Zirconia calcined material suitable for dental use

Abstract

Provided is a zirconia calcined body having suitable color tone, translucency, and strength. The present invention relates to a zirconia calcined body comprising a laminate structure having at least three layers, containing zirconia and a stabilizer capable of suppressing phase transition of the zirconia, the laminate structure comprising at least two layers having mutually different contents of the stabilizer with respect to the total number of moles of zirconia and the stabilizer, the laminate structure comprising at least two layers having substantially the same content of the stabilizer with respect to the total number of moles of zirconia and the stabilizer, and all of the layers that have substantially the same content of the stabilizer including a colorant component, the colorant components having mutually different compositions in said layers.

Description

[Technical Field]

[0001] The present invention relates to a zirconia calcined body suitable for dental use, a method for producing the same, and a method for producing dental products.

[0002] Zirconia is a compound in which phase transitions occur between multiple crystal systems. Therefore, partially-stabilized zirconia (PSZ) and fully-stabilized zirconia, which suppress phase transitions by solid-solving stabilizers such as yttria (yttrium oxide; Y2O3) into zirconia, are used in various fields.

[0003] In the dental field, zirconia has been used as a frame material due to its high strength. Furthermore, with the recent improvement in the translucency of zirconia, it has become increasingly common to fabricate dental prostheses using only zirconia. Examples of such zirconia materials are proposed in Patent Documents 1-3.

[0004] Patent Document 1 discloses a zirconia sintered body having a color gradient from the incisal edge towards the cervical area. Furthermore, Patent Document 2 discloses a zirconia sintered body in which the yttria content differs from layer to layer. By reducing the yttria content from the incisal edge towards the cervical area, appropriate translucency for a dental prosthesis is achieved. Patent Document 3 discloses a zirconia sintered body containing pigments with different yttria content in each layer, and by reducing the yttria content from the incisal edge towards the cervical area, it exhibits appropriate translucency for dental prostheses. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2019 / 131782 [Patent Document 2] U.S. Patent Application Publication No. 2013 / 0221554 [Patent Document 3] U.S. Patent Application Publication No. 2016 / 0120765 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As mentioned above, in recent years, it has become increasingly common for dental clinics to easily fabricate zirconia dental prostheses, and there is a need to achieve excellent aesthetics while maintaining strength using only zirconia. On the other hand, natural teeth have a structure consisting of enamel, dentin, and pulp inside, and the color and translucency of each part are intricately intertwined and influence each other to create the aesthetics (appearance) of natural teeth. Therefore, conventional methods have not been able to faithfully reproduce this aesthetic with zirconia alone.

[0007] In the calcined zirconia described in Patent Document 1, there is a color gradation after sintering, and it is thought to exhibit a certain level of aesthetics. However, the yttria content is constant from the cervical region to the incisal region, and there is a problem in that it is not possible to achieve both the translucency and color required at the incisal region and the strength and color required at the cervical region.

[0008] The zirconia described in Patent Documents 2 and 3 has layers with different yttria content and is thought to have appropriate translucency and strength as a dental prosthesis. However, since the yttria content is different in each layer, there is a problem in that it cannot faithfully reproduce the complex translucency and color gradation of natural teeth, where the color tone and translucency of each part are intricately intertwined and influence each other, as described above.

[0009] Therefore, there is a need for zirconia calcined bodies that possess the strength suitable for dental use after firing, while also retaining the complex color tones and translucency of natural teeth.

[0010] The present invention aims to provide a calcined zirconia body having suitable color tone, translucency, and strength. Furthermore, the objective is to provide a zirconia calcined body that combines the translucency and color required at the incisal edge with the strength and color required at the cervical area. [Means for solving the problem]

[0011] The inventors of the present invention conducted extensive research to solve the above problems and found that the above problems could be solved by creating a calcined zirconia body in which the content of stabilizers and coloring components in each layer was appropriately adjusted. Based on this finding, they furthered their research and completed the present invention.

[0012] This invention encompasses the following inventions. [1] A laminated structure comprising at least three layers containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, The aforementioned laminated structure comprises at least two layers in which the content of stabilizer relative to the total moles of zirconia and stabilizer differs from that of the other. The aforementioned laminated structure comprises at least two layers in which the content of the stabilizer relative to the total moles of zirconia and the stabilizer is approximately the same. A calcined zirconia body in which all layers with approximately the same stabilizer content contain a coloring component, and the composition of the coloring component in each layer differs from that of the other. [2] The calcined zirconia body according to [1], wherein layers having approximately the same stabilizer content are adjacent to each other. [3] The zirconia calcined body according to [1] or [2], wherein the coloring component comprises an oxide of at least one element selected from the group Ti, V, Cr, Mn, Fe, Co, Ni, Pr, Tb, and Er, or (Zr,V)O2. [4] The zirconia calcined body according to any one of [1] to [3], wherein the laminated structure comprises only one layer having the highest content of the stabilizer. [5] A calcined zirconia body according to any one of [1] to [4], wherein the layer with the highest content of the stabilizer does not contain any coloring components. [6] A calcined zirconia body according to any one of [1] to [4], wherein the layer with the highest content of the stabilizer contains a coloring component. [7] The calcined zirconia body according to [6], wherein the composition of the coloring component in the layer with the highest content of the stabilizer is different from the composition of the coloring components in the other layers. [8] Along a straight line extending in a first direction from one end to the other end of the zirconia calcined body, A zirconia calcined body according to any one of [1] to [7], wherein, for layers with different stabilizer contents, the trend of increasing or decreasing the stabilizer content relative to the total moles of zirconia and stabilizer from one end to the other does not change. [9] The zirconia calcined body according to any one of [1] to [8], wherein the stabilizer is yttria.

[10] Along a straight line extending in a first direction from one end to the other end of the zirconia calcined body, For layers with different yttria content, the trend of increasing or decreasing stabilizer content relative to the total moles of zirconia and stabilizer does not change from one end to the other. With respect to the total moles of the zirconia and yttria, The yttria content of the layer including the aforementioned end is 3.5 mol% or more and 6.5 mol% or less. The calcined zirconia body according to [9], wherein the yttria content of the layer including the other end is 2.5 mol% or more and less than 4.5 mol%.

[11] Along a straight line extending in a first direction from one end to the other end of the zirconia calcined body, For layers with different yttria content, the trend of increasing or decreasing stabilizer content relative to the total moles of zirconia and stabilizer does not change from one end to the other. With respect to the total moles of the zirconia and yttria, The zirconia calcined body according to

[10] , wherein the difference in yttria content between the layer containing one end and the layer containing the other end is 3.0 mol% or less.

[12] Regarding two layers included in a layer in which the content rate of the stabilizer in the sintered body produced by firing the zirconia green compact at an appropriate sintering temperature for 120 minutes is substantially the same, the color tone (L1 , * , a1 * , b1 * ) of the first layer and the color tone (L2 * , a2 * , b2 * ) of the second layer, when compared, the color difference ΔE2 * between the color tone of the first layer and the color tone of the second layer represented by the following formula (4) is 0.3 or more and 6.0 or less, the zirconia green compact according to any one of [1] to

[11] . ΔE2 * ={(L2 * - L1 * ) 2 +(a2 * - a1[[ID=二十九]] * ) 2 +(b2 * - b1 * ) 2} 1 / 2 (4) (In the formula, the color tone (L1 * , a1 * , b1 * ) represents the color tone of the first layer in which the content rate of the stabilizer is substantially the same, and the color tone (L2 * , a2 * , b2 * ) represents the color tone of the second layer in which the content rate of the stabilizer is substantially the same.)

