Dental milling blank

Abstract

The present invention pertains to: a dental milling blank formed from a laminate, wherein the laminate includes at least two layers of a layer (U) containing a thermoplastic resin (A) and a layer (L) containing a thermoplastic resin (B), the thermoplastic resin (A) is at least one type of substance selected from the group consisting of acrylics, polycarbonates, polyesters, polyurethane, polyamides, polyarylates, polysulfones, polyethersulfones, and polycyclo-olefin, and the thermoplastic resin (B) is at least one type of substance selected from the group consisting of polyether ketones, polyether ether ketones, polyether ketone ketones, polyacetals, polyphenylene ethers, polyphenylene sulfides, and polyimides; a method for producing the dental milling blank, the method including specific steps; and a method for producing a dental prosthesis, the method including a step for cutting the dental milling blank.

Description

Dental Mill Blanks

[0001] The present invention relates to a dental mill blank, a method for manufacturing the same, and a method for manufacturing a dental prosthesis using the dental mill blank.

[0002] In recent years, the use of CAD / CAM systems, in which dental prostheses such as inlays and crowns are designed by computer and then milled using a milling machine, has been increasing. In such systems, blocks of appropriate size, such as rectangular parallelepipeds, cylinders, or disks, are supplied, and these are set in a milling machine to be milled to obtain restorations in the shape of a crown or arch of teeth. Various materials have been proposed for the blocks, including glass ceramics, zirconia, titanium, acrylic resins, and composites containing polymer resins and inorganic fillers.

[0003] Among these block materials, composite materials containing a curable resin and an inorganic filler, known as resin blocks, are widely used because they are amenable to the application of conventional dental filling and restorative material technology and allow for easy color adjustment. Crown and dentition restoration treatments require an appearance that is as close as possible to the color of natural tissue. To meet such aesthetic requirements, simply cutting a block of a single color is insufficient. For this reason, for example, Patent Document 1 proposes a dental mill blank constructed from a laminate of multiple resin layers, each containing a curable resin and an inorganic filler and each with a different color, with the aim of achieving a color similar to that of natural teeth.

[0004] However, resin blocks made from such curable resins and inorganic fillers are brittle and prone to cracking, chipping, and fissures. Furthermore, because they do not melt, cutting chips cannot be reused. In response to these issues, attempts have been made in recent years to develop composite materials containing super engineering plastics, a type of thermoplastic resin, and inorganic fillers. For example, Patent Document 2 proposes dental block materials made from high-strength materials derived from rigid aromatic skeletons, such as polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polycarbonate (PC).

[0005] International Publication No. 2018 / 074605 Japanese Patent Application Laid-Open No. 2022-119683

[0006] However, dental mill blanks made of PEEK and PEKK have high resin crystallinity and low transparency, making it difficult to obtain good color and transparency similar to those of natural teeth simply by cutting a block of a single color. Furthermore, even when a mill blank is made from a laminate of multiple colors to improve color and transparency, it has been confirmed that a significant decrease in strength occurs. Therefore, an object of the present invention is to provide a dental mill blank that is excellent in strength and that provides dental prostheses with good color and transparency.

[0007] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by providing a dental mill blank that satisfies certain requirements. That is, the present invention encompasses the following inventions: [1] A dental mill blank composed of a laminate, wherein the laminate includes at least two layers: a layer (U) containing a thermoplastic resin (A) and a layer (L) containing a thermoplastic resin (B), the thermoplastic resin (A) is at least one selected from the group consisting of acrylic, polycarbonate, polyester, polyurethane, polyamide, polyarylate, polysulfone, polyethersulfone, and polycycloolefin, and the thermoplastic resin (B) is at least one selected from the group consisting of polyetherketone, polyetheretherketone, polyetherketoneketone, polyacetal, polyphenylene ether, polyphenylene sulfide, and polyimide. [2] The dental mill blank according to [1] above, wherein the laminate comprises at least one intermediate layer (M) between the layer (U) and the layer (L), and the intermediate layer (M) comprises at least one selected from the thermoplastic resin (A) and the thermoplastic resin (B). [3] The dental mill blank according to [1] or [2] above, wherein at least one layer selected from the layer (U) and the layer (L) contains an inorganic filler (C). [4] The dental mill blank according to [2] above, wherein at least one layer selected from the group consisting of at least one of the layers (M), the layer (U), and the layer (L) contains an inorganic filler (C). [5] The dental mill blank according to any one of [1] to [4] above, wherein at least one layer selected from the layer (U) and the layer (L) contains 1 to 60% by mass of the inorganic filler (C) relative to 100% by mass of the layer. [6] The dental mill blank according to any one of [2] to [6], wherein at least one layer selected from the group consisting of at least one of the layers (M), the layer (U), and the layer (L) contains 1 to 60 mass% of an inorganic filler (C) relative to 100 mass% of the layer. [7] The dental mill blank according to any one of [3] to [6], wherein the average primary particle diameter of the inorganic filler (C) is 5.0 μm or less.[8] The dental mill blank according to any one of [3] to [7], wherein at least the layer (U) contains the inorganic filler (C), and the refractive index of the inorganic filler (C) contained in the layer (U) is 1.35 or more and less than 1.65. [9] The dental mill blank according to any one of [3] to [8], wherein at least the layer (L) contains the inorganic filler (C), and the refractive index of the inorganic filler (C) contained in the layer (L) is 1.65 or more and less than 2.00.

[10] The dental mill blank according to any one of [1] to [9], wherein the thickness of the entire laminate is 4.0 to 26.0 mm.

[11] The dental mill blank according to any one of [1] to

[10] , which is for a central incisor, a lateral incisor, or a canine.

[12] A method for producing a dental mill blank according to any one of [1] to

[11] above, comprising a step of heating and melting at least one selected from the thermoplastic resin (A) and the thermoplastic resin (B).

[13] A method for producing a dental mill blank according to

[12] above, wherein the heating and melting is performed using a twin-screw extruder, and the L / D ratio of the twin-screw extruder is 25 or more.

[14] A method for producing a dental mill blank according to any one of [1] to

[11] above, comprising a step of molding at least one layer selected from the layer (U) and the layer (L) by injection molding.

[15] A method for producing a dental mill blank according to any one of [1] to

[11] above, comprising a step of press-molding a laminate sheet including at least the layer (U) and the layer (L) to form the laminate.

[16] A method for producing a dental prosthesis, comprising a step of cutting the dental mill blank according to any one of [1] to

[11] above.

[17] A method for producing a dental mill blank according to

[12] or

[13] , which includes a step of molding at least one layer selected from the layer (U) and the layer (L) by injection molding.

[18] A method for producing a dental mill blank according to any one of

[12] to

[14] , which includes a step of press-molding a laminated sheet including at least the layer (U) and the layer (L) to form the laminate.

[19] The method for producing a dental mill blank according to any one of [1] to

[11] , comprising the steps of: heating and melting at least one selected from the thermoplastic resin (A) and the thermoplastic resin (B); molding at least one layer selected from the layer (U) and the layer (L) by injection molding; and press-molding a laminated sheet including at least the layer (U) and the layer (L) to form the laminate, in this order.

[0008] According to the present invention, a dental mill blank can be provided which is excellent in strength and which produces a dental prosthesis with good color tone and transparency.

[0009] The present invention will be described in detail below using examples of embodiments (hereinafter also referred to as "one aspect of the present invention"). In this specification, the upper and lower limits of numerical ranges (e.g., the content of each component, each physical property, each condition in the production method, and a value calculated from each numerical value) can be combined as appropriate. For example, in this specification, the lower and upper limits of numerical ranges described in stages can be independently combined. For example, a description of "preferably 10 to 90 mass%, more preferably 20 to 80 mass%" for the same item can be combined with the "preferable lower limit (10 mass%)" and the "more preferable upper limit (80 mass%)" to obtain "10 to 80 mass%," or with the "more preferable lower limit (20 mass%)" and the "preferable upper limit (90 mass%)" to obtain 20 to 90 mass%. Furthermore, for example, based on the above description, the upper limit value can be specified as "10% by mass or more" or "20% by mass or more" without any particular upper limit value. Similarly, the upper limit value can be specified as "90% by mass or less" or "80% by mass or less" without any particular lower limit value. Unless otherwise specified, the expression "XX to YY% by mass" as a numerical range means "XX% by mass or more and YY% by mass or less" (XX represents the lower limit, and YY represents the upper limit). For example, simply describing a numerical range as "10 to 90% by mass" indicates a range of 10% by mass or more and 90% by mass or less. Similarly, for example, from the expression "preferably 10% by mass or more, more preferably 20% by mass or more" and the expression "preferably 90% by mass or less, more preferably 80% by mass or less" for the same item, the "preferable lower limit (10% by mass or more)" and the "more preferable upper limit (80% by mass or less)" can be combined to form "10% by mass or more and 80% by mass or less." Similarly, the lower limit can be specified as "10% by mass or more" or "20% by mass or more," and the upper limit can be specified as "90% by mass or less" or "80% by mass or less." The same applies when the numerical range includes a "more preferable range" or an "even more preferable range." The same applies when the upper limit of the numerical range is "less than" or the lower limit is "more than."For example, based on the description "preferably more than 10 and less than 90, more preferably 20 to 80," the upper and lower limits can be combined to form "more than 10 and less than 80" or "20 to less than 90." The above-mentioned numerical ranges are merely illustrative examples of the content in terms of mass percent, and the same applies to numerical ranges of parts by mass, etc. As described above, the same also applies to the ranges of physical properties, manufacturing method conditions, number of layers, thickness, other numerical ranges, and values ​​calculated from each numerical value. The present invention includes various combinations of all or part of the embodiments described herein within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved. Furthermore, the present invention also includes embodiments in which the details described herein are arbitrarily selected or arbitrarily combined. While preferred embodiments are shown in this specification, combinations of two or more of the individual preferred embodiments are also preferred. The preferred definitions can be selected arbitrarily, and for example, combinations of preferred definitions can be considered more preferable.

[0010] In this specification, unless otherwise specified, "strength" refers to the "flexural strength" and "flexural modulus" of a dental mill blank according to an embodiment of the present invention, each of which is specifically evaluated by the method described in the Examples. Furthermore, in this specification, unless otherwise specified, the terms "color tone," "transparency," and "ease of polishing" refer to the properties of a dental prosthesis obtained by processing a dental mill blank according to an embodiment of the present invention, each of which is specifically evaluated by the method described in the Examples.

[0011] [Dental Mill Blank] A dental mill blank (also abbreviated as "mill blank" in this specification) according to one embodiment of the present invention is a dental mill blank composed of a laminate, the laminate including at least two layers: a layer (U) containing a thermoplastic resin (A) and a layer (L) containing a thermoplastic resin (B), the thermoplastic resin (A) (also referred to as "component (A)" in this specification) being at least one selected from the group consisting of acrylic, polycarbonate, polyester, polyurethane, polyamide, polyarylate, polysulfone, polyethersulfone, and polycycloolefin, and the thermoplastic resin (B) (also referred to as "component (B)" in this specification) being at least one selected from the group consisting of polyetherketone, polyetheretherketone, polyetherketoneketone, polyacetal, polyphenylene ether, polyphenylene sulfide, and polyimide. Furthermore, from the viewpoint of making it easier to adjust the color tone to a color closer to that of natural teeth, it is preferable that the laminate include at least one intermediate layer (M) (also abbreviated as "layer (M)" in this specification) between layer (U) and layer (L). Also, from the viewpoint of making it easier to adjust the color tone to a color closer to that of natural teeth and making it easier to improve strength, it is more preferable that the laminate include at least one layer (M) between layer (U) and layer (L), and that layer (M) include at least one type selected from thermoplastic resin (A) and thermoplastic resin (B).

[0012] In one embodiment of the present invention, it is preferable that the layer (U) is the upper layer and the layer (L) is the lower layer in the relationship between the layer (U) and the layer (L). In this specification, the "upper layer" refers to the layer located on the incisal side of a dental prosthesis manufactured by machining a mill blank, and the "lower layer" refers to the layer located on the cervical side of a dental prosthesis manufactured by machining a mill blank. Therefore, it is preferable that the transparency of the layer (U) is higher than that of the layer (L).

