of a powder composition. The molded body can be used as a precursor for a calcined body or a sintered body. Instead of having a zirconia layer, the molded body has a powder composition layer (hereinafter also referred to as a "powder layer") made of a powder composition containing zirconia containing a stabilizing element, and has a structure equivalent to the laminate structure described for the sintered body. 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 may be in a state of solid solution in zirconia or in the state of an oxide or its precursor. 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. The surface powder composition layer may contain a coloring element. When a coloring element is contained, it is preferable that the coloring element contains at least an oxide.

[0094] The molded article preferably has a warpage of 1.0 mm or less, more preferably 0.3 mm or less, even more preferably 0.2 mm or less, even more preferably 0.1 mm or less, and even more preferably 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, even 0.05 mm or less, or even less than the measurement limit (less than 0.03 mm).

[0095] The deformation amount of the molded article is preferably 1.0 or less, more preferably 0.5 or less, more preferably 0.2 or less, and even more preferably 0.15 or less. The deformation amount can be, for example, 0 or more, further 0.01 or more, or even 0.05 or more.

[0096] The zirconia contained in the powder layer is preferably zirconia obtained by heat-treating a zirconia sol, more preferably zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of a zirconium compound, and even more preferably zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of zirconium oxychloride. The zirconia contained in the powder layer is preferably zirconia powder. The average particle size of the zirconia powder is preferably 0.3 μm or more and 0.7 μm or less, and more preferably 0.4 μm or more and 0.5 μm or less.

[0097] 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 fast 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.

[0098] [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 general device (for example, Tristar II 3020, manufactured by Shimadzu Corporation).

[0099] 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.

[0100] 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 one or more selected from the group consisting of polyvinyl alcohol, polyvinyl butyrate, wax, and acrylic resin, preferably one or more 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 one or more selected from the group consisting of polyacrylic acid, polymethacrylic acid, acrylic acid copolymers, and methacrylic acid copolymers, and derivatives thereof.

[0101] The contents of the stabilizing element and the coloring element in the compact and each powder layer are arbitrary, provided that they are the same as those in the sintered body of the present embodiment described above.

[0102] When each powder layer contains a binder, from the viewpoint of suppressing defects during molding, the binder content of each powder layer is preferably 1.5% by mass or more, more preferably 2.0% by mass or more, and even more preferably 2.5% by mass or more, and the binder content of each powder layer is preferably 8.0% by mass or less, more preferably 6.0% by mass or less, and even more preferably 5.5% by mass or less. Any combination of these upper and lower limits is acceptable. Therefore, the binder content of each powder layer is, for example, preferably 1.5% by mass or more, more preferably 1.5% by mass or more and 8.0% by mass or less, more preferably 2.0% by mass or more and 6.0% by mass or less, and even more preferably 2.5% by mass or more and 5.5% by mass or less.

[0103] 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, and the powder composition is produced. In order to suppress warping of the molded body, it is preferable to adjust the binder content of each powder layer depending on the stabilizing element content of the adjacent powder layer.

[0104] From the viewpoint of operability, the powder composition contained in the powder layer is preferably a powder in which the binder is granulated when it contains zirconia powder, a coloring element, and a binder (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, preferably 5 μm or more, and an upper limit of 150 μm or less, preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 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, for example, 1 μm or more and 150 μm or less, preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more and 50 μm or less, and even more preferably 5 μm or more and 30 μm or less. In another embodiment, a diameter of 20 μm or more and 50 μm or less can be exemplified. In this embodiment, the average agglomerate diameter is a diameter corresponding to 50% of the cumulative total in 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), and is the volume diameter of particles that are approximately spherical. As a pretreatment, prior to measurement, the granulated powder may be sieved using a sieve with 125 μm openings.

[0105] The molded body preferably includes at least a powder layer containing zirconia having a tetragonal or cubic crystal as a main phase.

