Manufacturing method of 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 regenerating (recycling) dental blanks, and further to a method for producing recycled powder obtained by recycling dental blanks made of calcined ceramic bodies. [Background technology]

[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, first, raw material powder is molded into a green compact (green compact), which is then calcined to produce a calcined body (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 (dental prosthesis), which is 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 and environmental load, etc. Known methods for recycling ceramic materials include, for example, 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). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-027358 [Patent Document 2] Japanese Patent Application Publication No. 10-218662 Summary of the Invention [Problem to be solved by the invention]

[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 related to recycling technologies for dental blanks, particularly for 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. [Means for solving the problem]

[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 recycling 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 dental blank scraps to obtain a ground product, and a grinding step of grinding dental blank scraps to obtain a ground product having a color tone of L. * is between 90 and 100, a * is between 0 and 1, b * A method for producing recycled powder, comprising: a recovery step of recovering powder having a value of 0 or more and 5 or less. [2] The method for producing recycled powder according to [1] above, further comprising a separation step of separating scraps prior to the pulverization step. [3] The separation method in the separation step is * is between 90 and 100, a * is between 0 and 1, b * A method for sorting scraps into a color tone unit consisting of scraps having a color tone different from the color tone of the scraps having a color tone of 0 to 5, and a method for producing recycled powder described in [2] above. [4] A method for producing recycled powder according to any one of [1] to [3] above, wherein the pulverization process comprises a coarse pulverization process in which scraps are dry-pulverized to obtain a coarsely pulverized material, and a particle size adjustment process in which the coarsely pulverized material is wet-pulverized. [5] The recovery method in the recovery step is to divide the pulverized material obtained in the pulverization step into a certain unit, and * is between 90 and 100, a * is between 0 and 1, b * The method for producing recycled powder according to any one of [1] to [4] above, 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 dental blank scraps to obtain a ground product, and obtaining a powder having a color tone of L from the ground product. * is between 90 and 100, a * is between 0 and 1, b * A method for recycling dental blanks, comprising: a recovering step of recovering powder having a value of 0 or greater and 5 or less. [7] A method for producing recycled dental blanks using recycled powder obtained by at least one of [1] to [5] above. [8] Color tone is L * is between 90 and 100, a * is between 0 and 1, b * Recycled powder with a value of 0 or more and 5 or less. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0012] [Figure 1] Flow diagram of a method for producing recycled powder without a separation process [Figure 2] Flow diagram of a method for producing recycled powder with a separation process DETAILED DESCRIPTION OF THE INVENTION

[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, which 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] "Recycled powder" refers to powder that has been recycled by regenerating sintered bodies, calcined bodies, or compacted bodies. The powder is obtained by the regeneration treatment of calcination, and a mixed powder containing the powder is also included. In this embodiment, the powder is particularly obtained by the regeneration treatment of calcination, and a mixed powder containing the powder is also included.

[0021] The term "synthetic powder" refers to powder other than powder obtained by the regeneration treatment of a sintered body, a calcined body, or a molded body, and is particularly 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 using a spectrophotometer (e.g., 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, using the SCI method against a black background. * a * b* The color tone is expressed in a color system. 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 as lightness L * and hue a * and b * It is the hue corresponding to the coordinates in the color space determined by the three values. [Method of manufacturing recycled powder] This embodiment includes a grinding step of grinding dental blank scraps to obtain a ground product, and a grinding step of grinding a dental blank scrap to obtain a ground product having a color tone of L. * is between 90 and 100, a * is between 0 and 1, b * and recovering powder having a value of 0 to 5. In the manufacture of dental prostheses, a wide variety of dental blanks are used, which are discarded (discarded) collectively. Therefore, the discarded scraps (aggregates) vary greatly in their characteristics, including color tone, chemical composition, and contained elements. In such a situation, the manufacturing method of this embodiment makes it possible to recover scraps (aggregates) having a specific color tone as powder. The recovered powder can be regenerated (recycled) as a 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 process> The grinding process for grinding dental blank scraps to obtain a pulverized material is a process for grinding the scraps to obtain a pulverized material. The pulverized material is the scraps in a powder form, and this itself can be considered a recycled powder. However, since the scraps used in the grinding process may contain many different materials, the pulverized material obtained by the recovery process described below becomes a recycled powder that is more suitable as a raw material powder for dental blanks.

