Method for producing recycled powder

Abstract

To provide at least one of recycled powder obtained by horizontal recycling of dental blank scraps, manufacturing method thereof, manufacturing method of recycled dental blanks, and recycled dental blanks obtained thereby.SOLUTION: A manufacturing method of recycled powder includes: a pulverization step of pulverizing dental blank scraps to obtain a pulverized product; and a recovery step of recovering, from the pulverized product, powder having a color tone of L* of 90 or more and 100 or less, a* of 0 or more and 1 or less, and b* of 0 or more and 5 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for producing recycled powder obtained by recycling dental blanks, and more particularly to a method for producing recycled powder obtained by recycling dental blanks made of green compacts of ceramics.

Background Art

[0002] Sintered bodies (ceramic materials) such as alumina and zirconia with excellent biocompatibility are widely used as dental materials. Among ceramics, sintered bodies of zirconia are frequently used as dental prostheses such as crowns, bridges, inlays, onlays, and abutments because they have both aesthetic properties similar to natural teeth and high mechanical strength.

[0003] In the method for producing a dental prosthesis made of a sintered body, first, raw material powder is molded into a molded body (compressed powder), and this is calcined to produce a green compact (dental blank). Next, the green compact is subjected to cutting in a dental laboratory or the like, and a shape of a dental prosthesis considering thermal shrinkage due to sintering is imparted. Then, the green compact is sintered to form a sintered body (dental prosthesis), and fine adjustment is performed, and finally, it is worn by a patient.

[0004] By the way, from the viewpoints of reducing industrial waste and environmental impact, the demand for recycling ceramic materials is increasing. As a method for recycling ceramic materials, for example, a technique for recycling an electrolyte sheet for a fuel cell made of a sintered body of zirconia (Patent Document 1) and a technique for recycling a grinding ball made of a sintered body of zirconia (Patent Document 2) are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] Green bodies such as dental blanks are considered suitable for recycling (especially horizontal recycling and closed-loop recycling) because they have not been sintered. However, both Patent Documents 1 and 2 relate to recycling technologies for sintered bodies, and not to recycling technologies for dental blanks, particularly the end materials of dental blanks generated after cutting.

[0007] In addition to this, multiple types of dental blanks are used according to the characteristics of the intended dental prosthesis. The end materials of dental blanks generated after cutting are a mixture of different compositions and types, making it difficult to recover them on the premise of recycling. Therefore, at present, there is only the possibility of cascade recycling such as disposal by processing companies such as dental laboratories or diversion to cement raw materials. Even if the end materials of dental blanks could be recovered, in horizontal recycling, it would be essential to separate them after analyzing the composition of the recovered individual end materials. For this reason, it has been practically impossible to horizontally recycle the end materials of dental blanks.

[0008] An object of the present disclosure is to provide at least any one of recycled powder obtained by horizontal recycling of end materials of dental blanks, a method for producing the same, a method for producing recycled dental blanks, and a recycled dental blank obtained thereby.

MEANS FOR SOLVING THE PROBLEM

[0009] In the present disclosure, the possibility of recycling dental blanks, particularly horizontal recycling, was studied by focusing on the color tone of the end materials of dental blanks after cutting. As a result, it was found that by performing a simple operation on the end materials of dental blanks discharged in the manufacturing process of dental prostheses, they can be recycled (recovered) as raw materials for dental blanks, and furthermore, the powder obtained by such recycling can be suitably used as a raw material for dental blanks.

[0010] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] A method for producing recycled powder, comprising: a pulverization step of pulverizing an end material of a dental blank to obtain a pulverized product; and a recovery step of recovering a powder having a color tone of L of 90 or more and 100 or less, a of 0 or more and 1 or less, and b of 0 or more and 5 or less from the pulverized product. * is 90 or more and 100 or less, a * is 0 or more and 1 or less, b * is 0 or more and 5 or less. [2] The method for producing recycled powder according to [1] above, further comprising a sorting step of sorting the end material prior to the pulverization step. [3] The method for producing recycled powder according to [2] above, wherein the sorting method in the sorting step is a method in which the end material is sorted into a color tone unit composed of an end material having a color tone of L of 90 or more and 100 or less, a of 0 or more and 1 or less, and b of 0 or more and 5 or less, and a color tone unit composed of an end material having a color tone different from the color tone. * is 90 or more and 100 or less, a * is 0 or more and 1 or less, b * is 0 or more and 5 or less. [4] The method for producing recycled powder according to any one of [1] to [3] above, wherein the pulverization step is a pulverization step having a rough pulverization step of dry-pulverizing the end material to obtain a roughly pulverized product and a particle size adjustment step of wet-pulverizing the roughly pulverized product. [5] The method for producing recycled powder according to any one of [1] to [4] above, wherein the recovery method in the recovery step is a recovery method of dividing the pulverized product obtained by the pulverization step into a certain unit and recovering a unit corresponding to the pulverized product having a color tone of L of 90 or more and 100 or less, a of 0 or more and 1 or less, and b of 0 or more and 5 or less. * is 90 or more and 100 or less, a * is 0 or more and 1 or less, b * is 0 or more and 5 or less. [6] A recycling method for a dental blank, comprising: a pulverization step of pulverizing an end material of the dental blank to obtain a pulverized product; and a recovery step of recovering a powder having a color tone of L of 90 or more and 100 or less, a of 0 or more and 1 or less, and b of 0 or more and 5 or less from the pulverized product. * is 90 or more and 100 or less, a * is 0 or more and 1 or less, b * is 0 or more and 5 or less. [7] A method for manufacturing a recycled dental blank using recycled powder obtained from at least one of [1] to [5] above. [8] The color tone has an L * of 90 or more and 100 or less, an a * of 0 or more and 1 or less, and a b * of 0 or more and 5 or less.

