Dental Mill Blanks

Abstract

The present invention provides a dental mill blank that can obtain, through a cutting process, a highly aesthetic dental prosthesis by reproducing a unique high transparency and gray taste in a natural tooth, particularly, a cut end portion, without reducing mechanical strength. The present invention relates to a dental mill blank including a laminate structure having three or more layers including a highest transparent layer, one or more intermediate layers, and a lowest transparent layer, wherein the highest transparent layer is disposed on the outermost layer, and the highest transparent layer satisfies all of conditions (1)-(3). (1) The thickness is 11-19 % with respect to the total thickness of the dental mill blank in the same direction. (2) The transparency ΔL* of a test piece having a thickness of 1.20 ± 0.01 mm according to a L*a*b* color system is 25.0-36.0. (3) The transparency difference ΔΔL* with respect to the adjacent layer is 5.0 or less.

Description

[Technical field]

[0001] The present invention relates to a dental mill blank used when producing a dental crown by a cutting machine based on three-dimensional coordinate data. [Background technology]

[0002] In recent years, there has been an increase in 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 device. In such systems, a block of an appropriate size, such as a rectangular parallelepiped, cylinder, or disk, is supplied, and this is set in a milling machine and milled out to obtain a restoration in the shape of a crown or dentition. Various materials have been proposed for the block, including glass ceramics, zirconia, titanium, acrylic resin, and composite materials containing polymer resin and inorganic filler.

[0003] In dental crown restoration treatment, it is required to obtain an appearance as close as possible to the color tone of natural tissue. In many cases, it is not sufficient to simply cut a block body made of a single component to meet such aesthetic requirements, and cutting blocks made of multiple colors have been proposed (for example, Patent Documents 1 to 5).

[0004] Patent Document 1 describes a resin block consisting of a dentin restorative resin layer and an enamel restorative resin layer. It states that by defining the contrast ratio and light diffusion of the dentin restorative resin layer, it is possible to achieve color reproduction similar to that of natural teeth even in a block with a simple two-layer structure.

[0005] Patent Document 2 describes a dental resin block that is characterized in that, in a dental mill blank composed of a laminate of three or more layers, by specifying the chromaticity difference ΔE* and transparency difference ΔΔL* between the top and bottom layers, and further the chromaticity difference ΔE* and transparency difference ΔΔL* between adjacent layers, it is possible to obtain a dental prosthesis having a color tone and transparency more similar to that of natural teeth.

[0006] Patent Document 3 describes how, in a dental mill blank composed of a laminate of two or more layers, it is possible to obtain a dental mill blank with excellent aesthetics by maintaining a specific relationship between contrast and color tone for each of the constituent layers.

[0007] Patent Document 4 states that even in dental ceramic blanks having a layer structure of four or more layers, it is possible to obtain dental mill blanks with excellent aesthetics by maintaining a specific contrast and color tone relationship for each constituent layer.

[0008] Patent Document 5 describes that in a dental mill blank containing three or more layers, a dental mill blank with excellent aesthetics can be obtained by maintaining a specific relationship between the contrast ratio and color tone of the 30% position layer. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2014-161440 A [Patent Document 2] International Publication No. 2018 / 074605 [Patent Document 3] JP 2017-105764 A [Patent Document 4] JP 2017-185163 A [Patent Document 5] JP 2018-86047 A Summary of the Invention [Problem to be solved by the invention]

[0010] The above-mentioned prior arts all relate to the color tone of mill blank materials used in dental CAD / CAM technology. However, these prior arts are still insufficient in terms of color design, and are unable to reproduce the high transparency and gray color characteristic of natural teeth, especially in the incisal edge, and it has been found that there is room for improvement in terms of aesthetics.

[0011] Therefore, an object of the present invention is to provide a dental mill blank that can be used to obtain highly aesthetic dental prostheses by cutting, reproducing the high transparency and grayish color characteristic of natural teeth, particularly at the incisal edge, without reducing mechanical strength. [Means for solving the problem]

[0012] As a result of extensive research into solving the above problems, the inventors have found that a dental mill blank that solves the above problems can be obtained by keeping the thickness and transparency ΔL* of the most transparent layer arranged on the outermost surface, and further the transparency difference ΔΔL* between the most transparent layer and the layer adjacent to it, within specific ranges. Based on this finding, the inventors conducted further research and completed the present invention.

[0013] That is, the present invention includes the following. [1] A laminated structure having three or more layers including a most transparent layer, one or more intermediate layers, and a least transparent layer; A dental mill blank, wherein the most transparent layer satisfies all of the following conditions (1) to (3): (1) The thickness is 11 to 19% of the overall thickness of the dental mill blank in the same direction. (2) The transparency △L* of a test piece having a thickness of 1.20±0.01 mm is 25.0 to 36.0 according to the L*a*b* color system. (3) The transparency difference △△L* between adjacent layers is 5.0 or less. [2] The dental mill blank according to [1], wherein the transparency difference ΔΔL* of all adjacent layers is 5.0 or less. [3] The dental mill blank according to [1] or [2], wherein the thickness of the minimum transparent layer is 38 to 50% of the total thickness of the dental mill blank in the same direction. [4] The dental mill blank according to any one of [1] to [3], wherein the one or more intermediate layers are adjacent to the most transparent layer. [5] A dental mill blank according to any one of [1] to [4], wherein the thickness of each of the one or more intermediate layers is 8 to 28% of the overall thickness of the dental mill blank in the same direction. [6] The dental mill blank according to any one of [1] to [5], wherein the laminated structure has two or more intermediate layers. [7] A dental mill blank as described in [6], wherein the difference in thickness between adjacent intermediate layers of the two or more intermediate layers is within 5% of the overall thickness of the dental mill blank in the same direction. [8] The dental mill blank according to any one of [1] to [7], wherein the layers constituting the laminated structure all have different transparencies. [9] The dental mill blank according to any one of [1] to [8], wherein the content of the inorganic filler is 40 mass% or more. Effect of the Invention

[0014] The dental mill blank of the present invention makes it possible to obtain highly aesthetic dental prostheses by cutting, which reproduce the high transparency and grayish color characteristic of natural teeth, particularly at the incisal edge, without reducing the mechanical strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The dental mill blank of the present invention has a laminated structure having three or more layers, including a most transparent layer, one or more intermediate layers, and a least transparent layer, It is important that the most transparent layer is disposed as the outermost layer and that the most transparent layer satisfies all of the following conditions (1) to (3). (1) The thickness is 11 to 19% of the overall thickness of the dental mill blank in the same direction. (2) The transparency △L* of a test piece having a thickness of 1.20±0.01 mm is 25.0 to 36.0 according to the L*a*b* color system. (3) The transparency difference △△L* between adjacent layers is 5.0 or less.

[0016] The enamel of natural teeth is translucent, but the refraction of light changes in the incisal region, resulting in a transparent, grayish area with a halo (halo effect). In order to reproduce the halo effect in the incisal region when a dental crown is produced by milling from a dental mill blank, the dental mill blank must have a laminated structure and the part that shows the halo effect, i.e., the most transparent layer, must be disposed in an appropriate position and thickness. In the dental mill blank of the present invention, the most transparent layer is disposed on the outermost layer in terms of the halo effect. The most transparent layer means the layer with the highest transparency ΔL* in the laminated structure. The least transparent layer means the layer with the lowest transparency ΔL* in the laminated structure. The intermediate layer means a layer with a transparency ΔL* lower than that of the most transparent layer and higher than that of the least transparent layer.

[0017] The thickness of the most transparent layer is 11-19% of the total thickness of the dental mill blank in the same direction, preferably 13-17%, and more preferably 14-16%. When the thickness of the most transparent layer is in the above range, suitable transparency and halo effect can be obtained without reducing mechanical strength when combined with other components. As a result, a dental prosthesis can be obtained that can reproduce the high transparency and grayness specific to natural teeth, especially the incisal end, has excellent mechanical strength, and has high aesthetics. The total thickness of the dental mill blank in the same direction means the stacking direction (thickness direction) of the most transparent layer, one or more intermediate layers, and the least transparent layer. If the thickness of the most transparent layer is less than 11% of the total thickness of the dental mill blank, the thickness of the most transparent layer contained in the dental crown obtained by milling is insufficient, and a suitable halo effect cannot be obtained. If the thickness of the most transparent layer is more than 19%, the most transparent layer is contained in too much of the obtained dental crown, and a dental prosthesis with excellent aesthetics cannot be obtained.