[13] On a straight line extending in the first direction from one end to the other end of the zirconia green compact, when the sintered (L*, a*, b*) in the L*a*b* color system of the first point in the section from the one end to 25% of the total length is (L1, a1, b1), and the sintered (L*, a*, b*) in the L*a*b* color system of the second point in the section from the other end to 25% of the total length is (L2, a2, b2), on the straight line connecting the first point and the second point, the zirconia green compact according to any one of [1] to

[12] , in which the increasing and decreasing tendency of the sintered L* value in the L*a*b* color system changes from the first point toward the second point.<>

[14] On the straight line connecting the first point and the second point, when the (L*, a*, b*) of the third point between the first and second points after sintering using the L*a*b* color system is (L3, a3, b3), L1 <l3>L2, the zirconia calcined body described in

[13] . A method for manufacturing a zirconia sintered body, comprising sintering a zirconia calcined body described in any of

[15] [1] to

[14] at a maximum sintering temperature of 1400°C to 1650°C. A method for manufacturing dental products, comprising machining a zirconia calcined body as described in any of

[16] [1] to

[14] and then sintering it.

[17] The method for manufacturing a dental product according to

[16] , wherein the cutting process is a cutting process using a CAD / CAM system. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a calcined zirconia body having suitable color tone, translucency, and strength. Furthermore, according to the present invention, it is possible to provide a zirconia calcined body that, after firing, has strength suitable for dental use while possessing the complex color tones and translucency of natural teeth. Furthermore, according to the present invention, it is possible to provide a zirconia calcined body that combines the translucency and color required at the incisal edge with the strength and color required at the cervical area. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of a calcined zirconia body. [Figure 2] This is a photograph of the appearance of a zirconia sintered body, which is relevant to determining the appropriate sintering temperature. [Modes for carrying out the invention]

[0015] The zirconia calcined body of the present invention comprises a laminated structure of at least three layers containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizer"), wherein the laminated structure comprises at least two layers in which the content of the stabilizer relative to the total moles of zirconia and stabilizer is different from that of the other (hereinafter also simply referred to as "layers with different stabilizer content"), and the laminated structure comprises at least two layers in which the content of the stabilizer relative to the total moles of zirconia and stabilizer is substantially the same (hereinafter also simply referred to as "layers with substantially the same stabilizer content"), wherein all layers with substantially the same stabilizer content contain a coloring component, and the composition of the coloring component in the layer is different from that of the other.

[0016] The zirconia calcined body of the present invention will be described. Zirconia calcined material can serve as a precursor (intermediate product) for zirconia sintered bodies. In this specification, a calcined zirconia body means, for example, a state in which zirconia particles (powder) are not completely sintered. The calcined zirconia body may be in block form (disk-shaped, rectangular parallelepiped-shaped). The density of the calcined zirconia is 2.7 g / cm³. 3 The above is preferable. Furthermore, the density of the zirconia calcined material is 4.0 g / cm³. 3 The following is preferable: 3.8 g / cm³ 3 The following is more preferable: 3.6 g / cm³ 3 The following is even more preferable: Processing can be easily performed within this density range. In this specification, the upper and lower limits of numerical ranges (such as the content of each component, the values ​​calculated from each component, and each physical property) can be combined as appropriate.

[0017] The zirconia calcined body of the present invention comprises a laminated structure of at least three layers, each layer containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia. The stabilizer is preferably capable of forming partially stabilized zirconia. Examples of the stabilizer include oxides such as calcium oxide (CaO), magnesium oxide (MgO), yttria (Y2O3), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium oxide (Nb2O5), lanthanum oxide (La2O3), and erbium oxide (Er2O3), with yttria being preferred. Stabilizers may be used individually or in combination of two or more. The content of the stabilizer in the zirconia calcined body and its sintered body according to the present invention can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis, or the like. In the zirconia calcined body and sintered body thereof of the present invention, the content of the stabilizer is preferably 0.1 to 18 mol%, more preferably 1 to 15 mol%, and even more preferably 1.5 to 10 mol%, relative to the total moles of zirconia and stabilizer. In one preferred embodiment, in a calcined zirconia body and its sintered body, the stabilizer is yttria, and the yttria content in all layers of the laminated structure is preferably in the range of 2.0 to 8.0 mol%, more preferably in the range of 2.2 to 7.5 mol%, even more preferably in the range of 2.5 to 7.0 mol%, and particularly preferably in the range of 2.8 to 6.5 mol%, relative to the total moles of zirconia and stabilizer, from the viewpoint of light transmittance and strength.

[0018] The zirconia calcined material of the present invention contains a coloring component. The coloring components are not particularly limited as long as they color the zirconia sintered body, and include pigments, composite pigments, and fluorescent agents.

[0019] Examples of the aforementioned pigments include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (excluding Y2O3, CeO2, and ZrO2), and it is preferable that the pigment contains an oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Pr, Tb, and Er. Examples of the composite pigments include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, (Co,Zn)Al2O4, and it is preferable that they contain (Zr,V)O2. Examples of the fluorescent agents include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 Examples include the EU.

[0020] The zirconia calcined body of the present invention comprises at least two layers in which the content of stabilizer relative to the total moles of zirconia and stabilizer differs from that of the other. The number of layers with different stabilizer content is not particularly limited as long as there are two or more layers; it may be three, four, or five or more layers. In this specification, "different from each other" means that the content of the stabilizers (for example, the content of yttria) is 0.1 mol% or more, preferably 0.3 mol% or more, and more preferably 0.5 mol% or more. Furthermore, the difference in the content of the stabilizer is preferably 3.0 mol% or less, more preferably 2.5 mol% or less, even more preferably 2.0 mol% or less, particularly preferably 1.5 mol% or less, and most preferably 1.0 mol% or less. Furthermore, the zirconia calcined body of the present invention comprises at least two layers in which the content of the stabilizer relative to the total moles of zirconia and stabilizer is substantially the same. The number of layers with approximately the same stabilizer content is not particularly limited as long as there are two or more layers; it may be three, four, or five or more layers. Furthermore, all layers with approximately the same stabilizer content contain coloring components, and the composition of the coloring components in each layer differs from one another. The zirconia calcined body of the present invention comprises layers with varying stabilizer content, as well as layers with substantially the same stabilizer content. Furthermore, all layers with substantially the same stabilizer content contain coloring components, and the composition of the coloring components in these layers differs from one another. This allows for the reproduction of translucency and color changes in the cervical region in the same manner as natural teeth, while also reproducing a gradual transition of translucency from the cervical region to the incisal edge, thus reproducing the translucency and color of the incisal edge, possessing appropriate strength, and exhibiting superior aesthetics. Layers with different coloring component compositions but approximately the same stabilizer content are preferably adjacent to each other, as this offers superior aesthetics.

[0021] In this specification, "approximately identical" means that the content of the stabilizer (for example, the content of yttria) is less than 0.1%, preferably less than 0.05%, and more preferably less than 0.03%. Furthermore, "different coloring component composition" includes cases where only the types of coloring components contained in each layer are different, and cases where only the percentage of coloring components in each layer is different. For example, as described later, regarding two layers in a sintered body made by firing a zirconia calcined body at an appropriate sintering temperature for 120 minutes, where the stabilizer content is approximately the same, the color difference ΔE2 between the color tone of the first layer and the color tone of the second layer is... * The type and amount of coloring components in each layer can be changed so that the result falls within the desired range. The coloring component only needs to be present in at least one layer of the zirconia calcined body. For example, in the preferred embodiment (X-1) described below, only one of the second or third layer may contain a coloring component. By having a calcined zirconia body that simultaneously contains layers with different stabilizer content and layers with the same stabilizer content but different coloring component compositions, it becomes possible to appropriately set the required translucency, color tone, and strength for each part (layer) within a single material in the resulting zirconia sintered body. The thickness of each layer is not particularly limited, but may be around 0.5 mm to 3 cm. In the zirconia calcined body of the present invention, the thickness of the layer including one end P of the zirconia calcined body 10 in Figure 1 (the layer corresponding to the cut end) is not particularly limited, but in order to sufficiently ensure the light transmittance and color tone of the cut end, it is preferably in the range of 10 to 45%, more preferably in the range of 15 to 40%, and even more preferably in the range of 20 to 35% of the total thickness of the laminated structure. Furthermore, in the zirconia calcined body of the present invention, the thickness of the layer that does not include either end P or the other end Q of the zirconia calcined body 10 in Figure 1 (the layer corresponding to the central part) is not particularly limited, but in order to facilitate a gradual transition of light transmission between the incisal edge and the cervical area, it is preferably in the range of 10 to 80%, more preferably in the range of 20 to 70%, and even more preferably in the range of 25 to 60% of the total thickness of the laminated structure. Furthermore, in the zirconia calcined body of the present invention, the thickness of the layer including the other end Q of the zirconia calcined body 10 in Figure 1 (the layer corresponding to the cervical region) is not particularly limited, but in order to sufficiently secure the strength and color tone required at the cervical region, it is preferably in the range of 10 to 45%, more preferably in the range of 15 to 40%, and even more preferably in the range of 20 to 35% of the total thickness of the laminated structure.