[0106] The molded body has a density of, for example, 2.4 g / cm ３ or more, preferably 3.1 g / cm ３ Above, 3.7g / cm ３ Preferably 3.5 g / cm or less ３ The density of the molded body can be calculated from the mass obtained by measuring the mass and the volume obtained by measuring the dimensions.

[0107] The color tone of the zirconia layer contained in the molded body may be different from that of the sintered body obtained by sintering it, or there may be no change in color tone. The molded 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% to 0.2%. The molded body only needs to have a strength sufficient to prevent cracking or chipping when used during calcination or sintering.

[0108] 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 back surface layer is filled into a mold to form the back surface layer. Then, a powder composition having a composition corresponding to the layer adjacent to the back surface layer is filled on top of the back surface layer. To obtain a compact having a structure in which three or more powder layers are laminated, a similar operation can be repeated to laminate the necessary powder compositions. After filling with a powder composition having a composition corresponding to the surface layer, the preform is obtained by uniaxial pressing at an appropriate pressure, and this is then subjected to cold isostatic pressing (hereinafter also referred to as "CIP") to obtain the compact. During lamination, 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 surface layer; it is preferable not to apply pressure before filling with the powder composition having a composition corresponding to the surface layer.

[0109] The molding pressure of the uniaxial pressing is preferably 15 MPa or more, more preferably 18 MPa or more, and preferably 200 MPa or less, and more preferably 100 MPa or less. In the uniaxial pressing, warping of the molded body tends to be suppressed as the molding pressure increases. The pressure of the CIP treatment can be 98 MPa or more and 392 MPa or less. By treating the molded body at a temperature below the sintering temperature, the molded body becomes a calcined body. Known methods can be used for the calcination method and calcination conditions.

[0110] The holding temperature during calcination (hereinafter also referred to as "calcination temperature") may be, for example, 800°C or higher but lower than 1200°C, preferably 900°C or higher but 1150°C or lower, and more preferably 950°C or higher but 1100°C or lower. The holding time at the calcination temperature (hereinafter also referred to as "calcination time") is, for example, preferably 0.5 hours or higher but 5 hours or lower, more preferably 0.5 hours or higher but 3 hours or lower. The temperature may be raised in multiple stages, with the temperature increase rate and holding time at the raised temperature being different. For example, calcination may be performed under conditions such as raising from room temperature to 300°C at 15°C / hour, holding at 300°C for 5 hours, raising from 300°C to 700°C at 15°C / hour, holding at 700°C for 1 hour, raising from 700°C to 1000°C at 50°C / hour, and holding at 1000°C for 2 hours.

[0111] The atmosphere in the calcination step (hereinafter also referred to as "calcination atmosphere") is preferably an atmosphere other than a reducing atmosphere, more preferably at least one of an oxygen atmosphere or an air atmosphere, and even more preferably an air atmosphere.

[0112] In the manufacturing method of this embodiment, either a compact or a calcined body (hereinafter, collectively referred to as "compact, etc.") is treated at 1200°C or higher and 1600°C or lower. This converts the compact, etc., into a sintered body. Prior to sintering, the compact, 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 only, 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 is a method of sintering by simply heating the material to be sintered without applying an external force during sintering.

[0113] 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, more preferably 1400°C or higher, even more preferably 1430°C or higher, and even more preferably 1480°C or higher, and an upper limit of 1650°C or lower, preferably 1580°C or lower, more preferably 1560°C or lower, even more preferably 1560°C or lower, and even more preferably 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, preferably 1300°C or higher and 1580°C or lower, more preferably 1400°C or higher and 1560°C or lower, even more preferably 1430°C or higher and 1560°C or lower, and even more preferably 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, and more preferably 1550°C or higher and 1650°C or lower. The heating rate to the sintering temperature can have a lower limit of 50°C / hour or higher, preferably 100°C / hour or higher, more preferably 150°C / hour or higher, and an upper limit of 800°C / hour or lower, preferably 700°C / hour or lower. Any combination of these upper and lower limits is acceptable. Therefore, the heating rate to the sintering temperature can be, for example, 50°C / hour or higher and 800°C / hour or lower, preferably 100°C / hour or higher and 800°C / hour or lower, more preferably 150°C / hour or higher and 800°C / hour or lower, and even more preferably 150°C / hour or higher and 700°C / hour or lower. The holding time at the sintering temperature (hereinafter also referred to as "sintering time") varies depending on the sintering temperature, but preferably the lower limit is 1 hour or more and the upper limit is 5 hours or less, more preferably 3 hours or less, and even more preferably 2 hours or less. Any combination of these upper and lower limits is acceptable. Therefore, the sintering time varies depending on, for example, the sintering temperature, but is preferably 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 heating from room temperature to 1500°C at 100°C / hour and holding at 1500°C for 2 hours.