[0024] The scraps used in the milling process are calcined bodies, and further, calcined bodies of ceramics, and even calcined bodies of zirconia (zirconium dioxide, ZrO2) (hereinafter also referred to as "zirconia calcined bodies"). Calcined bodies are composed of fused particles in the early stages of sintering, and 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, calcined bodies require very little energy to be milled, making them 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). 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, including as a solid solution in zirconia, or as oxides or other compounds.

[0027] The scrap material may have a structure consisting of one layer, that is, 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). In order to achieve aesthetics similar to that 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 (for example, 2 to 15 layers, further 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 so that a gradation is formed. The gradation may be formed by at least one of color tone and translucency. When the dental blank is made of two or more laminated layers In the case of such a structure, it is sufficient that the metal element such as the coloring element is contained in at least one layer, and it is preferable that at least one of the types and contents of the coloring element in each layer is different.

[0028] In the pulverization step, the pulverization may be such that the mill ends are pulverized to a level that allows them to be used as recycled powder. Examples of such pulverization include pulverization such that the mill ends have 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 mill ends have 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 crushed scraps can be determined by the planimetric method using an SEM image. Specifically, a circle of known area is drawn on the SEM image, and the number of crushed particles within the circle (Nc) and the number of crushed particles around the circumference of the circle (Ni) are counted so that the total number of particles (Nc + Ni) is 250 ± 50, and then the average particle size of the crushed material 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 and set (Nc + Ni) to 250 ± 50.

[0031] The pulverization method may be at least either dry pulverization or 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 process includes a coarse pulverization process in which mill ends are dry-pulverized to obtain a coarsely pulverized product, and a particle size adjustment process in which the coarsely pulverized product is wet-pulverized. The coarse pulverization process pulverizes the mill ends into coarse pulverized product on the order of mm, for example, 1 to 10 mm. By passing through the coarse pulverization process, the average particle size of the milled mill ends can be more efficiently adjusted, and the pulverization time in the pulverization process and the energy required for pulverization can be reduced. <Recovery process> In the manufacturing method of this embodiment, the pulverized material is * is between 90 and 100, a * is between 0 and 1, b * and recovering the powder having a color tone of L * is between 90 and 100, a * is between 0 and 1, b *Powders with a value of 0 to 5 (hereinafter referred to as "base powders" and the color tone is referred to as "base color tone") are powders obtained from scrap materials, and the base powders consist of the same components as dental blanks, which are the precursors of dental prostheses. Therefore, the base powders are suitable for horizontal recycling into dental blanks. Furthermore, the base powders are suitable for dental prostheses that have the lightest color tone in dental color samples (e.g., Vita Classical Shade). The color tone is similar to that of the dental blank that 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 resulting mixture 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 the base 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 is 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 color of the toning powder is L * is less than 90, a * is less than 0 or greater 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, dividing the units into units, and subjecting the units corresponding to the base powder to a particle size adjustment process, followed by solid-liquid separation and drying to recover the units. 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 and further as a raw material for various ceramic materials, and can be used as a powder particularly suitable as a raw material for dental blanks. <Separation process> The manufacturing method of this embodiment preferably includes a sorting step of sorting scraps prior to the pulverization step. 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 step makes it easier to predict the attributes of the scraps to be used in the pulverization step, i.e., the color of the pulverized material produced by the pulverization step. This simplifies or eliminates the need for unit sorting in the recovery step and coarse pulverization step, and is expected to enable more efficient recovery of the base powder.