[0013] In one aspect of the present invention, when the laminate does not include the layer (M), from the viewpoint of more easily achieving the effects of the present invention, it is preferable that the layer (U) and the layer (L) are directly laminated together, i.e., the layer (U) and the layer (L) are in direct contact with each other without any other layer interposed therebetween.

[0014] In one aspect of the present invention, when the laminate includes a layer (M), it is preferable that at least one layer selected from the layer (U) and the layer (L) is directly laminated with the layer (M), and it is more preferable that both the layer (U) and the layer (L) are directly laminated with the layer (M). As described above, "directly laminated with the layer (M)" means that the layer laminated with the layer (M) and the layer (M) are in direct contact with each other, without any other layer interposed between them. Furthermore, in one aspect of the present invention, when the laminate includes a layer (M), it is even more preferable that the laminate includes only the layer (M) (a single layer of layer (M) or multiple layers of layer (M)) between the layer (U) and the layer (L), from the viewpoint of more easily achieving the effects of the present invention. That is, it is preferable that the layers (U) and (M) are in direct contact with each other without any other layer interposed between them, and that the layers (M) and (L) are in direct contact with each other without any other layer interposed between them. Furthermore, when the laminate includes a plurality of layers (M), the compositions, properties, and thicknesses of the plurality of layers (M) may be the same for some or all of the layers (M), or may be different for some or all of the layers (M). Therefore, when the laminate includes a plurality of layers (M) and both the layer (U) and the layer (L) are directly laminated with the layer (M), the compositions, properties, and thicknesses of the layers (M) in contact with the layer (U) and the layer (M) in contact with the layer (L) may be the same or different from each other. Furthermore, as will be described later, when the laminate contains a laminated portion formed by, for example, previously preparing layers having the same composition (layers formed from the same thermoplastic resin or resin composition) and directly laminating the layers having the same composition together, the laminated portion is considered to be a single layer.

[0015] In one aspect of the present invention, from the viewpoint of further improving strength, it is preferable that at least one layer selected from the layer (U) and the layer (L) in the laminate contains an inorganic filler (C) (also referred to as "component (C)" in this specification), and it is more preferable that both the layer (U) and the layer (L) contain the inorganic filler (C). From the same viewpoint, in one aspect of the present invention, when the laminate includes an intermediate layer (M), it is preferable that at least one layer selected from the group consisting of the layer (M), the layer (U), and the layer (L) in the laminate contains the inorganic filler (C), it is more preferable that at least one layer selected from the layer (U) and the layer (L) contains the inorganic filler (C), it is even more preferable that at least one layer of the layer (M), the layer (U), and the layer (L) all contain the inorganic filler (C), and it is even more preferable that all of the layer (M) (when the layer (M) is a single layer, the single layer (M)), the layer (U), and the layer (L) all contain the inorganic filler (C).

[0016] In one aspect of the present invention, from the viewpoint of making it easier to adjust the color tone to one close to that of natural teeth, it is preferable that at least one layer selected from the group consisting of the layers constituting the laminate contains, in addition to the inorganic filler (C), a pigment (D) (also referred to in this specification as "component (D)"). From the same viewpoint, in one aspect of the present invention, it is more preferable that at least one layer selected from layer (U) and layer (L) in the laminate contains component (C) and component (D), and it is even more preferable that both layer (U) and layer (L) contain component (C) and component (D). From a similar viewpoint, in one embodiment of the present invention, when the laminate includes an intermediate layer (M), it is more preferable that in the laminate, at least one layer selected from the group consisting of layers (U), (M), and (L) contains component (C) and component (D), it is even more preferable that at least one layer selected from layers (U) and (L) contains component (C) and component (D), and it is still more preferable that all of layers (U), (M), and (L) contain component (C) and component (D).

[0017] <Layer (U)> The layer (U) contains a thermoplastic resin (A). From the viewpoint of further improving strength, the layer (U) preferably contains a thermoplastic resin (A) and an inorganic filler (C), and from the viewpoint of further improving strength and making it easier to adjust the color tone to be close to that of natural teeth, the layer (U) more preferably contains a thermoplastic resin (A), an inorganic filler (C), and a pigment (D).

[0018] (Thermoplastic resin (A)) The thermoplastic resin (A) may be at least one selected from the group consisting of acrylic, polycarbonate, polyester, polyurethane, polyamide, polyarylate, polysulfone, polyethersulfone, and polycycloolefin. Among these, from the viewpoint of improving strength, transparency, and moldability (also simply referred to as "moldability" in this specification) when molded into a mill blank, at least one selected from the group consisting of acrylic, polycarbonate, polyester, polyurethane, polysulfone, and polyethersulfone is preferred, at least one selected from the group consisting of acrylic, polycarbonate, and polysulfone is more preferred, at least one selected from polycarbonate and polysulfone is even more preferred, and polycarbonate is even more preferred.

[0019] Examples of the acrylic include polymethyl methacrylate, polyethyl methacrylate, polyisobornyl methacrylate, polyacrylic acid ester-polymethacrylic acid ester copolymer, and polymethacrylic acid ester-styrene copolymer, with polymethyl methacrylate being preferred. Furthermore, while there are no particular limitations as long as the effects of the present invention are achieved, it is preferable that the MFR of the acrylic be 1 to 20 g / 10 min at a temperature of 230°C and a load of 37.3 N. Furthermore, while there are no particular limitations as long as the effects of the present invention are achieved, it is preferable that the acrylic have a flexural strength of 70 MPa or more. In one embodiment of the acrylic, the flexural strength may be, for example, 70 to 150 MPa or 70 to 100 MPa. Furthermore, while there are no particular limitations as long as the effects of the present invention are achieved, it is preferable that the acrylic have a total light transmittance of 90% or more. In addition, commercially available products may be used as the acrylic, and examples of commercially available products include "Parapet (registered trademark)" (manufactured by Kuraray Co., Ltd.), "Acrypet (registered trademark)" (manufactured by Mitsubishi Chemical Corporation), and "Sumipex (registered trademark)" (manufactured by Sumitomo Chemical Co., Ltd.).

[0020] Examples of the polycarbonate include polycarbonates polymerized with an aromatic diol such as bisphenol A as the primary diol component, and polycarbonates polymerized with a non-aromatic diol such as isosorbide as the primary diol component. The term "primary component in the diol component" refers to the diol component with the highest content among the diol components used as raw materials, and is preferably 30 to 100 mol%, more preferably 50 to 100 mol%, and even more preferably 70 to 100 mol% of 100 mol% of the diol component. The polycarbonate is not particularly limited as long as the effects of the present invention are achieved, but it is preferred that the polycarbonate have an MFR of 1 to 20 g / 10 min at a temperature of 300°C and a load of 11.8 N. Furthermore, although there are no particular limitations as long as the effects of the present invention are achieved, it is preferred that the flexural strength of the polycarbonate be 70 MPa or greater. In one embodiment of the polycarbonate, the flexural strength may be, for example, 70 to 150 MPa, or 70 to 100 MPa. There are no particular limitations as long as the effects of the present invention are achieved, but it is preferable that the polycarbonate have a total light transmittance of 90% or more. Commercially available polycarbonates may be used, and examples of commercially available products include "Iupilon (registered trademark)" (manufactured by Mitsubishi Engineering Plastics Corporation), "Toughlon (registered trademark)" (manufactured by Idemitsu Kosan Co., Ltd.), "Panlite (registered trademark)" (manufactured by Teijin Limited), and "DURABIO (registered trademark)" (manufactured by Mitsubishi Chemical Corporation).

[0021] The polysulfone is not particularly limited as long as the effects of the present invention are achieved, but it is preferable that the polysulfone have an MFR of 1 to 10 g / 10 min under conditions of a temperature of 343°C and a load of 21.2 N. Furthermore, although there is no particular limitation as long as the effects of the present invention are achieved, it is preferable that the polysulfone have a flexural strength of 90 MPa or more. In one embodiment of the polysulfone, the flexural strength may be, for example, 90 to 200 MPa or 90 to 150 MPa. Furthermore, although there is no particular limitation as long as the effects of the present invention are achieved, it is preferable that the polysulfone have a total light transmittance of 80% or more. Furthermore, commercially available polysulfones may be used, and examples of commercially available products include Udel (registered trademark) (manufactured by Solvay).

[0022] From the viewpoint of obtaining better transparency, it is preferable to use one type of component (A) in the layer (U) without mixing two or more types. When two or more types of component (A) are contained, the content of the component (A) with the highest content is preferably 90 to 99.9 mass%, more preferably 95 to 99.9 mass%, and even more preferably 99 to 99.9 mass%, based on 100 mass% of the total components (A).

[0023] In order to more easily achieve the effects of the present invention, the content of component (A) in layer (U) is preferably 37 to 99% by mass, more preferably 40 to 99% by mass, even more preferably 50 to 95% by mass, even more preferably 55 to 94% by mass, even more preferably 60 to 92% by mass, and even more preferably 70 to 90% by mass, based on 100% by mass of layer (U). A content of component (A) of 37 to 99% by mass is preferred from the viewpoint of achieving better strength in the dental mill blank without impairing transparency and adhesion to layer (L) or layer (M). Furthermore, when layer (U) contains two or more types of component (A), the content of component (A) in layer (U) refers to the total content of the two or more types of component (A). Furthermore, in this specification, the term "100% by mass of layer (U)" refers to the total content (100% by mass) of all components constituting layer (U).

[0024] (Inorganic Filler (C)) As the inorganic filler (C), for example, known inorganic fillers used as fillers for dental composite resins can be used. Specific examples of component (C) that can be used include various types of glasses (silicon dioxide (quartz, quartz glass, silica gel, etc.) or glasses containing silicon as the main component and at least one selected from boron and aluminum along with various heavy metals; glasses containing heavy metal elements such as zirconium, barium, titanium, lanthanum, and strontium), alumina, various ceramics, diatomaceous earth, kaolin, clay minerals (montmorillonite, etc.), activated clay, synthetic zeolite, mica, silica, calcium fluoride, ytterbium fluoride, calcium phosphate, barium sulfate, zirconium dioxide (zirconia), titanium dioxide (titania), barium titanate, hydroxyapatite, praseodymium compounds, erbium compounds, manganese compounds, and other inorganic oxides containing various heavy metal elements (zirconium, barium, titanium, lanthanum, strontium, etc.). These inorganic fillers may be used alone or in combination of two or more.

[0025] In addition, physical properties desired for dental prostheses include transparency, strength, and X-ray contrast similar to those of natural teeth. From the viewpoint of more easily obtaining transparency similar to that of natural teeth, it is preferable to match the refractive indexes of component (A) and component (C) as closely as possible. From the viewpoint of imparting better strength, it is preferable to use at least one selected from the group consisting of various glasses and various ceramics as component (C). From the viewpoint of imparting better X-ray contrast, it is preferable to use at least one selected from inorganic oxides containing heavy metal elements and glasses containing heavy metal elements as component (C). The heavy metal elements contained in the inorganic oxides containing heavy metal elements and the heavy metal elements contained in the glasses containing heavy metal elements are each independently at least one selected from the group consisting of zirconium, barium, titanium, lanthanum, and strontium, for example.

[0026] The refractive index of component (C) that may be contained in layer (U) is not limited as long as the effects of the present invention are achieved, but since the refractive index of component (A) is preferably 1.35 or more and less than 1.65, from the viewpoint of further improving transparency, the refractive index of component (C) is preferably 1.35 or more and less than 1.65, more preferably 1.40 or more and 1.63 or less, and even more preferably 1.45 or more and 1.60 or less. The refractive index values ​​are specifically values ​​evaluated by the method described in the Examples. From the viewpoint of making it easier to satisfy the refractive index, examples of the component (C) that the layer (U) may contain include glass containing at least one selected from boron and aluminum, ytterbium fluoride, barium glass, lanthanum glass, strontium boroaluminosilicate glass, fluoroaluminosilicate glass, silica, and quartz. These inorganic fillers can be combined to adjust the refractive index difference to a small value, making it easier to obtain a mill blank with high transparency. Therefore, at least one selected from the group consisting of ytterbium fluoride, barium glass, lanthanum glass, and fluoroaluminosilicate glass is more preferred, and at least one selected from lanthanum glass and fluoroaluminosilicate glass is even more preferred, since it can also impart X-ray contrast properties.

