Method for producing recycled powder

Abstract

Provided is at least one of a recycled powder obtained through horizontal recycling of scrap from dental blanks, a method for producing the recycled powder, a method for producing a recycled dental blank, and a recycled dental blank obtained by the method.　This method for producing a recycled powder comprises: a pulverization step for pulverizing scrap from dental blanks to obtain a pulverized product; and a recovery step for recovering a powder having a color tone where L* is 90-100 inclusive, a* is 0-1 inclusive, and b* is 0-5 inclusive from the pulverized product.

Description

Manufacturing method for recycled powder

[0001] The present disclosure relates to a method for producing recycled powder obtained by regenerating (recycling) dental blanks, and further to a method for producing recycled powder obtained by recycling dental blanks made of calcined ceramic bodies.

[0002] Sintered bodies (ceramic materials) such as alumina and zirconia, which have excellent biocompatibility, are widely used as dental materials. Among ceramics, zirconia sintered bodies combine aesthetics close to natural teeth with high mechanical strength, making them widely used in dental prostheses such as crowns, bridges, inlays, onlays, and abutments.

[0003] In a method for producing a dental prosthesis made of a sintered body, a raw material powder is first molded into a green compact (a green compact), which is then calcined to produce a calcined body (a dental blank). The calcined body is then machined in a dental laboratory or the like to give it the shape of the dental prosthesis, taking into account thermal shrinkage due to sintering. The calcined body is then sintered to produce a sintered body (a dental prosthesis), which is then finely adjusted and finally fitted to the patient.

[0004] Meanwhile, there is an increasing demand for recycling ceramic materials from the viewpoint of reducing industrial waste, reducing environmental impact, etc. Known methods for recycling ceramic materials include a technology for recycling electrolyte sheets for fuel cells made of sintered zirconia (Patent Document 1) and a technology for recycling grinding balls made of sintered zirconia (Patent Document 2).

[0005] JP2010-027358A JP10-218662A

[0006] Since dental blanks and other calcined bodies are not subjected to a sintering process, they are considered suitable for recycling (particularly horizontal recycling and closed-loop recycling). However, both Patent Documents 1 and 2 relate to recycling technologies for sintered bodies, and are not recycling technologies for dental blanks, particularly dental blank scraps generated after cutting.

[0007] In addition, multiple types of dental blanks are used depending on the characteristics of the desired dental prosthesis. Dental blank scraps generated after cutting are a mixture of different compositions and types, making recovery with the intention of recycling difficult. Therefore, currently, the only possibilities are for them to be disposed of by processing companies such as dental laboratories, or for cascade recycling, such as converting them into cement raw materials. Even if dental blank scraps could be recovered, horizontal recycling requires that each recovered scrap be separated after undergoing compositional analysis. For this reason, horizontal recycling of dental blank scraps has been practically impossible.

[0008] The present disclosure aims to provide at least one of a recycled powder obtained by horizontal recycling of dental blank scraps and a method for manufacturing the same, a method for manufacturing recycled dental blanks, and recycled dental blanks obtained thereby.

[0009] In this disclosure, we have investigated the possibility of recycling dental blanks, particularly horizontal recycling, focusing on the color tone of dental blank scraps after cutting. As a result, we have found that dental blank scraps discarded in the manufacturing process of dental prostheses can be recycled as raw materials for dental blanks by performing a simple operation, and further that the powder obtained by such a recycling process can be suitably used as raw materials 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 grinding step of grinding an end piece of a dental blank to obtain a ground material, and a grinding step of grinding an end piece of a dental blank to obtain a ground material having a color tone of L. ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ [2] A method for producing recycled powder according to the above [1], which comprises a recovery step of recovering powder having a value of 0 or more and 5 or less. [3] A method for producing recycled powder according to the above [1], which comprises a separation step of separating scraps prior to the pulverization step. ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊[4] A method for producing recycled powder according to any one of [1] to [3] above, wherein the pulverization step is a pulverization step comprising a coarse pulverization step of dry-pulverizing the scraps to obtain a coarsely pulverized material, and a particle size adjustment step of wet-pulverizing the coarsely pulverized material. [5] A method for producing recycled powder according to any one of [1] to [3] above, wherein the recovery method in the recovery step comprises dividing the pulverized material obtained by the pulverization step into a certain unit, and adjusting the color tone of the pulverized material by the color tone L. ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ [6] A method for producing recycled powder according to any one of [1] to [4], which is a recovery method for recovering units corresponding to pulverized material having a color tone of 0 to 5. [6] A method for producing recycled powder according to any one of [1] to [4], which comprises a pulverization step of pulverizing dental blank scraps to obtain a pulverized material, and a step of recovering units corresponding to pulverized material having a color tone of L from the pulverized material. ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ [7] A method for producing a recycled dental blank using the recycled powder obtained by at least one of the above [1] to [5]. [8] A method for producing a recycled dental blank using the recycled powder obtained by at least one of the above [1] to [5]. ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ A recycled powder having a value of 0 or more and 5 or less.