Advantages of the Invention

[0011] According to the present disclosure, it is possible to provide at least one of recycled powder obtained by horizontal recycling of end materials of dental blanks, a method for manufacturing the same, a method for manufacturing a recycled dental blank, and a recycled dental blank obtained thereby.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0013] Hereinafter, an example of an embodiment will be shown and the present disclosure will be described. In addition, any combination of the configurations and numerical values in this specification is also included in the present disclosure, and any range formed by any combination of the upper limit value and the lower limit value of the numerical values disclosed in this specification is also included in the present disclosure. Hereinafter, the main terms in the present disclosure will be shown.

[0014] The "dental prosthesis" is at least one of a crown, a bridge, an inlay, an onlay, an abutment, other dentures, and dental coatings, and in particular, at least one of dentures and dental coatings made of a ceramic material (sintered body).

[0015] The "dental blank" is a composition that is a precursor of a dental prosthesis, and in particular, a green body of a ceramic suitable as a precursor of a dental prosthesis. A dental prosthesis can be obtained by sintering the dental blank.

[0016] The "edge material of a dental blank (hereinafter, also simply referred to as 'edge material')" is a dental blank after cutting by machining such as CAD / CAM machining to cut out the shape of a dental prosthesis, and is a dental blank having one or more holes (perforations) in the shape of the dental prosthesis, and at least one of its divided parts.

[0017] The "recycled dental blank (hereinafter, also referred to as'regenerated blank')" is a dental blank manufactured by using recycled powder (described later) for part or all of the raw materials.

[0018] The "sintered body" is a composition composed of crystal particles of ceramics and having a certain shape, and is a composition obtained by molding (and pre-sintering if necessary) and sintering ceramic powder.

[0019] The "pre-sintered body" is a composition composed of fused particles of ceramics and having a certain shape, and is a composition obtained by subjecting a molded body (compressed powder body) obtained by molding ceramic powder to pre-sintering (preliminary firing, semi-firing).

[0020] The "recycled powder" is powder obtained by recycling treatment (recycling) of a sintered body, pre-sintered body or molded body, and mixed powder containing the same. In the present embodiment, in particular, it is powder obtained by recycling treatment of pre-sintering and mixed powder containing the same.

[0021] The "synthetic powder" is powder other than powder obtained by recycling treatment of a sintered body, pre-sintered body or molded body, and in particular, is powder obtained by one or more selected from the group of hydrothermal synthesis method, hydrolysis method and neutralization coprecipitation method, and other liquid phase methods.

[0022] The "color tone" is measured by using a spectrophotometer (for example, CM-700d, manufactured by Konica Minolta Inc.) equipped with an illumination / light-receiving optical system conforming to the geometric condition c of JIS Z 8722, in the SCI method using a black background, and L * a * b* It is a color tone represented by a color system. The color tone of a composition having fluidity such as powder is the color tone measured as a molded body (compressed powder). Note that L * a * b * The color tone represented by the color system is the lightness L * and the hue a * and b * corresponds to the coordinates in the color space determined by three values of [Method for manufacturing recycled powder] This embodiment includes a pulverization step of pulverizing the end material of a dental blank to obtain a pulverized product, and a recovery step of recovering powder having a color tone of L * of 90 or more and 100 or less, a * of 0 or more and 1 or less, and b * of 0 or more and 5 or less from the pulverized product. In the production of dental prostheses, a wide variety of dental blanks are used, and these are discharged (discarded) together. Therefore, the discharged end materials (aggregates) greatly differ in nature including color tone, chemical composition, and contained elements. In such a situation, in the production method of this embodiment, those having a specific color tone can be recovered as powder from such end materials (aggregates of end materials). The recovered powder can be recycled as recycled powder suitable as the raw material powder of the dental blank.