[0018] Each layer of the dental mill blank of the present invention preferably contains an inorganic filler. In addition, in dental prostheses, it is common to adjust the color tone using an inorganic pigment. In order to increase the transparency of the most transparent layer, the content of the inorganic pigment relative to the content of the inorganic filler may be reduced, but since the inorganic pigment does not chemically bond with the polymerizable monomer, the mechanical strength of each layer is different when fillers with different inorganic pigment contents are laminated. The greater the transparency difference (difference in pigment content) between adjacent laminated layers, the more disadvantageous the mechanical strength in the laminate interface direction becomes. In contrast, the dental mill blank of the present invention has an appropriate configuration in which the most transparent layer has high transparency and also maintains mechanical strength. Details will be described below.

[0019] In the dental mill blank of the present invention, the transparency ΔL* of a test piece having a thickness of 1.20±0.01 mm according to the L*a*b* color system for the most transparent layer disposed on the outermost layer is 25.0 to 36.0, preferably 28.0 to 35.0, and more preferably 30.0 to 33.0. By being in the above range, when combined with other configurations such as the thickness of the most transparent layer, suitable transparency and halo effect can be obtained without reducing mechanical strength. As a result, a dental prosthesis is obtained that reproduces the high transparency and gray color characteristic of natural teeth, especially the incisal end, has excellent mechanical strength, and has high aesthetics. The test piece is a test piece of a hardened product consisting of only the most transparent layer. If the transparency ΔL* is less than 25.0, the high transparency characteristic of natural teeth, especially the incisal end, cannot be reproduced, and if it exceeds 36.0, light reflection cannot be obtained and the gray color cannot be reproduced. The transparency ΔL* of an arbitrary layer (x layer) is calculated by measuring the chromaticity of a white background (standard white plate) and a black background (standard black plate) using a spectrophotometer, and calculating the L* value (JIS Z 8781-4:2013 Colorimetry - Part 4: CIE 1976 L*a*b* color space) using the following formula. ΔL*x=Lw*x-Lb*x (In the formula, Lw*x represents the lightness value of the xth layer on a white background (standard white board), and Lb*x represents the lightness value of the xth layer on a black background (standard black board).) The transparency ΔL* can be measured by the method described in the Examples below.

[0020] The transparency difference ΔΔL* between the most transparent layer and the adjacent layer (preferably, the intermediate layer) is 5.0 or less, preferably 4.0 or less, and more preferably 3.0 or less. By being in the above range, when combined with other configurations such as the thickness of the most transparent layer, suitable transparency and gradation can be obtained without reducing mechanical strength. As a result, a dental prosthesis having excellent mechanical strength and high aesthetics can be obtained. When ΔΔL* exceeds 5.0, the interface with the adjacent layer is clearly visible, so that a natural gradation is not obtained. In order to reduce the transparency difference ΔΔL* between the most transparent layer and the adjacent layer, for example, the number of layers, particularly the number of intermediate layers between the most transparent layer and the least transparent layer, may be increased while taking into account the thickness of each layer. The transparency difference ΔΔL* is the transparency difference ΔΔL* between any layer (x layer) and any other layer (y layer) (y-x) is measured using a spectrophotometer and calculated using the following formula based on the L*, a*, and b* values. ΔΔL* (y-x) =(Lw*y-Lb*y)-(Lw*x-Lb*x) (In the formula, Lw*x is the value of the x layer, Lw*y is the value of the y layer, and these represent values ​​on a white background (standard white board), and Lb*x is the value of the x layer, Lb*y is the value of the y layer, and these represent values ​​on a black background (standard black board).) The transparency difference ΔΔL* can be measured by the method described in the Examples below.

[0021] The inorganic filler used in the intermediate layer (hereinafter sometimes simply referred to as "intermediate layer filler") can be prepared by mixing the filler used in the most transparent layer (hereinafter sometimes referred to as "most transparent layer filler") and the filler used in the least transparent layer (hereinafter sometimes referred to as "least transparent layer filler") while adjusting the ratio according to the number of intermediate layers. Specifically, when there is one intermediate layer (total number of layers: 3 layers), the intermediate layer filler is prepared by mixing the most transparent layer filler and the least transparent layer filler in a 1:1 ratio, and when there are two intermediate layers (total number of layers: 4 layers), the intermediate layer filler is prepared by mixing the most transparent layer filler and the least transparent layer filler in a 2:1 ratio and a 1:2 ratio, respectively. When the number of intermediate layers is three (total number of layers: five), the fillers for the second to fourth intermediate layers may be a mixture of the filler for the most transparent layer and the filler for the least transparent layer in a mass ratio of 3:1, 1:1, or 1:3. When the number of intermediate layers is four (total number of layers: six), the fillers for the second to fifth intermediate layers may be a mixture of the filler for the most transparent layer and the filler for the least transparent layer in a mass ratio of 4:1, 3:2, 2:3, or 1:4. As long as the effects of the present invention can be obtained, the laminated structure of the dental mill blank of the present invention also includes a structure having, in addition to the three or more layers, a layer adjacent to the least transparent layer and having a transparency ΔL* substantially the same as that of the least transparent layer (for example, a transparency difference ΔΔL* from the transparency ΔL* of the least transparent layer is less than ±1.5, etc.).

[0022] As described above, the dental mill blank of the present invention can be manufactured, for example, by the following manufacturing method. For example, the inorganic filler containing the inorganic pigment is laminated in a mold so as to have the above-mentioned mass ratio, and the inorganic filler containing the inorganic pigment is press-molded (dry molded) in the mold to obtain a molded body, and then the molded body is brought into contact with a polymerizable monomer containing a polymerization initiator, and then polymerized and hardened to obtain the dental mill blank. The press molding may be a one-time press. Alternatively, as another manufacturing method, a paste-like material containing inorganic filler, polymerizable monomer, polymerization initiator, and inorganic pigment as main components is prepared, and the paste-like material is polymerized and hardened in a mold of a desired shape. Below, each of the components that can be used in the dental mill blank of the present invention will be described.

[0023] The content of the inorganic filler used in the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, and particularly preferably 60% by mass or more, based on the total mass of the dental mill blank from the viewpoint of the strength of the dental mill blank obtained. The content of the inorganic filler can be measured by a known method, for example, the method described in the Examples below. The upper limit of the content of the inorganic filler is not particularly limited, but may be 98% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less.

[0024] The inorganic filler is not limited in type as long as the most transparent layer satisfies all of the conditions (1) to (3) and the effects of the present invention are achieved, and known inorganic particles can be used. Specific examples of inorganic particles include various glasses (mainly composed of silicon dioxide (quartz, quartz glass, silica gel, etc.) or silicon, containing boron and / or aluminum together with various heavy metals), diatomaceous earth, kaolin, clay minerals (montmorillonite, etc.), activated clay, synthetic zeolite, mica, silica, calcium fluoride, ytterbium fluoride, calcium phosphate, barium sulfate, alumina, various ceramics such as zirconium dioxide (zirconia), titanium oxide, hydroxyapatite, and other conventionally known particles. Preferred inorganic particles include various glasses mainly composed of silicon dioxide or silicon, containing boron and / or aluminum together with various heavy metals, various ceramics such as alumina and zirconia, and silica. The inorganic filler may include organic-inorganic composite particles (organic-inorganic composite filler) obtained by adding a polymerizable monomer to the inorganic particles in advance to form a paste, polymerizing and curing the mixture, and pulverizing the mixture. As the inorganic filler, the inorganic particles or the organic-inorganic composite particles may be used alone or in combination of two or more kinds.