[0011] The present disclosure can provide at least one of a recycled powder obtained by horizontal recycling of dental blank scraps and a method for manufacturing the same, a method for manufacturing recycled dental blanks, and recycled dental blanks obtained thereby.

[0012] Flow diagram of a method for producing recycled powder without a separation process Flow diagram of a method for producing recycled powder with a separation process

[0013] The present disclosure will be described below with reference to an example embodiment. Any combination of the configurations and numerical values ​​in this specification is also included in the present disclosure, and any combination of the upper and lower limits of the numerical values ​​disclosed in this specification is also included in the present disclosure. The main terms used in this disclosure are listed below.

[0014] "Dental prosthesis" refers to at least one of crowns, bridges, inlays, onlays, abutments, and other dentures and dental coatings, and in particular to at least one of dentures and dental coatings made of ceramic materials (sintered bodies).

[0015] A "dental blank" is a composition that serves as a precursor to a dental prosthesis, and is particularly a calcined ceramic body suitable as a precursor to a dental prosthesis. A dental prosthesis is obtained by sintering the dental blank.

[0016] "Dental blank scraps (hereinafter simply referred to as "scrap scraps")" are dental blanks that have been cut into the shape of a dental prosthesis by cutting processes such as CAD / CAM processing, and are at least one of dental blanks that have one or more holes (perforations) in the shape of the dental prosthesis, and divided pieces thereof.

[0017] A "recycled dental blank (hereinafter also referred to as a "recycled blank")" is a dental blank manufactured using recycled powder (described below) as part or all of the raw material.

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

[0019] A "calcined body" is a composition composed of fused ceramic particles and having a fixed shape, and is obtained by calcining (pre-firing, semi-firing) a compact (pressed powder) obtained by molding ceramic powder.

[0020] The "recycled powder" refers to a powder obtained by regenerating (recycling) a sintered body, a calcined body, or a molded body, as well as a mixed powder containing the same. In this embodiment, the "recycled powder" particularly refers to a powder obtained by regenerating a calcined body and a mixed powder containing the same.

[0021] The "synthetic powder" refers to a powder other than a powder obtained by the regeneration treatment of a sintered body, a calcined body, or a molded body, and in particular, a powder obtained by one or more liquid phase methods selected from the group consisting of hydrothermal synthesis, hydrolysis, and neutralization coprecipitation.

[0022] "Color tone" is measured by the SCI method using a spectrophotometer (for example, CM-700d, manufactured by Konica Minolta) equipped with an illumination and light-receiving optical system conforming to the geometric condition c of JIS Z 8722, and is measured using a black background. ＊ a ＊ b ＊ The color tone of a composition having fluidity such as a powder is the color tone measured when it is molded into a compact (pressed powder). ＊ a ＊ b ＊ The color tone expressed in the color system is expressed by the lightness L ＊ and hue a ＊ and b ＊ The color tone corresponds to the coordinates in the color space determined by the three values ​​of L. [Method for producing recycled powder] This embodiment includes a pulverization step of pulverizing dental blank scraps to obtain a pulverized material, and a method for producing recycled powder from the pulverized material. ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ and recovering powder having a % saturation index (SAR) of 0 to 5. In the manufacture of dental prostheses, a wide variety of dental blanks are used, which are then discarded (discarded) collectively. Therefore, the discarded scraps (aggregates) vary greatly in their properties, including color, chemical composition, and elemental content. In this situation, the manufacturing method of this embodiment makes it possible to recover scraps (aggregates) with a specific color tone as powder. The recovered powder can be regenerated (recycled) as recycled powder suitable as a raw material powder for dental blanks.