[0027] The form of component (C) is not particularly limited, and various forms such as crushed, plate-like, scale-like, fibrous (short fibers, long fibers), needle-like, whisker-like, and spherical forms can be used. Primary particles of these forms may be aggregated, or different forms may be combined. The form may be one that has been subjected to a process such as pulverization to have the above-mentioned form.

[0028] The particle size of component (C) is not limited as long as the effects of the present invention are achieved, but from the viewpoint of improving moldability, transparency, and strength, the average primary particle size is preferably 5.0 μm or less, more preferably 2.5 μm or less, even more preferably 1.0 μm or less, and even more preferably 0.70 μm or less. The smaller the average primary particle size, the more uniformly dispersed the particles are, and the easier it is to achieve excellent moldability and transparency. Furthermore, from the viewpoint of easily adjusting the flowability to an appropriate level and easily achieving good moldability, the average primary particle size is preferably 0.01 μm or more, more preferably 0.025 μm or more, even more preferably 0.05 μm or more, and even more preferably 0.10 μm or more. As described above, the preferred ranges for the average primary particle diameter of component (C) can be independently combined. For example, in one embodiment of component (C), the average primary particle diameter is preferably 0.01 to 5.0 μm, more preferably 0.025 to 2.5 μm, even more preferably 0.05 to 1.0 μm, and even more preferably 0.10 to 0.70 μm. The average primary particle diameter can be determined by a laser diffraction scattering method. For example, it can be measured on a volume basis using a 0.2% aqueous solution of sodium hexametaphosphate as a dispersion medium with a laser diffraction particle size distribution analyzer (such as the "SALD (registered trademark)-7500 nano" manufactured by Shimadzu Corporation). The average primary particle diameter is the D50 value on a volume basis.

[0029] Component (C) may be surface-treated with a known surface treatment agent before use, if necessary, to adjust its miscibility with component (A). Examples of the surface treatment agent include alcohols such as trimethylolethane, trimethylolpropane, and pentaerythritol; alkanolamines such as triethylamine; organosilicone compounds such as organopolysiloxane; higher fatty acids such as stearic acid (preferably higher fatty acids having 12 to 24 carbon atoms); fatty acid metal salts such as calcium stearate and magnesium stearate (preferably fatty acid metal salts having 12 to 24 carbon atoms); hydrocarbon lubricants such as polyethylene wax and liquid paraffin; basic amino acids such as lysine and arginine; polyglycerin and derivatives thereof; and coupling agents such as silane coupling agents, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. Examples of the surface treatment agent include at least one selected from the group consisting of alcohols, alkanolamines, organic silicone compounds, higher fatty acids, fatty acid metal salts, hydrocarbon lubricants, basic amino acids, polyglycerin and derivatives thereof, and coupling agents.

[0030] The content of component (C) in layer (U) is not particularly limited as long as the effects of the present invention are achieved, but from the viewpoint of improving moldability, transparency, and strength, it is preferably 1 to 60 mass%, more preferably 5 to 50 mass%, even more preferably 6 to 45 mass%, still more preferably 8 to 44 mass%, even more preferably 9 to 42 mass%, and still more preferably 10 to 40 mass%, based on 100 mass% of layer (U). When the content of component (C) is 1 mass% or more, good strength is maintained, and when it is 60 mass% or less, good moldability and transparency are maintained, which is preferable.

[0031] In one embodiment of the present invention, when the layer (U) contains both the component (A) and the component (C), from the viewpoint of more easily achieving the effects of the present invention, the total content of the component (A) and the component (C) in the layer (U) is preferably 90 to 100 mass%, more preferably 94 to 100 mass%, even more preferably 95 to 100 mass%, still more preferably 98 to 100 mass%, and still more preferably 99 to 100 mass%, based on 100 mass% of the layer (U).

[0032] (Pigment (D)) Pigment (D) is used for the purpose of toning the mill blank. Examples of pigment (D) include known pigments used in dental composite resins. Pigment (D) can be at least one selected from inorganic and organic pigments. Examples of inorganic pigments include chromates such as yellow lead, zinc yellow, and barium yellow; ferrocyanides such as iron blue; sulfides such as vermilion, cadmium yellow, zinc sulfide, antimony white, and cadmium red; sulfates such as barium sulfate, zinc sulfate, and strontium sulfate; oxides such as zinc oxide, titanium oxide, iron oxide red (red iron oxide), iron oxide black, iron oxide yellow, and chromium oxide; hydroxides such as aluminum hydroxide; silicates such as calcium silicate and ultramarine; and carbon such as carbon black and graphite. In this specification, inorganic pigments that are also used as the inorganic filler (C) are considered to be inorganic fillers (C), even if they are inorganic pigments that can be involved in toning. Examples of the organic pigments include nitroso pigments such as Naphthol Green B and Naphthol Green Y; nitro pigments such as Naphthol S and Lithol Fast Yellow 2G; insoluble azo pigments such as Permanent Red 4R, Brilliant Fast Scarlet, Hansa Yellow, and Benzidine Yellow; sparingly soluble azo pigments such as Lithol Red, Lake Red C, and Lake Red D; soluble azo pigments such as Brilliant Carmine 6B, Permanent Red F5R, Pigment Scarlet 3B, and Bordeaux 10B; phthalocyanine pigments such as Phthalocyanine Blue, Phthalocyanine Green, and Sky Blue; basic dye pigments such as Rhodamine Lake, Malachite Green Lake, and Methyl Violet Lake; and acid dye pigments such as Peacock Blue Lake, Eosin Lake, and Quinoline Yellow Lake. These pigments may be used alone or in combination of two or more, and are selected appropriately depending on the desired color tone of the dental mill blank. Among these pigments, inorganic pigments such as titanium oxide, red iron oxide, iron oxide black, and iron oxide yellow, which are excellent in heat resistance and light resistance, are preferred.

[0033] The total content of pigment (D) in layer (U) is not particularly limited as it is adjusted appropriately depending on the desired color tone, but is preferably 0.000001 to 0.9 parts by mass, and more preferably 0.00001 to 0.5 parts by mass, per 100 parts by mass of component (C) in layer (U).

[0034] In one embodiment of the present invention, when layer (U) contains all of component (A), component (C), and component (D), from the viewpoint of more easily achieving the effects of the present invention, the total content of component (A), component (C), and component (D) in layer (U) is preferably 95 to 100 mass%, more preferably 98 to 100 mass%, even more preferably 99 to 100 mass%, and still more preferably 99.5 to 100 mass%, based on 100 mass% of layer (U).

[0035] (Other Components) The layer (U) may contain other components in addition to the component (A) and the components (C) and (D) that may be contained as needed, depending on the purpose, as long as the effects of the present invention are achieved. Examples of the other components include pH adjusters, ultraviolet absorbers, antioxidants, polymerization inhibitors, colorants, antibacterial agents, X-ray contrast agents, thickeners, and fluorescent agents. One type of the other components may be used alone, or two or more types may be used in combination.

[0036] When layer (U) contains other components, there are no particular limitations on the total content of the other components as long as the effects of the present invention are achieved, and an amount that provides the required effect may be used. For example, the total content of the other components is preferably 0.000001 to 5 parts by mass, and more preferably 0.00001 to 1 part by mass, relative to 100 parts by mass of the total of components other than the other components contained in layer (U) (component (A), and components (C) and (D) that may be contained as necessary).

[0037] <Layer (L)> The layer (L) contains a thermoplastic resin (B). From the viewpoint of further improving strength, the layer (L) preferably contains a thermoplastic resin (B) and an inorganic filler (C), and from the viewpoint of further improving strength and making it easier to adjust the color tone to be close to that of natural teeth, the layer (L) more preferably contains a thermoplastic resin (B), an inorganic filler (C), and a pigment (D).

[0038] (Thermoplastic resin (B)) The thermoplastic resin (B) may be at least one selected from the group consisting of polyether ketone, polyether ether ketone, polyether ketone ketone, polyacetal, polyphenylene ether, polyphenylene sulfide, and polyimide. Among these, at least one selected from the group consisting of polyether ether ketone and polyether ketone ketone is preferred from the viewpoint of improving the strength of the mill blank.

[0039] The polyether ether ketone is not particularly limited as long as the effects of the present invention are achieved. However, the polyether ether ketone should have an MVR of 10 to 80 cm under conditions of a temperature of 380° C. and a load of 49 N. ３ / 10 min is preferable. Furthermore, although there are no particular limitations as long as the effects of the present invention are achieved, the flexural strength of the polyether ether ketone is preferably 120 MPa or more and preferably 300 MPa or less. Furthermore, commercially available products may be used as the polyether ether ketone, and examples of commercially available products include "Vestakeep (registered trademark)" (manufactured by Polypla-Evonik Co., Ltd.), "Ketron (registered trademark)" (manufactured by Mitsubishi Chemical Advanced Materials Corporation), "Victrex (registered trademark) PEEK" (manufactured by Victrex), and "KetaSpire (registered trademark) PEEK" (manufactured by Solvay).

[0040] The polyether ketone ketone is not particularly limited as long as the effects of the present invention are exhibited. However, the MVR of the polyether ketone ketone under conditions of 380° C. and 49 N is preferably 10 to 80 cm ３ / 10 min. Furthermore, although there are no particular limitations as long as the effects of the present invention are achieved, the flexural strength of the polyetherketoneketone is preferably 120 MPa or more and preferably 300 MPa or less. Furthermore, commercially available products may be used as the polyetherketoneketone, and examples of commercially available products include "Kepstan (registered trademark) PEKK" (manufactured by Arkema) and "NovaSpire (registered trademark) PEKK" (manufactured by Solvay).

[0041] From the viewpoint of obtaining better transparency, it is preferable to use one kind of component (B) without mixing two or more kinds of component (B) in the layer (L). When the layer (L) contains two or more kinds of component (B), the content of the component (B) with the highest content is preferably 90 to 99.9 mass%, more preferably 95 to 99.9 mass%, and even more preferably 99 to 99.9 mass%, based on 100 mass% of the total components (B).

[0042] In order to more easily achieve the effects of the present invention, the content of component (B) in layer (L) is preferably 37 to 99 mass%, more preferably 40 to 99 mass%, even more preferably 50 to 95 mass%, even more preferably 55 to 94 mass%, even more preferably 60 to 92 mass%, and even more preferably 70 to 90 mass% based on 100 mass% of layer (L). A content of component (B) of 37 to 99 mass% is preferred from the viewpoint of enabling the mill blank to exhibit better strength without impairing moldability. Furthermore, when layer (L) contains two or more types of component (B), the content of component (B) in layer (L) represents the total content of the two or more types of component (B). Furthermore, in this specification, the term "100 mass% of layer (L)" refers to the total content (100 mass%) of all components constituting layer (L).

[0043] (Inorganic Filler (C)) Examples of the inorganic filler (C) that may be contained in the layer (L) include the same inorganic fillers as those described above in the section on the layer (U) as the inorganic filler (C) that may be contained in the layer (U), and suitable embodiments thereof (specific inorganic filler, shape, particle size, etc.) are the same as those described in the section on the layer (U) except for the following points.

[0044] The refractive index of component (C) that may be contained in layer (L) is not limited as long as the effects of the present invention are achieved, but since the refractive index of component (B) is preferably 1.65 to 1.75, from the viewpoint of further improving transparency, the refractive index of component (C) is preferably 1.65 or more and less than 2.00, more preferably 1.65 to 1.90, and even more preferably 1.70 to 1.80. The above-mentioned refractive index value is specifically a value evaluated by the method described in the examples. From the viewpoint of making it easier to satisfy the refractive index requirement, the component (C) that the layer (L) may contain is preferably alumina, various ceramics, diatomaceous earth, kaolin, clay minerals (montmorillonite, etc.), activated clay, synthetic zeolite, mica, silica, calcium fluoride, ytterbium fluoride, calcium phosphate, barium sulfate, zirconium dioxide (zirconia), titanium dioxide (titania), hydroxyapatite, barium titanate, lanthanum glass, praseodymium compounds, erbium compounds, manganese compounds, or the like, because even when these inorganic fillers are combined, the refractive index difference can be adjusted to be small, making it easier for the obtained mill blank to have high transparency. At least one selected from the group consisting of alumina, zirconium dioxide (zirconia), titanium dioxide (titania), barium titanate, lanthanum glass, praseodymium compounds, erbium compounds, and manganese compounds is more preferred, and at least one selected from barium titanate and lanthanum glass is even more preferred.