[0023] Hereinafter, each step in the production method of the recycled powder of this embodiment will be described by taking the case where the end material of the dental blank is the end material of the calcined body of zirconia as an example. <Pulverization step> The pulverization step of pulverizing the end material of the dental blank to obtain a pulverized product is a step of pulverizing the end material to obtain a pulverized product. The pulverized product is the one in which the end material has become powdery, and this itself can also be regarded as recycled powder. However, since the end materials used in the pulverization step may contain many materials with different natures, the pulverized product obtained through the subsequent recovery step becomes more suitable recycled powder as the raw material powder of the dental blank.

[0024] The starting material to be subjected to the grinding process is a calcined body, more specifically a calcined body of ceramics, and even more specifically a calcined body of zirconia (zirconium dioxide, ZrO2) (hereinafter also referred to as "zirconia calcined body"). The calcined body is composed of sintering initial fused particles, and the fused particles are particles in a state where the particles are necked together. Compared with a sintered body in which crystal particles are firmly bonded to each other via grain boundaries, the calcined body requires very little energy for grinding and is suitable for recycling treatment by pulverization.

[0025] The zirconia calcined body may be a calcined body made of zirconia, but the main component is zirconia and it may contain metal elements such as stabilizing elements and coloring elements as sub-components.

[0026] One or more selected from the group of yttrium (Y), calcium (Ca), and magnesium (Mg) are mentioned as stabilizing elements, and one or more selected from the group of titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd), terbium (Tb), erbium (Er), and ytterbium (Yb) are mentioned as coloring elements, respectively. Also, one or more selected from the group of aluminum (Al), silicon (Si), and germanium (Ge) are mentioned as other metal elements. The existence state of these metal elements is arbitrary, but they may be dissolved in zirconia or may exist as oxides or other compounds.

[0027] The end material may have a structure composed of one layer, that is, a structure composed of the overall composition. On the other hand, for dental restorations, harmony in aesthetics with the surrounding dentin (the patient's natural teeth) is required. In order to achieve the same aesthetics as that of natural teeth where the aesthetics changes from the tooth root to the cutting part, the end material may have a structure composed of two or more layers (for example, two or more and 15 or less layers, further two or more and 10 or less layers, and still further three or more and eight or less layers). In this case, the end material is not limited to a structure laminated so that the boundary of each layer is clear, and may be a structure in which two or more layers are laminated so that a gradation is formed. Note that the gradation may be a gradation formed by at least either the color tone or the translucency. When the dental blank has a structure in which two or more layers are laminated If it has a structure, it is sufficient that a metal element such as a coloring element is contained in at least one layer, and it is preferable that at least either the type or the content of the coloring element in each layer is different.

[0028] In the pulverization process, the pulverization may be any pulverization that can obtain a pulverized product to such an extent that the end material can be used as recycled powder. Examples of such pulverization include pulverization in which the average particle size of the pulverized product of the end material is 0.1 μm or more, 0.3 μm or more, or 0.4 μm or more, and is 10 μm or less, 5 μm or less, or 1 μm or less. Pulverization in which the average particle size of the pulverized product of the end material is 0.1 μm or more and 10 μm or less, or 0.4 μm or more and 1 μm or less, is preferable.

[0029] The average particle size of the pulverized product of the end material can be determined by the planimetric method using a SEM observation image. Specifically, draw a circle with a known area on the SEM observation image, measure the number of particles (Nc) of the pulverized product inside the circle and the number of particles (Ni) of the pulverized product on the circumference of the circle, and after making the total number of particles (Nc + Ni) 250 ± 50, the average particle size of the pulverized product may be determined using the following formula (1).

[0030] Average particle size = 2 / {π × (Nc + (1 / 2) × Ni) / (A / M 2 )} 0.5 ··· (1) In formula (1), Nc is the number of particles of the crushed material inside the circle, Ni is the number of particles of the crushed material on the circumference of the circle, A is the area of the circle, and M is the magnification of SEM observation (for example, 5000 to 10000 times). When the number of particles (Nc + Ni) in one SEM observation image is less than 200, (Nc + Ni) may be set to 250 ± 50 using a plurality of SEM observation images.

[0031] The pulverization method may be at least one of dry pulverization and wet pulverization, and may be dry pulverization or wet pulverization. Examples of dry pulverization include pulverization methods using one or more selected from the group consisting of a jaw crusher, a hammer crusher, a shredder, a roll crusher, a hammer mill, a cutting mill, a rod mill, a roller mill, a rotor mill, an impact crusher, a jet mill, a ball mill, and a mortar. Examples of wet pulverization include pulverization methods using one or more selected from the group consisting of a ball mill, a bead mill, a planetary mill, a wet jet mill, a colloid mill, and a homogenizer. A preferred pulverization method is wet pulverization using zirconia spheres (at least one of zirconia balls and zirconia beads) as the pulverization medium. This makes it less likely for impurities to contaminate due to pulverization.