[0114] 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 about 18 to 23% by volume. Preferred sintering conditions in the sintering step include atmospheric sintering in an air atmosphere.

[0115] The laminate of the present disclosure will be described below using examples, but the present disclosure is not limited to these examples.

[0116] (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

[0117] (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 used as the measurement sample.

[0118] (Warpage and Deformation Amount) A disk-shaped laminate (a compact, a calcined body, or a sintered body) was used as a measurement sample, and the amount of deformation of each was calculated using the following formula (3): Amount of deformation = (Warpage: mm) / (Dimensions: mm) × 100 (3)

[0119] 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 powder used in the laminate) Molding pressure: Uniaxial pressing: 49 MPa + CIP treatment: 196 MPa Molding process: Raw material powder for forming the first layer is placed in the mold → leveling → Raw material powder for forming the second layer is placed in the mold → leveling → (repeated) → Uniaxial pressing → CIP treatment

[0120] In the production of the laminate, a schematic diagram of the uniaxial pressing molding process is shown in Figure 6, and a schematic diagram of the CIP treatment molding process is shown in Figure 7. Figure 6 shows the process of (a) pouring a powder composition (61) into a mold (62), (b) leveling the powder composition, (c) (forming the second layer in the same way, and repeating thereafter), and (d) uniaxial pressing (63) to pressurize the powder composition. Figure 7 shows the process of placing the uniaxially pressed powder (laminate) (71) in a high-pressure vessel, filling the vessel with a solvent (72), and isotropically pressing the powder.

[0121] 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.

[0122] The warpage of each laminate of the green body, calcined body, and sintered body was measured using the measurement method shown in Figure 3. The test sample was positioned so that its convex portion was in contact with the horizontal plate. A thickness gauge (product name: 75A19, manufactured by Nagai Gauge Manufacturing Co., Ltd.) conforming to JIS B 7524:2008 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.

[0123] Synthesis Example 1 (Synthesis of Zirconia Powder) (Zirconia Powder A1) A hydrated zirconia sol was obtained by hydrolysis of an aqueous solution of zirconium oxychloride. ２ O ３ The yttrium chloride and erbium concentration were adjusted to 5.09 mol% in terms of Er ２ O ３ Erbium oxide was added to the hydrated zirconia sol to a concentration of 0.07 mol% in terms of iron oxide, and the sol was then dried at 180°C. The dried zirconia sol was calcined at 1175°C for 2 hours, washed with pure water, and dried at 110°C in an air atmosphere. α-alumina, iron oxide as an oxide coloring element, and pure water were mixed 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 0.06 mass% iron as an oxide coloring element in terms of iron oxide, with the remainder being 5.09 mol% yttrium and 0.07 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 at 180°C in an air atmosphere to obtain zirconia powder A1. The resulting zirconia powder had a BET specific surface area of ​​10.1 m ２The composition of zirconia powder A1 is shown in Table 1 below.

[0124] Zirconia powder A1 was subjected to uniaxial pressing at a pressure of 49 MPa and CIP treatment at a pressure of 196 MPa to obtain a powder layer of zirconia powder A1. The obtained powder layer was calcined and sintered under the following conditions to obtain a 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, 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.