[0025] The particle size of the inorganic filler is not limited as long as the effect of the present invention is obtained, but from the viewpoint of smoothness durability due to toothbrush wear, a microfiller having an average particle size of 2 μm or less, or a submicron filler having an average particle size of less than 1 μm is preferable, and a nanofiller having an average particle size of 30 to 700 nm is more preferable. The smaller the average particle size, the smaller the unevenness caused by toothbrush wear, and the smoothness (aesthetics) of the tooth surface is maintained. The average particle size (average primary particle size) can be determined by a laser diffraction scattering method or by observing the particles with an electron microscope. Specifically, the laser diffraction scattering method is used to measure the particle size of particles of 0.1 μm or more, and electron microscope observation is convenient for measuring the particle size of ultrafine particles of less than 0.1 μm. 0.1 μm is a value measured by the laser diffraction scattering method. For example, the laser diffraction scattering method can be measured by using a 0.2% sodium hexametaphosphate aqueous solution as a dispersion medium and using a laser diffraction type particle size distribution measuring device (SALD-2300, manufactured by Shimadzu Corporation) on a volume basis. For electron microscope observation, a scanning electron microscope (SU3800, S-4000, etc., manufactured by Hitachi High-Technologies Corporation) can be used. Electron microscope observation can be performed by taking an electron microscope photograph of the particles and measuring the particle size of the particles (200 or more) observed within a unit field of view of the photograph using image analysis particle size distribution measurement software (Mac-View (Mountec Co., Ltd.)). In this case, the particle size is calculated as the arithmetic mean value of the longest and shortest lengths of the particles, and the average primary particle size is calculated from the number of particles and their particle size.

[0026] In addition, inorganic particles that have been surface-treated in advance can be used as the inorganic filler. By subjecting inorganic particles to a surface treatment with a surface treatment agent, the molding density during press molding can be improved, the mechanical strength of the mill blank can be improved, and the compatibility with the polymerizable monomer can be improved, making it easier for the composition of the inorganic filler and the polymerizable monomer to become a paste. As the surface treatment agent, a known surface treatment agent can be used, and an organometallic compound such as an organosilicon compound, an organotitanium compound, an organozirconium compound, or an organoaluminum compound, and an acidic group-containing organic compound having at least one acidic group such as a phosphoric acid group, a pyrophosphoric acid group, a thiophosphoric acid group, a phosphonic acid group, a sulfonic acid group, or a carboxylic acid group can be used. The surface treatment agent may be used alone or in combination of two or more types. When two or more types of surface treatment agents are used, the surface treatment agent layer may be a mixture of two or more types of surface treatment agents, or the surface treatment agent layer may be a multi-layer structure in which a plurality of surface treatment agent layers are laminated. In addition, a known method can be used as the surface treatment method without any particular limitation.

[0027] Specific examples of the organosilicon compound include methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, isobutyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, 3,3,3-trifluoropropyltrimethoxysilane, Methyl-3,3,3-trifluoropropyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, N-(β-aminoethyl)γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl) N-(β-aminoethyl)γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, trimethylsilanol, methyltrichlorosilane, methyldichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane Examples of such silanes include vinyltrichlorosilane, trimethylbromosilane, diethylsilane, vinyltriacetoxysilane, ω-(meth)acryloxyalkyltrimethoxysilane [number of carbon atoms between the (meth)acryloxy group and the silicon atom: 3 to 12, e.g., γ-methacryloxypropyltrimethoxysilane, etc.], and ω-(meth)acryloxyalkyltriethoxysilane [number of carbon atoms between the (meth)acryloxy group and the silicon atom: 3 to 12, e.g., γ-methacryloxypropyltriethoxysilane, etc.]. In the present invention, the term "(meth)acryloxy" is used to include both methacryloxy and acryloxy.

[0028] The inorganic filler of the present invention preferably contains an inorganic pigment. As the inorganic pigment, any known pigment used in dental prostheses may be used without any restrictions as long as the effect of the present invention is achieved. Examples of such 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; carbon such as carbon black and graphite. These pigments may be used alone or in combination of two or more, and are appropriately selected according to the desired color tone of the dental mill blank. Among these pigments, titanium oxide, red iron oxide, iron oxide black, and iron oxide yellow, which are inorganic pigments excellent in heat resistance or light resistance, are particularly preferred for the dental mill blank of the present invention.

[0029] When the inorganic filler contains the inorganic pigment, the inorganic filler and the particulate inorganic pigment can be mixed and dispersed uniformly before use. As a method for uniformly mixing and dispersing the inorganic filler and the inorganic pigment, any known powder mixing and dispersing method can be used without any restrictions, and either a dry method or a wet method can be used. On the other hand, in order to mix and disperse each particle more uniformly, a method in which the inorganic filler and the inorganic pigment are dispersed in the presence of a solvent, and then the solvent is removed or distilled off is preferred. Dispersion can be performed by adopting a method known in the field. For example, a dispersing machine such as a sand mill, a bead mill, an attritor, a colloid mill, a ball mill, an ultrasonic crusher, a homomixer, a dissolver, or a homogenizer can be used. The dispersion conditions vary depending on the particle size and amount of the inorganic filler or inorganic pigment, the type and amount of the solvent, or the type of dispersing machine, but the dispersion conditions such as the dispersion time, the stirring tool, and the rotation speed can be appropriately selected depending on the dispersion state of the particles. As the solvent used for wet dispersion, water and / or a solvent compatible with water is preferred. Examples of the solvent include alcohols (e.g., ethanol, methanol, isopropanol), ethers, ketones (e.g., acetone, methyl ethyl ketone), etc. As a method for distilling off the solvent, either reduced pressure distillation using a rotary evaporator or a drying method using a spray dryer can be selected, but from the viewpoint of mass production, a drying method using a spray dryer is preferred.

[0030] The polymerizable monomer will be described below. As the polymerizable monomer of the present invention, known polymerizable monomers used in dental composite resins and the like can be used without any restrictions, but generally, radical polymerizable monomers are preferably used. Specific examples of radical polymerizable monomers include esters such as α-cyanoacrylic acid, (meth)acrylic acid, α-halogenated acrylic acid, crotonic acid, cinnamic acid, sorbic acid, maleic acid, itaconic acid, (meth)acrylamide, (meth)acrylamide derivatives, vinyl esters, vinyl ethers, mono-N-vinyl derivatives, and styrene derivatives. Among these, (meth)acrylic acid esters and (meth)acrylamide derivatives are preferred, and (meth)acrylic acid esters are more preferred. In the present invention, the term "(meth)acrylic" is used to include both methacrylic and acrylic. Examples of (meth)acrylate-based polymerizable monomers and (meth)acrylamide derivative-based polymerizable monomers are shown below.

[0031] (I) Monofunctional (meth)acrylate and (meth)acrylamide derivatives Methyl (meth)acrylate, isobutyl (meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, 2-(N,N-dimethylamino)ethyl (meth)acrylate, 2,3-dibromopropyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerin mono(meth)acrylate, erythritol mono Examples of such compounds include (meth)acrylate, N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N,N-bis(2-hydroxyethyl) (meth)acrylamide, (meth)acryloyloxydodecylpyridinium bromide, (meth)acryloyloxydodecylpyridinium chloride, (meth)acryloyloxyhexadecylpyridinium chloride, (meth)acryloyloxydecyl ammonium chloride, and 10-mercaptodecyl (meth)acrylate.

[0032] (II) Difunctional (meth)acrylate Ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 2,2-bis[4-[3-acryloyloxy-2-hydroxypropoxy]phenyl]propane, 2,2-bis[4-[3-methacryloyloxy-2-hydroxypropoxy]phenyl]propane (commonly known as "Bis-GMA") , 2,2-bis[4-(meth)acryloyloxyethoxyphenyl]propane, 2,2-bis[4-(meth)acryloyloxypolyethoxyphenyl]propane, 1,2-bis[3-(meth)acryloyloxy-2-hydroxypropoxy]ethane, pentaerythritol di(meth)acrylate, [2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)]dimethacrylate (commonly known as "UDMA"), 2,2,3,3,4,4-hexafluoro-1,5-pentyl di(meth)acrylate, and the like.