[0045] As described above, the component (C) that may be contained in the layer (L) may be surface-treated in advance with a known surface treatment agent, if necessary, to adjust its miscibility with the component (B). Examples of the surface treatment agent include the same surface treatment agents as those described above as the surface treatment agents for the inorganic filler (C) in the section for the layer (U), and preferred embodiments thereof are also the same as those described in the section for the layer (U).

[0046] The content of component (C) in layer (L) is not particularly limited, but from the viewpoint of improving moldability, transparency, and strength, it is preferably 1 to 60 mass%, more preferably 5 to 50 mass%, even more preferably 6 to 45 mass%, still more preferably 8 to 44 mass%, even more preferably 9 to 42 mass%, and still more preferably 10 to 40 mass%, based on 100 mass% of layer (L). When the content of component (C) is 1 mass% or more, good strength is maintained, and when it is 60 mass% or less, good moldability and transparency are maintained, which is preferable.

[0047] In one embodiment of the present invention, when the layer (L) contains both the component (B) and the component (C), from the viewpoint of more easily achieving the effects of the present invention, the total content of the component (B) and the component (C) in the layer (L) is preferably 90 to 100 mass%, more preferably 94 to 100 mass%, even more preferably 95 to 100 mass%, still more preferably 98 to 100 mass%, and still more preferably 99 to 100 mass%, based on 100 mass% of the layer (L).

[0048] (Pigment (D)) Examples of the pigment (D) that may be contained in layer (L) include the same pigments as those described above in the section for layer (U) as the pigment (D) that may be contained in layer (U), and suitable embodiments thereof are also the same as those described in the section for layer (U). The total content of pigment (D) in layer (L) is not particularly limited as it is adjusted appropriately depending on the desired color tone, but is preferably 0.000001 to 0.9 parts by mass, and more preferably 0.00001 to 0.5 parts by mass, per 100 parts by mass of component (C) in layer (L).

[0049] In one embodiment of the present invention, when the layer (L) contains all of the component (B), the component (C), and the component (D), from the viewpoint of more easily achieving the effects of the present invention, the total content of the component (B), the component (C), and the component (D) in the layer (L) is preferably 95 to 100 mass%, more preferably 98 to 100 mass%, even more preferably 99 to 100 mass%, and still more preferably 99.5 to 100 mass%, based on 100 mass% of the layer (L).

[0050] (Other Components) The layer (L) may contain other components in addition to the component (B) and the components (C) and (D) that may be contained as needed, depending on the purpose, as long as the effects of the present invention are achieved. Examples of the other components include pH adjusters, ultraviolet absorbers, antioxidants, polymerization inhibitors, colorants, antibacterial agents, X-ray contrast agents, thickeners, and fluorescent agents. One type of the other components may be used alone, or two or more types may be used in combination.

[0051] When the layer (L) contains other components, there are no particular limitations on the total content of the other components as long as the effects of the present invention are achieved, and an amount that provides the required effect may be used. For example, the total content of the other components is preferably 0.000001 to 5 parts by mass, and more preferably 0.00001 to 1 part by mass, relative to 100 parts by mass of the total of components other than the other components contained in the layer (L) (component (B), and components (C) and (D) that may be contained as necessary).

[0052] <Intermediate layer (M)> As described above, from the viewpoint of facilitating adjustment to a color tone closer to that of natural teeth, the laminate preferably further includes at least one intermediate layer (M) between layers (U) and (L). Furthermore, from the viewpoint of facilitating adjustment to a color tone closer to that of natural teeth and facilitating improvement in strength, the laminate more preferably includes at least one layer (M) between layers (U) and (L), and layer (M) includes at least one resin selected from thermoplastic resin (A) and thermoplastic resin (B). From the viewpoint of obtaining better transparency, layer (M) is preferably used alone without mixing component (A) and component (B). Furthermore, when layer (M) contains two or more types of at least one thermoplastic resin selected from component (A) and component (B), the content of the thermoplastic resin with the largest content is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, based on 100% by mass of the total of the two or more thermoplastic resins, and is preferably 99.9% by mass or less, more preferably 99.8% by mass or less, even more preferably 99.5% by mass or less.

[0053] From the viewpoint of further improving strength, the layer (M) preferably contains an inorganic filler (C) in addition to at least one selected from the component (A) and the component (B). From the viewpoint of further improving strength and making it easier to adjust the color tone to a color close to that of natural teeth, the layer (M) more preferably contains an inorganic filler (C) and a pigment (D) in addition to at least one selected from the component (A) and the component (B).

[0054] Component (A) that may be contained in layer (M) includes the same thermoplastic resins as those described above as component (A) in the section for layer (U), and preferred embodiments thereof are also the same as those described in the section for layer (U). Component (B) that may be contained in layer (M) includes the same thermoplastic resins as those described above as component (B) in the section for layer (L), and preferred embodiments thereof are also the same as those described in the section for layer (L).

[0055] In layer (M), the total content of at least one selected from components (A) and (B) is preferably 37 to 99 mass%, more preferably 40 to 99 mass%, even more preferably 50 to 95 mass%, even more preferably 55 to 94 mass%, even more preferably 60 to 92 mass%, and even more preferably 70 to 90 mass%, based on 100 mass% of layer (M), from the viewpoint of more easily achieving the effects of the present invention. When the total content of at least one selected from components (A) and (B) in layer (M) is 37 to 99 mass%, it is preferable from the viewpoint of being able to exhibit good strength in the mill blank without impairing moldability. Furthermore, when layer (M) contains two or more of components (A) and (B), the total content of at least one selected from components (A) and (B) in layer (M) represents the total content of those components. In addition, in this specification, the term "100% by mass of the layer (M)" refers to the total content (100% by mass) of all components constituting the layer (M).

[0056] Examples of the component (C) that may be contained in the layer (M) include the same inorganic fillers as those described above as the inorganic filler (C) that may be contained in each layer in the sections for the layer (U) and the layer (L). However, for example, when the layer (M) contains the component (A) most abundantly as a resin, the preferred aspects of the component (C) that may be contained in the layer (M) (specific inorganic filler, shape, refractive index, particle size, etc.) are the same as the preferred aspects of the component (C) described in the section for the layer (U); and when the layer (M) contains the component (B) most abundantly as a resin, the preferred aspects of the component (C) that may be contained in the layer (M) (specific inorganic filler, shape, refractive index, particle size, etc.) are the same as the preferred aspects of the component (C) described in the section for the layer (L).

[0057] The content of component (C) in layer (M) is not particularly limited, but from the viewpoint of improving moldability, transparency, and strength, it is preferably 1 to 60 mass%, more preferably 5 to 50 mass%, even more preferably 6 to 45 mass%, still more preferably 8 to 44 mass%, even more preferably 9 to 42 mass%, and still more preferably 10 to 40 mass%, based on 100 mass% of layer (M). A content of component (C) of 1 mass% or more maintains good strength, and a content of 60 mass% or less is preferred because good moldability and transparency are maintained.

[0058] In one embodiment of the present invention, when the layer (M) contains at least one selected from the components (A) and (B), and the component (C), from the viewpoint of more easily achieving the effects of the present invention, the total content of the at least one selected from the components (A) and (B), and the component (C) in the layer (M) is preferably 90 to 100% by mass, more preferably 94 to 100% by mass, even more preferably 95 to 100% by mass, still more preferably 98 to 100% by mass, and still more preferably 99 to 100% by mass, based on 100% by mass of the layer (M).

[0059] Examples of the pigment (D) that may be contained in layer (M) include the same pigments as those described above in the section for layer (U) as the pigment (D) that may be contained in layer (U), and suitable embodiments thereof are also the same as those described in the section for layer (U). The content of pigment (D) in layer (M) is not particularly limited as it is adjusted appropriately depending on the desired color tone, but is preferably 0.000001 to 0.9 parts by mass, and more preferably 0.00001 to 0.5 parts by mass, per 100 parts by mass of component (C) in layer (M).

[0060] In one embodiment of the present invention, when the layer (M) contains at least one selected from the components (A) and (B), the component (C), and all of the component (D), from the viewpoint of more easily achieving the effects of the present invention, the total content of the at least one selected from the components (A) and (B), the component (C), and the component (D) in the layer (M) is preferably 95 to 100% by mass, more preferably 98 to 100% by mass, even more preferably 99 to 100% by mass, and still more preferably 99.5 to 100% by mass, based on 100% by mass of the layer (M).

[0061] Layer (M) may contain other components described in the sections for Layer (U) and Layer (L) depending on the purpose, as long as the effects of the present invention are achieved. Examples of such other components include pH adjusters, ultraviolet absorbers, antioxidants, polymerization inhibitors, colorants, antibacterial agents, X-ray contrast agents, thickeners, and fluorescent agents. One type of such other component may be used alone, or two or more types may be used in combination.

[0062] When the layer (M) contains other components, there are no particular limitations on the total content of the other components as long as the effects of the present invention are achieved, and an amount that provides the required effects may be used. For example, the total content of the other components is preferably 0.000001 to 5 parts by mass, and more preferably 0.00001 to 1 part by mass, relative to 100 parts by mass of the total of the components other than the other components contained in the layer (M) (resin components such as at least one selected from components (A) and (B), component (C), and component (D)).

[0063] From the viewpoint of enabling coloring to a color tone closer to that of natural teeth, the mill blank has a transparency difference ΔΔL between the layer (U) and the layer (L).＊ Ｔ is 5.0 to 15.0, and the transparency ΔL of the layer (U) ＊ Ｕ is 13.5 to 25.0, and the transparency ΔL of the layer (L) ＊ Ｌ As described above, in this specification, the upper and lower limits of the numerical ranges (characteristics such as transparency difference, the content of each component, values ​​calculated from each component, etc.) and the respective components can be combined as appropriate.

[0064] In the mill blank, the transparency difference ΔΔL between the layer (U) and the layer (L) ＊ Ｔ is preferably 5.0 to 15.0, more preferably 5.5 to 14.0, even more preferably 6.0 to 13.0, still more preferably 7.0 to 12.0, even more preferably 8.0 to 11.0, and still more preferably 9.0 to 10.0. ＊ Ｔ When ΔΔL is 5.0 or more, the change in transparency of the cut crown is not too small, and it becomes easy to reproduce the change in transparency from the cervical part to the incisal edge part of a natural tooth (especially anterior tooth). ＊ Ｔ When the transparency difference ΔΔL is 15.0 or less, the difference in transparency of the cut crown does not become too large, and it becomes easy to reproduce the change in transparency from the cervical part to the incisal edge part of a natural tooth (especially anterior tooth). ＊ Ｔ Specifically, is a value evaluated by the method described in the Examples.

[0065] In the mill blank, it is preferable to have an intermediate layer (M) from the viewpoint of improving the reproducibility of the color change from the cervical part to the incisal edge part of a natural tooth (especially anterior tooth). Here, the mill blank composed of a laminate having the layer (M) has a transparency difference ΔΔL between each layer. ＊ ＭThat is, the transparency difference ΔΔL between the layer (U) and the layer (M) closest to the layer (U), the transparency difference between the layer (M) closest to the layer (L) and the layer (L), and when there are multiple layers (M), the transparency difference between adjacent layers (M) are each independently preferably 1.0 to 12.0, more preferably 1.5 to 11.0, and even more preferably 2.0 to 10.0. ＊ Ｍ and the transparency ΔL of the more transparent layer, respectively. ＊ From the value of ＊ It can be calculated by subtracting the value of

[0066] Transparency ΔL of layer (U) ＊ Ｕ From the viewpoint of further improving the reproducibility of the change in transparency from the cervical region to the incisal edge region of natural teeth (particularly anterior teeth), the transparency ΔL of the layer (U) is preferably 13.5 to 25.0, more preferably 14.0 to 24.0, and even more preferably 14.5 to 23.5. ＊ Ｕ Specifically, the transparency ΔL of the layer (L) is a value evaluated by the method described in the Examples. ＊ Ｌ From the viewpoint of further improving the reproducibility of the change in transparency from the cervical region to the incisal edge region of natural teeth (particularly anterior teeth), the transparency ΔL of layer (L) is preferably 3.5 to 13.5, more preferably 7.0 to 13.0, more preferably 7.5 to 12.5, and even more preferably 8.0 to 12.0. ＊ Ｌ Specifically, the value is evaluated by the method described in the examples. When the layer (M) is provided, the transparency ΔL of the layer (M) ＊ Ｍ From the viewpoint of further improving the reproducibility of the change in transparency from the cervical region to the incisal edge region of natural teeth (particularly anterior teeth), the transparency ΔL of the layer (M) is preferably 6.0 to 20.0, more preferably 8.0 to 19.0, even more preferably 9.0 to 18.5, and still more preferably 10.0 to 18.0. ＊ Ｍ Specifically, is a value evaluated by the method described in the Examples.