[0032] A preferred pulverization process includes a rough pulverization process of dry-pulverizing the end material to obtain a roughly pulverized material, and a particle size adjustment process of wet-pulverizing the roughly pulverized material. By the rough pulverization process, the end material is made into a roughly pulverized material on the order of mm, for example, a roughly pulverized material of 1 to 10 mm. By going through the rough pulverization process, the average particle size of the pulverized material of the above-mentioned end material can be made more efficiently, and the pulverization time in the pulverization process can be shortened and the energy required for pulverization can be reduced. <Recovery process> The manufacturing method of this embodiment recovers a powder having a color tone where L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, and b * is 0 or more and 5 or less, having a recovery process. The color tone where L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, and b *The powder with a value between 0 and 5 (hereinafter also referred to as "base powder", and the said color tone as "base color tone") is the powder obtained from the end material, and the base powder is composed of the same components as the dental blank which is the precursor of the dental prosthesis. Therefore, the base powder is suitable for horizontal recycling into the dental blank. Furthermore, the base powder has the same color tone as that of the dental blank from which the dental prosthesis with the lightest color tone in the dental color sample (for example, Vita Classical Shade) can be obtained. has the same color tone as that of the dental blank.

[0033] The base powder can be directly used as the raw material powder of the dental blank. In addition, by making it a mixed powder with the powder having a color tone different from that of the base powder (hereinafter also referred to as "toning powder"), it can also be used as the raw material powder of the dental blank suitable for the dental prosthesis having a color tone other than the base color tone.

[0034] The color tone of the base powder only needs to have the base color tone, but it is preferably to satisfy the following lightness L * and hue a * and b * Note that the lightness L * and hue a * and b * represent one color tone corresponding to the coordinates indicated by these three values, and each does not independently represent a color tone.

[0035] Lightness L * : 90 or more or 95 or more, and 100 or less or 99 or less, Hue a * : 0 or more or 0.2 or more, and 1 or less or 0.8 or less, Hue b * : 0 or more or 0.2 or more, and 5 or less, 3 or less or 0.8 or less.

[0036] The toning powder has a color tone such that L * is less than 90, a * is less than 0 or more than 1, or b *It is a powder that is less than 0 or more than 5, and any powder containing the same components as the above-mentioned base powder may be used, and it may be at least either a powder composed only of zirconia or a powder of zirconia containing a stabilizing element. Specific color-adjusting powders include at least either a pulverized product of end materials having a color tone different from that of the base powder and a synthetic powder.

[0037] Usually, dental blanks contain coloring elements. The recovered end materials have different contents of coloring elements and are an aggregate of residues of dental blanks after cutting. Therefore, the color tone of the end materials becomes darker compared to the basic color tone. In this case, since the color tone of the pulverized product obtained in the pulverization process also becomes darker than the base color tone, it is preferable to mix a powder with a lighter color tone, such as yttrium-stabilized zirconium powder, as a color-adjusting powder.

[0038] If the base powder can be recovered, the recovery method in the recovery process is arbitrary. For example, there is a recovery method in which the pulverized product obtained by the pulverization process is divided into certain units, and the unit corresponding to the pulverized product having the base color tone is recovered. Also, a similar operation is performed on the coarsely pulverized product obtained in the coarse pulverization process by unit division, and the unit corresponding to the base powder is subjected to a particle size adjustment process, and then recovered by solid-liquid separation and drying. In addition, the "unit" in these may be at least either a mass unit or a volume unit, or any unit that becomes a lot suitable for the process and equipment of recycling treatment.

[0039] The recovered base powder can be recycled as recycled powder and further as a raw material for various ceramic materials. In particular, it can be used as a powder suitable as a raw material for dental blanks. <Separation process> The manufacturing method of the present embodiment preferably includes a sorting step of sorting end materials prior to the grinding step. The end materials are dental blanks after cutting and are collected from processing businesses such as dental laboratories as aggregates of used dental blanks with different color tones and compositions. By having the sorting step, it becomes easier to predict the attributes of the end materials to be subjected to the grinding step, that is, the color tone of the ground materials generated by the grinding step. As a result, unit separation in the collection step and the coarse grinding step becomes simple or unnecessary, and more efficient recovery of base tone powder can be expected.

[0040] In the sorting step, the end materials are sorted. The sorting may be any method of dividing the end materials into units based on certain attributes, but it is preferably a method of dividing the units according to at least one of the composition and the color tone, and more preferably a method of dividing the units according to the color tone.

[0041] For example, when sorting the end materials according to the color tone, if the color tone is L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, b * is 0 or more and 5 or less, the end materials may be sorted into a color tone unit (hereinafter, also referred to as a "base tone unit") and a color tone unit having a color tone different from the base color tone (hereinafter, also referred to as a "non-base tone unit"). Also, when sorting the end materials according to the composition, it may be any method of sorting them into a composition unit composed of end materials having a composition presenting a base color tone and a composition unit composed of end materials having a composition presenting a color tone different from the base color tone. Note that analysis of the composition requires sample collection and instrumental analysis for each end material, whereas analysis of the color tone can be easily performed by non-contact optical analysis (for example, during transportation by a belt conveyor). Therefore, the sorting method is preferably sorting by a unit (color tone unit) based on the color tone rather than sorting by a unit (composition unit) based on the composition.