[0022] In the zirconia calcined body of the present invention, layers with different stabilizer content may partially overlap with layers with substantially the same stabilizer content. Specific examples are given below. One preferred embodiment (X-1) is a calcined zirconia having a three-layer laminated structure containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, wherein the stabilizer content in the first and second layers is different from that of the second and third layers, and the stabilizer content in the second and third layers is substantially the same. In the above embodiment (X-1), the first layer is, for example, a layer including one end P of the zirconia calcined body 10 shown in Figure 1, the second layer is a layer adjacent to the layer including the one end P, and the third layer is a layer adjacent to the second layer, for example, a layer including the other end Q of the zirconia calcined body 10 shown in Figure 1. Another preferred embodiment (X-2) is a calcined zirconia having a four-layer laminated structure containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, wherein the stabilizer content in the first, second, and third layers is different from that of the third and fourth layers, and the stabilizer content in the third and fourth layers is substantially the same. In the above embodiment (X-2), the first layer is, for example, a layer including one end P of the zirconia calcined body 10 shown in Figure 1, the second layer is a layer adjacent to the layer including the one end P, the third layer is a layer adjacent to the second layer, and the fourth layer is a layer adjacent to the third layer, for example, a layer including the other end Q of the zirconia calcined body 10 shown in Figure 1. Another preferred embodiment (X-3) is a calcined zirconia having a four-layer laminated structure containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, wherein the stabilizer content in the first and second layers is different from that of the second, third, and fourth layers, and the stabilizer content in the second, third, and fourth layers is substantially the same. In the above embodiment (X-3), the first layer is, for example, a layer including one end P of the zirconia calcined body 10 shown in Figure 1, the second layer is a layer adjacent to the layer including the one end P, the third layer is a layer adjacent to the second layer, and the fourth layer is a layer adjacent to the third layer, for example, a layer including the other end Q of the zirconia calcined body 10 shown in Figure 1. Furthermore, in the laminated structure of the zirconia calcined body of the present invention, it is preferable that the layer with the highest stabilizer content is the one layer located at the end face. For example, on a straight line extending in the first direction Y from one end P to the other end Q of the zirconia calcined body 10 in Figure 1, the layer including the one end P may be the layer with the highest stabilizer content. In one preferred embodiment, a calcined zirconia body is used, in which the laminated structure contains only one layer with the highest stabilizer content, as this provides a suitable color for dental use. In the calcined zirconia body of the present invention, the layer with the highest stabilizer content may contain a coloring component. When the layer with the highest stabilizer content contains a coloring component, it is preferable that the composition of the coloring component in that layer differs from the composition of the coloring components in the other layers. Examples of zirconia calcined bodies in which the composition of coloring components in the layer with the highest stabilizer content differs from the composition of coloring components in other layers include zirconia calcined bodies in which the composition of coloring components differs from that of layers with approximately the same stabilizer content, such as by reducing the content of coloring components or changing the type of coloring components, so that the layer with the highest stabilizer content corresponds to the layer containing the incisal edge. Furthermore, in one embodiment, the stabilizer content in the layer with the highest stabilizer content may be the yttria content of the layer containing one end P of the zirconia calcined body 10, as described later, when the stabilizer is yttria. In another embodiment, the stabilizer content in layers with substantially the same stabilizer content may be the yttria content of the layer containing the other end Q of the zirconia calcined body 10, as described later, when the stabilizer is yttria.

[0023] From the viewpoint of achieving a suitable color tone and strength for dental use, the zirconia calcined body of the present invention preferably includes multiple layers along a straight line extending in a first direction Y from one end P to the other end Q, where the content of the stabilizer (preferably yttria) relative to the total moles of zirconia and stabilizer is approximately the same from one end to the other, while maintaining a consistent overall trend of increase or decrease. In other words, it is preferable that the content of the stabilizer (preferably yttria) increases or decreases monotonically. Furthermore, from the viewpoint of obtaining suitable light transmittance, it is preferable that the zirconia calcined body contains multiple layers with substantially the same content of a stabilizer (preferably yttria) along a straight line extending in the first direction Y from one end P to the other end Q, while maintaining an overall trend of increase or decrease in the stabilizer content. The following explanation will use Figure 1 as a schematic diagram of a zirconia calcined body. In the straight line extending in the first direction Y from one end P to the other end Q of the zirconia calcined body 10 in Figure 1, it is preferable that the increasing or decreasing trend in the stabilizer content does not change in the opposite direction. That is, if the stabilizer content is decreasing along the straight line from one end P to the other end Q, it is preferable that there is no section in which the stabilizer content substantially increases, even though it contains multiple layers with the same stabilizer (preferably yttria).

[0024] From the viewpoint of strength and light transmittance of the zirconia sintered body made from the calcined zirconia body of the present invention, yttria is preferred as the stabilizer. The following describes an embodiment where yttria is the stabilizer. The yttria content of the layer containing P at one end of the zirconia calcined body 10 in Figure 1 is preferably 3.5 mol% or more, more preferably 3.7 mol% or more, even more preferably 3.8 mol% or more, particularly preferably 4.0 mol% or more, and also preferably 6.5 mol% or less, more preferably 6.0 mol% or less, even more preferably 5.8 mol% or less, and particularly preferably 5.5 mol% or less, relative to the total moles of zirconia and yttria. When the yttria content in the layer containing the aforementioned end P is 3.5 mol% or more and 6.5 mol% or less, the translucency of the zirconia sintered body can be increased, and appropriate translucency for the incisal edge of a dental prosthesis can be obtained. Furthermore, the yttria content of the layer containing Q at the other end of the zirconia calcined body 10 is preferably 2.5 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.3 mol% or more, particularly preferably 3.5 mol% or more, and also preferably less than 4.5 mol%, more preferably 4.2 mol% or less, even more preferably 4.1 mol% or less, and particularly preferably 4.0 mol% or less, based on the total moles of zirconia and yttria. When the yttria content in the layer containing the other end Q is 2.5 mol% or more and less than 4.5 mol%, the strength of the zirconia sintered body can be increased, and appropriate strength for the cervical portion of a dental prosthesis can be obtained. Furthermore, when the yttria content is between 2.5 mol% and 4.5 mol%, the translucency does not become excessively high, and appropriate translucency can be obtained for the cervical portion of dental prostheses. Furthermore, the zirconia calcined body of the present invention includes at least one intermediate layer between the layer containing P at one end and the layer containing Q at the other end, wherein the yttria content differs from that of either the layer containing P or the layer containing Q. This allows for a gradual transition in translucency from the cervical region to the incisal edge, resulting in translucency similar to that of natural teeth. Furthermore, the zirconia calcined body of the present invention is preferable in which, along a straight line extending in a first direction from one end to the other, the increasing or decreasing trend of the yttria content relative to the total moles of zirconia and yttria does not change for layers with different yttria content from one end to the other, and the yttria content of each layer is within a predetermined range.

