Method for manufacturing recycled powder

Abstract

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

Description

Technical Field

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

Background Art

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

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

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

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

[0007] In addition to this, multiple types of dental blanks corresponding to the characteristics of the intended dental prosthesis are used. The end materials of dental blanks generated after cutting are difficult to recover on the premise of recycling because they are mixtures of different compositions and types. Therefore, at present, there is only the possibility of cascade recycling such as disposal by processing companies such as dental laboratories or diversion to cement raw materials. Even if the end materials of dental blanks could be recovered, in horizontal recycling, it is essential to separate the recovered individual end materials after compositional analysis. For this reason, in reality, horizontal recycling of the end materials of dental blanks has been impossible.

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

Means for Solving the Problems

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

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

Advantages of the Invention

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

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

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

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

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

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

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

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

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

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

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

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

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

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

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

[0026] One or more selected from the group consisting of yttrium (Y), calcium (Ca), and magnesium (Mg) are listed as the stabilizing element, and 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) are listed as the coloring element, respectively. Also, one or more selected from the group consisting of aluminum (Al), silicon (Si), and germanium (Ge) are listed as other metal elements. The existence state of these metal elements is arbitrary, but they may be dissolved in zirconia or may exist as oxides or other compounds.

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

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

[0029] The average particle diameter of the pulverized product of the end material can be determined by the planimetric method using an SEM observation image. Specifically, draw a circle with a known area on the SEM observation image, measure the number of particles (Nc) of the pulverized product inside the circle and the number of particles (Ni) of the pulverized product on the circumference of the circle, and after making the total number of particles (Nc + Ni) be 250 ± 50, the average particle diameter of the pulverized product may 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 particles of the crushed material inside the circle, Ni is the number of particles of the crushed material on the circumference of the circle, A is the area of the circle, and M is the magnification of SEM observation (for example, 5000 to 10000 times). When the number of particles (Nc + Ni) in one SEM observation image is less than 200, (Nc + Ni) may be set to 250 ± 50 using a plurality of SEM observation images.

[0031] The pulverization method may be at least either dry pulverization or wet pulverization, and may be dry pulverization or wet pulverization. Examples of dry pulverization include pulverization methods using one or more selected from the group consisting of jaw crushers, hammer crushers, shredders, roll crushers, hammer mills, cutting mills, rod mills, roller mills, rotor mills, impact pulverizers, jet pulverizers, ball mills, and mortars. Examples of wet pulverization include pulverization methods using one or more selected from the group consisting of ball mills, bead mills, planetary mills, wet jet mills, colloid mills, and homogenizers. Preferred pulverization methods include wet pulverization using zirconia spheres (at least either zirconia balls or zirconia beads) as the pulverization medium. This makes it less likely for impurities to contaminate due to pulverization.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0052] The recycling method of this embodiment is the same as the pulverization step and the recovery step in the above-described method for producing recycled powder, and may also include at least one of the classification step and the impurity reduction step in the above-described method for producing recycled powder. [Recycled powder] The recycled powder obtained by the production method of this embodiment may be any powder that can be used as a raw material for a recycled blank. Preferred recycled powders include, for example, 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 (hereinafter also referred to as "this recycled powder").

[0053] This recycled powder has 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 further L * a * b * Lightness L in the color system * , hue a * and hue b * preferably satisfy the following.

[0054] Lightness L * : 90 or more or 95 or more, and 100 or less or 99 or less, Hue a * : 0 or more or 0.2 or more, and 1 or less or 0.8 or less, Hue b * : 0 or more or 0.2 or more, and 5 or less, 3 or less or 0.8 or less Since this recycled powder exhibits such a color tone, it can be used as a base powder. That is, this recycled powder can be used as it is in the method for manufacturing a green body (dental blank). In addition to this, the recycled powder containing a coloring element can be used as a base powder. That is, conventionally, it was a powder mixing system based on a powder containing no coloring element as a base powder, and a powder containing a coloring element was mixed with the base powder to produce a green body (dental blank) suitable for dental prostheses. In contrast, by using this recycled powder, in addition to enabling horizontal recycling of the green body (dental blank), it is possible to realize a powder mixing system based on a powder containing a coloring element, which has never existed before. By such a powder mixing system, a green body (dental blank) suitable for dental prostheses can be produced, and in addition to a powder containing no coloring element, or instead of a powder containing no coloring element at all, a dental prosthesis exhibiting an arbitrary color tone can be obtained using this recycled powder as a base powder.