[0067] Furthermore, the mill blank preferably satisfies the following formulas [I] and [II] regarding transparency: ΔL ＊ Ｌ <ΔL ＊ Ｍ（１） [I] ΔL ＊ Ｍ（ｐ） <ΔL ＊ Ｕ [II] (In formula [I], ΔL ＊ Ｌ is the transparency of the layer (L), and ΔL ＊ Ｍ（１） is the intermediate layer (M １ In formula [II], ΔL ＊ Ｕ is the transparency of the layer (U), and ΔL ＊ Ｍ（ｐ） is the intermediate layer (M) closest to the layer (U). Ｐ Furthermore, if there are two or more intermediate layers (M) (p is a natural number of 2 or more), the transparency of the kth intermediate layer (k is any natural number from 2 to p) is ΔL ＊ Ｍ（ｋ－１） <ΔL ＊ Ｍ（ｋ） It is preferable that the following relationship is satisfied.

[0068] The mill blank is preferably composed of a laminate of multiple colors. Natural teeth are composed of a highly transparent enamel layer and a relatively opaque, colored dentin layer. Furthermore, in anterior teeth (especially central incisors, lateral incisors, and canines), the proportions of their constituent components vary from the cervical to the incisal edge, and the proportions of the constituent components also vary between dentin and enamel. Therefore, since the incisal edge is highly transparent and lightly colored, while the cervical edge is less transparent and darker, it is preferable that the mill blank be colored in the same manner. For the same reason, as described above, in a dental mill blank according to one embodiment of the present invention, layer (U) is preferably the upper layer and layer (L) is the lower layer in relation to layer (U) and layer (L). In other words, the dental mill blank according to one embodiment of the present invention is preferably a laminate in which layers are stacked so that, when the mill blank is processed, layer (U) is more transparent than layer (L) and is closer to the incisal edge. Furthermore, as one embodiment of the mill blank, it is more preferable that the layer (U) is the layer closest to the incisal edge and the layer (L) is the layer closest to the cervical region. That is, as one embodiment of the mill blank, it is more preferable that the upper layer (U) is the outermost layer having higher transparency than the layer (L), and the lower layer (L) is the other outermost layer having lower transparency than the layer (U).

[0069] The number of layers of the laminate constituting the dental mill blank is at least 2, preferably 3 to 8, and more preferably 4 to 6. That is, p in the formula [II] is preferably a natural number of 1 to 6, and more preferably a natural number of 2 to 4.

[0070] The thickness of the entire laminate constituting the mill blank is preferably 4.0 to 26.0 mm, more preferably 5.0 to 25.0 mm, even more preferably 8.0 to 23.0 mm, still more preferably 9.0 to 22.0 mm, and even more preferably 10.0 to 20.0 mm.

[0071] The thickness of the layer (U) is preferably 2.0 mm or more, more preferably 2.0 to 21.0 mm, even more preferably 2.0 to 20.0 mm, still more preferably 2.0 to 18.0 mm, still more preferably 2.0 to 15.0 mm, still more preferably 2.0 to 12.0 mm, and still more preferably 2.0 to 9.0 mm. The thickness of the layer (L) is preferably 2.0 mm or more, more preferably 2.0 to 21.0 mm, still more preferably 2.0 to 20.0 mm, still more preferably 3.0 to 19.0 mm, still more preferably 3.0 to 18.0 mm, still more preferably 5.0 to 16.0 mm, and still more preferably 5.0 to 15.0 mm.

[0072] Furthermore, when the mill blank includes at least one layer (M), the thickness of each layer (M) is independently preferably 1.0 mm or more, more preferably 1.0 to 10.0 mm, even more preferably 1.5 to 8.0 mm, and still more preferably 2.0 to 7.0 mm.

[0073] As described above, the preferred ranges for the thickness of each layer can be independently combined. For example, in one embodiment of the laminate constituting the mill blank, the thickness of layer (U) may be in the more preferred range of 2.0 to 12.0 mm, and the thickness of layer (L) may be in the more preferred range of 2.0 to 20.0 mm. Furthermore, in one embodiment of the laminate constituting the mill blank, the thickness of layer (U) may be in the more preferred range of 2.0 to 12.0 mm, the thickness of layer (L) may be in the more preferred range of 2.0 to 20.0 mm, and the thickness of layer (M) may be in the more preferred range of 2.0 to 7.0 mm. Combinations of different preferred ranges for the thickness of each layer are also possible. Furthermore, in one embodiment of the laminate constituting the mill blank, when the preferred ranges for each layer are combined, it is even more preferable that the sum of the thicknesses selected from the preferred ranges for each layer satisfies the preferred range for the thickness of the entire laminate described above. The thickness of each layer can be measured, specifically, by the method described in the Examples.

[0074] An embodiment (W1), which is an example of a preferred embodiment of the mill blank, is, for example, a dental mill blank composed of a laminate, wherein the laminate includes at least two layers, an upper layer (U) and a lower layer (L), the upper layer (U) constituting the laminate includes a thermoplastic resin (A) and an inorganic filler (C) having a refractive index of 1.35 or more and less than 1.65, and, if necessary, a pigment (D), and the lower layer (L) includes a thermoplastic resin (B), an inorganic filler (C) having a refractive index of 1.65 or more and less than 2.00, and a pigment (D), and the transparency difference ΔΔL between the upper layer (U) and the lower layer (L) is ＊ Ｔ is 5.0 to 15.0, and the transparency ΔL of the upper layer (U) ＊ Ｕ is 13.5 to 25.0, and the transparency ΔL of the lower layer (L) ＊ Ｌ The dental mill blanks include those having a tensile strength of 3.5 to 13.5.

[0075] An embodiment (W2), which is an example of a preferred embodiment of the mill blank, is, for example, a dental mill blank composed of a laminate, the laminate including at least three layers of an upper layer (U), at least one intermediate layer (M), and a lower layer (L), the upper layer (U) including a thermoplastic resin (A) and an inorganic filler (C) having a refractive index of 1.35 or more and less than 1.65, and optionally a pigment (D), the intermediate layer (M) and the lower layer (L) each independently including a thermoplastic resin (B), an inorganic filler (C) having a refractive index of 1.65 or more and less than 2.00, and a pigment (D), and the transparency difference ΔΔL between the upper layer (U) and the lower layer (L) is ＊ Ｔ is 5.0 to 15.0, and the transparency ΔL of the upper layer (U) ＊ Ｕ is 13.5 to 25.0, and the transparency ΔL of one or more intermediate layers (M) ＊ Ｍ are each independently 6.0 to 20.0, and the transparency ΔL of the lower layer (L) ＊ Ｌ The dental mill blanks include those having a tensile strength of 3.5 to 13.5.

[0076] An embodiment (W3), which is an example of a preferred embodiment of the mill blank, is, for example, a dental mill blank composed of a laminate, the laminate including at least three layers of an upper layer (U), at least one intermediate layer (M), and a lower layer (L), the upper layer (U) including a thermoplastic resin (A) and an inorganic filler (C) having a refractive index of 1.35 or more and less than 1.65, and optionally a pigment (D), the intermediate layer (M) including a thermoplastic resin (A), an inorganic filler (C) having a refractive index of 1.35 or more and less than 1.65, and the pigment (D), the lower layer (L) including a thermoplastic resin (B), an inorganic filler (C) having a refractive index of 1.65 or more and less than 2.00, and the pigment (D), and the difference in transparency ΔΔL between the upper layer (U) and the lower layer (L) ＊ Ｔ is 5.0 to 15.0, and the transparency ΔL of the upper layer (U) ＊ Ｕ is 13.5 to 25.0, and the transparency ΔL of the intermediate layer (M) ＊ Ｍ is 6.0 to 20.0, and the transparency ΔL of the lower layer (L) ＊ Ｌ The dental mill blanks include those having a tensile strength of 3.5 to 13.5.

[0077] One embodiment of the present invention is a dental mill blank having a thermoplastic resin (A) on the outermost surface (US) and a thermoplastic resin (B) on the outermost surface (LS) opposite the outermost surface (US). A preferred example is a dental mill blank having a thermoplastic resin (A) as the main component of the resin component on the outermost surface (US) and a thermoplastic resin (B) as the main component of the resin component on the outermost surface (LS) opposite the outermost surface (US). The term "main component of the resin component" refers to the component with the highest content (by mass%) among the resin components forming the surface. For example, the main component is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, even more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass, of 100% by mass of the resin components forming the surface. Further, one embodiment of the present invention is a dental mill blank having an outermost surface (US) formed from at least a thermoplastic resin (A), and an outermost surface (LS) opposite the outermost surface (US) and formed from at least a thermoplastic resin (B).Preferably, the dental mill blank has an outermost surface (US) formed from a thermoplastic resin (A) as the main component of the resin components, and an outermost surface (LS) opposite the outermost surface (US) and formed from a thermoplastic resin (B) as the main component of the resin components.In any of the above embodiments, the outermost surface (US) may be formed from a thermoplastic resin (A) and an inorganic filler (C), or from a thermoplastic resin (A), an inorganic filler (C), and a pigment (D), or from a thermoplastic resin (A), an inorganic filler (C), a pigment (D), and other components, as necessary. In any of the above-mentioned embodiments, the outermost surface (LS) may be formed, as necessary, from a thermoplastic resin (B) and an inorganic filler (C), or from a thermoplastic resin (B), an inorganic filler (C), and a pigment (D), or from a thermoplastic resin (B), an inorganic filler (C), a pigment (D), and other components.In any of the above embodiments, the thermoplastic resin (A), thermoplastic resin (B), inorganic filler (C), pigment (D), and other components are the same as the respective components described above, and their preferred embodiments are also the same. Furthermore, the preferred embodiments and amounts of each component in the outermost surface (US) are the same as the embodiments and contents of each component in the layer (U) described above, and their preferred ranges are also the same. Furthermore, the preferred embodiments and amounts of each component in the outermost surface (LS) are the same as the embodiments and contents of each component in the layer (L) described above, and their preferred ranges are also the same. Furthermore, it is preferable that the transparency of the outermost surface (US) is higher than that of the outermost surface (LS), and the preferred ranges for the transparency of the outermost surface (US) and the transparency of the outermost surface (LS), as well as the difference in transparency between the outermost surface (US) and the outermost surface (LS), are the same as the preferred ranges for the transparency of the layer (U) and the transparency of the layer (L), as well as the difference in transparency between the layer (U) and the layer (L).

[0078] <Method for Manufacturing Dental Mill Blanks> There are no particular limitations on the method for manufacturing the dental mill blanks, as long as it is possible to produce dental mill blanks composed of the laminate and the effects of the present invention are achieved. However, the method for manufacturing the dental mill blanks preferably includes at least one of the following steps (1) to (3), and more preferably includes the following steps (1) to (3) in this order. In the following description, the layers (U), (L), and (M) are the same as the layers described above, and their preferred embodiments are also the same, so details will be omitted. Similarly, in the following description, the thermoplastic resin (A), thermoplastic resin (B), inorganic filler (C), pigment (D), and other components are the same as those described above, and their preferred embodiments are also the same, so details will be omitted. Step (1): A step of heating and melting at least one selected from the thermoplastic resin (A) and the thermoplastic resin (B); Step (2): A step of molding at least one layer selected from the layer (U) and the layer (L) by injection molding; Step (3): A step of molding the laminate by stacking and press-molding laminate sheets including at least the layer (U) and the layer (L).