[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, * is between 90 and 100, a * is between 0 and 1, b * Any method can be used as long as it separates scrap into color units (hereinafter also referred to as "base units") consisting of scraps with a color tone of 0 to 5 and color units (hereinafter also referred to as "non-base units") consisting of scraps with a color tone different from the base color tone. Furthermore, when separating scraps according to their composition, any method can be used as long as it separates scraps into composition units consisting of scraps with a composition that exhibits the base color tone and scraps with a composition that exhibits a color tone different from the base color tone. While analyzing the composition requires sample collection and instrumental analysis for each scrap, analyzing the color tone 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 units (color tone units) rather than on composition units (composition 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 scraps in the separation process, the scraps are preferably dental blank scraps tagged with an information tag containing at least specific information linked to material information. The "specific information" is information that can be linked to 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). Furthermore, the "shade code" is a code that represents each shade in the dental shade sample, and is, for example, a code indicated by an alphabet and a number, such as A1 to D4, in the Vita Classical Shade.

[0046] The specific information preferably includes at least one of the model number and manufacturer name of the dental blank (scrap) (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 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 collection deadline, and even more preferably includes the collection deadline. Including the manufacturing information enables not only recycling but also traceability. Note that the "manufacturing year" is information that can identify the time of manufacturing, and the manufacturing month or manufacturing date may be used instead of the manufacturing 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 read by a code symbol reading means, specifically, at least one of a barcode reader and image analysis, etc., to easily separate the scrap material. The information tag may include one or more characters selected from the group consisting of letters, numbers, and symbols. The type, size, display format, etc. of the code symbol may be appropriately selected depending on the amount of information to be attached to the information tag, the shape of the dental blank, etc., and may be, for example, 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 one that allows the information to be read even if part of it is missing. <Cleaning process> An impurity reduction step for reducing impurities may be included before or after each of the separation step, pulverization step, coarse pulverization step, particle size adjustment step, and recovery step, thereby reducing impurities associated with the recovered scraps and impurities mixed in before and after each step.

[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, 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 the water physically adsorbed on the scraps, and examples include drying in the air at 80°C to 150°C. 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 includes an impurity reduction step as the first step, and preferably includes the impurity reduction step prior to the pulverization step (or the fractionation step if a fractionation step is included). The impurity reduction step may be an independent step, or may be performed when transferring scraps or the like to each step. [How to recycle dental blank scraps] The method for producing recycled powder of this embodiment includes a crushing step of crushing dental blank scraps to obtain a crushed material, and a crushing step of crushing dental blank scraps to obtain a powder having a color tone of L. * is between 90 and 100, a * is between 0 and 1, 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 raw material powder for dental blanks, and the scraps can be recycled horizontally.

[0052] The recycling method of this embodiment is similar to the pulverization process and recovery process in the above-mentioned method for producing recycled powder, and may also include at least one of the separation process and impurity reduction process 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 between 90 and 100, a * is between 0 and 1, 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 between 90 and 100, a * is between 0 and 1, b * is between 0 and 5, and L * a * b * Lightness L in the color system * , hue a * and hue b * It is preferable that satisfies the following:

[0054] Lightness L * : 90 or more or 95 or more, and is 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 Because the recycled powder exhibits this color tone, it can be used as a base powder. In other words, the recycled powder can be used directly in the manufacturing method of calcined bodies (dental blanks). In addition, the recycled powder containing coloring elements can be used as a base powder. Conventional powder mixing systems use a powder containing no coloring elements as the base powder, and calcined bodies (dental blanks) suitable for dental prostheses are manufactured by mixing a powder containing coloring elements 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 new powder mixing system based on powder containing coloring elements. This powder mixing system can produce calcined bodies (dental blanks) suitable for dental prostheses, and dental prostheses with any color tone can be obtained by using the recycled powder as the base powder in addition to or instead of powder containing no coloring elements.