[0042] The end materials sorted into the non-base tone unit can be recycled as raw materials for toning powder and other ceramic materials, similar to the base powder, through the above-described grinding treatment and recovery treatment.

[0043] The non-base units may be classified into two or more sub-units. As a result, the color tone and composition of the end materials contained in each sub-unit become more subdivided and uniform, making it more suitable for color tone control by mixing with the base powder and recycling for other uses.

[0044] Since it becomes easier to separate the end materials in the separation process, the end materials are preferably the end materials of a dental blank with an information tag attached that contains at least specific information linked to the material information. The "specific information" is information that can be linked to the material information, and the "material information" preferably includes one or more selected from the group of composition information, product information, and manufacturing information (all described later).

[0045] The specific information preferably includes one or more selected from the group of raw material ratio, composition (chemical composition), average composition, contained elements, color tone, color tone code, average color tone, and average color tone code (hereinafter also referred to as "composition information"). The properties of the end materials can be directly confirmed by the composition information. The specific information preferably includes one or more selected from the group of raw material ratio, composition, contained elements, color tone, and color tone code, and preferably includes at least one of the composition and the color tone code. Also, when the end material has a structure composed of two or more layers, the composition information preferably includes one or more selected from the group of average composition, average color tone, and average color tone code in addition to, or instead of, the composition, color tone, and color tone code. The "raw material ratio" is information regarding the type (e.g., product name of the powder) and usage amount of each raw material used in the manufacture of the dental blank, and the color tone is the target color tone of the dental prosthesis obtained by sintering the end material (dental blank). Also, the "color tone code" is a code representing each color tone in the dental color sample book, for example, a code indicated by any alphabet and number from A1 to D4 in the Vita Classical Shade.

[0046] The specific information preferably includes at least one of the model number and the name of the manufacturer of the dental blank (end material) (hereinafter also referred to as "product information"), and preferably includes at least the name of the manufacturer. The "model number" is the product name of the dental blank at the manufacturer of the dental blank. By including the product information in the specific information, rough sorting becomes possible after collection. That is, the end materials collected from processing businesses such as dental laboratories may contain products from different manufacturers of dental blanks. In this case, first, sorting can be performed for each manufacturer or for each manufacturer and product, and sorting for horizontal recycling can be efficiently and easily carried out.

[0047] The specific information preferably includes one or more selected from the group of the manufacturing lot, manufacturing location, manufacturing year, and collection deadline of the dental blank (hereinafter also referred to as "manufacturing information"), more preferably includes at least one of the manufacturing year and the collection deadline, and even more preferably includes the collection deadline. By including the manufacturing information, not only recycling but also traceability becomes possible. Note that the "manufacturing year" is information that can specify the manufacturing time, and instead of the manufacturing year, it may be the manufacturing month or the manufacturing date.

[0048] The specific information is preferably attached by an information tag consisting of a code symbol such as a code tag. The information tag can be read by a means for reading the code symbol, specifically, at least one of a barcode reader and image analysis, etc., so that the end materials can be easily sorted. The information tag may include one or more selected from the group of letters, numbers, and symbols. The type, size, display format, etc. of the code symbol may be appropriately selected according to the amount of information attached to the information tag, the shape of the dental blank, etc. For example, it may be at least one of one-dimensional and two-dimensional code symbols, specifically, at least one of a barcode and a QR code (registered trademark). The information tag may include its own code, etc. Also, it is preferable that the code symbol can read the information even when a part of it is missing. <Washing process> Prior to or after each of the separation process, the pulverization process, the coarse pulverization process, the particle size adjustment process, or the recovery process, an impurity reduction process for reducing impurities may be included. Thereby, impurities attached to the recovered end material and impurities mixed before and after each process can be reduced.

[0049] The method for reducing impurities may be any method as long as it reduces the impurities of the end material, the pulverized material, or the recycled powder (hereinafter also referred to as "end material, etc."), and washing, and more preferably, water washing may be used.

[0050] When impurity reduction is performed by water washing, etc., after the impurity reduction process, a drying process for drying the end material, etc. after water washing may be provided. The drying method may be any method as long as it reduces the water physically adsorbed on the end material, etc., and examples thereof include drying in an air atmosphere at 80°C or higher and 150°C or lower. The drying time may be appropriately adjusted according to the amount of the end material, etc. to be dried and the characteristics of the dryer, and 30 minutes or more and 24 hours or less can be exemplified.