[0023] Hereinafter, each step in the method for producing recycled powder according to this embodiment will be described using an example in which the dental blank scraps are scraps of calcined zirconia bodies. <Crushing step> The crushing step in which dental blank scraps are crushed to obtain a crushed material is a step in which the scraps are crushed to obtain a crushed material. The crushed material is the scraps that have been turned into a powder, and this itself can also be considered recycled powder. However, because the scraps used in the crushing step may contain many different materials, the crushed material obtained by the recovery step described below becomes a recycled powder that is more suitable as a raw material powder for dental blanks.

[0024] The milled materials to be subjected to the pulverization process are calcined bodies, and further calcined bodies of ceramics, and further zirconia (zirconium dioxide, ZrO ２ The calcined body is a calcined body of zirconia (hereinafter also referred to as "zirconia calcined body"). The calcined body is composed of fused particles in the early stages of sintering, and the fused particles are particles in a necked state. Compared to sintered bodies, in which crystal particles are firmly bonded to each other via grain boundaries, the energy required to pulverize the calcined body is very small, making it suitable for regeneration processing by powdering.

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

[0026] Examples of stabilizing elements include one or more selected from the group consisting of yttrium (Y), calcium (Ca), and magnesium (Mg), and examples of coloring elements include one or more selected from the group consisting 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). Other metal elements include one or more selected from the group consisting of aluminum (Al), silicon (Si), and germanium (Ge). These metal elements may be present in any state, and may be solid-solved in zirconia, or may exist as oxides or other compounds.

[0027] The scrap material may have a structure consisting of one layer, i.e., a structure consisting of the entire composition. On the other hand, dental prostheses are required to be aesthetically harmonious with the surrounding tooth structure (the patient's natural teeth). To achieve aesthetics similar to those of natural teeth, whose aesthetics change from the root to the cutting area, the scrap material may have a structure consisting of two or more layers (e.g., 2 to 15 layers, or even 2 to 10 layers, or even 3 to 8 layers). In this case, the scrap material is not limited to a structure in which the boundaries between each layer are clearly defined, but may also have a structure in which two or more layers are laminated to form a gradation. The gradation may be formed by at least one of color tone and translucency. When the dental blank has a structure in which two or more layers are laminated, it is sufficient that metal elements such as coloring elements are contained in at least one layer, and it is preferable that at least one of the types and contents of the coloring elements in each layer differ.

[0028] In the pulverization step, the pulverization may be performed to such an extent that the milled material can be pulverized to a level that allows it to be used as recycled powder. Examples of such pulverization include pulverization such that the milled material has an average particle size of 0.1 μm or more, 0.3 μm or more, or 0.4 μm or more, and 10 μm or less, 5 μm or less, or 1 μm or less, and preferably pulverization such that the milled material has an average particle size of 0.1 μm to 10 μm, or 0.4 μm to 1 μm.

[0029] The average particle size of the milled scraps can be determined by a planimetric method using an SEM image. Specifically, a circle of known area is drawn on the SEM image, and the number of milled particles within the circle (Nc) and the number of milled particles around the circle (Ni) are measured so that the total number of particles (Nc + Ni) is 250±50. Then, the average particle size of the milled scraps can be determined using the following formula (1):

[0030] Average particle diameter = 2 / {π×(Nc+(1 / 2)×Ni) / (A / M ２ ) ０．５... (1) In formula (1), Nc is the number of pulverized particles within the circle, Ni is the number of pulverized particles on the circumference of the circle, A is the area of ​​the circle, and M is the magnification of the SEM observation (for example, 5000 to 10000 times). If the number of particles (Nc + Ni) in one SEM observation image is less than 200, it is sufficient to use multiple SEM observation images to set (Nc + Ni) to 250 ± 50.

[0031] The pulverization method may be at least one of dry pulverization and wet pulverization, and may be either dry pulverization or wet pulverization. Examples of dry pulverization include pulverization methods using one or more devices selected from the group consisting of a jaw crusher, hammer crusher, shredder, roll crusher, hammer mill, cutting mill, rod mill, roller mill, rotor mill, impact pulverizer, jet pulverizer, ball mill, and mortar. Examples of wet pulverization include pulverization methods using one or more devices selected from the group consisting of a ball mill, bead mill, planetary mill, wet jet mill, colloid mill, and 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 reduces the risk of impurity contamination during pulverization.