[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, uniaxially pressing it at a pressure of 19.6 MPa, and then performing CIP processing at a pressure of 196 MPa to form it into a disk shape with a thickness of 3.0 ± 0.5 mm. The measurement surface of this disk can then be polished to 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 that are incorporated into zirconia in a different state than the state of the coloring elements incorporated by immersion in a coloring solution or the state of the coloring elements incorporated by solid-phase mixing. Therefore, it is preferable that at least a portion of the coloring elements in the present recycled powder are incorporated as a solid solution in zirconia, and it is more preferable that at least a portion of the transition metal elements are incorporated as a solid solution in zirconia. Alternatively, the coloring elements may be incorporated as other compounds (e.g., oxides). [Manufacturing method for recycled blanks] The dental blank manufacturing method of this embodiment may be any method for manufacturing a recycled dental blank (regenerated blank) using the recycled powder obtained by the manufacturing method of this embodiment (hereinafter also referred to as "the recycled powder"), and may use the recycled powder as a raw material powder in a manner similar to known dental blank manufacturing methods. Furthermore, in the method for manufacturing a recycled dental blank using the recycled powder, a powder containing the recycled powder may be used as the raw material powder, and a mixed powder containing the recycled powder, for example, a mixed powder of the recycled powder and a synthetic powder, may also 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 can be adjusted in color and composition to suit the desired color of the dental prosthesis. For example, when producing a dental blank (calcined body) for a dental prosthesis with a color equivalent to the A1 shade of the Vita Classical shade, recycled powder can be used as the base powder. On the other hand, when producing a dental blank (calcined body) for a dental prosthesis with a color darker than the A1 shade of the Vita Classical shade, recycled powder can be used as a mixed powder of the base powder and the toning powder. In the mixed powder, the base powder acts as a diluent for the toning powder, while the toning powder acts as a coloring element for the base powder. Therefore, when a dental prosthesis with a darker color is desired, the proportion of the toning powder in the mixed powder can 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. Any molding method may be used as long as it 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. [Example]

[0064] The present disclosure will be described below with reference to examples, but 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 air at 1000°C for 1 hour. <Average particle size> The average particle size of the powder sample was determined by the planimetric method using an SEM image. That is, a circle of known area was drawn on an SEM 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 counted so that the total number of particles (Nc + Ni) was 250 ± 50, and the average particle size of the pulverized material was calculated using the above formula (1).

[0065] Acceleration magnification: 15V Observation magnification: 5000x <Density of calcined body> The mass of the calcined body was determined by measuring it with an electronic balance, and the volume was determined from the dimensions measured with a vernier caliper. The actual density was calculated from the obtained mass and volume, and this was taken as the density of the calcined body. <Sintered body density> The mass of the calcined body was determined by measuring it with an electronic balance, and the volume was determined by the Archimedes method in accordance with JIS R 1634. The measured density was calculated 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> The color tone was measured using a spectrophotometer (device name: CM-700d, manufactured by Konica Minolta) equipped with an illumination and light-receiving optical system conforming to geometric condition c of JIS Z 8722, using a method in which a black calibration box was placed as the background for 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 CIP-processing at a pressure of 196 MPa to form into a disk 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> The 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 the method in accordance with JIS K 7361-1. The measurement sample used was a circular sintered body with a thickness of 1.0±0.1 mm, which had been polished on both sides to a surface roughness of Ra≦0.02 μm.

[0069] Synthesis example <Preparation of calcined body> Calcined bodies with compositions and properties equivalent to those of dental blanks were prepared as simulated dental blank scrap samples using 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; and Zpex-Smile, Zpex-Smile-Yellow, 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 at the powder blending ratios [mass %] shown in Tables 1 to 3, and the container was agitated for dry mixing. 26 g of the resulting powder was loaded into a 57 mm × 34 mm mold and subjected to uniaxial pressing at 19.6 MPa, followed by CIP at 196 MPa to obtain a compact. The resulting molded body was fired under the following conditions to obtain a calcined body.