[0033] (III) Tri- or higher functional (meth)acrylate Examples of the acrylates include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, N,N'-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxaheptane.

[0034] In addition to these (meth)acrylic acid ester-based and (meth)acrylamide derivative-based polymerizable monomers, oxirane compounds and oxetane compounds capable of cationic polymerization are also preferably used. The above-mentioned polymerizable monomers may be used alone or in combination of two or more. The polymerizable monomers used in the present invention are preferably liquid, but are not necessarily liquid at room temperature. Furthermore, even if the polymerizable monomer is solid, it can be mixed and dissolved with other liquid polymerizable monomers and used. The preferred viscosity range (25°C) of the polymerizable monomer is 10 Pa·s or less, more preferably 5 Pa·s or less, and even more preferably 2 Pa·s or less. However, when two or more polymerizable monomers are mixed and dissolved or further diluted with a solvent, the viscosity of the above-mentioned polymerizable monomers does not need to be in the above viscosity range for each polymerizable monomer, and it is preferable that the viscosity range is in the state of the composition to be mixed and dissolved and used.

[0035] Next, the polymerization initiator used for obtaining a polymer by polymerizing and curing the polymerizable monomer will be described. The polymerization initiator can be selected from polymerization initiators used in general industry, and among them, polymerization initiators used for dental purposes are preferably used, including thermal polymerization initiators, photopolymerization initiators, and chemical polymerization initiators. The polymerization initiator may be used alone or in combination of two or more kinds.

[0036] Examples of the thermal polymerization initiator include organic peroxides and azo compounds. Examples of the organic peroxides include ketone peroxides, hydroperoxides, diacyl peroxides, dialkyl peroxides, peroxyketals, peroxyesters, and peroxydicarbonates. Examples of the ketone peroxides include methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, methylcyclohexanone peroxide, and cyclohexanone peroxide. Examples of the hydroperoxides include 2,5-dimethylhexane-2,5-dihydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, and 1,1,3,3-tetramethylbutyl hydroperoxide.

[0037] Examples of the diacyl peroxide include acetyl peroxide, isobutyryl peroxide, benzoyl peroxide, decanoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, 2,4-dichlorobenzoyl peroxide, and lauroyl peroxide.

[0038] Examples of the dialkyl peroxide include di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,3-bis(t-butylperoxyisopropyl)benzene, and 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne. Examples of the peroxy ketal include 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)octane, and 4,4-bis(t-butylperoxy)valeric acid-n-butyl ester.

[0039] Examples of the peroxy ester include α-cumyl peroxy neodecanoate, t-butyl peroxy neodecanoate, t-butyl peroxy pivalate, 2,2,4-trimethylpentyl peroxy-2-ethylhexanoate, t-amyl peroxy-2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, di-t-butyl peroxy isophthalate, di-t-butyl peroxy hexahydroterephthalate, t-butyl peroxy-3,3,5-trimethylhexanoate, t-butyl peroxy acetate, t-butyl peroxy benzoate, and t-butyl peroxy maleic acid.

[0040] Examples of the peroxydicarbonate include di-3-methoxyperoxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, bis(4-t-butylcyclohexyl)peroxydicarbonate, diisopropylperoxydicarbonate, di-n-propylperoxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate, and diallylperoxydicarbonate.

[0041] Among these organic peroxides, diacyl peroxides are preferably used from the viewpoint of the overall balance of safety, storage stability, and radical generating ability, and among them, benzoyl peroxide is more preferably used.

[0042] Examples of the azo compound include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 4,4'-azobis(4-cyanovaleric acid), 1,1'-azobis(cyclohexane-1-carbonitrile), dimethyl-2,2'-azobis(isobutyrate), and 2,2'-azobis(2-amidinopropane) dihydrochloride.

[0043] Examples of the photopolymerization initiator include (bis)acylphosphine oxides, α-diketones, and coumarins.

[0044] Among the (bis)acylphosphine oxides, examples of the acylphosphine oxides include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide, 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide, benzoyldi(2,6-dimethylphenyl)phosphonate, and salts thereof. Examples of the bisacylphosphine oxides include bis(2,6-dichlorobenzoyl)phenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, bis(2,6-dimethoxybenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,5,6-trimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, and salts thereof. Among these (bis)acylphosphine oxides, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and 2,4,6-trimethylbenzoylphenylphosphine oxide sodium salt are preferred.

[0045] Examples of the α-diketones include diacetyl, benzyl, camphorquinone, 2,3-pentadione, 2,3-octadione, 9,10-phenanthrenequinone, 4,4′-oxybenzyl, acenaphthenequinone, etc. Among these, camphorquinone is preferred.

[0046] Examples of the coumarins include 3,3'-carbonylbis(7-diethylaminocoumarin), 3-(4-methoxybenzoyl)coumarin, 3-thienoylcoumarin, 3-benzoyl-5,7-dimethoxycoumarin, 3-benzoyl-7-methoxycoumarin, 3-benzoyl-6-methoxycoumarin, 3-benzoyl-8-methoxycoumarin, 3-benzoylcoumarin, 7-methoxy-3-(p-nitrobenzoyl)coumarin, and 3-(p-nitrobenzoyl)coumarin. 3,5-carbonylbis(7-methoxycoumarin), 3-benzoyl-6-bromocoumarin, 3,3'-carbonylbiscoumarin, 3-benzoyl-7-dimethylaminocoumarin, 3-benzoylbenzo[f]coumarin, 3-carboxycoumarin, 3-carboxy-7-methoxycoumarin, 3-ethoxycarbonyl-6-methoxycoumarin, 3-ethoxycarbonyl-8-methoxycoumarin, 3-acetylbenzo[f]coumarin, 7-methoxy-3-(p-nitro benzoyl)coumarin, 3-(p-nitrobenzoyl)coumarin, 3-benzoyl-6-nitrocoumarin, 3-benzoyl-7-diethylaminocoumarin, 7-dimethylamino-3-(4-methoxybenzoyl)coumarin, 7-diethylamino-3-(4-methoxybenzoyl)coumarin, 7-diethylamino-3-(4-diethylamino)coumarin, 7-methoxy-3(4-methoxybenzoyl)coumarin, 3-(4-nitrobenzoyl)benzo[f]coumarin , 3-(4-ethoxycinnamoyl)-7-methoxycoumarin, 3-(4-dimethylaminocinnamoyl)coumarin, 3-(4-diphenylaminocinnamoyl)coumarin, 3-[(3-dimethylbenzothiazol-2-ylidene)acetyl]coumarin, 3-[(1-methylnaphtho[1,2-d]thiazol-2-ylidene)acetyl]coumarin, 3,3'-carbonylbis(6-methoxycoumarin), 3,3'-carbonylbis(7-acetoxycoumarin), 3,3'-Carbonylbis(7-dimethylaminocoumarin), 3-(2-benzothiazolyl)-7-(diethylamino)coumarin, 3-(2-benzothiazolyl)-7-(dibutylamino)coumarin, 3-(2-benzimidazolyl)-7-(diethylamino)coumarin, 3-(2-benzothiazolyl)-7-(dioctylamino)coumarin, 3-acetyl-7-(dimethylamino)coumarin, 3,3'-carbonylbis(7-dibutylaminocoumarin), 3,3'-carbonyl-7-diethylaminocoumarin-7'-bis(butoxyethyl)aminocoumarin Examples of compounds include those described in JP-A-9-3109 and JP-A-10-245525, such as phosphorus, 10-[3-[4-(dimethylamino)phenyl]-1-oxo-2-propenyl]-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one, and 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one.

[0047] Among the above-mentioned coumarins, 3,3'-carbonylbis(7-diethylaminocoumarin) and 3,3'-carbonylbis(7-dibutylaminocoumarin) are preferred.

[0048] Among these photopolymerization initiators, it is preferable to use at least one selected from the group consisting of (bis)acylphosphine oxides, α-diketones, and coumarins, which are widely used in dental curable compositions.