[0032] A preferred pulverization step includes a coarse pulverization step in which scraps are dry-pulverized to obtain a coarsely pulverized product, and a particle size adjustment step in which the coarsely pulverized product is wet-pulverized. The coarse pulverization step converts the scraps into coarsely pulverized product on the order of mm, for example, 1 to 10 mm. By passing through the coarse pulverization step, the average particle size of the pulverized product of the scraps can be more efficiently adjusted, and the pulverization time in the pulverization step and the energy required for pulverization can be reduced. <Recovery step> In the manufacturing method of this embodiment, a material having a color tone of L is recovered from the pulverized product. ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ and recovering the powder having a color tone of L ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊A powder having a value of 0 to 5 (hereinafter also referred to as "base powder" and the color tone thereof is referred to as "base color tone") is a powder obtained from scrap material, and the base powder is composed of the same components as dental blanks, which are precursors of dental prostheses. Therefore, the base powder is suitable for horizontal recycling into dental blanks. Furthermore, the base powder has a color tone similar to the color tone of dental blanks from which dental prostheses having the lightest color tone in a dental color tone sample (e.g., Vita Classical Shade) can be obtained.

[0033] The base powder can be used as a raw material powder for dental blanks as it is. In addition, by mixing the base powder with a powder having a different color tone from the base powder (hereinafter also referred to as "coloring powder"), the base powder can be used as a raw material powder for dental blanks suitable for dental prostheses having a color tone other than the base color tone.

[0034] The color tone of the base powder may be any color tone, but the following lightness L ＊ and hue a ＊ and b ＊ It is preferable that the lightness L ＊ and hue a ＊ and b ＊ indicates one color tone corresponding to the coordinates indicated by these three values, and each does not indicate a color tone independently.

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

[0036] The color of the toning powder is L ＊ is less than 90, a ＊ is less than 0 or more than 1, or b ＊The powder may be a powder having a color tone different from that of the base powder, and may be at least one of a powder consisting of zirconia alone and a powder of zirconia containing a stabilizing element. Specific examples of the color-tuning powder include at least one of a powder made of pulverized scraps and having a color tone different from that of the base powder, and a synthetic powder.

[0037] Dental blanks typically contain coloring elements. The scraps collected are a collection of dental blank residues after cutting, with different coloring element contents. Therefore, the color tone of the scraps is darker than the base color. In this case, the color tone of the pulverized material obtained in the grinding process is also darker than the base color, so it is preferable to mix a lighter color powder, such as yttrium-stabilized zirconium powder, as a color-tuning powder.

[0038] As long as the base powder can be recovered, any recovery method can be used in the recovery process. For example, the pulverized material obtained in the pulverization process can be divided into certain units, and the units corresponding to the pulverized material having the base color can be recovered. Alternatively, a similar operation can be performed on the coarsely pulverized material obtained in the coarse pulverization process, and the units corresponding to the base powder can be subjected to a particle size adjustment process, followed by solid-liquid separation and drying to recover the resulting product. The "unit" in these cases can be at least one of a mass unit and a volume unit, or any other unit that can be used to determine a lot suitable for the recycling process and equipment.

[0039] The recovered base powder can be recycled as a recycled powder or even as a raw material for various ceramic materials, and can be used particularly as a powder suitable for use as a raw material for dental blanks. <Sorting Process> The manufacturing method of this embodiment preferably includes a sorting process for sorting scraps prior to the pulverization process. The scraps are dental blanks after cutting, and are collected from processing companies such as dental laboratories as a collection of used dental blanks with different colors and compositions. The sorting process makes it easier to predict the attributes of the scraps to be used in the pulverization process, i.e., the color of the pulverized material produced by the pulverization process. This simplifies or eliminates the need for unit sorting in the recovery process and coarse pulverization process, and more efficient recovery of the base powder can be expected.

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

[0041] For example, when sorting scraps according to color tone, ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ Any method can be used as long as it separates scrap into a color unit (hereinafter also referred to as a "base unit") consisting of scrap having a color tone different from the base color tone, and a color unit (hereinafter also referred to as a "non-base unit") consisting of scrap having a color tone different from the base color tone. Furthermore, when separating scrap according to composition, any method can be used as long as it separates scrap into a composition unit consisting of scrap having a composition that exhibits the base color tone, and a composition unit consisting of scrap having a composition that exhibits a color tone different from the base color tone. While composition analysis requires sample collection and instrumental analysis for each scrap, color analysis can be easily performed by non-contact optical analysis (e.g., during transport on a conveyor belt). Therefore, it is preferable that the separation method be based on color tone (color unit) rather than on compositional units (compositional units).