[0025] In the zirconia calcined body 10, the difference in the yttria content between the layer containing P at one end and the layer containing Q at the other end of the zirconia calcined body 10 is preferably 3.0 mol% or less, more preferably 2.5 mol% or less, and even more preferably 2.0 mol% or less, relative to the total moles of zirconia and yttria. Furthermore, it is preferable that the difference in yttria content between the layer containing P at one end and the layer containing Q at the other end be 0.3 mol% or more, more preferably 0.5 mol% or more, and even more preferably 1.0 mol% or more. When the difference in yttria content between the layer containing P at one end and the layer containing Q at the other end of the zirconia calcined body 10 is 3.0 mol% or less, the difference in translucency between the incisal edge and the cervical area of ​​the dental prosthesis made from the zirconia calcined body 10 does not become too large, and appropriate translucency for a dental prosthesis can be obtained. Furthermore, if the difference in yttria content is 3.0 mol% or less, it becomes possible to keep the difference in firing shrinkage rate between the layer containing P at one end and the layer containing Q at the other end within 0.3%, thereby preventing crack formation and deformation when fabricating dental prostheses from the zirconia calcined body 10. In one embodiment, the zirconia calcined body of the present invention includes at least one intermediate layer between a layer containing P at one end and a layer containing Q at the other end, wherein the yttria content of the intermediate layer differs from the yttria content of either the layer containing P at one end or the layer containing Q at the other end. The difference in yttria content between the intermediate layer and a layer with a different yttria content (for example, a layer containing P at one end or a layer containing Q at the other end) is preferably 2.0 mol% or less, more preferably 1.5 mol% or less, and even more preferably 1.0 mol% or less. Furthermore, it is preferable that the difference in yttria content is 0.1 mol% or more, more preferably 0.3 mol% or more, and even more preferably 0.5 mol% or more. In one preferred embodiment, a calcined zirconia body is provided in which the difference in yttria content between the intermediate layer and a layer with a different yttria content (for example, a layer containing P at one end or a layer containing Q at the other end) is greater than 0.5 mol%.

[0026] As explained above using the schematic diagram in Figure 1, in the present invention, for example, when the zirconia calcined body and its sintered body have a tooth crown shape, it is preferable that the above-mentioned "one end" and "other end" refer to one point on the incisal end and one point on the root end (cervical end). This point may be a point on the end face or a point on the cross section.

[0027] When the calcined zirconia has a disc-like or hexahedral shape such as a rectangular parallelepiped, the terms "one end" and "the other end" preferably refer to a point on the top and bottom (bottom) surfaces. This point may be a point on the end face or a point on the cross-section.

[0028] In this invention, the "first direction from one end to the other" refers to the direction in which the yttria content changes. For example, the first direction is preferably the direction in which the powder is layered in the manufacturing method described later. For example, if the zirconia calcined body has a tooth crown shape, the first direction is preferably the direction connecting the incisal end and the cervical end.

[0029] In one embodiment, in addition to any of the above-described configurations of the zirconia calcined body, Along a straight line extending in a first direction from one end to the other end of the zirconia calcined body, Let (L1, a1, b1) be the (L*, a*, b*) of the first point in the section from one end to 25% of the total length after sintering using the L*a*b* color system. When the second point in the section from the other end up to 25% of the total length, after sintering using the L*a*b* color system, is denoted as (L2,a2,b2), On the straight line connecting the first point and the second point, One example is a zirconia calcined body in which the trend of increasing or decreasing L* value after sintering according to the L*a*b* color system changes from the first point to the second point. By using such a zirconia calcined body, a zirconia calcined body can be obtained that has a better balance between the translucency and color tone required at the incisal edge and the strength and color tone required at the cervical area, in relation to the content of the stabilizing agent in each layer of the laminated structure, and can be applied to a wide range of dental applications.

[0030] In a zirconia calcined body in which the trend of increasing or decreasing L* value changes, in relation to the content of the stabilizer in each layer of the laminated structure, the balance between the translucency and color required at the incisal edge and the strength and color required at the cervical area is superior, and L* is increased from the first point to the second point. * a * b * It is preferable that the increase / decrease trend of a* and b* after sintering, according to the color system, does not change.

[0031] In a zirconia calcined body in which the increasing or decreasing trend of the L* value changes, when the (L*, a*, b*) after sintering according to the L*a*b* color system at a third point between the first and second points on the straight line connecting the first and second points is defined as (L3, a3, b3), in relation to the content of the stabilizing agent in each layer of the laminated structure, L1 is superior in terms of reproducing the complex color tone and translucency of natural teeth. <l3>L2 is preferred.

[0032] In a calcined zirconia body in which the trend of increasing or decreasing the L* value changes, the difference between L1 and L2 is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 5.0 or less.

[0033] In the calcined zirconia body in which the trend of increasing or decreasing the L* value changes, it is preferable that L1 is 65.0 or more and 93.0 or less, more preferably 67.0 or more and 91.0 or less, and even more preferably 70.0 or more and 90.0 or less.

[0034] In a calcined zirconia body in which the trend of increasing or decreasing L* value changes, a1 is preferably -3.0 to 4.5, more preferably -2.7 to 4.0, and even more preferably -2.5 to 3.7, in order to have the complex color tone and translucency of natural teeth when combined with the L* value.

[0035] In a calcined zirconia body in which the L* value tends to increase or decrease, it is preferable that b1 be 0.0 or more and 24.0 or less, more preferably 0.3 or more and 23.0 or less, and even more preferably 0.5 or more and 22.0 or less, in order to have the complex color tone and translucency of natural teeth when combined with the L* value.

[0036] In a calcined zirconia body in which the trend of increasing or decreasing L* value changes, it is preferable that L2 be 60.0 to 92.0, more preferably 63.0 to 90.0, and even more preferably 65.0 to 88.0, in order to have the complex color tone and translucency of natural teeth when combined with the L* value.

[0037] In a calcined zirconia body in which the trend of increasing or decreasing L* value changes, it is preferable that a2 be between -2.0 and 7.0, more preferably between -1.5 and 6.5, and even more preferably between -1.2 and 6.0, in order to have the complex color tone and translucency of natural teeth when combined with the L* value.

[0038] In the zirconia green body in which the increasing and decreasing tendency of the L* value changes, from the viewpoint of having the complex color tone and translucency of natural teeth when combined with the L* value, b2 is preferably 4.0 or more and 28.0 or less, more preferably 5.5 or more and 26.0 or less, and even more preferably 7.0 or more and 24.0 or less.

[0039] In the zirconia green body in which the increasing and decreasing tendency of the L* value changes, it is preferable that a1 < a2 and b1 < b2.

[0040] In the zirconia green body in which the increasing and decreasing tendency of the L* value changes, L3 is preferably not less than 66.0 and not more than 95.0, more preferably not less than 69.0 and not more than 94.0, and even more preferably not less than 72.0 and not more than 93.0.

[0041] In the zirconia green body in which the increasing and decreasing tendency of the L* value changes, from the viewpoint of having the complex color tone and translucency of natural teeth when combined with the L* value, a3 is preferably not less than -2.5 and not more than 6.0, more preferably not less than -2.0 and not more than 5.7, and even more preferably not less than -1.5 and not more than 5.5.

[0042] In the zirconia green body in which the increasing and decreasing tendency of the L* value changes, from the viewpoint of having the complex color tone and translucency of natural teeth when combined with the L* value, b3 is preferably not less than 1.5 and not more than 26.0, more preferably not less than 2.0 and not more than 25.0, and even more preferably not less than 2.5 and not more than 23.0.

[0043] In the zirconia green body in which the increasing and decreasing tendency of the L* value changes, from the viewpoint of having the complex color tone and translucency of natural teeth when combined with the L* value, it is preferable that a1 < a3 < a2 and b1 < b3 < b2.