[0049] Furthermore, such a photopolymerization initiator may be further combined with a polymerization promoter, as necessary, to enable photopolymerization to be carried out efficiently in a shorter time.

[0050] Polymerization accelerators suitable for photopolymerization initiators include mainly tertiary amines, aldehydes, compounds having a thiol group, sulfinic acid and / or salts thereof, and the like.

[0051] Examples of tertiary amines include N,N-dimethylaniline, N,N-dimethyl-p-toluidine, N,N-dimethyl-m-toluidine, N,N-diethyl-p-toluidine, N,N-dimethyl-3,5-dimethylaniline, N,N-dimethyl-3,4-dimethylaniline, N,N-dimethyl-4-ethylaniline, N,N-dimethyl-4-isopropylaniline, N,N-dimethyl-4-t-butylaniline, and N,N-dimethyl-3,5-di-t-butylaniline. , N,N-bis(2-hydroxyethyl)-3,5-dimethylaniline, N,N-di(2-hydroxyethyl)-p-toluidine, N,N-bis(2-hydroxyethyl)-3,4-dimethylaniline, N,N-bis(2-hydroxyethyl)-4-ethylaniline, N,N-bis(2-hydroxyethyl)-4-isopropylaniline, N,N-bis(2-hydroxyethyl)-4-t-butylaniline, N,N-bis(2-hydroxyethyl)-3,5-diisopropylaniline, N,N-bis(2-hydroxyethyl)-4-t-butylaniline, Propylaniline, N,N-bis(2-hydroxyethyl)-3,5-di-t-butylaniline, 4-(N,N-dimethylamino)benzoate n-butoxyethyl, 4-(N,N-dimethylamino)benzoate (2-methacryloyloxy)ethyl, 4-(N,N-dimethylamino)benzoate ethyl, 4-(N,N-dimethylamino)benzoate butyl, N-methyldiethanolamine, 4-(N,N-dimethylamino)benzophenone, trimethylamine, triethylamine, N-methyldiethanolamine, N-ethyldiethanolamine, Nn-butyldiethanolamine, N-lauryldiethanolamine, triethanolamine, 2-(dimethylamino)ethyl methacrylate, N-methyldiethanolamine dimethacrylate, N-ethyldiethanolamine dimethacrylate, triethanolamine monomethacrylate, triethanolamine dimethacrylate, triethanolamine trimethacrylate, and the like.

[0052] Examples of the aldehydes include dimethylaminobenzaldehyde, terephthalaldehyde, etc. Examples of the compounds having a thiol group include 2-mercaptobenzoxazole, decanethiol, 3-mercaptopropyltrimethoxysilane, thiobenzoic acid, etc.

[0053] Examples of sulfinic acid and its salts include benzenesulfinic acid, sodium benzenesulfinate, potassium benzenesulfinate, calcium benzenesulfinate, lithium benzenesulfinate, p-toluenesulfinic acid, sodium p-toluenesulfinate, potassium p-toluenesulfinate, calcium p-toluenesulfinate, lithium p-toluenesulfinate, 2,4,6-trimethylbenzenesulfinic acid, sodium 2,4,6-trimethylbenzenesulfinate, potassium 2,4,6-trimethylbenzenesulfinate, and 2,4,6-trimethylbenzenesulfinate. Examples of such sulfinates include calcium benzenesulfinate, lithium 2,4,6-trimethylbenzenesulfinate, 2,4,6-triethylbenzenesulfinic acid, sodium 2,4,6-triethylbenzenesulfinate, potassium 2,4,6-triethylbenzenesulfinate, calcium 2,4,6-triethylbenzenesulfinate, 2,4,6-triisopropylbenzenesulfinic acid, sodium 2,4,6-triisopropylbenzenesulfinate, potassium 2,4,6-triisopropylbenzenesulfinate, and calcium 2,4,6-triisopropylbenzenesulfinate.

[0054] As the chemical polymerization initiator, redox polymerization initiators such as organic peroxides and amines; organic peroxides, amines, and sulfinic acids (or their salts) are preferably used. When using a redox polymerization initiator, the oxidizing agent and reducing agent are packaged separately, and they must be mixed immediately before use. As the oxidizing agent for the redox polymerization initiator, an organic peroxide can be used. As the oxidizing agent for the redox polymerization initiator, the organic peroxide is not particularly limited, and known organic peroxides can be used. Specifically, the organic peroxides exemplified in the heat polymerization initiator can be used.

[0055] Among these organic peroxides, diacyl peroxides are preferably used from the viewpoint of the overall balance of safety, storage stability, and radical generating ability, and among them, benzoyl peroxide is more preferably used.

[0056] As a reducing agent for a redox polymerization initiator, a tertiary aromatic amine having no electron-withdrawing group in the aromatic ring is usually used. Examples of tertiary aromatic amines having no electron-withdrawing group in the aromatic ring include N,N-dimethylaniline, N,N-dimethyl-p-toluidine, N,N-dimethyl-m-toluidine, N,N-diethyl-p-toluidine, N,N-dimethyl-3,5-dimethylaniline, N,N-dimethyl-3,4-dimethylaniline, N,N-dimethyl-4-ethylaniline, N,N-dimethyl-4-isopropylaniline, N,N-dimethyl-4-t-butylaniline, N,N-dimethyl-3,5-di-t-butylaniline, N,N-bis(2-hydroxyethyl) ... N,N-bis(2-hydroxyethyl)-3,5-dimethylaniline, N,N-bis(2-hydroxyethyl)-p-toluidine, N,N-bis(2-hydroxyethyl)-3,4-dimethylaniline, N,N-bis(2-hydroxyethyl)-4-ethylaniline, N,N-bis(2-hydroxyethyl)-4-isopropylaniline, N,N-bis(2-hydroxyethyl)-4-t-butylaniline, N,N-bis(2-hydroxyethyl)-3,5-diisopropylaniline, and N,N-bis(2-hydroxyethyl)-3,5-di-t-butylaniline.

[0057] The chemical polymerization initiator may be used in combination with a polymerization accelerator as necessary. The polymerization accelerator of the chemical polymerization initiator can be selected from polymerization accelerators used in general industry, and among them, polymerization accelerators used for dental applications are preferably used. The polymerization accelerator is used alone or in appropriate combination of two or more. Specific examples include amines, sulfinic acid and its salts, copper compounds, tin compounds, etc.

[0058] Amines used as polymerization accelerators for chemical polymerization initiators are divided into aliphatic amines and aromatic amines having an electron-withdrawing group on the aromatic ring. Examples of aliphatic amines include primary aliphatic amines such as n-butylamine, n-hexylamine, and n-octylamine; secondary aliphatic amines such as diisopropylamine, dibutylamine, and N-methylethanolamine; and tertiary aliphatic amines such as N-methyldiethanolamine, N-ethyldiethanolamine, Nn-butyldiethanolamine, N-lauryldiethanolamine, 2-(dimethylamino)ethyl methacrylate, N-methyldiethanolamine dimethacrylate, N-ethyldiethanolamine dimethacrylate, triethanolamine monomethacrylate, triethanolamine dimethacrylate, triethanolamine trimethacrylate, triethanolamine, trimethylamine, triethylamine, and tributylamine. Among these, tertiary aliphatic amines are preferred from the viewpoint of curability and storage stability of the composition, and N-methyldiethanolamine and triethanolamine are more preferably used.

[0059] In addition, examples of tertiary aromatic amines having an electron-withdrawing group in an aromatic ring used as a polymerization accelerator for a chemical polymerization initiator include ethyl 4-(N,N-dimethylamino)benzoate, methyl 4-(N,N-dimethylamino)benzoate, n-butoxyethyl 4-(N,N-dimethylamino)benzoate, 2-(methacryloyloxy)ethyl 4-N,N-dimethylaminobenzoate, 4-(N,N-dimethylamino)benzophenone, butyl 4-(N,N-dimethylamino)benzoate, etc. Among these, from the viewpoint of imparting excellent curability to the composition, at least one selected from the group consisting of N,N-di(2-hydroxyethyl)-p-toluidine, ethyl 4-(N,N-dimethylamino)benzoate, n-butoxyethyl 4-(N,N-dimethylamino)benzoate, and 4-(N,N-dimethylamino)benzophenone is preferably used.