[0125] The sintered 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.

[0126] (Three-Point Bending Strength) The three-point bending strength was measured by the method according to JIS R 1601 shown in FIG. 4 as described above.

[0127] (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 disk-shaped sample was used as the measurement sample. Prior to measurement, an arbitrary location of the sintered body was cut horizontally, and then both sides of the sample were mirror-polished to a thickness of 1.0±0.1 mm and a surface roughness (Ra) of 0.02 μm or less.

[0128] (Tone L ＊ , a ＊ , b ＊ , ΔL ＊ and △C ＊) The color tone of the sintered body was measured using a spectrophotometer (device name: CM-700d, manufactured by Konica Minolta) equipped with an illumination and light-receiving optical system conforming to geometric condition c of JIS Z 8722. The measurement conditions were as follows: Light source: D65 light source Viewing angle: 10° Measurement method: SCI Background: Black plate After cutting out any part of the sintered body horizontally as a measurement sample, both sides of the sample were mirror-polished to a diameter of 20 mm, a thickness of 1.0±0.1 mm, and a surface roughness (Ra) of 0.02 μm or less. The measurement sample was placed on a black plate, and both surfaces after polishing were used as evaluation surfaces, and the color tone (L ＊ , a ＊ and b ＊ ) was measured (black background measurement). ＊ The absolute value of the difference between ＊ Let a ＊ and b ＊ C was obtained from ＊ The absolute value of the difference between ＊ The effective area for color tone evaluation was 10 mm in diameter.

[0129] The evaluation results of the properties of the sintered body using zirconia powder A1 are shown in Tables 1 and 2.

[0130] (Zirconia powder A2) Yttrium concentration is Y ２ O ３ The yttrium chloride and erbium concentrations were adjusted to 5.14 mol% in terms of Er ２ O ３ Zirconia powder A2 having the composition shown in Table 1 was prepared in the same manner as zirconia powder A1, except that erbium oxide was added so that the content was 0.03 mol % in terms of erbium oxide, and iron oxide and cobalt oxide were used as oxide coloring elements, with the contents changed as shown in Table 1. A sintered body layer was prepared using zirconia powder A2 in the same manner as zirconia powder A1, and the properties of the sintered body layer were evaluated. The evaluation results are shown in Tables 1 and 2.

[0131] (Zirconia Powder A3) Zirconia powder A3 having the composition shown in Table 1 was produced in the same manner as zirconia powder A1, except that alumina was not used. A sintered body layer was produced using zirconia powder A3 in the same manner as zirconia powder A1, and the properties of the sintered body layer were evaluated. The evaluation results are shown in Tables 1 and 2.

[0132] (Zirconia Powders B1 to B3 and C1 to C10) Zirconia powders B1 to B3 and C1 to C10 having the compositions shown in Table 1 were produced in the same manner as zirconia powder A1, 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. Sintered body layers were also produced using zirconia powders B1 to B3 and C1 to C10, and the properties of the sintered body layers were evaluated. The evaluation results are shown in Tables 1 and 2.

[0133]

[0134] Example 1 (Molded Body) 141.0 g of zirconia powder C6 was filled into a mold with an inner diameter of 110 mm, and the mold was then tapped to form a fourth powder layer (corresponding to the second compositionally gradient powder composition layer). 98.7 g of zirconia powder C2 was filled on top of the fourth powder layer, and the mold was then tapped to form a third powder layer (corresponding to the third compositionally gradient powder composition layer). 89.3 g of zirconia powder B1 was filled on top of the third powder layer, and the mold was then tapped to form a second powder layer (corresponding to the first compositionally gradient powder layer). 141.0 g of zirconia powder A1 was filled on top of the second powder layer, and the mold was then tapped to form a first powder layer (corresponding to the surface powder composition layer), followed by uniaxial pressing at a pressure of 98 MPa. Subsequently, a CIP process was performed at a pressure of 196 MPa to obtain a four-layer laminate, which was used as the molded body of this example.