[0044] When the sintered (L*, a*, b*) of the fourth point between the third point and the second point on the straight line connecting the first point and the second point is (L4, a4, b4) in the L*a*b* color system, it is preferable that L4 > L2 from the viewpoints of the complex color tone and translucency of natural teeth. L3 and L4 can be changed according to the desired color tone and translucency, and L3 < L4 or L3 > L4 may be satisfied.

[0045] Further, when the sintered (L*, a*, b*) of the fourth point in the L*a*b* color system is (L4, a4, b4), it is preferable that a4 < a2 and b4 < b2 from the viewpoints of the complex color tone and translucency of natural teeth when combined with the L* value.

[0046] The flexural strength of the zirconia green body of the present invention is preferably 15 MPa or more in order to ensure the strength enabling machining. Further, the flexural strength of the zirconia green body is preferably 70 MPa or less, more preferably 60 MPa or less, in order to facilitate machining.

[0047] The flexural strength can be measured in accordance with ISO 6872:2015, but the measurement is performed using a test piece with a size of 5 mm × 10 mm × 50 mm by changing only the conditions of the size of the test piece. The surface and the C surface (the chamfered surface at an angle of 45° of the corner of the test piece) of the test piece are surface-finished in the longitudinal direction with 600-grit sandpaper. The test piece is arranged such that the widest surface faces the vertical direction (loading direction). In the flexural test measurement, the span is 30 mm and the crosshead speed is 0.5 mm / min.

[0048] The zirconia green body of the present invention may contain additives other than zirconia, stabilizers, and coloring components as long as the effects of the present invention are achieved. Further, the layer having the highest content rate of the stabilizer may or may not contain a coloring component. Examples of the additive include alumina (Al2O3), titanium oxide (TiO2), silica (SiO2), and the like.

[0049] The zirconia calcined body of the present invention can be manufactured by calcining (i.e., calcining) a zirconia molded body, which is formed from a raw material powder containing zirconia, a stabilizer, and a coloring component, at a temperature at which the zirconia particles do not sinter (calcination process). The stabilizers and coloring components may or may not be solid-dissolved in the zirconia at the raw material powder stage or at the calcined stage. The zirconia molded article is not particularly limited and can be manufactured using a raw material powder containing zirconia particles and a stabilizer, using known methods (e.g., press molding). In the calcination process, the calcination temperature (calcination temperature) is preferably 800°C or higher, more preferably 900°C or higher, and even more preferably 950°C or higher, in order to ensure block formation. Furthermore, in order to improve processability, the calcination temperature is preferably 1200°C or lower, more preferably 1150°C or lower, and even more preferably 1100°C or lower. For example, in the method for producing a calcined zirconia body according to the present invention, a temperature of 800°C to 1200°C is preferred.

[0050] The zirconia calcined body of the present invention may be a molded body having a predetermined shape. For example, the zirconia calcined body may be disc-shaped, rectangular parallelepiped-shaped, or have the shape of a dental product (e.g., a tooth crown shape). Dental products (e.g., tooth crown-shaped prostheses) processed from calcined zirconia discs using a CAD / CAM (Computer-Aided Design / Computer-Aided Manufacturing) system are also included in the calcined body.

[0051] In the calcined zirconia body of the present invention, the crystal system of zirconia is not limited, and the main crystal system may be monoclinic, tetragonal, or cubic. One embodiment is a calcined zirconia body in which the primary crystal system is monoclinic. In this specification, "the dominant crystal system is monoclinic" means the monoclinic content f in zirconia, calculated using the following formula (1) relative to the total amount of all crystal systems (monoclinic, tetragonal, and cubic) in zirconia. m This means that it accounts for 50% or more. Content f of monoclinic crystals m This can be calculated from equation (1) below, based on the peaks of the X-ray diffraction (XRD) pattern caused by CuKα rays. f m = I m / ( I m +I t +I c ) × 100 (1) (In the formula, f m This represents the monoclinic content (%) of the zirconia raw material, and in XRD measurement, I m This represents the area intensity of the main peak of the monoclinic system around 2θ=28°, and I t This represents the area intensity of the main peak of the tetragonal crystal system around 2θ=30°, and I c This represents the area intensity of the main peak of the cubic crystal system around 2θ = 30°. Since the main peak positions are similar for tetragonal and cubic crystal systems, information on sub-peak positions is also considered to determine which crystal system is present. If both tetragonal and cubic crystal systems are found to be present, the area intensity of the main peaks for each is calculated using peak separation. In some embodiments, tetragonal and cubic crystal peaks may not be substantially detected in the zirconia calcined body of the present invention. That is, the monoclinic content f of the zirconia calcined body m This can be set to 100%.

[0052] In one embodiment, in the calcined zirconia body of the present invention, the monoclinic content f in the zirconia calculated by formula (1) above is used. m The amount of monoclinic, tetragonal, and cubic crystals is preferably 55% or more of the total amount, and from the viewpoint of shortening the firing time and exhibiting suitable translucency and excellent strength for dental use, it is more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, particularly preferably 80% or more, even more particularly preferably 85% or more, and most preferably 90% or more.

[0053] Other embodiments include calcined zirconia in which the primary crystal system is tetragonal and / or cubic. "The dominant crystal system is tetragonal and / or cubic" means the tetragonal content f in zirconia, calculated using the following formulas (2) and / or (3) relative to the total amount of all crystal systems (monoclinic, tetragonal, and cubic) in zirconia. t and / or cubic crystal system content f c This refers to items that account for 50% or more of the total. Tetragonal content f t This can be calculated from equation (2) below, based on the peaks of the X-ray diffraction (XRD) pattern caused by CuKα rays. f t = I t / ( I m +I t +I c ) × 100 (2) (In the formula, f t This represents the tetragonal content (%) of the zirconia raw material, and in XRD measurement, I m , I t , and I c This has the same meaning as equation (1). Cubic crystal content f c This can be calculated from equation (3) below, based on the peaks of the X-ray diffraction (XRD) pattern caused by CuKα rays. f c = I c / ( I m +I t +I c ) × 100 (3) (In the formula, f c This represents the cubic crystal content (%) of the zirconia raw material, and in XRD measurement, I m , I t , and I c This has the same meaning as equation (1). In one embodiment, the calcined zirconia body of the present invention contains the tetragonal content f of the zirconia calculated by formula (2) above. t The amount of monoclinic, tetragonal, and cubic crystals is preferably 55% or more of the total amount, and from the viewpoint of exhibiting suitable translucency and excellent strength for dental use, it is more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, particularly preferably 80% or more, even more particularly preferably 85% or more, and most preferably 90% or more. In another embodiment, in the calcined zirconia body of the present invention, the tetragonal content f in the zirconia calculated by formulas (2) and (3) above is used. t and the content of the cubic crystal system f c The amount of monoclinic, tetragonal, and cubic crystals is preferably 55% or more of the total amount, and from the viewpoint of exhibiting suitable translucency and excellent strength for dental use, it is more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, particularly preferably 80% or more, even more particularly preferably 85% or more, and most preferably 90% or more. In yet another embodiment, in the calcined zirconia body of the present invention, the cubic crystal content f in the zirconia calculated by formula (3) above is used. c The amount of monoclinic, tetragonal, and cubic crystals is preferably 55% or more of the total amount, more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, particularly preferably 80% or more, even more preferably 85% or more, and most preferably 90% or more.