[0060] Examples of the sulfinic acid and its salts used as the polymerization accelerator include those exemplified as the polymerization accelerator for the photopolymerization initiator described above, and sodium benzenesulfinate, sodium p-toluenesulfinate, and sodium 2,4,6-triisopropylbenzenesulfinate are preferred.

[0061] As the copper compound used as the polymerization accelerator, for example, copper acetylacetonate, copper acetate, copper oleate, copper chloride, copper bromide, etc. are preferably used.

[0062] Examples of tin compounds used as polymerization accelerators include di-n-butyltin dimaleate, di-n-octyltin dimaleate, di-n-octyltin dilaurate, di-n-butyltin dilaurate, etc. Particularly suitable tin compounds are di-n-octyltin dilaurate and di-n-butyltin dilaurate.

[0063] Among these, it is preferable to use a photopolymerization initiator and a thermal polymerization initiator in combination, and a combination of a (bis)acylphosphine oxide and a diacyl peroxide is more preferable.

[0064] The content of the polymerization initiator is not particularly limited, but from the viewpoint of the curability of the obtained composition, it is preferably 0.001 to 30 parts by mass relative to 100 parts by mass of the polymerizable monomer. When the content of the polymerization initiator is 0.001 parts by mass or more relative to 100 parts by mass of the polymerizable monomer, the polymerization proceeds sufficiently and there is no risk of a decrease in mechanical strength, and it is more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more. On the other hand, when the content of the polymerization initiator is 30 parts by mass or less relative to 100 parts by mass of the polymerizable monomer, sufficient mechanical strength is obtained even when the polymerization performance of the polymerization initiator itself is low, and there is no risk of precipitation from the composition, and it is more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

[0065] The size of the dental mill blank of the present invention can be set in a commercially available dental CAD / CAM system, and is preferably processed to an appropriate size according to the prescribed part.Preferred sizes include 14mm x 18mm x 20mm prism or 14mm disk shape for anterior full crown, and 10mm x 12mm x 15mm or 14.5mm x 14.5mm x 18mm prism or 10mm, 14.5mm disk shape for molar full crown.The shape of the dental mill blank of the present invention is not particularly limited and can be appropriately set, for example, prism, disk, etc.

[0066] The dental mill blank of the present invention is a laminate of three or more layers, and the most transparent layer arranged on the outermost layer satisfies all of the above (1) to (3). This makes it possible to obtain a highly aesthetic (transparency, gray tone, natural gradation) dental prosthesis by cutting, which reproduces the incisal edge of a natural tooth without reducing mechanical strength.

[0067] Moreover, the transparency difference ΔΔL* between all adjacent layers is preferably 5.0 or less, and more preferably 3.0 or less, so that the boundaries between the layers are made unclear and a more natural gradation is achieved.

[0068] The minimum transparent layer of the dental mill blank of the present invention corresponds to the cervical part of a natural tooth, and the thickness of this minimum transparent layer is preferably 38 to 50% of the total thickness of the dental mill blank in the same direction, more preferably 38 to 48%, and even more preferably 38 to 45%. A dental crown machined from this has a chroma that matches the selected shade, and good color matching can be obtained.

[0069] Regarding the minimum transparent layer of the dental mill blank of the present invention, the transparency ΔL* of a test piece having a thickness of 1.20±0.01 mm according to the L*a*b* color system is preferably 10.0 to 23.0, more preferably 11.0 to 22.0, and even more preferably 12.0 to 21.0, in view of the good color matching of the machined dental crown. The test piece is a test piece of a cured product consisting of only the minimum transparent layer. The transparency ΔL* can be measured by the method described in the Examples below.

[0070] The dental mill blank of the present invention has one or more intermediate layers. The thickness of each of the one or more intermediate layers is preferably 8 to 28% of the total thickness of the dental mill blank in the same direction, more preferably 9 to 25%, and even more preferably 10 to 20%. In addition, a preferred embodiment is a dental mill blank having a laminated structure with two or more intermediate layers. Furthermore, in the case of a dental mill blank having a laminated structure with two or more intermediate layers, the difference in thickness between adjacent intermediate layers is preferably within 5% of the total thickness of the dental mill blank in the same direction, more preferably within 3%, and even more preferably within 1%. In the case of a dental mill blank having a laminated structure with two or more intermediate layers, from the viewpoint of high aesthetics, it is preferable that the transparency ΔL* of the intermediate layer closer to the most transparent layer is higher than the transparency ΔL* of the intermediate layer closer to the least transparent layer. In another embodiment, in the case of a dental mill blank having a laminated structure with two or more intermediate layers, when the number of intermediate layers is p (any natural number equal to or greater than 2), the following relationship is satisfied for the transparency ΔL*. ΔL M(1) *<ΔL HIGH * (I) ΔL M(k) *<ΔL M(k-1) * (II) ΔL LOw *<ΔL HIGH * (III) ΔL LOw *<ΔL M(k) * (IV) (In the formula, ΔL HIGH* indicates the transparency of the most transparent layer, ΔL M(1) * indicates the transparency of the intermediate layer (M1 layer) closest to the most transparent layer, and ΔL M(k) * indicates the kth (k is any natural number between 2 and p) intermediate layer (M k layer), and ΔL LOw * indicates the transparency of the lowest transparent layer. k is a natural number of 2 or more.) In another preferred embodiment, in the case of a dental mill blank having a laminated structure with one intermediate layer, it is preferable that the transparency ΔL* satisfies the following relationship: ΔL LOw *<ΔL M(1) *<ΔL HIGH * (V) (In the formula, ΔL HIGH *, ΔL M(1) *, ΔL HIGH * has the same meaning as above.) As described above, in the dental mill blank of the present invention, the layers constituting the laminated structure are preferably all different in transparency from the viewpoint of high aesthetic quality.

[0071] The manufacturing method of the dental mill blank of the present invention includes a method of stacking inorganic fillers having different transparencies in a mold, pressing the molded body, contacting it with a polymerizable monomer, and then curing it (press impregnation method), and a method of stacking pastes having different chromaticities, which are made by mixing inorganic fillers and polymerizable monomers, and curing them, but the press impregnation method is preferred from the viewpoint of making the interface between adjacent layers more unclear. Furthermore, in the press impregnation method, when stacking inorganic fillers having different chromaticities in a mold and pressing them, it is preferable to vibrate the lower mold to roughen the interface between the stacked inorganic fillers. This vibration operation not only makes the boundary between layers unclear, resulting in a more natural appearance, but also suppresses the decrease in mechanical strength at the boundary between layers caused by the difference in pigment content.

[0072] The dental mill blank of the present invention may contain other components as long as they do not impair the effects of the present invention, for example, diethyl 2,5-dihydroxyterephthalate as an organic fluorescent agent, and 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole as a stabilizer. The content of the other components is preferably 0.006% by mass or less, more preferably 0.003% by mass or less, based on the total mass of the dental mill blank.

[0073] By cutting the dental mill blank of the present invention, a highly aesthetic dental prosthesis that reproduces the incisal edge of a natural tooth can be obtained by cutting without reducing the mechanical strength. Examples of dental prostheses include crown restorations such as inlays, onlays, veneers, crowns, and bridges, as well as abutments, dental posts, dentures, denture bases, and implant members (fixtures, abutments). Cutting is preferably performed using a commercially available dental CAD / CAM system, and examples of such CAD / CAM systems include the CEREC system manufactured by Sirona Dental Systems Co., Ltd. and the "Katana (registered trademark) system" manufactured by Kuraray Noritake Dental Co., Ltd. EXAMPLES

[0074] Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples, and many modifications can be made by those having ordinary skill in the art within the scope of the technical concept of the present invention.