[0042] The scraps separated into non-basic units can be recycled as raw materials for toning powder and other ceramic materials in the same way as the basic powder, by undergoing the above-mentioned crushing and recovery processes.

[0043] The non-basic unit may be separated into two or more sub-units, which allows the color and composition of the scrap contained in each sub-unit to be more refined and uniform, making it more suitable for color control by mixing with the basic powder or for recycling for other purposes.

[0044] In order to facilitate the separation of the scraps in the separation step, the scraps are preferably dental blank scraps tagged with an information tag including 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 information selected from the group consisting of composition information, product information, and manufacturing information (all of which will be described later).

[0045] The specific information preferably includes one or more items selected from the group consisting 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 composition information allows the identity of the scrap to be directly confirmed. The specific information preferably includes one or more items selected from the group consisting of raw material ratio, composition, contained elements, color tone, and color tone code, and preferably includes at least one of composition and color tone code. Furthermore, when the scrap has a structure consisting of two or more layers, the composition information preferably includes one or more items selected from the group consisting 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., powder product name) and amount of each raw material used in manufacturing the dental blank, and the color tone is the target color tone of the dental prosthesis obtained by sintering the scrap (dental blank). The "color code" is a code that represents each color tone in the dental color sample, and is, for example, a code indicated by any of the alphabets A1 to D4 in the Vita Classical Shade, and numbers.

[0046] The specific information preferably includes at least one of the dental blank (scrap) model number and the manufacturer's name (hereinafter also referred to as "product information"), and preferably includes at least the manufacturer's name. The "model number" is the product name of the dental blank as determined by the dental blank manufacturer. By including product information in the specific information, rough sorting becomes possible after collection. In other words, scrap collected from processing businesses such as dental laboratories may contain a mixture of products from different dental blank manufacturers. In this case, sorting by manufacturer or by manufacturer and product becomes possible, making it easier to sort efficiently for horizontal recycling.

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

[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 easily sorted by reading it using a code symbol reading means, specifically, at least one of a barcode reader and image analysis. The information tag may include one or more characters selected from the group consisting of letters, numbers, and symbols. The type, size, and display format of the code symbol can be appropriately selected depending on the amount of information to be attached to the information tag and the shape of the dental blank. For example, it may be at least one-dimensional or two-dimensional code symbol, specifically, at least one of a barcode and a QR code (registered trademark). The information tag may include a unique code, etc. Furthermore, it is preferable that the code symbol be readable even if part of it is missing. <Washing Process> An impurity reduction process for reducing impurities may be included before or after each of the sorting process, crushing process, coarse crushing process, particle size adjustment process, and recovery process. This reduces impurities associated with the recovered scrap and impurities mixed in before and after each process.

[0049] The method for reducing impurities may be any method that reduces impurities in scraps, crushed material, or recycled powder (hereinafter also referred to as "scrap, etc."), and may be washing or even water washing.

[0050] When impurities are reduced by washing with water, for example, a drying step of drying the washed scraps may be performed after the impurity reduction step. The drying method may be any method that reduces water physically adsorbed on the scraps, and examples include drying in the air at 80°C or higher and 150°C or lower. The drying time may be adjusted appropriately depending on the amount of scraps to be dried and the characteristics of the dryer, and can be, for example, 30 minutes to 24 hours.

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

[0052] The recycling method of this embodiment is similar to the pulverization step and recovery step in the above-mentioned method for producing recycled powder, and may also include at least one of the separation step and impurity reduction step in the above-mentioned method for producing 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 recycled blanks. Preferred recycled powders include, for example, L ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ The recycled powder has a value of 0 or more and 5 or less (hereinafter, also referred to as "the recycled powder").