[0054] As described above, in the zirconia calcined body of the present invention, the laminated structure comprises at least two layers having substantially the same stabilizer content. In other words, the laminated structure comprises at least a first layer and a second layer having substantially the same stabilizer content. In one embodiment, with respect to two layers in a sintered body produced by firing a calcined zirconia body at an appropriate sintering temperature for 120 minutes, where the content of the stabilizer is approximately the same, the color tone of the first layer (L1 * a1 * , b1 * ) and the color tone of the second layer (L2 * a2 * , b2 * When compared with the following, the color difference ΔE2 between the color tone of the first layer and the color tone of the second layer represented by the following formula (4) * is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more, from the viewpoint of reproducing the color tone change in the cervical region of natural teeth in the sintered body. Also, the color difference ΔE2 * is preferably 6.0 or less, more preferably 5.0 or less, even more preferably 4.5 or less, and particularly preferably 4.0 or less. ΔE2 * ={(L2 * -L1 * ) 2 +(a2 * -a1 * ) 2 +(b2 * -b1 * ) 2} 1 / 2 (4) (In the formula, the color tone (L1 * , a1 * , b1 * ) represents the color tone of the first layer with substantially the same stabilizer content, and the color tone (L2 * , a2 * , b2 * ) represents the color tone of the second layer with substantially the same stabilizer content.)

[0055] In another embodiment, from the viewpoint of reproducing the color tone change in the cervical region of natural teeth in the sintered body, in the laminated structure of the zirconia green body of the present invention, for all layers with substantially the same stabilizer content, the color difference ΔE2 between adjacent layers * is preferably within the above range.

[0056] The zirconia sintered body of the present invention will be described. In the present specification, the zirconia sintered body is one in which zirconia particles (powder) have reached a sintered state. In particular, the zirconia sintered body of the present invention refers to one produced from the zirconia green body of the present invention. The relative density of the zirconia sintered body is preferably 99.5% or more. The relative density can be calculated as the ratio of the measured density measured by the Archimedes method to the theoretical density.

[0057] The zirconia sintered body of the present invention includes not only sintered bodies obtained by sintering molded zirconia particles under normal pressure or without pressure, but also sintered bodies obtained by densifying through high-temperature and high-pressure treatment such as HIP (Hot Isostatic Pressing).

[0058] The content of zirconia and stabilizers in the zirconia sintered body of the present invention is the same as the content in the calcined body before the sintering process.

[0059] The method for producing the zirconia sintered body of the present invention is described below. The zirconia sintered body of the present invention can be manufactured by firing a calcined zirconia body at a temperature at which zirconia particles sinter (sintering temperature) (sintering process). The sintering temperature in the sintering process (for example, the maximum sintering temperature) is preferably 1400°C or higher, and more preferably 1450°C or higher. Furthermore, the sintering temperature is preferably 1650°C or lower, and more preferably 1600°C or lower. The heating rate and cooling rate are preferably 300°C / min or less. That is, in the method for producing a zirconia sintered body of the present invention, it is preferable to sinter the zirconia calcined body at a maximum sintering temperature of 1400°C to 1650°C. The appropriate sintering temperature for the zirconia calcined body may be the above maximum sintering temperature.

[0060] In the sintering process, the holding time at the sinterable temperature (e.g., the maximum sintering temperature) can be 120 minutes, but is not particularly limited. For example, it can be 120 minutes or less, 90 minutes or less, 75 minutes or less, 60 minutes or less, 45 minutes or less, 30 minutes or less, or 15 minutes or less. Furthermore, the holding time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more.

[0061] The heating rate and cooling rate in the sintering process are not particularly limited, but the heating rate to the maximum sintering temperature can be, for example, 5°C / min or more, 10°C / min or more, 50°C / min or more, 100°C / min or more, 120°C / min or more, 150°C / min or more, or 200°C / min or more. The cooling rate from the maximum sintering temperature should preferably be set at a rate that does not cause defects such as cracks in the sintered body. For example, after heating is complete, the sintered body can be allowed to cool at room temperature. The maximum sintering temperature refers to the highest temperature reached during the sintering process.

[0062] The zirconia sintered body obtained by firing the zirconia calcined body of the present invention can be suitably used in dental products. Examples of dental products include copings, frameworks, crowns, crown bridges, long-span bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, laminate veneers, and the like. Furthermore, while an appropriate manufacturing method can be selected depending on the application, for example, dental products can be obtained by machining the zirconia calcined body of the present invention and then sintering it. It is preferable to use a CAD / CAM system in the machining process.

[0063] The present invention includes embodiments that combine the above configurations in various ways, within the scope of the technical idea of ​​the present invention, as long as they achieve the effects of the present invention. [Examples]

[0064] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples, and many modifications can be made within the scope of the technical idea of ​​the present invention by those with ordinary skill in the art.

[0065] [Preparation of zirconia calcined bodies] The zirconia calcined bodies of each example and comparative example were prepared according to the following procedure.

[0066] The method for preparing the raw material powder used to produce the zirconia calcined bodies of Examples 1-3 and Comparative Examples 1 and 2 will be described. First, a mixture was prepared using monoclinic zirconia powder and yttria powder to achieve the composition shown in Table 1. Next, this mixture was added to water to prepare a slurry, which was wet-milled and mixed in a ball mill until the average particle size was 0.13 μm or less. The slurry was dried in a spray dryer, and the resulting powder was calcined at 950°C for 2 hours to produce a primary powder. The average particle size was determined by laser diffraction scattering. The laser diffraction scattering method was performed using a laser diffraction particle size distribution analyzer (SALD-2300: manufactured by Shimadzu Corporation) with a 0.2% sodium hexametaphosphate aqueous solution as the dispersion medium.

[0067] To the obtained primary powder, coloring components were added according to the composition shown in Table 1. Then, the powder with the added coloring components was added to water to prepare a slurry, which was wet-milled and mixed in a ball mill until the average particle size was 0.13 μm or less. After grinding, a binder was added to the slurry, and it was dried in a spray dryer to produce a powder (secondary powder). The prepared secondary powder was used as the raw material powder in the production of the zirconia calcined body described later.

[0068] Furthermore, as raw material powders used to produce the zirconia calcined bodies in Examples 4, 5 and Comparative Example 3, "Zpex® Smile" manufactured by Tosoh Corporation was used for the first layer of Examples 4 and 5, "Zpex® 4" manufactured by Tosoh Corporation was used for the second and third layers of Example 4, the second layer of Example 5, and the first to third layers of Comparative Example 3, and "Zpex®" manufactured by Tosoh Corporation was used for the third and fourth layers of Example 5.

[0069] Next, we will explain the method for manufacturing calcined zirconia. First, the raw material powders are filled into a mold with internal dimensions of 20 mm x 25 mm in the order listed in Table 1, and then molded using a single-screw press machine at a surface pressure of 300 kg / cm². 2 The primary press-formed body was subjected to a press molding process for 90 seconds. The resulting primary press-formed body was given a pressure of 1700 kg / cm². 2 A molded body with a layered structure was fabricated by CIP molding for 5 minutes. In Examples 3 and 5, which have a four-layer laminated structure, the filling amount for each layer was 7.5g, while in Examples 1, 2, and 4 and Comparative Examples 1 to 3, which have a three-layer laminated structure, the filling amount for each layer was 10g. The resulting molded bodies were fired at 1000°C for 2 hours to produce zirconia calcined bodies. Regarding the crystal system of the obtained calcined zirconia, in Examples 1-3 and Comparative Examples 1 and 2, the main crystal system of zirconia was monoclinic; in the first layer of Examples 4 and 5 using "Zpex(registered trademark) Smile," the main crystal system of zirconia was cubic; in the second and third layers of Example 4, the second layer of Example 5, and the first to third layers of Comparative Example 3 using "Zpex(registered trademark) 4," the main crystal system of zirconia was tetragonal or cubic; and in the third and fourth layers of Example 5 using "Zpex(registered trademark)," the main crystal system of zirconia was tetragonal.