[0079] (Step (1)) Step (1) is a step of heating and melting at least one selected from the thermoplastic resin (A) and the thermoplastic resin (B). The heating and melting is preferably carried out using a kneader or the like, and the kneader is preferably a multi-screw kneader, more preferably a multi-screw extruder, and even more preferably a twin-screw extruder. For example, when the thermoplastic resin or resin composition that forms the layer (U) is obtained by the heating and melting, a known mixing method can be used, such as a method of melt-kneading component (A) with at least one selected from optional components (C) and (D), and, if necessary, the other components, using a kneader or the like. Furthermore, for example, when the thermoplastic resin or resin composition that forms the layer (L) is obtained by the heating and melting, a known mixing method can be used, such as a method of melt-kneading component (A) with at least one selected from optional components (C) and (D), and, if necessary, the other components, using a kneader or the like. Furthermore, for example, in the case where the thermoplastic resin or resin composition that forms the layer (M) is obtained by the heat melting, a known mixing method can be used, such as a method of melt-kneading at least one selected from component (A) and component (B) with at least one selected from optional component (C) and component (D), and, if necessary, the other components, using a kneader or the like.

[0080] When component (C) is also kneaded in step (1), from the viewpoint of easily mixing the inorganic filler finely and uniformly, a multi-screw extruder is preferred as the kneader, and a twin-screw extruder is more preferred. That is, the heat-melting in step (1) is preferably melt-extrusion kneading using a multi-screw extruder, and more preferably melt-extrusion kneading using a twin-screw extruder. The L (shaft length) / D (shaft diameter) ratio of the twin-screw extruder is preferably 25 or more, more preferably 35 or more, and even more preferably 45 or more. The upper limit of the L / D is not particularly limited, but is preferably 100 or less, for example. As described above, the preferred ranges of the L / D can be independently combined. For example, in one embodiment of the twin-screw extruder, the L / D ratio is preferably 25 to 100, more preferably 35 to 100, and even more preferably 45 to 100.

[0081] Examples of a method for adding at least one selected from component (C) and component (D), and the other components that may be included as necessary, to at least one selected from component (A) and component (B) include a method in which pellets of at least one selected from component (A) and component (B), at least one selected from component (C) and component (D), and the other components as necessary are mixed together in a container such as a plastic bag or a tumbler before kneading, and then the mixture is charged into a kneader; or a method in which at least one selected from component (A) and component (B) is first charged into a kneader and heated to melt, and then at least one selected from component (C) and component (D), and the other components as necessary, are charged into the middle of the kneader.

[0082] Furthermore, from the viewpoint of preventing deterioration of molding processability and the thermoplastic resin, the kneading temperature of the kneader (the highest temperature among the set temperatures of each part that can be set from the time when the raw materials are charged into the kneader until the kneaded resin composition is taken out) is preferably set to 200 to 360°C in consideration of the glass transition temperature, melting point, melt viscosity, etc. of the thermoplastic resin used as component (A) when component (A) is used, and is preferably set to 360 to 400°C in consideration of the glass transition temperature, melting point, melt viscosity, etc. of the thermoplastic resin used as component (B) when component (B) is used.

[0083] In one embodiment of the step (1), the thermoplastic resin (A) and the thermoplastic resin (B) are each independently heated and melted together with at least one selected from component (C) and component (D), and, if necessary, the other components. In another embodiment of the step (1), the thermoplastic resins or resin compositions for forming the layer (U) and layer (L), and the optional layer (M), are each independently obtained through the step (1), and more preferably obtained by molding the thermoplastic resins or resin compositions into pellets.

[0084] As an example of a method for producing the dental mill blank, for example, a method in which the thermoplastic resin or resin composition pellets obtained in step (1) are extruded in a strip-like form using a plurality of single-screw extruders, and the thermoplastic resin or resin composition corresponding to each layer is extruded and laminated while being cut to obtain a laminated dental mill blank; or a method in which the thermoplastic resin or resin composition corresponding to each layer is extruded and laminated directly from the kneader in step (1) in a strip-like form, and the thermoplastic resin or resin composition is extruded and laminated while being cut to obtain a laminated dental mill blank;

[0085] (Step (2)) Step (2) is a step of molding at least one layer selected from the layer (U) and the layer (L) by injection molding. In one embodiment of step (2), it is preferable to mold both the layer (U) and the layer (L) by injection molding. Furthermore, in one embodiment of step (2), when the mill blank includes a layer (M), it is preferable to mold the layer (M) by injection molding as well, and it is more preferable to mold all of the layer (U), the layer (M), and the layer (L) by injection molding.

[0086] Furthermore, from the viewpoint of moldability and preventing deterioration of the thermoplastic resin, the melt temperature of the injection molding machine used during the injection molding (the highest set temperature among the various set temperatures that can be set in the injection molding machine after the resin composition is charged until a molded body is obtained) is preferably set to 200 to 360°C when component (A) is used, taking into consideration the glass transition temperature, melting point, melt viscosity, etc. of the thermoplastic resin used as component (A), and is preferably set to 360 to 400°C when component (B) is used, taking into consideration the glass transition temperature, melting point, melt viscosity, etc. of the thermoplastic resin used as component (B).

[0087] As described above, the layer (U) and the layer (L) formed in step (2), and the layer (M) formed as needed, are the same as those described above for each layer, and the preferred embodiments thereof, including the composition of each layer, the thickness of each layer, the transparency of each layer, and the difference in transparency between each layer, are also the same.

[0088] In the injection molding, for example, sheets corresponding to each layer may be molded independently by monochromatic injection molding. Furthermore, in the injection molding, for example, by performing the molding and lamination of each layer almost simultaneously using an injection molding capable of multicolor molding, it is also possible to directly obtain a laminated dental mill blank through step (2). Furthermore, a resin composition containing a mixture of components forming each layer is used for injection molding, and it is preferable to use the resin composition in pellet form. Therefore, in step (2), it is preferable to use the resin composition obtained through step (1), and it is more preferable to use the resin composition in pellet form obtained through step (1).

[0089] (Step (3)) Step (3) is a step of press-molding a laminate sheet including at least the layer (U) and the layer (L) to form the laminate. In one embodiment of step (3), when the laminate obtained in step (3) includes the layer (M), it is preferable to form the laminate by press-molding a laminate sheet including at least the layer (U), the layer (M), and the layer (L).

[0090] A known press molding machine can be used for the press molding. The press temperature during press molding is preferably 200 to 360°C, more preferably 240 to 300°C, from the viewpoints of moldability and preventing deterioration of the thermoplastic resin. The "press temperature" refers to the highest temperature set in the press machine during pressing. The press pressure (gauge pressure) during press molding is not particularly limited as long as the layers are fusible and the effects of the present invention are achieved. However, from the viewpoint of more easily fusing the layers together and more easily achieving the effects of the present invention, it is preferably 0.1 to 1.0 MPa. The press time during press molding is not particularly limited as long as the layers are fusible and the effects of the present invention are achieved. However, from the viewpoint of more easily fusing the layers together and avoiding deterioration and discoloration of the layers and more easily achieving the effects of the present invention, it is preferably 3 to 10 minutes.

[0091] In one embodiment of step (3), the layers (U) and (L) used in step (3), as well as the optional layer (M), can each be a layer obtained by press molding into a sheet corresponding to each layer. For example, a method can be used in which sheets corresponding to each layer are molded by press molding from pellets of a thermoplastic resin or resin composition obtained through step (1), etc., and then the resulting sheets are stacked and press-molded again to obtain a laminated dental mill blank. In one embodiment of step (3), the layers (U) and (L) used in step (3), as well as the optional layer (M), are preferably layers obtained through step (2), and more preferably layers obtained through steps (1) and (2). For example, a method can be used in which sheets corresponding to each layer are molded by monochromatic injection molding in step (2) from pellets of a thermoplastic resin or resin composition obtained through step (1), etc., and then the sheets obtained in step (3) are stacked and press-molded to obtain a laminated dental mill blank.

[0092] Furthermore, as an embodiment of the step (3), when the laminate obtained in the step (3) contains the layer (M), examples thereof include a method in which the layer (U) and the layer (M) are stacked and press-molded, and then the layer (L) is stacked on the layer (M) of the laminate of the layer (U) and the layer (M) and press-molded; a method in which the layer (L) and the layer (M) are stacked and press-molded, and then the layer (U) is stacked on the layer (M) of the laminate of the layer (L) and the layer (M) and press-molded; and a method in which the layer (U), the layer (M), and the layer (L) are stacked and press-molded simultaneously; and the like. The method in which the layer (U), the layer (M), and the layer (L) are stacked and press-molded simultaneously is preferred. Furthermore, when the layer (M) is composed of multiple layers, methods such as press-molding a laminate of multiple pre-prepared layers (M) with at least one layer selected from layers (U) and (L) can also be used. Alternatively, methods such as press-molding a laminate of pre-prepared layers (U) and (M) (including multiple layers) with a laminate of pre-prepared layers (L) and (M) (including multiple layers) can be used, with the layers (M) contacting each other's surfaces, or with an additional layer (M) (including multiple layers) sandwiched between the layers (M). The pre-prepared laminates of each layer can be, for example, laminates molded in advance by press molding, or laminates molded by extruding and cutting thermoplastic resins or resin compositions corresponding to each layer in a strip shape using an extruder or the like. Furthermore, if the laminate contains a laminated portion in which layers of the same composition are directly laminated together and molded by press molding or the like, the laminated portion can be considered a single layer. For example, when there is a laminated portion formed by previously preparing layers having the same composition (layers formed from the same thermoplastic resin or the same resin composition) and directly laminating the layers having the same composition together, the laminated portion is considered to be a single layer. Therefore, for example, the expression "a laminated sheet including the layer (U) and the layer (L)" also includes an embodiment in which a plurality of layers having the same composition as the previously prepared layer (U) are laminated together, and further a plurality of layers having the same composition as the previously prepared layer (L), and in this embodiment as well, it is considered to be a laminated sheet in which two layers, a single layer (U) having a single composition and a single layer (L) having a single composition, are laminated together.This is because, when a laminated sheet having a plurality of layers of the same composition laminated thereon is molded by press molding or the like, it is difficult to distinguish the boundaries between the layers of the same composition, and the composition of the entire laminated portion is the same as when it is molded as a single layer. The same applies when layer (M) is made up of a plurality of layers of the same composition.

[0093] As described above, there are no particular limitations on the molding method for the mill blank, as long as it is possible to produce a dental mill blank composed of the laminate and the effects of the present invention are achieved. However, one embodiment of the mill blank manufacturing method includes, for example, a method in which a thermoplastic resin or resin composition forming each layer is first molded into pellets using a twin-screw extruder, and then the resulting pellets are injection-molded to obtain a laminated dental mill blank; a method in which sheets corresponding to each layer are molded from the resulting pellets using single-color injection molding, and then the resulting sheets are stacked and press-molded to obtain a laminated dental mill blank; a method in which sheets corresponding to each layer are molded from the resulting pellets using press molding, and then the resulting sheets are stacked and press-molded again to obtain a laminated dental mill blank; or a method in which resins corresponding to each layer are extruded and stacked in a strip shape using multiple single-screw extruders, and then cut while being laminated, to obtain a laminated dental mill blank. As described above, it is preferable to use the above-mentioned step (1) as the step for obtaining the pellets, and it is preferable to use the above-mentioned step (2) as the step for injection molding.

[0094] The mill blank is preferably obtained by the above-described manufacturing method. The obtained mill blank may be cut to a desired size, machined, and surface polished as necessary.

[0095] The mill blank is preferably machined to an appropriate size so that it can be set in a commercially available dental CAD / CAM system. Preferred sizes include, for example, a 40 mm x 20 mm x 15 mm prism suitable for fabricating a single-tooth missing bridge; a 17 mm x 10 mm x 10 mm prism suitable for fabricating an inlay or onlay; a 14 mm x 18 mm x 20 mm prism suitable for fabricating a full crown; and a disk shape with a diameter of 100 mm and a thickness of 10 to 28 mm suitable for fabricating a long-span bridge or denture base. However, the size is not limited to these.