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

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

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

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

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

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

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

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

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

Examples

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

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

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

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

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

[0069] Synthesis example <Preparation of calcined body> As a simulated sample of the end material of a dental blank, a calcined body having the same composition and characteristics as a dental blank was prepared by the following method. Commercially available zirconia powder (synthetic powder; 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 are manufactured by Tosoh Corporation) was filled into a 200 mL polypropylene container at the blending ratio [mass%] of the powders shown in Tables 1 to 3, and this was dry-mixed by stirring the container. 26 g of the obtained powder was filled into a mold of 57 mm × 34 mm, and after subjecting it to uniaxial pressure molding at a pressure of 19.6 MPa, a compact was obtained by CIP treatment at a pressure of 196 MPa. The obtained compact 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: Atmospheric atmosphere Cooling rate: 300 °C / hour The same operation was repeated to produce four pieces each of the calcined bodies 1 to 12 shown in Tables 1 to 3. The remainder in the calcined body composition in the following table is zirconia.

[0071]

Table 1

[0072]

Table 2

[0073]

Table 3

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

[0075]

Table 4

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

[0077] Tempering temperature: 1000 °C Tempering time: 1 hour Heating rate: 50 °C / hour Tempering atmosphere: air atmosphere Cooling rate: 300 °C / hour The evaluation results of the obtained recycled blanks are shown in the following table.

[0078]

Table 5

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

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

[0081]

Table 6

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

[0083]

Table 7

[0084]

Table 8

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

[0086]

Table 9

Claims

1. A pulverizing step of pulverizing an end material of a dental blank to obtain a pulverized material, and the pulverized 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 ＊ is 0 or more and 5 or less, and a recovery step of recovering a powder, wherein the recovery method in the recovery step divides the pulverized material obtained by the pulverizing step into a certain unit, and the color tone is L ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ is a recovery method of recovering a unit corresponding to a pulverized material having a color tone of 0 or more and 5 or less, a method for producing recycled powder.

2. The method for producing recycled powder according to claim 1, including a separation step of separating edge materials prior to the pulverization step.

3. The sorting method in the respective processes is such that the color tone is L ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ A method in which the end materials are sorted into a color tone unit composed of end materials having a reference color tone where is 0 or more and 5 or less, and a color tone unit composed of end materials having a color tone different from the reference color tone, the method for producing recycled powder according to claim 2.

4. The method for producing recycled powder according to claim 1 or 2, wherein the pulverization step includes a rough pulverization step of dry-pulverizing edge materials to obtain a roughly pulverized product, and a particle size adjustment step of wet-pulverizing the roughly pulverized product.

5. The method for producing recycled powder according to claim 1 or 2, wherein the edge materials of the dental blank are unfired ceramics.

6. A grinding step of grinding the end material of a dental blank to obtain a ground material, and from the ground material, the color tone is L ＊ is 90 or more and 100 or less, a ＊ is 0 or more and 1 or less, b ＊ A recycling method of a dental blank, including a recovery step of recovering a powder that is 0 or more and 5 or less, wherein the recovery method in the recovery step divides the ground material obtained by the grinding step into a certain unit, and the color tone is L* is 90 or more and 100 or less, a* is 0 or more and 1 or less, and b* is 0 or more and 5 or less. The recovery method is to recover the unit corresponding to the ground material having the color tone.

7. The method for producing a recycled dental blank, using the recycled powder obtained in claim 1 or 2.

Images