[0070] [Definition and Measurement of the Appropriate Sintering Temperature for Zirconia Calcined Bodies] In this invention, the appropriate sintering temperature for the calcined zirconia body refers to the sintering temperature specified by the manufacturer when using commercially available zirconia. On the other hand, if there is no specific information regarding the sintering temperature, it can be defined as follows: First, multiple zirconia calcined bodies of the same shape were heated to various temperatures at a heating rate of 10°C / min. These zirconia calcined bodies were then fired at various temperatures for 120 minutes, and subsequently, both sides were polished using #600 grit sandpaper to obtain zirconia sintered body samples with a thickness of 0.5 mm. The appearance of the obtained samples was visually observed, and the appropriate sintering temperature for each zirconia calcined body was determined based on the transparency of the samples according to the following criteria. As shown in the sample on the left in Figure 2, a state where the sample is highly transparent and the background is visible through it can be considered that the zirconia calcined body has been sufficiently fired. On the other hand, a sample with low transparency or a cloudy appearance, as shown on the right side of Figure 2, can be judged as under-fired. In this invention, the lowest temperature at which the zirconia calcined body can be considered sufficiently fired, as shown in the sample on the left side of Figure 2, was determined to be the appropriate sintering temperature. Furthermore, in the case of a zirconia calcined body, the appropriate sintering temperature of the layer with the highest yttria content is defined as the appropriate sintering temperature of that zirconia calcined body.

[0071] Based on the measurements above, the appropriate sintering temperature for the zirconia calcined bodies used in each example and comparative example was 1500°C for Example 1, and 1550°C for Examples 2 and 3, and Comparative Examples 1 and 2. On the other hand, the firing temperature specified by the manufacturer for "Zpex®" and "Zpex® Smile" manufactured by Tosoh Corporation is 1450°C, while the firing temperature specified by the manufacturer for "Zpex® 4" manufactured by Tosoh Corporation is 1500°C. In Examples 4 and 5, the firing temperature specified by the manufacturer differs for each layer. In this case, the higher firing temperature was used, and the appropriate sintering temperature for Examples 4 and 5 was determined to be 1500°C. Comparative Example 3 uses "Zpex(registered trademark) 4" manufactured by Tosoh Corporation for all layers, and the appropriate sintering temperature is 1500°C.

[0072] [Aesthetic evaluation of zirconia sintered bodies] Zirconia sintered bodies were fabricated using the calcined zirconia bodies of each example and comparative example by the following method, and their aesthetics were evaluated visually in comparison to the appearance of natural teeth. For the evaluation, a commercially available shade guide with an appearance equivalent to natural teeth was used. The commercially available shade guide used was the "VITA Classical" shade guide manufactured by VITA Corporation. First, the zirconia calcined bodies 10 of the examples and comparative examples, prepared using the method described above, were machined into the shape of a tooth crown using a CAD / CAM system ("Katana® CAD / CAM System," Kuraray Noritake Dental Co., Ltd.). The resulting machined zirconia calcined bodies were then fired at an appropriate sintering temperature for 120 minutes to produce a sintered zirconia body. The length of the zirconia sintered bodies in the stacking direction was approximately 8 mm in all cases. The obtained zirconia sintered bodies were visually evaluated according to the following criteria (n=1). The results are shown in Table 1. <Evaluation Criteria> ○: The translucency and color gradation are similar to those of natural teeth, with appropriate variations in each area (incisal edge, central part, and cervical area), and the aesthetics of natural teeth are faithfully reproduced. △: While it has similar translucency and color to natural teeth, and there is a gradation of translucency and / or color, the changes are monotonous, and it cannot be considered that the aesthetics of natural teeth are faithfully reproduced. ×: The translucency or change in color is insufficient, and the aesthetics of natural teeth cannot be considered to have been reproduced.

[0073] (Examples 1-5 and Comparative Examples 1-3) In Examples 1 to 5, each zirconia sintered body showed a gradient in which the translucency gradually decreased and the color deepened from the region corresponding to the layer containing one end P of the zirconia calcined body 10 shown in Figure 1 to the region corresponding to the layer containing the other end Q. This reproduced the translucency and color changes in the cervical region and the translucency and color of the incisal edge, exhibiting an appearance similar to that of natural teeth.

[0074] On the other hand, in Comparative Example 1, which corresponds to Patent Document 1, although there was a tendency for the color to darken from the region corresponding to the layer containing one end P of the zirconia calcined body 10 shown in Figure 1 to the region corresponding to the layer containing the other end Q, the change in translucency was insufficient due to the yttria content being the same throughout all layers. As a result, it could not be said that it exhibited an appearance similar to that of natural teeth, as it was not possible to reproduce the translucency of the cervical region in the same way as natural teeth, and to show a gradual transition in translucency between the cervical region and the incisal edge, thus failing to exhibit a translucency gradient. In Comparative Example 2, as shown in Figure 1, the translucency gradually decreased and the color became darker as the yttria content and pigment content changed from the region corresponding to the layer containing P at one end to the region corresponding to the layer containing Q at the other end. However, because both the yttria content and the composition of the coloring components changed, it was not possible to achieve both translucency and color change in the cervical region, and it could not be said to be similar to natural teeth. In Comparative Example 3, similar to Comparative Example 1, although there was a tendency for the color to darken from the region corresponding to the layer containing P at one end of the zirconia calcined body 10 shown in Figure 1 to the region corresponding to the layer containing Q at the other end, the change in translucency was insufficient due to the yttria content being the same throughout all layers, and it could not be said that it exhibited an appearance similar to that of natural teeth. In particular, Comparative Examples 1 and 3 demonstrate that even by changing only the composition (type and content) of the pigment, it is difficult to faithfully reproduce the aesthetic appearance of natural teeth, where the color tone and translucency of enamel, dentin, and pulp are intricately intertwined and influenced by each other. In Comparative Example 2, although a gradient was observed due to changes in the yttria and pigment content, it was not possible to achieve both translucency and color change in the cervical region. Furthermore, the results from Comparative Example 2 show that when a calcined zirconia body with a varying yttria content is sintered, a sintered zirconia body with excellent translucency and color can be obtained at the incisal edge, but a sintered zirconia body with both translucency and color changes in the cervical region cannot be obtained. This demonstrates that it is difficult to faithfully reproduce the appearance of a natural tooth, where the color and translucency of the enamel, dentin, and pulp are intricately intertwined and influenced by each other in the incisal edge, central part, and cervical part of the sintered zirconia body obtained after sintering. In contrast, the zirconia sintered bodies of Examples 1 to 5 reproduced the translucency and color change in the cervical region in the same way as natural teeth, while also reproducing a gradual transition in translucency from the cervical region to the incisal edge, including the central part, without a clear boundary line, thus reproducing the translucency and color of the incisal edge. The color change and the translucency gradation worked together without interfering with each other's effects, resulting in an appearance similar to natural teeth where each structure is intricately intertwined and influences the others. Furthermore, the zirconia sintered bodies of Examples 1 to 5 exhibit increasing strength from the incisal end towards the cervical end, with sufficiently high strength in the central and cervical regions, and possessing appropriate strength for dental use.

[0075] [Color evaluation of zirconia sintered bodies] For the color tone of each layer of the zirconia sintered bodies in each example and comparative example, each layer was prepared individually using the following method, and the L*a*b* color system (JIS Z 8781-4:2013 Colorimetry - Part IV: CIE 1976 L*a*b* color space) was used to determine the color tone of each layer. * ,a * ,b * ) was measured. First, after polishing both sides of the resulting zirconia sintered body with #600 abrasive paper, the size was adjusted in advance and press-molded to obtain a zirconia sintered body with a thickness of 1.2 mm, thereby producing molded bodies consisting of the raw material powders for each layer in each example and comparative example. Next, the molded bodies were fired at 1000°C for 2 hours to produce zirconia calcined bodies. Then, the zirconia calcined bodies were fired at an appropriate sintering temperature for 120 minutes to produce zirconia sintered bodies. After polishing both sides of the obtained zirconia sintered bodies with #600 abrasive paper to obtain zirconia sintered bodies with a thickness of 1.2 mm, the color tone was measured using a Konica Minolta CM-3610A spectrophotometer with a D65 light source, SCI measurement mode, measurement diameter / illumination diameter = φ8 mm / φ11 mm, and a white background. Furthermore, the color difference ΔE2 between the second and third layers of Examples 1, 2, and 4, and between the third and fourth layers of Examples 3 and 5. * This can be calculated using the following formula (4). ΔE2 * ={(L2 * -L1 * ) 2 +(a2 * -a1 * ) 2 +(b2 * -b1 * ) 2 } 1 / 2 (4) (In the formula, color tone (L1 * a1 * , b1 * ) represents the color tone of the first layer (the second layer in Examples 1, 2, and 4, and the third layer in Examples 3 and 5) where the stabilizer content is approximately the same, and the color tone (L2 * a2 * , b2 * ) represents the color tone of the second layer (the third layer in Examples 1, 2, and 4, and the fourth layer in Examples 3 and 5) where the stabilizer content is approximately the same. Based on the color values ​​shown in Table 1, the results of Examples 1-3 demonstrate that the color changes in the cervical region were reproduced, and together with the incisal edge, this confirms why they appear to have a color similar to natural teeth to the naked eye.