[0053] This recycled powder 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, and L ＊ a ＊ b ＊ Lightness L in the color system ＊ , hue a ＊ and hue b ＊ It is preferable that:

[0054] Lightness L＊ : 90 or more or 95 or more and 100 or less or 99 or less, hue a ＊ hue b: 0 or more or 0.2 or more and 1 or less or 0.8 or less; ＊ : 0 or more or 0.2 or more, and 5 or less, 3 or less, or 0.8 or less. The recycled powder exhibiting such a color tone can be used as a base powder. That is, the recycled powder can be used directly in the production of a calcined body (dental blank). In addition, the recycled powder containing a coloring element can be used as a base powder. Conventional powder mixing systems use a powder containing no coloring element as the base powder, and calcined bodies (dental blanks) suitable for dental prostheses are produced by mixing a powder containing a coloring element with the base powder. In contrast, the use of the recycled powder not only enables horizontal recycling of calcined bodies (dental blanks) but also realizes a previously unseen powder mixing system based on a powder containing a coloring element. Such a powder mixing system can produce calcined bodies (dental blanks) suitable for dental prostheses, and dental prostheses exhibiting any color tone can be obtained by using the recycled powder as the base powder in addition to or instead of a powder containing no coloring element.

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

[0056] Since the recycled powder is made from dental blanks, it is a powder whose main component is zirconia and which contains metal elements such as stabilizing elements and coloring elements as secondary components.

[0057] The recycled powder contains one or more stabilizing elements selected from the group consisting of yttrium, calcium, and magnesium. The recycled powder contains one or more coloring elements selected from the group consisting of titanium, iron, cobalt, nickel, manganese, praseodymium, neodymium, europium, gadolinium, terbium, erbium, and ytterbium, and preferably contains one or more transition metal elements selected from the group consisting of titanium, iron, cobalt, nickel, and manganese, and one or more rare earth elements selected from the group consisting of praseodymium, neodymium, europium, gadolinium, terbium, erbium, and ytterbium.

[0058] The present recycled powder is obtained by pulverizing a calcined body that has undergone molding and calcination. Because of these processes, the present recycled powder is believed to contain coloring elements incorporated into zirconia in a state different from that of the coloring elements incorporated by immersion in a coloring solution or by solid-phase mixing. Therefore, the coloring elements in the present recycled powder are preferably present as a solid solution in zirconia, and more preferably as a solid solution in zirconia, with at least a portion of the transition metal elements being present. Alternatively, the coloring elements may be present as other compounds (e.g., oxides). [Method for Manufacturing Recycled Blanks] The dental blank manufacturing method 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 "the present recycled powder"), and may be a method similar to known dental blank manufacturing methods, in which the present recycled powder is used as a raw material powder. Furthermore, in the method for manufacturing recycled dental blanks using the present recycled powder, a powder containing the present recycled powder may be used as the raw material powder, or a mixed powder containing the present recycled powder, for example, a mixed powder of the present recycled powder and a synthetic powder, may be used as the raw material powder.

[0059] A specific manufacturing method 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] The recycled powder used in the molding process may be one whose color tone and composition have been adjusted appropriately depending on the color tone of the desired dental prosthesis. For example, when producing a dental blank (calcined body) for fabricating a dental prosthesis having a color tone equivalent to Vita Classical Shade A1, recycled powder may be used as the base powder. On the other hand, when producing a dental blank (calcined body) for fabricating a dental prosthesis having a color tone darker than Vita Classical Shade A1, recycled powder may be used as a mixed powder of base powder and toning powder. In the mixed powder, the base powder functions as a diluting component for the toning powder, while the toning powder functions as a coloring element for the base powder. Therefore, when a dental prosthesis with a darker color tone is desired, the proportion of toning powder in the mixed powder may be increased.

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

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

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

[0064] The present disclosure will be described below with reference to examples. However, the present disclosure is not limited to these 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 in an air atmosphere at 1000°C for 1 hour. <Average Particle Diameter> The average particle diameter of the powder sample was determined by a planimetric method using an SEM observation image. That is, a circle of known area was drawn on an SEM observation image obtained under the following conditions, and the number of particles of the pulverized material within the circle (Nc) and the number of particles of the pulverized material around the circumference of the circle (Ni) were measured. The total number of particles (Nc + Ni) was adjusted to 250±50, and the average particle diameter of the pulverized material was then calculated using the above-mentioned formula (1).