[0135] (Calcined body) The compact was heated from room temperature to 300°C at 15°C / hour, held at 300°C for 5 hours, heated from 300°C to 700°C at 15°C / hour, held at 700°C for 1 hour, heated from 700°C to 1000°C at 50°C / hour, held at 1000°C for 2 hours, and then cooled in the furnace and calcined to obtain a laminate, which was the calcined body of this example. The thickness ratio of the calcined body in each layer is shown in Table 2.

[0136] (Sintered body) The calcined body was sintered at a temperature increase rate of 100°C / hour, a sintering temperature of 1500°C, and a sintering time of 2 hours to obtain a laminate, which was used as the sintered body of this example.

[0137] The measurement results of the warpage and deformation amount for the green body, the calcined body, and the sintered body are shown in the following Table 2. The measurement result of the warpage of the sintered body of Example 1 was less than the measurement limit (0.03 mm).

[0138] (Examples 2 to 15 and Comparative Example 1) Laminates shown in Table 2 were produced in the same manner as in Example 1, except that the type of powder used, the powder mass, and the stacking order of the powders used were changed as shown in Table 2. The warpage and deformation amount were measured for the compacts, calcined bodies, and sintered bodies of each example. The measurement results are shown in Table 2. In Table 2, the warpage measurement results marked "N.D." mean that the result is less than the measurement limit, "less than 0.03 mm." Also, in Table 2, ΔL ＊ and △C ＊ are the differences in lightness and chroma between the unit zirconia layers constituting the compositionally graded zirconia layer. For example, in Example 1, ΔL ＊ is 5.8 and △C ＊ 5.4, ​​and the ΔL of the third compositionally graded zirconia layer obtained from powder C2 and the second compositionally graded zirconia layer obtained from powder C6 ＊ is 0.7 and △C ＊ is 0.7.

[0139]

[0140] In Examples 1 to 15, in which the stabilizing element content of the surface layer was lower than that of the adjacent first composition gradient layer, the three-point bending strength of the surface layer was 800 MPa or higher, which was 150 MPa or higher than that of the first composition gradient layer, resulting in laminates with high mechanical strength. Furthermore, Examples 1 to 15, which had a composition gradient layer, were laminates with translucency and color gradation that could give an impression similar to that of natural teeth. On the other hand, in Comparative Example 1, in which the stabilizing element content of the surface layer was higher than that of the adjacent first composition gradient layer, although the surface layer had a translucency and color gradation, the three-point bending strength of the surface layer was approximately 600 MPa, and the laminate did not have as high mechanical strength as the Examples. The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2022-023814, filed on February 18, 2022, are hereby incorporated by reference as part of the disclosure of the specification of the present disclosure.

[0141] 100, 200, 500, 600: Zirconia sintered body 10: Surface zirconia layer 20: Compositionally graded zirconia layer 21: First compositionally graded zirconia layer 22: Second compositionally graded zirconia layer 23: Compositionally graded intermediate zirconia layer 23a: Third compositionally graded zirconia layer 23b: Fourth compositionally graded zirconia layer 31: Horizontal plate 32A, 32B: Thickness gauge 33: Size of sintered body 41: Load 42: Distance between supports 51: Zirconia having necking structure 61: Powder composition 62: Mold 63: Uniaxial pressing 71: Uniaxially pressed powder (laminated body) 72: Solvent

Claims

1. A laminate having a surface layer containing zirconia containing a stabilizing element and a compositionally graded layer composed of two or more unit layers, each of which contains zirconia containing a stabilizing element and a coloring element, and wherein the compositionally graded layer is constructed by stacking the unit layers such that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the compositionally graded layer does not vary or decreases from the surface layer side toward the surface side of the laminate opposite to the surface layer, wherein the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface layer is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first compositionally graded layer, which is a unit layer adjacent to the surface layer among the unit layers constituting the compositionally graded layer.