[0096] In one aspect of the present invention, the bending strength of the mill blank is preferably 150 MPa or more, more preferably 160 MPa or more, even more preferably 170 MPa or more, even more preferably 180 MPa or more, and even more preferably 190 MPa or more. The upper limit is not particularly limited as long as the effects of the present invention are achieved, but is preferably 300 MPa, which is preferable from the viewpoint of the machinability of the mill blank and the ease of polishing the resulting dental prosthesis. As mentioned above, the preferred ranges of bending strength can be independently combined. For example, in one aspect of the mill blank, the bending strength is preferably 150 to 300 MPa, more preferably 160 to 300 MPa, even more preferably 170 to 300 MPa, even more preferably 180 to 300 MPa, and even more preferably 190 to 300 MPa. In one embodiment of the present invention, the flexural modulus of the mill blank is preferably 5.0 GPa or more, more preferably 6.0 GPa or more, even more preferably 7.0 GPa or more, even more preferably 7.5 GPa or more, and even more preferably 8.0 GPa or more. The upper limit is not particularly limited as long as the effects of the present invention are achieved, but from the viewpoint of easily obtaining an elastic modulus close to that of tooth structure, it is preferably 20 GPa. As described above, the preferred ranges of the flexural modulus can be independently combined. For example, in one embodiment of the mill blank, the flexural modulus is preferably 5.0 to 20 GPa, more preferably 6.0 to 20 GPa, even more preferably 7.0 to 20 GPa, even more preferably 7.5 to 20 GPa, and even more preferably 8.0 to 20 GPa. The flexural strength and flexural modulus values ​​of the mill blank are specifically values ​​evaluated by the methods described in the Examples.

[0097] [Dental Prosthesis] A dental prosthesis according to one embodiment of the present invention is manufactured from the mill blank. Examples of the dental prosthesis include crown restorations such as inlays, onlays, veneers, crowns, and bridges, as well as abutments, dental posts, dentures, denture bases, and implant components (fixtures and abutments).

[0098] The dental prosthesis is preferably manufactured by cutting the dental mill blank. That is, a method for manufacturing a dental prosthesis according to one aspect of the present invention includes a step of cutting the dental mill blank. The cutting is preferably performed using, for example, a commercially available dental CAD / CAM system, such as the CEREC (registered trademark) system from Dentsply Sirona K.K. and the Katana (registered trademark) system from Kuraray Noritake Dental Co., Ltd.

[0099] By cutting the mill blank according to one embodiment of the present invention, a dental prosthesis with high aesthetics can be provided, in which the color tone and transparency at the boundaries between layers transition smoothly and the color tone conforms to a shade guide that reproduces the color tone distribution of natural teeth. Because the dental mill blank according to one embodiment of the present invention has high aesthetics, it is useful as a dental prosthesis not only for molars (first premolar, second premolar, first molar, second molar, third molar) but also for anterior teeth (central incisors, lateral incisors, canines). Among these, the dental mill blank according to one embodiment of the present invention can be more preferably used for anterior teeth, i.e., central incisors, lateral incisors, or canines.

[0100] The present embodiment will be explained in more detail below by showing examples and comparative examples, but the present embodiment is not limited to the following examples.

[0101] The components used in the manufacture of dental mill blanks according to the examples and comparative examples are explained below together with their abbreviations. The following properties of each component were measured by the following methods.

[0102] <Refractive Index> The refractive indexes of the thermoplastic resin and the inorganic filler (C) were measured by the following method. Measurement was performed in an environment of 25°C using an Abbe refractometer (product name: DR-A1, NAR series; manufactured by Atago Co., Ltd.). The refractive index of the inorganic filler (C) was measured by a liquid immersion method. Specifically, the inorganic filler (C) was dispersed in ethanol to form a slurry, and 1-bromonaphthalene was gradually added dropwise to this slurry. The refractive index of the dispersion liquid at which the boundary between the inorganic filler (C) and the liquid could no longer be visually confirmed was taken as the refractive index of the inorganic filler (C).

[0103] <Average primary particle diameter> The average primary particle diameter of the inorganic filler (C) was measured using a 0.2% aqueous solution of sodium hexametaphosphate as a dispersion medium with a laser diffraction particle size distribution analyzer (product name "SALD (registered trademark)-7500 nano", manufactured by Shimadzu Corporation). The average primary particle diameter is the D50 value based on volume.

[0104] [Thermoplastic resin (A) (component (A))] Polycarbonate (abbreviated as "PC"): product name "Iupilon (registered trademark) S2000" (manufactured by Mitsubishi Engineering Plastics Corporation, refractive index 1.58) Acrylic (abbreviated as "PMMA"): product name "Parapet (registered trademark) HR-S" (manufactured by Kuraray Co., Ltd., refractive index 1.49) Polysulfone (abbreviated as "PSU"): product name "Udel (registered trademark) P-1700" (manufactured by Solvay Specialty Polymers, refractive index 1.63)

[0105] [Thermoplastic resin (B) (component (B))] Polyether ether ketone (abbreviated as "PEEK"): product name "VESTAKEEP (registered trademark)-J ZV0401" (manufactured by POLYPLASTICS EVONIK, refractive index 1.70) Polyether ketone ketone (abbreviated as "PEKK"): product name "Kepstan (registered trademark)" (manufactured by Arkema, refractive index 1.70)

[0106] [Thermoplastic resins other than component (A) and component (B)] Acrylonitrile butadiene styrene resin (abbreviated as "ABS"): product name "Toyolac (registered trademark) 920 555U" (manufactured by Toray Industries, Inc., refractive index 1.55) High impact polystyrene (abbreviated as "HIPS"): product name "DicStyrene (registered trademark) HIPS GH-9600-2" (manufactured by DIC Corporation, refractive index 1.59) High density polyethylene (abbreviated as "HDPE"): product name "Novatec (registered trademark) HD ​​HJ560" (manufactured by Japan Polyethylene Co., Ltd., refractive index 1.54)

[0107] [Inorganic Filler (C) (Component (C))] Inorganic filler (C)-1 (abbreviation "(C)-1"): lanthanum glass GM31684 (manufactured by SCHOTT, average primary particle size 0.4 μm, refractive index 1.58, crushed, silane surface treatment) Inorganic filler (C)-2 (abbreviation "(C)-2"): lanthanum glass GM31684 (manufactured by SCHOTT, average primary particle size 2.0 μm, refractive index 1.58, crushed, silane surface treatment) Inorganic filler (C)-3 (abbreviation "(C)-3"): fluoroaluminosilicate glass G018-090 (manufactured by SCHOTT, average primary particle size 0.4 μm, refractive index 1.50, crushed, silane surface treatment) Inorganic filler (C)-4 (abbreviation "(C)-4"): Lanthanum glass G018-161 (manufactured by SCHOTT, average primary particle size 0.4 μm, refractive index 1.83, crushed, silane surface treatment) Inorganic filler (C)-5 (abbreviation "(C)-5"): Barium titanate (manufactured by Toda Kogyo Co., Ltd., average primary particle size 0.15 μm, refractive index 2.4, crushed, silane surface treatment)

[0108] [Antioxidant] PEP-36: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (manufactured by ADEKA Corporation, trade name "ADEKA STAB (registered trademark) PEP-36")

[0109] The thermoplastic resin compositions used in the examples and comparative examples were produced by the following method. The compositions of the produced resin compositions are shown in Tables 1 and 2 below.

[0110] [Production Example 1] As shown in Table 1 below, 80 parts by mass of PC as the thermoplastic resin (A), 20 parts by mass of inorganic filler (C)-1 as the inorganic filler (C), 0.1 parts by mass of PEP-36 as an antioxidant, and trace amounts of titanium oxide, iron oxide black, iron oxide red (red iron oxide), and iron oxide yellow as the pigment (D) were premixed, and then all of the premixed mixture was fed into a twin-screw extruder (manufactured by Technovel Co., Ltd., model name "KZW15-45MG", shaft diameter φ15 mm, L / D = 45) and melt-kneaded at a kneading temperature of 300°C (the highest temperature among the extruder set temperatures from the raw material inlet to the discharge outlet) and a rotation speed of 180 rpm. The mixture was extruded into strands and cut with a strand cutter to produce pellets of Resin Composition 1. The blend amount of the pigment (D) was adjusted to achieve the color tone and transparency shown in Table 1 below. The color tone and transparency shown in Table 1 below were measured by the methods shown below.

[0111] [Production Examples 2 to 14] Pellets of resin compositions 2 to 14 were produced in the same manner as in Production Example 1, except that thermoplastic resin (A), thermoplastic resin (B), and inorganic filler (C), and trace amounts of titanium oxide (JP), iron oxide black, iron oxide red (red iron oxide), and iron oxide yellow were used as pigment (D) in the proportions (parts by mass) shown in Tables 1 and 2 below, respectively, and that the resin compositions were melt-kneaded at the kneading temperatures shown in Tables 1 and 2 below. The amount of pigment (D) in each resin composition was adjusted to an amount that would result in the color tone and transparency shown in Tables 1 and 2 below. The color tone and transparency of the resulting resin compositions 2 to 14 were each evaluated by the methods shown below, similar to Production Example 1.

[0112] <Evaluation of Color Tone and Transparency of Resin Composition> Pellets of each resin composition obtained in each production example were used, and each was subjected to an injection molding process using an injection molding machine ("IS-55EPN" manufactured by Toshiba Machine Co., Ltd., mold clamping pressure 55×10 ３kg) was used and injection molded under the melt temperature (the highest set temperature among the set temperatures at each location of the injection molding machine) and mold temperature conditions shown in Tables 1 and 2 below to produce circular disks with a thickness of 3.0 mm and a diameter of 10 cm. From each of the obtained disks, a diamond cutter was used to cut out test pieces with a thickness of 1.2 mm x 10 mm x 10 mm, and both surfaces of the test pieces were polished under dry conditions with #1500 abrasive paper, #2000 abrasive paper, and #3000 abrasive paper in that order. For the test pieces obtained for the transparency of the polished surface, the color tone and transparency ΔL of the polished surface were measured using a spectrophotometer ("CM-3610d" manufactured by Konica Minolta Japan, Inc., in accordance with JIS Z 8722:2009, condition c, D65 light source). The transparency ΔL is defined by the following formula: ΔL = L ＊ W-L ＊ b L ＊ w is the L measured on a white background ＊ a ＊ b ＊ Lightness index L in the color system ＊ represents L ＊ b is the L measured on a black background ＊ a ＊ b ＊ Lightness index L in the color system ＊ Represents.

[0113]

[0114]

[0115] [Example 1] (Injection molding) Using the pellets of Resin Composition 1 obtained in Production Example 1, an injection molding machine ("IS-55EPN" manufactured by Toshiba Machine Co., Ltd., mold clamping pressure 55 × 10 ３Using a 1000 lb (1 kg) resin composition, the resin composition was injection molded at a melt temperature of 300°C and a mold temperature of 80°C to produce a 3.0 mm thick x 10 cm diameter disc. Also, using the pellets of resin composition 7 obtained in Production Example 7, the resin composition was injection molded at a melt temperature of 380°C and a mold temperature of 100°C to produce a 3.0 mm thick x 10 cm diameter disc. (Press Molding) Two discs of the obtained resin composition 1 and three discs of resin composition 7 were stacked in this order in a 15 mm thick x 10 cm diameter mold, and the discs were fused together using a press molding machine (Iwaki Kogyo Co., Ltd., "37 ton heating and cooling press molding machine") at a press temperature of 270°C under conditions of 0.5 MPa for 5 minutes to produce a 15 mm thick x 10 cm diameter disc-shaped laminated disc (a mill blank composed of a laminate). The physical properties of this mill blank were measured using the methods described below. The results are shown in Table 3 below. Regarding the layer structure described in Table 3 below, the layer structure of Example 1 indicates a mill blank composed of a laminate in which, from top to bottom, an upper layer (U) and a lower layer (L) are directly laminated. As mentioned above, when layers made of the same resin composition are directly laminated, the laminated portion is considered to be a single layer. Therefore, since layer (U) of Example 1 is formed by directly laminating and press-molding two 3 mm thick disks of resin composition 1, it is considered to be a single 6 mm thick layer (U). The same applies to layer (L), which is formed by directly laminating and press-molding three disks of resin composition 7.