[0065] Acceleration magnification: 15 V Observation magnification: 5000x <Density of calcined body> The mass of the calcined body was determined by measuring with an electronic balance, and the volume was determined from the dimensions measured with a vernier caliper. The measured density was determined from the obtained mass and volume, and was used as the density of the calcined body. <Density of sintered body> The mass of the calcined body was determined by measuring with an electronic balance, and the volume was determined by the Archimedes method in accordance with JIS R 1634. The measured density was determined from the obtained mass and volume, and was used as the density of the calcined body. The Archimedes method used ion-exchanged water as the solvent, and pretreatment was performed by boiling. <Color Tone> Color tone was measured using a spectrophotometer (device name: CM-700d, manufactured by Konica Minolta) equipped with an illumination and light-receiving optical system in accordance with geometric condition c of JIS Z 8722, using a method in which a black calibration box was placed as the background of the measurement sample (black background measurement). The measurement conditions were as follows.

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

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

[0068] The sintered body samples were 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> Total light transmittance was measured using a haze meter (device name: NDH4000, manufactured by Nippon Denshoku Co., Ltd.) with a D65 light source according to a method in accordance with JIS K 7361-1. The measurement sample was a disk-shaped sintered body with a thickness of 1.0±0.1 mm, which had been polished on both sides to a surface roughness Ra≦0.02 μm.

[0069] Synthesis Example <Preparation of Calcined Body> As simulated samples of dental blank scraps, calcined bodies having compositions and properties equivalent to those of dental blanks were prepared by the following method. Commercially available zirconia powders (synthetic powders; Zpex, Zpex-Yellow, Zpex-Gray, and Zpex-Pink for calcined bodies 1 to 4; Zpex4, Zpex4-Yellow, Zpex-Gray, and Zpex-Pink for calcined bodies 5 to 8; Zpex-Smile, Zpex-SmileYellow, Zpex-Smile-Gray, and Zpex-Pink for calcined bodies 9 to 12; all manufactured by Tosoh Corporation) were filled into a 200 mL polypropylene container in the powder blending ratios [mass %] shown in Tables 1 to 3, and the container was stirred to dry mix the powders. 26 g of the obtained powder was filled into a 57 mm × 34 mm mold, uniaxially pressed at a pressure of 19.6 MPa, and then 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 Heating rate: 50°C / hour Calcination atmosphere: air Temperature decreasing rate: 300°C / hour The same procedure was repeated to prepare four calcined bodies 1 to 12 shown in Tables 1 to 3. The remainder of the calcined body compositions in the tables below was zirconia.

[0071]

[0072]

[0073] Examples 1 to 12 <Production of Recycled Powder> The calcined bodies were pulverized to obtain pulverized products by the following method. That is, four calcined bodies 1 were prepared and coarsely pulverized in a zirconia mortar until they passed through a sieve with 1 mm mesh, obtaining coarsely pulverized products. The obtained coarsely pulverized products were pulverized using a ball mill using zirconia balls as the grinding medium to obtain pulverized products with an average particle size of 0.4 μm, which were designated as the recycled powder of Example 1. The same procedure was performed on calcined bodies 2 to 12 to obtain pulverized products with an average particle size of 0.4 μm, which were designated as the recycled powder of Examples 2 to 12, respectively.

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

[0075] The recycled powder obtained had a brightness of L ＊ is 90 or more and 100 or less (95.2 or more and 97.9 or less), hue a ＊ is 0 or more and 1 or less (0.0 or more and 0.6 or less), hue b ＊ is 0 or more and 5 or less (3.0 or more and 3.9 or less), and chroma C ＊ The values ​​were 3.0 or more and 3.9 or less, and all of the powders were recyclable as base powders.

[0076] Examples 13 to 25 <Production of recycled blanks> 3 g of each of the recycled powders of Examples 1 to 12 was filled into a mold having a diameter of 25 mm, and subjected to uniaxial pressing at a pressure of 19.6 MPa, followed by CIP treatment at a pressure of 196 MPa to obtain a green body. The obtained green body was fired under the following conditions to obtain the recycled blanks of Examples 13 to 25.

[0077] Calcination temperature: 1000°C Calcination time: 1 hour Temperature increase rate: 50°C / hour Calcination atmosphere: air Temperature decrease rate: 300°C / hour The evaluation results of the obtained recycled blanks are shown in the table below.

[0078] It was confirmed that the recycled powder produced by the method of the present invention can be molded and calcined, and can be used as raw material powder for calcined bodies (recycled blanks). It was also confirmed that the calcined bodies (recycled blanks) obtained exhibit a color tone equivalent to that of recycled blanks obtained from synthetic powders.