[0051] The manufacturing method of the present embodiment preferably has an impurity reduction process as the first process, and preferably has an impurity reduction process prior to the pulverization process (the separation process if the separation process is included). Further, the impurity reduction process may be an independent process, or may be performed when transferring the end material, etc. to each process. [Recycling method of the end material of the dental blank] The manufacturing method of the recycled powder of the present embodiment includes a pulverization process of pulverizing the end material of the dental blank to obtain a pulverized material, and a recovery process of recovering a powder having an L * of 90 or more and 100 or less, an a * of 0 or more and 1 or less, and a b * of 0 or more and 5 or less from the pulverized material, and can also be regarded as a recycling method of the end material of the dental blank (hereinafter also referred to as "the recycling method of the present embodiment"). As described above, the recycled powder can be used as a raw material powder for dental blanks, and horizontal recycling of the end material is possible.

[0052] The recycling method of this embodiment is the same as the pulverization process and the recovery process in the above-described method for manufacturing recycled powder, and may also include at least one of the classification process and the impurity reduction process in the above-described method for manufacturing recycled powder. [Recycled powder] The recycled powder obtained by the manufacturing method of this embodiment may be any powder that can be used as a raw material for a recycled blank. Preferred recycled powders include, for example, * where L is 90 or more and 100 or less, a * is 0 or more and 1 or less, and b * is 0 or more and 5 or less (hereinafter also referred to as "this recycled powder").

[0053] This recycled powder has L * of 90 or more and 100 or less, a * of 0 or more and 1 or less, b * of 0 or more and 5 or less, and further L * a * b * in the colorimetric system, the lightness L * , the hue a * and the hue b * preferably satisfy the following.

[0054] Lightness L * : 90 or more or 95 or more, and 100 or less or 99 or less, Hue a * : 0 or more or 0.2 or more, and 1 or less or 0.8 or less, Hue b * : 0 or more or 0.2 or more, and 5 or less, 3 or less or 0.8 or less Since this recycled powder exhibits such a color tone, it can be used as a base powder. That is, this recycled powder can be used as it is in the method for manufacturing a green body (dental blank). In addition to this, the recycled powder containing a coloring element can be used as a base powder. That is, conventionally, it was a powder mixing system based on a powder not containing a coloring element, and a green body (dental blank) suitable for a dental prosthesis was produced by mixing a powder containing a coloring element into the base powder. In contrast, by using this recycled powder, in addition to enabling horizontal recycling of the green body (dental blank), a powder mixing system based on a powder containing a coloring element, which has never existed before, can be realized. By such a powder mixing system, a green body (dental blank) suitable for a dental prosthesis can be produced, and a dental prosthesis exhibiting an arbitrary color tone can be obtained with this recycled powder as the base powder in addition to or instead of a powder not containing a coloring element.

[0055] The color tone of the recycled powder can be measured by filling 3.0 g of the powder into a mold with a diameter of 25 mm, performing uniaxial pressing at a pressure of 19.6 MPa, then subjecting it to CIP treatment at a pressure of 196 MPa to form a disk with a thickness of 3.0 ± 0.5 mm, and polishing the measurement surface by 0.1 mm using #800 waterproof abrasive paper and then measuring.

[0056] Since this recycled powder is a powder made from a dental blank as a raw material, it can be mentioned that the main component is zirconia and it is a powder containing metal elements such as a stabilizing element and a coloring element as sub-components.

[0057] At least one selected from the group consisting of yttrium, calcium, and magnesium is included as a stabilizing element contained in the recycled powder. Further, as a coloring element contained in the recycled powder, at least one selected from the group consisting of titanium, iron, cobalt, nickel, manganese, praseodymium, neodymium, europium, gadolinium, terbium, erbium, and ytterbium is included, and at least one transition metal element selected from the group consisting of titanium, iron, cobalt, nickel, and manganese, and at least one rare earth element selected from the group consisting of praseodymium, neodymium, europium, gadolinium, terbium, erbium, and ytterbium are preferably included.

[0058] The recycled powder is a powder obtained by pulverizing a calcined body that has undergone molding and calcination. In order to go through these steps, in this recycled powder, it is considered to include the state of the coloring element contained by immersion in a coloring solution and the state of the coloring element contained by solid-phase mixing, as well as the coloring element contained in zirconia in a different state. Therefore, in the recycled powder, it is preferable that at least a part of the coloring element is contained in solid solution in zirconia, and it is more preferable that at least a part of the transition metal element is contained in solid solution in zirconia. On the other hand, the coloring element may be contained as other compounds (for example, oxides). [Method for manufacturing a recycled blank] The method for manufacturing a dental blank of the present embodiment may be a method for manufacturing a recycled dental blank (recycled blank) using the recycled powder obtained by the manufacturing method of the present embodiment (hereinafter, also referred to as "this recycled powder"). In a method similar to a known method for manufacturing a dental blank, this recycled powder may be used as a raw material powder. Further, in the method for manufacturing a recycled dental blank using this recycled powder, a powder containing this recycled powder may be used as a raw material powder, and a mixed powder containing this recycled powder, for example, a mixed powder of this recycled powder and a synthetic powder, may be used as a raw material powder.