[0116] [Examples 2 to 9 and Comparative Examples 1 to 3] When manufacturing a disk of each resin composition by injection molding, each disk was manufactured at the injection temperature shown in Tables 1 and 2 below for the corresponding resin composition No., and laminated disks (mill blanks composed of laminates) were manufactured in the same manner as in Example 1, except that the layer structure and press conditions during press molding were changed to those shown in Tables 3 and 4 below. Regarding the description of the layer structure in Table 3 below, for example, the layer structure of Examples 2 and 3 represents a mill blank composed of a laminate in which, from top to bottom, an upper layer (U) and a lower layer (L) are directly laminated. The layer structure of Examples 4 to 8 represents a mill blank composed of a laminate in which, from top to bottom, an upper layer (U), an intermediate layer (M), and a lower layer (L) are directly laminated in this order. Similarly, the layer structure of Example 9 represents a mill blank composed of a laminate in which, from top to bottom, an upper layer (U), an intermediate layer (M)-1, an intermediate layer (M)-2, and a lower layer (L) are directly laminated in this order. Furthermore, as mentioned above, when layers made of the same resin composition are directly laminated, the laminated portion is considered to be a single layer. For example, layer (U) in Example 2 is formed by directly laminating two 3 mm thick discs of resin composition 2 and press-molding them, and is therefore considered to be a single 6 mm thick layer (U). The same applies to layer (L), which is formed by directly laminating three discs of resin composition 7 and press-molding them. The same applies to the other Examples. The same applies to the layer configurations in Table 4. The physical properties of each of the obtained laminated discs were measured using the methods described below. The results are shown in Tables 3 and 4 below.

[0117] Reference Example 1: A disk (3.0 mm thick x 10 cm diameter) of resin composition 7 was produced in the same manner as in Example 1. Five of these disks were then directly stacked and press-molded in the same manner as in Example 1, except for the changes in the press conditions shown in Table 4 below, to produce a mill blank. As mentioned above, when layers made of the same resin composition are directly stacked, the laminated portion is considered a single layer. Therefore, the mill blank of Reference Example 1 was formed by directly stacking five disks made of resin composition 7, each 3 mm thick, and press-molding them, and therefore is considered a single layer with a thickness of 15 mm. The physical properties of the obtained mill blank, other than color tone, were measured using the methods described below. The results are shown in Table 4 below. In Table 4, "NA" indicates that the configuration of Reference Example 1 could not be evaluated, and therefore, was not evaluated.

[0118] <Thickness of Each Layer> The thickness of each layer of each mill blank obtained in each Example, Comparative Example, and Reference Example was measured using the following method. The obtained mill blank was cut using a diamond cutter in a direction perpendicular to a plane parallel to the surface of layer (U) so that the cross section of each layer could be confirmed. Then, samples were cut out parallel to the cut surface to a thickness of 1 mm so that the cross section of each layer could be confirmed. Both cut surfaces of the cut sample (the observation surface and the surface opposite thereto) were polished under dry conditions using #1500 abrasive paper, #2000 abrasive paper, and #3000 abrasive paper in that order to prepare measurement samples with transparency on the polished surfaces. A light source was installed as needed, and the sample was held up to the light source. The thickness of each layer was measured using vernier calipers while observing the sample from the surface opposite the light source. The results are shown in Tables 3 and 4 below. Furthermore, if the boundary lines between the layers are still unclear even after the above-mentioned method, the boundary lines between the layers can also be determined by measuring the color of the sample while sliding it using the above-mentioned spectrophotometer ("CM-3610d" manufactured by Konica Minolta Japan Inc., compliant with JIS Z 8722:2009, condition c, D65 light source) and checking the location where the transparency changes.

[0119] <Transparency ΔL of each layer, transparency difference ΔΔL ＊ , transparency difference ΔΔL ＊ ＴThe transparency ΔL value of the resin composition forming each layer was taken as the transparency ΔL value of each layer formed from the resin composition. In addition, the transparency difference ΔΔL of each layer shown in Tables 3 and 4 below ＊ was calculated by subtracting the ΔL value of the layer with lower transparency from the ΔL value of the layer with higher transparency among the adjacent layers. Similarly, the transparency difference ΔΔL between the layer (U) and the layer (L) shown in Tables 3 and 4 below ＊ Ｔ was calculated by subtracting the ΔL value of the lower layer (L) having low transparency from the ΔL value of the upper layer (U) having high transparency.

[0120] <Flexural Strength and Flexural Modulus> Test pieces measuring 1.2 mm thick x 4.0 mm wide x 14.0 mm long were cut from each mill blank obtained in each Example, Comparative Example, and Reference Example using a diamond cutter in the vertical direction (i.e., so that the thickness direction of each mill blank was the length direction of the test piece). The obtained test pieces were evaluated by performing a flexural strength test in accordance with JADMAS 245:2017, "Resin Materials for Dental Machining of CAD / CAM Crowns." That is, a flexural test was performed at a crosshead speed of 1 mm / min using a universal testing machine (Shimadzu Corporation, "Autograph (registered trademark) AG-100kNI") (n = 10).

[0121] <Color Tone, Transparency, and Ease of Polishing> (Manufacturing of Dental Prosthesis by Cutting) The mill blanks obtained in each Example and Comparative Example were machined into the shape of a crown for the first right front tooth of the maxilla using a cutting machine "DWX-50" (manufactured by Kuraray Noritake Dental Co., Ltd.) to manufacture a dental prosthesis (hereinafter also simply referred to as "crown"). At this time, the layer (U) was machined to be on the incisal side of the crown, and the layer (L) was machined to be on the cervical side.

[0122] (Color Tone Evaluation of Dental Prosthesis) The crown obtained by the cutting process was polished in the same manner as in the method for evaluating polishability described below. The polished crown was attached to an abutment tooth made of a dental abutment buildup material ("Clearfil (registered trademark) DC Core Automix (registered trademark) ONE", dentin color, manufactured by Kuraray Noritake Dental Co., Ltd.). Five people visually evaluated the difference in the boundary between each layer of the crown. If five out of five people considered the color tone of the boundary to be a smooth transition, it was rated as "A", if four out of five people considered it to be a smooth transition, it was rated as "B", and if three out of five people or less considered it to be unusable, it was rated as "F".

[0123] (Transparency Evaluation of Dental Prosthesis) The crown obtained by the cutting process was polished in the same manner as in the polishability evaluation described below. The polished crown was attached to an abutment tooth made of a dental abutment buildup material ("Clearfil (registered trademark) DC Core Automix (registered trademark) ONE", dentin color, manufactured by Kuraray Noritake Dental Co., Ltd.). The transparency of the incisal edge (upper layer) of the crown was visually evaluated by five people. If five out of five people rated it as transparent and similar to natural teeth, it was given an "A", if four out of five people rated it as transparent, it was given a "B", and if three out of five people or less rated it as unusable, it was given an "F".

[0124] (Easy Polishing of Dental Prosthesis) The crown obtained by the cutting process was polished from the center to the incisal edge using a dental unit ("Portacare 21", manufactured by Morita Seisakusho Co., Ltd.) under running water with a dental rubber abrasive ("Compomaster (registered trademark) CA No. 13S", manufactured by Shofu Co., Ltd.). When five people polished this test piece, if five out of five people evaluated that it could be polished smoothly without any resistance, it was rated as "A", if four out of five people evaluated that it could be polished smoothly, it was rated as "B", and if three out of five people or less evaluated that it could not be used, it was rated as "F".

[0125]

[0126]

[0127] As shown in Tables 3 and 4, the dental mill blanks of Examples 1 to 9 were confirmed to have superior strength (flexural strength and flexural modulus) compared to the dental mill blanks of Comparative Examples 1 to 3. The dental prostheses obtained from the dental mill blanks of Examples 1 to 9 were superior in color tone and transparency, with transitional color tone and transparency at the boundary, resulting in an appearance closer to that of natural teeth. The appearance of the dental prostheses obtained from the dental mill blanks of Examples 1 to 9 was also superior to that of the dental prosthesis obtained from the dental mill blank of Comparative Example 3. Furthermore, it was confirmed that the dental prostheses obtained from the dental mill blanks of Examples 1 to 9 not only had good color tone and transparency and excellent strength, but also had superior polishability compared to the dental prostheses obtained from the dental mill blanks of Comparative Examples 1 to 3 and Reference Example 1.

[0128] By using the dental mill blank according to one aspect of the present invention, it is possible to provide a dental prosthesis that has a color and transparency similar to that of natural teeth while also exhibiting excellent strength. Furthermore, the resulting dental prosthesis also exhibits excellent polishability. Furthermore, the dental mill blank is suitable for use as a mill blank for CAD / CAM. That is, it is suitable for use in producing dental prostheses with high aesthetic appeal by cutting using a CAD / CAM system.

Claims

1. A dental mill blank composed of a laminate, wherein the laminate comprises at least two layers: a layer (U) containing a thermoplastic resin (A) and a layer (L) containing a thermoplastic resin (B), wherein the thermoplastic resin (A) is at least one selected from the group consisting of acrylic, polycarbonate, polyester, polyurethane, polyamide, polyarylate, polysulfone, polyethersulfone, and polycycloolefin, and the thermoplastic resin (B) is at least one selected from the group consisting of polyetherketone, polyetheretherketone, polyetherketoneketone, polyacetal, polyphenylene ether, polyphenylene sulfide, and polyimide.

2. A dental mill blank according to claim 1, wherein the laminate comprises at least one intermediate layer (M) between the layer (U) and the layer (L), and the intermediate layer (M) comprises at least one selected from the thermoplastic resin (A) and the thermoplastic resin (B).

3. A dental mill blank according to claim 1, wherein at least one layer selected from the layer (U) and the layer (L) contains an inorganic filler (C).

4. A dental mill blank according to claim 2, wherein at least one layer selected from the group consisting of at least one of the layers (M), the layer (U), and the layer (L) contains an inorganic filler (C).

5. A dental mill blank according to claim 1, wherein at least one layer selected from the layer (U) and the layer (L) contains 1 to 60% by mass of inorganic filler (C) relative to 100% by mass of the layer.

6. A dental mill blank according to claim 2, wherein at least one layer selected from the group consisting of at least one of the layers (M), the layer (U), and the layer (L) contains 1 to 60% by mass of an inorganic filler (C) relative to 100% by mass of the layer.

7. A dental mill blank according to any one of claims 3 to 6, wherein the inorganic filler (C) has an average primary particle size of 5.0 μm or less.

8. A dental mill blank according to any one of claims 3 to 6, wherein at least the layer (U) contains the inorganic filler (C), and the refractive index of the inorganic filler (C) contained in the layer (U) is 1.35 or more and less than 1.

65.

9. A dental mill blank according to any one of claims 3 to 6, wherein at least the layer (L) contains the inorganic filler (C), and the refractive index of the inorganic filler (C) contained in the layer (L) is 1.65 or more and less than 2.

00.

10. A dental mill blank according to claim 1 or 2, wherein the thickness of the entire laminate is 4.0 to 26.0 mm.

11. A dental mill blank according to claim 1 or 2, which is for a central incisor, a lateral incisor or a canine.

12. A method for producing a dental mill blank according to claim 1 or 2, comprising a step of heating and melting at least one selected from the thermoplastic resin (A) and the thermoplastic resin (B).

13. The method for producing a dental mill blank according to claim 12, wherein the heating and melting is carried out using a twin-screw extruder, and the L / D ratio of the twin-screw extruder is 25 or more.

14. A method for manufacturing a dental mill blank according to claim 1 or 2, comprising a step of molding at least one layer selected from the layer (U) and the layer (L) by injection molding.

15. A method for manufacturing a dental mill blank according to claim 1 or 2, comprising a step of forming the laminate by press-molding a laminate sheet including at least the layer (U) and the layer (L).

16. A method for manufacturing a dental prosthesis, comprising the step of cutting the dental mill blank according to claim 1 or 2.

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