[0075] (Measurement of inorganic filler content (mass%)) The content of inorganic filler can be confirmed by the weight change (ignition residue) before and after the organic components are removed by heating the obtained mill blank at high temperature in an electric furnace or the like. Specifically, in this embodiment, the platinum crucible was precisely weighed (m1), and about 1 g of the sample was taken in the platinum crucible and precisely weighed (m2). After that, it was ignited in an electric furnace at 575±25°C for 60±3 minutes, the platinum crucible was removed from the electric furnace, cooled in a desiccator for 30 minutes, and precisely weighed (m3), and the ignition residue value was calculated by the following formula. Ignition residue (%)=[(m3-m1) / (m2-m1)]×100

[0076] (Measurement of transparency and transparency difference) A 14.5 mm x 18.0 mm, 1.6 mm thick chromaticity plate was cut out using a diamond cutter (ISOMET-1000) from a 14.5 mm x 18.0 mm x 14.5 mm rectangular prism-shaped dental mill blank obtained in the Examples and Comparative Examples described below, and finished to a thickness of 1.20 ± 0.01 mm using waterproof abrasive paper (#1000, #2000, #3000) to prepare a test specimen. The test pieces, which were plate-like objects after polishing, were measured for L*, a*, and b* values ​​(JIS Z 8781-4:2013 Colorimetry-Part 4: CIE 1976 L*a*b* color space) on a white background and a black background using a spectrophotometer (CM-3610A: manufactured by Konica Minolta, Inc., conforming to JIS Z 8722:2009, condition c, D65 light source, di:8°, de:8°, diffuse illumination: 8° light reception, measurement mode SCI, measurement diameter / illumination diameter = φ8mm / φ11mm) (n=1). The transparency ΔL* and transparency difference ΔΔL* were calculated using the above formula from the measured value for the lightness index L*. The results are shown in Table 1. The ΔL* of each layer was calculated by preparing a single-layer cured product and a chromaticity plate for each layer and measuring them using the above method.

[0077] (Esthetic evaluation of dental prostheses) The dental mill blanks obtained in the Examples and Comparative Examples described below were machined using a dental CAD / CAM milling machine "DWX-51D" (manufactured by Roland DG Corporation) to fabricate a crown for the first upper right anterior tooth (n=1). The fabricated crown was tried in the oral cavity and visually observed by five observers. If five out of five observers rated the aesthetics as good, they were rated as "◎: very good aesthetics", if four observers rated it as "○: good aesthetics", and if three or less observers rated it as "×: room for aesthetic improvement".

[0078] (Three-point bending strength measurement of dental prostheses) The three-point bending strength of the polymerizable cured product prepared in each Example and Comparative Example was measured by the following method. That is, a test piece (1.2 mm × 4.0 mm × 14.0 mm) was prepared from the manufactured dental mill blank using a diamond cutter. After that, it was finished to a thickness of 1.20 mm using two sheets of waterproof abrasive paper (#1000, #2000). Ten of these test pieces were prepared for each specimen, and immersed in water for one week in a thermostatic bath at 37 ° C. for measurement. These were set in a universal testing machine (manufactured by Shimadzu Corporation), and the three-point bending strength of each test piece was measured (n = 10) by a three-point bending test method (JDMAS 245:2017 regulations applied mutatis mutandis) under conditions of a crosshead speed of 1 mm / min and a support distance of 12 mm. The average values ​​of the measured values ​​are shown in Table 1.

[0079] [Production Example of Inorganic Filler] Commercially available ultrafine silica particles (Aerosil® OX 50, manufactured by Nippon Aerosil Co., Ltd., average primary particle size: 40 nm, refractive index: 1.46, BET specific surface area: 50 m 230 g of γ-methacryloxypropyltrimethoxysilane (1.5 g / g) was dispersed in 120 mL of water to prepare a dispersion. A solution of 1.5 g of γ-methacryloxypropyltrimethoxysilane, 15 mL of water, and 0.108 g of acetic acid, which had been previously stirred, was added to this dispersion, and the mixture was stirred at room temperature for 1 hour. Next, a predetermined amount of inorganic pigment (Japanese Pharmacopoeia titanium oxide, iron oxide black, iron oxide red (red iron oxide), and iron oxide yellow) was added, and the mixture was stirred at room temperature for 10 minutes. The solvent was removed from the solution by vacuum distillation, and the solution was further dried at 90°C for 3 hours. By such surface treatment, fillers (hereinafter sometimes simply referred to as "fillers for the most transparent layer") A-1 to A-4 to be used in the most transparent layer that had been surface-treated, and further fillers (hereinafter sometimes simply referred to as "fillers for the least transparent layer") B-1 and B-2 to be used in the least transparent layer were obtained by the same method. The amount of inorganic pigment added was adjusted according to the desired shade. The filler used in the intermediate layer in the laminated structure (hereinafter, sometimes simply referred to as "intermediate layer filler") was obtained by dry mixing the most transparent layer filler A and the least transparent layer filler B in a ratio according to the number of layers. For example, in the case of a three-layer molding, the intermediate layer filler for the second layer was prepared by mixing the most transparent layer filler A and the least transparent layer filler B in a mass ratio of 1:1. Similarly, in the case of four-layer molding, the filler for the second and third layers was mixed with Filler A for the most transparent layer and Filler B for the least transparent layer in mass ratios of 2:1 and 1:2, respectively; in the case of five-layer molding, the filler for the second, third and fourth layers was mixed with Filler A for the most transparent layer and Filler B for the least transparent layer in mass ratios of 3:1, 1:1 and 1:3, respectively; and in the case of six-layer molding, the filler for the second, third, fourth and fifth layers was mixed with Filler A for the most transparent layer and Filler B for the least transparent layer in mass ratios of 4:1, 3:2, 2:3 and 1:4, respectively.

[0080] [Production Example of Polymerizable Monomer-Containing Composition] A polymerizable monomer-containing composition (m) was prepared by dissolving 1.5 parts by mass of benzoyl peroxide, which is also a thermal polymerization initiator, in 70 parts by mass of [2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)]dimethacrylate (UDMA) and 30 parts by mass of triethylene glycol dimethacrylate (TEGDMA).

[0081] [Example 1] 0.81 g of filler A-1 for the most transparent layer was placed on the lower punch bar of a rectangular press die measuring 14.5 x 18.0 mm for the first layer, which was the outermost layer. After smoothing the filler A-1 for the most transparent layer by tapping, 0.72 g of filler for the second layer (filler A-1:filler B-1 = 2:1 (mass ratio)) was then added while vibrating the die. At this time, vibration was applied by hitting the frame or lower die of the die with a hammer. Similarly, 0.72 g of filler A-1:filler B-1 = 1:2 (mass ratio) for the third layer was added while vibrating the die. Next, 2.25 g of filler B-1 for the least transparent layer was added to the fourth layer in the same way. The upper punch bar was placed in a specified position, and uniaxial pressing was performed using a press machine (press pressure 60 MPa (16.1 kN), time 1 minute). The upper punch and the lower punch were removed from the mold, and the four-layer molded body was taken out. Then, the molded body was placed inside a polyethylene bag, and the polymerizable monomer-containing composition (m) was introduced into the bag, and the inside of the bag was decompressed, so that the molded body was impregnated with the polymerizable monomer-containing composition (m). After standing at room temperature for 1 day under reduced pressure, the molded body was then heated at 55°C for 18 hours using a hot air dryer, and then further heated at 110°C for 3 hours to polymerize the polymerizable monomer, thereby obtaining the intended four-layer dental mill blank. The obtained dental mill blank was a prism of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue value of 61%.