[0059] As a specific manufacturing method, there is a method for manufacturing a recycled dental blank, which includes a molding step of molding the recycled powder to obtain a molded body, and a calcination step of calcining the molded body.

[0060] For the recycled powder used in the molding step, the recycled powder with appropriately adjusted color tone and composition may be used according to the color tone of the target dental prosthesis. For example, when manufacturing a dental blank (calcined body) for producing a dental prosthesis having a color tone corresponding to A1 of Vita Classical Shade, recycled powder may be used as the base powder. On the other hand, when manufacturing a dental blank (calcined body) for producing a dental prosthesis having a color tone darker than A1 of Vita Classical Shade, recycled powder may be used in the mixed powder of the base powder and the color adjusting powder. In the mixed powder, the base powder functions as a diluting component for the color adjusting powder, while the color adjusting powder functions as a coloring element for the base powder. Therefore, when aiming for a dental prosthesis with a darker color tone, the content ratio of the color adjusting powder in the mixed powder may be increased.

[0061] The molding method in the molding step may be any method that can form the recycled powder into a molded body (compressed powder body). For example, one or more selected from the group of press molding, injection molding, sheet molding, extrusion molding, and casting molding may be mentioned. The molding method may be any molding method suitable for the manufacture of dental blanks, and press molding is preferred.

[0062] The calcination step may be a calcination (heat treatment) in which the particles constituting the recycled powder become fused particles, and it may be the calcination in the manufacture of known dental blanks. Examples of the calcination conditions include treatment in an air atmosphere at 800°C or higher and lower than 1200°C.

[0063] The obtained recycled blank can be made into a sintered body (dental prosthesis) by a known sintering method. Examples of the sintering method include sintering treatment at a temperature of 1200°C or higher and 1600°C or lower in an air atmosphere.

Example

[0064] Hereinafter, the present disclosure will be described by way of examples. However, the present disclosure is not limited to the examples. <Composition analysis> The composition of the composition was measured by ICP analysis. As a pretreatment for the analysis, the sample powder was heat-treated at 1000 °C for 1 hour in an air atmosphere. <Average particle size> The average particle size of the powder sample was determined by the planimetric method using SEM observation images. That is, a circle with a known area was drawn on the SEM observation image obtained under the following conditions, and the number of pulverized particles (Nc) inside the circle and the number of pulverized particles (Ni) on the circumference of the circle were measured. After making the total number of particles (Nc + Ni) 250 ± 50, the average particle size of the pulverized material was determined using the above formula (1).

[0065] Acceleration magnification: 15V Observation magnification: 5000 times <Green body density> The mass of the green body was determined by measuring with an electronic balance, and the volume was determined from the dimensions measured with calipers. The measured density was obtained from the obtained mass and volume and used as the green body density. <Sintered body density> The mass of the green body was determined by measuring with an electronic balance, and the volume was determined by the Archimedes method according to JIS R 1634. The measured density was obtained from the obtained mass and volume and used as the green body density. For the Archimedes method, ion-exchanged water was used as the solvent, and the pretreatment was carried out by the boiling method. <Color tone> The color tone was measured by a spectrophotometer (device name: CM-700d, manufactured by Konica Minolta Inc.) equipped with an illumination and light-receiving optical system conforming to the geometric condition c of JIS Z 8722, using a method of placing a black calibration box as the background of the measurement sample (black background measurement). The measurement conditions are as follows.

[0066] Light source: D65 light source Viewing angle: 10° Measurement method: SCI The color tone of the powder sample was measured after filling 3.0 g of the powder into a mold with a diameter of 25 mm, performing uniaxial pressure molding at a pressure of 19.6 MPa, then subjecting it to CIP treatment at a pressure of 196 MPa to form a disk with a thickness of 3.0 ± 0.5 mm, and polishing the measurement surface with #800 waterproof abrasive paper by 0.1 mm.

[0067] The color tone of the calcined body sample could be measured after polishing the measurement surface with #800 waterproof abrasive paper by 0.1 mm.

[0068] The sintered body sample was measured after mirror-polishing both sides of the sintered body to a thickness of 1.0 ± 0.1 mm and a surface roughness (Ra) of 0.02 μm or less. <Total light transmittance> The total light transmittance was measured using a haze meter (device name: NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) with a D65 light source according to the method compliant with JIS K 7361-1. The measurement sample used was a disk-shaped sintered body with a thickness of 1.0 ± 0.1 mm that was polished on both sides so that the surface roughness Ra ≤ 0.02 μm.