[0079] The calcined body was then sintered under the following conditions to obtain a sintered body.

[0080] Sintering method: atmospheric sintering Sintering atmosphere: air 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 table below, along with the evaluation results of sintered bodies obtained by sintering the main calcined bodies obtained in the synthesis examples under similar conditions. The color names indicate colors according to the Vita Classical Shade index.

[0081] From the above table, it was confirmed that the recycled blanks obtained in the examples can produce sintered bodies with aesthetic properties suitable for dental prostheses. Furthermore, comparisons of Example 13 and calcined body 1, Example 17 and calcined body 5, and Example 21 and calcined body 9 showed that the dental prostheses obtained from the recycled blanks of the examples exhibited the same translucency and sintered body density as dental blanks obtained from synthetic powder, and also exhibited similar color tones. This confirmed that the sintered bodies (dental prostheses) obtained from recycled powder are equivalent to the sintered bodies (dental prostheses) obtained from synthetic powder.

[0082] Example 25 <Production of recycled blank using 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) were used as toning powders, and the blending ratios were as shown in the table below.

[0083]

[0084] Except for using the obtained mixed powder, recycled blanks were produced in the same manner as in Examples 13 to 24. The evaluation results of the obtained recycled blanks are shown in the table below.

[0085] These results confirmed that the recycled powder of this example can be used as a mixed powder for the raw material of recycled blanks. The calcined body (recycled blank) was sintered in the same manner as in Examples 13 to 24, except that it was used, to obtain a sintered body.

[0086] The results are shown in the table below.

[0087] From the above table, it was confirmed that by mixing the recycled powder of the Examples with a toning powder to form a mixed powder, a sintered body with a darker color tone and aesthetics suitable for a dental prosthesis can be obtained, and that the recycled powder can be used as a recycled raw material for that purpose. At the same time, it was confirmed that the recycled powder of the Examples can be used to obtain a sintered body (dental prosthesis) exhibiting any color tone suitable for a dental prosthesis, whether the zirconia powder containing a coloring element is used as the base powder or a powder mixing system is used.

[0088] The entire contents of the specifications, claims, drawings and abstracts of Japanese Patent Application No. 2023-201429 filed on November 29, 2023 and Japanese Patent Application No. 2024-006646 filed on January 19, 2024 are hereby incorporated by reference as the disclosure of the specification of the present disclosure.

Claims

1. A grinding step of grinding dental blank scraps to obtain a ground product, and a grinding step of obtaining a ground product having a color tone of L from the ground product. ＊ is 90 or more and 100 or less, a ＊ is 0 to 1, b ＊ A method for producing recycled powder, comprising: a recovery step of recovering powder having a molecular weight of 0 or more and 5 or less.

2. The method for producing recycled powder according to claim 1, further comprising a separation step of separating scraps prior to the pulverization step.

3. A method for producing recycled powder as described in claim 2, wherein the separation method in the separation step separates the scraps into a color unit consisting of scraps having a base color tone and a color unit consisting of scraps having a color tone different from the base color tone.

4. A method for producing recycled powder according to any one of claims 1 to 3, wherein the crushing process includes a coarse crushing process in which scraps are dry-crushed to obtain a coarsely crushed product, and a particle size adjustment process in which the coarsely crushed product is wet-crushed.

5. The recovery method in the recovery step is to divide the pulverized material obtained in the pulverization step into a certain unit and to obtain a pulverized material having a color tone of L. ＊ is 90 or more and 100 or less, a ＊ is 0 to 1, b ＊ The method for producing recycled powder according to any one of claims 1 to 4, which is a recovery method for recovering units corresponding to pulverized material having a color tone of 0 or more and 5 or less.

6. A grinding step of grinding the dental blank scraps to obtain a ground product, and a grinding step of obtaining a ground product having a color tone of L from the ground product. ＊ is 90 or more and 100 or less, a ＊ is 0 to 1, b ＊ and recovering the powder having a β-to-β ratio of 0 to 5.

7. A method for producing recycled dental blanks, using the recycled powder obtained according to claim 1 or 2.

8. L color tone ＊ is 90 or more and 100 or less, a ＊ is 0 to 1, b ＊ A recycled powder having a value of 0 or more and 5 or less.

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