[0082] [Example 2] 0.68g of filler A-1 for the most transparent layer was placed on the lower punch bar of a rectangular press die of 14.5 x 18.0 mm for the first layer, which was the outermost layer. After the filler A-1 for the most transparent layer was leveled by tapping, 0.77g of filler for the second layer was added while vibrating the die. At this time, the frame or lower die of the die was hit with a hammer to vibrate. Similarly, 0.81g of filler for the third layer was added while vibrating the die. Next, 2.25g of filler B-1 for the least transparent layer was added as the fourth layer in the same manner. The upper punch bar was placed in a predetermined position, and uniaxial pressing was performed using a press machine (press pressure 60 MPa (16.1 kN), time 1 minute). The upper punch and lower punch were removed from the die, and the four-layer molded body was taken out. Then, the molded body was placed in a polyethylene bag, and the polymerizable monomer-containing composition (m) was introduced into the bag, and the inside of the bag was decompressed, so that the molded body was impregnated with the polymerizable monomer-containing composition (m). After standing at room temperature for 1 day under reduced pressure, the molded body was then heated at 55°C for 18 hours using a hot air dryer, and then further heated at 110°C for 3 hours to polymerize the polymerizable monomer, thereby obtaining the desired four-layer dental mill blank. The obtained dental mill blank was a prism of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue of 61%.

[0083] [Example 3] As in Examples 1 and 2, 0.72g of the most transparent layer filler A-1 was added to the first layer, which was the outermost layer, 0.5g, 0.5g, 0.54g, and 0.54g of the intermediate layer fillers corresponding to the second to fifth layers, respectively, and 1.71g of the least transparent layer filler B-1 was added to the sixth layer, and the same treatment was carried out thereafter to obtain the desired six-layer dental mill blank. The obtained dental mill blank was a prism shape of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue value of 61%.

[0084] [Example 4] 0.72g of the most transparent layer filler A-2 was added to the first layer, which was the outermost layer, 0.99g, 0.54g, and 0.54g of the intermediate layer fillers corresponding to the second to fourth layers, respectively, and 1.71g of the least transparent layer filler B-1 was added to the fifth layer, and the same treatment as in Examples 1 to 3 was carried out thereafter to obtain the intended five-layer dental mill blank. The obtained dental mill blank was a prism shape of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue value of 60%.

[0085] [Example 5] 0.72g of the most transparent layer filler A-2 was added to the first layer, which was the outermost layer, 0.5g, 0.5g, 0.54g, and 0.54g of the intermediate layer fillers corresponding to the second to fifth layers, respectively, and 1.71g of the least transparent layer filler B-1 was added to the sixth layer, and the same treatment as in Examples 1 to 4 was carried out to obtain the desired six-layer dental mill blank. The obtained dental mill blank was a prism of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue of 60%.

[0086] [Example 6] 0.72g of the most transparent layer filler A-1 was added to the first layer, which was the outermost layer, 1.08g of the intermediate layer filler to the second layer, and 2.25g of the least transparent layer filler B-2 to the third layer, and thereafter, the same treatment as in Examples 1 to 5 was carried out to obtain the intended three-layer dental mill blank. The obtained dental mill blank was a prism shape of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue value of 63%.

[0087] [Comparative Example 1] 1.71g of the most transparent layer filler A-3 was added to the first layer, which was the outermost layer, 0.54g and 0.54g of the intermediate layer fillers corresponding to the second and third layers, respectively, and 1.71g of the least transparent layer filler B-1 was added to the fourth layer, and the same treatment as in Examples 1 to 6 was carried out thereafter to obtain the intended four-layer dental mill blank. The obtained dental mill blank was a prism of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue of 61%.

[0088] [Comparative Example 2] 0.9g of the most transparent layer filler A-1 was added to the first layer, which was the outermost layer, 0.68g and 0.68g of the intermediate layer fillers corresponding to the second and third layers, respectively, and 2.25g of the least transparent layer filler B-1 was added to the fourth layer, and the same treatment as in Examples 1 to 6 was carried out thereafter to obtain the intended four-layer dental mill blank. The obtained dental mill blank was a prism of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue of 61%.

[0089] [Comparative Example 3] 0.45g of the most transparent layer filler A-2 was added to the first layer, which was the outermost layer, 0.9g and 0.9g of the intermediate layer fillers corresponding to the second and third layers, respectively, and 2.25g of the least transparent layer filler B-1 was added to the fourth layer, and the same treatment as in Examples 1 to 6 was carried out thereafter to obtain the intended four-layer dental mill blank. The obtained dental mill blank was a prism of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue of 60%.

[0090] [Comparative Example 4] 0.68g of the most transparent layer filler A-2 was added to the first layer, which was the outermost layer, 0.77g and 0.81g of the intermediate layer fillers corresponding to the second and third layers, respectively, and 2.25g of the least transparent layer filler B-1 was added to the fourth layer, and the same treatment as in Examples 1 to 6 was carried out thereafter to obtain the intended four-layer dental mill blank. The obtained dental mill blank was a prism shape of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue value of 60%.

[0091] [Comparative Example 5] 0.45g of the most transparent layer filler A-2 was added to the first layer, which was the outermost layer, 0.45g, 0.54g, and 0.54g of the intermediate layer fillers corresponding to the second, third, and fourth layers, respectively, and 2.25g of the least transparent layer filler B-1 was added to the fifth layer, and the same treatment as in Examples 1 to 6 was performed thereafter to obtain the intended five-layer dental mill blank. The obtained dental mill blank was a prism shape of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue value of 60%.

[0092] [Comparative Example 6] 0.72g of the most transparent layer filler A-4 was added to the first layer, which was the outermost layer, 0.5g, 0.5g, 0.54g, and 0.54g of the intermediate layer fillers corresponding to the second to fifth layers, respectively, and 1.71g of the least transparent layer filler B-1 was added to the sixth layer, and the same treatment as in Examples 1 to 6 was carried out to obtain the desired six-layer dental mill blank. The obtained dental mill blank was a prism of 14.5mm x 18.0mm x 14.5mm, and had an ignition residue of 64%.

[0093] [Table 1]

[0094] By comparing Examples 1 to 6 with Comparative Examples 1 to 6, it was found that if the proportion of the most transparent layer arranged in the outermost layer is in the range of 11 to 19% and its ΔL* is in the range of 25.0 to 36.0, then when an anterior crown is machined from the mill blank, the most transparent layer will be moderately included in the crown, resulting in good color reproduction in the oral cavity, and if the difference in transparency ΔL* between the most transparent layer and the layer adjacent to it is 5.0 or less, then the mill blank will also be excellent in terms of mechanical strength. These results show that the dental mill blank of the present invention, which satisfies all of these conditions simultaneously, is excellent in aesthetics without reducing mechanical strength. [Industrial Applicability]

[0095] According to the present invention, a highly aesthetic dental prosthesis can be obtained by machining, which reproduces the high transparency and grayish color characteristic of natural teeth, particularly at the incisal edge, without reducing mechanical strength.

Claims

1. A laminate structure having three or more layers including a most transparent layer, one or more intermediate layers, and a least transparent layer, The most transparent layer is disposed as the outermost layer, and A dental mill blank, wherein the most transparent layer satisfies all of the following conditions (1) to (3): (1) The thickness is 11 to 19% of the overall thickness of the dental mill blank in the same direction. (2) The transparency ΔL* of a test piece having a thickness of 1.20±0.01 mm is 28.0 to 36.0 according to the L*a*b* color system. (3) The transparency difference ΔΔL* between adjacent layers is 5.0 or less.

2. 2. The dental mill blank of claim 1, wherein the transparency difference ΔΔL* of all adjacent layers is less than or equal to 5.

0.

3. 3. The dental mill blank according to claim 1, wherein the thickness of the minimum transparent layer is 38 to 50% of the total thickness of the dental mill blank in the same direction.

4. The dental mill blank according to any one of claims 1 to 3, wherein the one or more intermediate layers are adjacent to the most transparent layer.

5. 5. The dental mill blank according to claim 1, wherein the one or more intermediate layers are two or more layers, and the thickness of each intermediate layer is 8 to 28% of the total thickness of the dental mill blank in the same direction.

6. 6. The dental mill blank according to claim 5, wherein the difference in thickness between adjacent intermediate layers of the two or more intermediate layers is within 5% of the overall thickness of the dental mill blank in the same direction.

7. The dental mill blank according to any one of claims 1 to 6, wherein the layers constituting the laminated structure all have different transparencies.

8. The dental mill blank according to any one of claims 1 to 7, wherein the content of the inorganic filler is 40 mass% or more.

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