2. The laminate according to claim 1, wherein the surface layer further contains a coloring element.

3. The laminate according to claim 1 or 2, wherein the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface layer is 2.5 mol % or more and 6.0 mol % or less.

4. A laminate according to any one of claims 1 to 3, wherein the difference between the stabilizing element content of said surface layer and the stabilizing element content of said first composition gradient layer is 0.2 mol % or more.

5. A laminate according to any one of claims 1 to 4, wherein the content of the stabilizing element in the zirconia containing the stabilizing element contained in the first composition gradient layer is 2.5 mol % or more and 6.0 mol % or less.

6. A laminate according to any one of claims 1 to 5, wherein the stabilizing element is 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).

7. The laminate according to any one of claims 1 to 6, wherein the coloring element is at least one of a transition metal element and a lanthanoid rare earth element.

8. A laminate according to any one of claims 1 to 7, wherein the content of the coloring element is 0.01% by mass or more and 1.0% by mass or less.

9. A laminate according to any one of claims 1 to 8, which has a warpage of 1.0 mm or less as measured using a thickness gauge in accordance with JIS B 7524:2008.

10. The laminate according to any one of claims 1 to 9, wherein the laminate is a sintered body.

11. The laminate according to claim 10, wherein the three-point bending strength of the surface layer measured according to a method in accordance with JIS R 1601 is 700 MPa or more.

12. The laminate according to any one of claims 1 to 9, wherein the laminate is a calcined body.

13. A method for producing a laminate according to any one of claims 1 to 11, comprising: a step of sintering a compact at 1200°C or higher and 1600°C or lower, the compact having a surface powder composition layer containing zirconia containing a stabilizing element; and a compositionally gradient powder composition layer composed of two or more unit powder composition layers, each of which contains zirconia containing a stabilizing element and a coloring element; the compositionally gradient powder composition layer is formed by stacking the unit powder composition layers so that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the compositionally gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact on the opposite side from the surface powder composition layer; and the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface powder composition layer is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first compositionally gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the compositionally gradient powder composition layer.

14. A process of calcining a compact at 800°C or higher but lower than 1200°C to form a calcined body, the compact having a surface powder composition layer containing zirconia containing a stabilizing element and a compositionally gradient powder composition layer composed of two or more unit powder composition layers, each of which contains zirconia containing a stabilizing element and a coloring element, the compositionally gradient powder composition layer being constructed by stacking the unit powder composition layers so that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the compositionally gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact opposite to the surface powder composition layer, and the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface powder composition layer is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first compositionally gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the compositionally gradient powder composition layer, and The method for producing the laminate according to claim 1 , further comprising a step of sintering the calcined body at 1200° C. or higher and 1600° C. or lower.

15. A method for producing a laminate according to any one of claims 1 to 9 and 12, comprising a step of calcining a compact at 800°C or higher but lower than 1200°C, the compact having a surface powder composition layer containing zirconia containing a stabilizing element, and a compositionally gradient powder composition layer composed of two or more unit powder composition layers, each of which contains zirconia containing a stabilizing element and a coloring element, the compositionally gradient powder composition layer being constructed by stacking the unit powder composition layers such that the content of the stabilizing element in the zirconia containing the stabilizing element contained in the compositionally gradient powder composition layer does not vary or decreases from the surface powder composition layer side toward the surface powder composition side of the compact on the opposite side from the surface powder composition layer, and the content of the stabilizing element in the zirconia containing the stabilizing element contained in the surface powder composition layer is smaller than the content of the stabilizing element in the zirconia containing the stabilizing element contained in a first compositionally gradient powder composition layer, which is a unit powder composition layer adjacent to the surface powder composition layer among the unit powder composition layers constituting the compositionally gradient powder composition layer.

16. The manufacturing method according to any one of claims 13 to 15, wherein the surface powder composition layer further contains a coloring element.

17. The manufacturing method according to any one of claims 13 to 16, wherein the powder composition contained in the powder composition layer is a powder in a granulated state.

18. A dental material comprising a laminate according to any one of claims 1 to 12.