[0069] Synthesis example <Preparation of calcined body> As a simulated sample of the end material of a dental blank, a calcined body having the same composition and properties as the dental blank was prepared by the following method. Commercially available zirconia powder (synthetic powder; in calcined bodies 1 to 4, Zpex, Zpex - Yellow, Zpex - Gray, and Zpex - Pink. In calcined bodies 5 to 8, Zpex4, Zpex4 - Yellow, Zpex - Gray, and Zpex - Pink. In calcined bodies 9 to 12, Zpex - Smile, Zpex - SmileYellow, Zpex - Smile - Gray, and Zpex - Pink. All are manufactured by Tosoh Corporation) was filled into a 200 mL polypropylene container at the blending ratio [mass%] of the powders shown in Tables 1 to 3, and this was dry - mixed by stirring the container. 26 g of the obtained powder was filled into a mold of 57 mm × 34 mm, and after performing uniaxial pressure molding at a pressure of 19.6 MPa, it was subjected to CIP treatment at a pressure of 196 MPa to obtain a molded body. The obtained molded body was fired under the following conditions to obtain a calcined body.

[0070] Calcination temperature: 1000 °C Calcination time: 1 hour Temperature rising rate: 50 °C / hour Calcination atmosphere: Atmospheric atmosphere Temperature dropping rate: 300 °C / hour The same operation was repeated to produce four pieces each of the calcined bodies 1 to 12 shown in Tables 1 to 3. Note that the remainder in the calcined body composition in the following table is zirconia.

[0071]

Table 1

[0072]

Table 2

[0073]

Table 3

[0074] The evaluation results of the obtained recycled powder are shown in the following table.

[0075]

Table 4

[0076] Examples 13 to 25 <Manufacture of recycled blanks> 3 g of the recycled powders of Examples 1 to 12 were each filled into a mold with a diameter of 25 mm, uniaxially pressed at a pressure of 19.6 MPa, and then subjected to CIP treatment at a pressure of 196 MPa to obtain a compact. The obtained compact was fired under the following conditions to obtain the recycled blanks of Examples 13 to 25.

[0077] Temperature for preliminary firing: 1000 °C Time for preliminary firing: 1 hour Rate of temperature increase: 50 °C / hour Atmosphere for preliminary firing: air atmosphere Rate of temperature decrease: 300 °C / hour The evaluation results of the obtained recycled blanks are shown in the following table.

[0078]

Table 5

[0079] Furthermore, the obtained preliminarily fired bodies were sintered under the following conditions to obtain sintered bodies.

[0080] Sintering method: normal pressure sintering Sintering atmosphere: air atmosphere Holding temperature: 1450 °C (Examples 13 to 16, 21 to 24) 1500 °C (Examples 17 to 20) Holding time: 2 hours The evaluation results of the obtained sintered bodies are shown in the following table together with the evaluation results of the sintered bodies obtained by sintering the main calcined bodies obtained in the synthesis examples under the same conditions. The color tone names indicate colors in accordance with the indicators of Vita Classical Shades.

[0081]

Table 6

[0082] Example 25 <Manufacture of Recycled Blank with Mixed Powder> A mixed powder was obtained in the same manner as in Synthesis Example 1, except that the recycled powders obtained in Examples 5 to 8 and synthetic powders (product names: Zpex4 - Yellow, Zpex - Gray, and Zpex - Pink, all manufactured by Tosoh Corporation) as color - adjusting powders were used, and the mixing ratios shown in the following table were used.

[0083]

Table 7

[0084]

Table 8

[0085] The results are shown in the following table.

[0086]

Table 9

Claims

1. A sorting step of sorting end materials, a pulverizing step of pulverizing the end materials of a dental blank to obtain a pulverized product, and a recovery step of recovering a powder having a color tone of L ＊ of 90 or more and 100 or less, a ＊ of 0 or more and 1 or less, b ＊ of 0 or more and 5 or less, the sorting method in the sorting step being a method in which the end materials are sorted into a color tone unit composed of end materials having a base color tone of L ＊ of 90 or more and 100 or less, a ＊ of 0 or more and 1 or less, b ＊ of 0 or more and 5 or less and a color tone unit composed of end materials having a color tone different from the base color tone, the manufacturing method of recycled powder.

2. The method for producing recycled powder according to claim 1, wherein the pulverization step includes a coarse pulverization step of dry-pulverizing the end material to obtain a coarsely pulverized product, and a particle size adjustment step of wet-pulverizing the coarsely pulverized product.

3. The method for producing recycled powder according to claim 1 or 2, wherein the end material of the dental blank is a pre-fired body of ceramics.

4. The method for producing recycled powder according to claim 1 or 2, wherein the end material has a structure composed of one layer.

5. The method for producing recycled powder according to claim 1 or 2, wherein the end material has a structure composed of two or more layers.

6. The method for producing a recycled dental blank, which uses the recycled powder obtained in claim 1 or 2.

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