[0070] Calcining temperature: 1000℃ Pre-baking time: 1 hour Heating rate: 50°C / hour Calcination atmosphere: air Cooling rate: 300℃ / hour The same procedure was repeated to prepare four each of calcined bodies 1 to 12 shown in Tables 1 to 3. The balance in the calcined body compositions in the tables below was zirconia.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3] Examples 1 to 12 <Production of recycled powder> The calcined bodies were pulverized to obtain pulverized products in the following manner. Specifically, four calcined bodies 1 were prepared and coarsely pulverized in a zirconia mortar until they passed through a 1 mm mesh sieve, obtaining coarsely pulverized products. The obtained coarsely pulverized products were pulverized in a ball mill using zirconia balls as the pulverizing 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 powders of Examples 2 to 12, respectively.

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

[0075] [Table 4] The obtained recycled powder has a lightness of L * is 90 or more and 100 or less (95.2 or more and 97.9 or less), hue a * is 0 to 1 (0.0 to 0.6), hue b *is 0 to 5 (3.0 to 3.9), and saturation 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> Three grams of each recycled powder from Examples 1 to 12 was packed into a mold with 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 resulting green body was fired under the following conditions to obtain the recycled blanks of Examples 13 to 25.

[0077] Calcining temperature: 1000℃ Pre-baking time: 1 hour Heating rate: 50°C / hour Calcination atmosphere: air Cooling rate: 300℃ / hour The evaluation results of the obtained recycled blanks are shown in the table below.

[0078] [Table 5] 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 pressure 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] [Table 6] 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 between 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 blanks using mixed powder> Mixed powders were 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] [Table 7] 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.

[0084] [Table 8] 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.

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

[0086] [Table 9] As can be seen from the table above, the recycled powder in the example is more effective when mixed with the toning powder to create a mixed powder. A sintered body having aesthetic properties suitable for a dark-colored dental prosthesis can be obtained, and At the same time, it was confirmed that the recycled powders of the examples can be used as recycled raw materials for dental prostheses. Even when zirconia powder containing coloring elements is used as the base powder, or when a powder mixing system is used, sintered bodies (dental prostheses) exhibiting any color tone suitable for dental prostheses can be obtained.

Claims

1. L ＊ a ＊ b ＊ Lightness L in the color system ＊ , hue a ＊ and hue b ＊ Recycled powder that meets the following criteria: Lightness L ＊ :90 or above and below 100, Hue a ＊ :0 or more and 1 or less, Hue b ＊ :0 or above and 5 or below

2. Saturation C ＊ The recycled powder according to claim 1, wherein the σ is 3.0 or more and 3.9 or less.

3. 3. The recycled powder according to claim 1, further comprising a stabilizing element and a coloring element.

4. 4. The recycled powder according to claim 3, wherein the stabilizing element contains one or more elements selected from the group consisting of yttrium, calcium, and magnesium.

5. 5. The recycled powder according to claim 3, wherein the coloring element is one or more selected from the group consisting of titanium, iron, cobalt, nickel, manganese, praseodymium, neodymium, europium, gadolinium, terbium, erbium, and ytterbium.

6. 5. The recycled powder according to claim 3, wherein at least a part of the coloring element is contained in the zirconia as a solid solution.

7. 5. The recycled powder according to claim 3, wherein the content of the stable elements is 2.849 mol% or more and 5.245 mol% or less.

8. 3 g of the recycled powder was filled into a mold having a diameter of 25 mm, and subjected to uniaxial pressing at a pressure of 19.6 MPa. After that, a green body was obtained by CIP treatment at a pressure of 196 MPa. The green body thus obtained was fired under the following conditions to obtain a recycled blank having a calcined body density of 3.20 g / cm. ３ 3.36g / cm or more ３ 3. The recycled powder according to claim 1 or 2, wherein: Calcining temperature: 1000℃ Pre-baking time: 1 hour Heating rate: 50°C / hour Calcination atmosphere: Air atmosphere Cooling rate: 300℃ / hour

9. The color tone is L ＊ is less than 90, a ＊ is less than 0 or more than 1, or b ＊ A mixed powder of a powder having a ρ of less than 0 or more than 5 and the recycled powder according to claim 1 or 2.

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