[0076] [Table 1]

[0077] [Measurement of the bending strength of zirconia sintered bodies] (Examples 1-3) Using the raw material powders from the third layer of Example 1, the third layer of Example 2, and the fourth layer of Example 3, zirconia calcined bodies were prepared according to the calcined body manufacturing method described above. Subsequently, sintering was performed at the appropriate sintering temperature listed in Table 1 for 120 minutes to obtain zirconia sintered bodies. In accordance with ISO 6872, the bending strength was measured under the conditions of a sample size of 1.2 mm × 4.0 mm × 16.0 mm, a support distance (span length) of 12 mm, and a crosshead speed of 0.5 mm / min. The results were 1310 MPa for the third layer of Example 1, 1157 MPa for the third layer of Example 2, and 1170 MPa for the fourth layer of Example 3, confirming that these materials possess the necessary strength for the cervical portion of dental prostheses.

[0078] With respect to the numerical ranges described herein, any number or range that falls within that range should be interpreted as being specifically described herein, even if not otherwise stated. [Industrial applicability]

[0079] The zirconia calcined body and sintered body of the present invention can be used in dental products such as prosthetics. [Explanation of Symbols]

[0080] 10 Zirconia calcined body P one end Q Other end L total length Y First direction

Claims

1. A dental zirconia calcined body having a laminated structure of at least three layers containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, wherein the main crystal system of the zirconia is tetragonal and / or cubic. The aforementioned stabilizer is yttria, The aforementioned laminated structure comprises at least two layers in which the yttria content relative to the total molars of zirconia and yttria differs from that of the other. The aforementioned laminated structure comprises at least two layers in which the yttria content relative to the total mol of zirconia and yttria is substantially the same. The difference in yttria content between layers with different yttria content is 0.3 mol% or more. The difference in yttria content between layers with approximately the same yttria content is less than 0.1 mol%, All layers with approximately the same yttria content contain coloring components, and the composition of the coloring components in each layer differs from one another. In layers where the composition of the coloring components differs from one another, the types of coloring components are different, and / or the content of the coloring components is different. On a straight line extending in a first direction from one end to the other end of the aforementioned dental zirconia calcined body, For layers with different yttria content, the trend of increasing or decreasing yttria content relative to the total mol of zirconia and yttria from one end to the other remains unchanged, and the yttria content increases or decreases monotonically. With respect to the total moles of the zirconia and yttria, The yttria content of the layer including the aforementioned end is 3.5 mol% or more and 6.5 mol% or less. The yttria content of the layer including the other end is 2.5 mol% or more and less than 4.5 mol%, The yttria content in all layers of the laminated structure is within the range of 2.5 mol% to 6.5 mol%, The thickness of each layer is between 0.5 mm and 3 cm. Dental zirconia calcined body.

2. The dental zirconia calcined body according to claim 1, wherein layers having substantially the same yttria content are adjacent to each other.

3. The coloring component is an oxide of at least one element selected from the group Ti, V, Cr, Mn, Fe, Co, Ni, Pr, Tb, and Er, or (Zr,V)O 2 A dental zirconia calcined body according to claim 1 or 2, comprising:

4. The dental zirconia calcined body according to claim 1 or 2, wherein the laminated structure comprises only one layer having the highest yttria content.

5. The dental zirconia calcined body according to claim 1 or 2, wherein the layer with the highest yttria content does not contain any coloring components.

6. The dental zirconia calcined body according to claim 1 or 2, wherein the layer with the highest yttria content contains a coloring component.

7. The composition of the coloring components in the layer with the highest yttria content differs from the composition of the coloring components in the other layers. In layers where the composition of the coloring components differs from one another, the types of coloring components are different, and / or the content of the coloring components is different. The dental zirconia calcined body according to claim 6.

8. On a straight line extending in a first direction from one end to the other end of the aforementioned dental zirconia calcined body, For layers with different yttria content, the trend of increasing or decreasing yttria content relative to the total mol of zirconia and stabilizer does not change from one end to the other, and the yttria content increases or decreases monotonically. With respect to the total moles of the zirconia and yttria, The dental zirconia calcined body according to claim 1 or 2, wherein the difference in yttria content between the layer containing one end and the layer containing the other end is 3.0 mol% or less.

9. Regarding two layers included in a layer in which the content rate of the yttria in the sintered body produced by firing the dental zirconia green body at a maximum sintering temperature of 1400 ° C or higher and 1650 ° C or lower for 120 minutes is substantially the same, the color tone (L 1 * , a 1 * , b 1 * ) and the color tone (L 2 * , a 2 * , b 2 * ) of the second layer, when compared, The color difference ΔE between the color tone of the first layer and the color tone of the second layer is expressed by the following equation (4). 2 * However, it is between 0.3 and 6.

0. The difference in yttria content between layers with approximately the same yttria content is less than 0.1 mol%. The dental zirconia calcined body according to claim 1 or 2. ΔE 2 * ={(L 2 * -L 1 * ) 2 +(a 2 * -a 1 * ) 2 +(b 2 * -b 1 * ) 2 } 1 / 2 (4) (In the formula, color tone (L 1 * a 1 * , b 1 * ) represents the color tone of the first layer where the yttria content is approximately the same, and the color tone (L 2 * a 2 * , b 2 * ) represents the color tone of the second layer, where the yttria content is approximately the same.

10. On a straight line extending in a first direction from one end to the other end of the aforementioned dental zirconia calcined body, Let (L1, a1, b1) be the (L*, a*, b*) of the first point in the section from one end to 25% of the total length after sintering using the L*a*b* color system. When the (L*, a*, b*) of the second point in the section from the other end to 25% of the total length, after sintering using the L*a*b* color system, is defined as (L2, a2, b2), On the straight line connecting the first point and the second point, The dental zirconia calcined body according to claim 1 or 2, wherein the tendency of increase or decrease in the L* value after sintering according to the L*a*b* color system changes from the first point to the second point.

11. On the straight line connecting the first point and the second point, when the (L*, a*, b*) of the third point between the first and second points after sintering using the L*a*b* color system is denoted as (L3, a3, b3), A dental zirconia calcined body according to claim 10, wherein L1 < L3 > L2.

12. The difference between L1 and L2 is 10.0 or less. L1 is between 65.0 and 93.0, a1 is between -3.0 and 4.5, and b1 is between 0.0 and 24.

0. L2 is between 60.0 and 92.0, a2 is between -2.0 and 7.0, and b2 is between 4.0 and 28.

0. The dental zirconia calcined body according to claim 11.

13. A method for producing a dental zirconia sintered body, comprising sintering the dental zirconia calcined body according to claim 1 or 2 at a maximum sintering temperature of 1400°C to 1650°C.

14. A method for manufacturing a dental product, comprising machining and then sintering a dental zirconia calcined body according to claim 1 or 2.

15. The method for manufacturing a dental product according to claim 14, wherein the cutting process is a cutting process using a CAD / CAM system.

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