JP7574999B2 - Laminated Dental Machining Resin Blanks - Google Patents

Description

The present invention relates to a laminated dental mill blank for cutting, which has a cutting part made of a laminate of multiple resin-based material layers.

In dental treatment, the use of digital technology is progressing in the manufacture of dental restorations (or dental prostheses) such as inlays, onlays, crowns, bridges, and implant superstructures. For example, as disclosed in Patent Document 1, a CAD/CAM system that uses a CAD/CAM device based on computer-aided design (CAD) and computer-aided manufacturing (CAM) technology to cut a dental blank made of a nonmetallic material to form a dental restoration is becoming more common. Here, the dental blank refers to a cut object (also called a mill blank) that can be attached to a cutting machine in a CAD/CAM system, and generally known examples include a (solid) block formed into a rectangular or cylindrical shape, or a (solid) disk formed into a plate or plate shape. In addition, dental cutting blanks are often joined with retaining pins to secure them to a cutting machine, and in such a configuration, the one integrated with the retaining pin is sometimes called a dental cutting blank. In this invention, the dental cutting blank includes such a configuration integrated with the retaining pin. The main body of the workpiece (dental cutting blank main body) is sometimes called the part to be cut.

Various materials such as glass ceramics, zirconia, titanium, and resin are used as the material to be machined in dental machining blanks. Among these, resin-based materials (also called hybrid resins) consisting of a hardened product of a hardening composition containing an inorganic filler such as silica, a polymerizable monomer such as methacrylate resin, and a polymerization initiator, are attracting attention due to their high workability (machinability), high aesthetics, strength, etc.

In dental treatment, it is required to give the appearance of the tooth a color as close as possible to that of natural teeth. In order to meet such aesthetic requirements, various pigments and dyes have been added in varying amounts to adjust the color of the dental resin blanks for cutting. These include single-layered resin blanks for cutting dental teeth made of a single component, and multi-layered resin blanks for cutting dental teeth made by layering components of different colors.

For example, Patent Document 2 proposes a resin block for dental CAD/CAM in which a dentin repair resin layer and an enamel repair resin layer are laminated as a resin blank for dental cutting processing that is highly versatile and productive, and is also highly capable of reproducing the aesthetic appearance of natural teeth, and in which at least the dentin repair resin layer contains light diffusing particles and has a specific diffusion ratio. Patent Document 3 also describes a dental mill blank that can provide a dental prosthesis having a color tone and transparency similar to those of natural teeth by cutting, the laminate including at least three layers, a top layer, at least one intermediate layer, and a bottom layer, each layer including a filler (A) and a polymer (B), the filler (A) in each layer including at least one type of inorganic particle (a) and at least one type of pigment (C), the chromaticity difference ΔE* _T between the top layer and the bottom layer being 5.0 or more and 15.0 or less, the transparency difference ΔΔL* _T between the top layer and the bottom layer being 5.0 or more and 15.0 or less, the chromaticity difference ΔE* between all adjacent layers being 1.0 or more and 5.5 or less, the transparency difference ΔΔL* between all adjacent layers being 1.0 or more and 5.0 or less, the transparency ΔL* _H of the top layer being 13.5 or more and 25.0 or less, and the transparency ΔL* of the bottom layer being 1.0 or more and 5.0 or less. A dental mill blank has been proposed in which _L is 7.0 or more and 13.0 or less.

It is also known that single-layer resin blanks for dental cutting can exhibit so-called structural colors, allowing for color harmony with natural teeth without the use of pigments, etc. That is, Patent Document 4 discloses "a resin-based block for dental cutting, which contains a resin matrix (A) and a spherical filler (B) having an average particle size in the range of 230 nm to 1000 nm, wherein 90% or more of the individual particles constituting the spherical filler (B) are present within a 5% range around the average particle size, and the resin-based block for dental cutting is characterized in that the colorimetric values of the Munsell color system of colored light under a black background and a white background measured with a color difference meter at a thickness of 10 mm are less than 5.0 in brightness (V) and less than 2.0 in chroma (C), and the colorimetric values of the Munsell color system of colored light under a black background measured with a color difference meter at a thickness of 1 mm are less than 5.0 in brightness (V) and less than 0.05 in chroma (C), and the colorimetric values of the Munsell color system of colored light under a white background are more than 6.0 in brightness (V) and less than 2.0 in chroma." According to Patent Document 4, the resin-based block for dental cutting is such that 90% or more of the individual particles constituting the spherical filler (B) are present within a 5% range around the average particle diameter, and the resin matrix (A) and the spherical filler (B) satisfy the condition nP<nF, where nP is the refractive index of the resin matrix (A) at 25°C and nF is the refractive index of the spherical filler (B) at 25°C. In response to this condition, a colored light of a specific tone is expressed as a structural color according to the particle size of the spherical filler (B), and a unique reflection spectrum corresponding to the colored light is clearly observed against a black background, but against a white background, a substantially uniform reflectance is shown over substantially the entire range of the visible spectrum, and no light of the visible spectrum is observed, demonstrating the effect of harmonizing widely with various surrounding environments.

It is known that a composite material in which inorganic particles are dispersed in a resin matrix, which corresponds to the hybrid resin that is the cutting portion of the resin-based block for dental cutting described above in Patent Document 4, will produce a structural color that is consistent with changes in the angle of incidence of light when the shape and particle size distribution of the inorganic particles, the relationship between the refractive index of the inorganic particles and the refractive index of the resin matrix, and the dispersion state of the inorganic particles satisfy certain conditions (see Patent Document 5).

Special table 2016-535610 publication JP 2017-213394 A International Publication No. 2018/074605 International Publication No. 2019/189698 International Publication No. 2020/050123

Natural teeth are opaque and reddish yellow in the cervical area, gradually changing to a white, transparent color toward the incisal edge. Not only are the incisal and cervical areas of natural teeth very different in color, but the overall color tone (sometimes called shade) of natural teeth varies from person to person. Therefore, in order to reproduce the color tone of natural teeth to a high degree, it is necessary to prepare multi-layered mill blanks (of different colors) (hereinafter also referred to as "multi-layered mill blanks") for each overall color tone (shade) in order to reproduce the color change from the cervical area to the incisal edge. Not only is production laborious, but when using them, it is necessary to carefully check the shade of each patient's teeth and select a multi-layered mill blank that matches it from among many candidates.

On the other hand, when a dental cutting resin block (hereinafter also referred to as a "structural color resin blank") having a cutting portion made of a hybrid resin that exhibits a structural color, as described in Patent Document 4, is used, the above-mentioned effect makes it possible to harmonize the color tone of the dental prosthesis manufactured using this with the color tone of the underlying natural tooth.

However, the inventors of the present invention conducted various studies on dental prostheses made using the structurally colored resin blanks described in Patent Document 4 and found that, depending on the form, it may not be possible to perform highly aesthetic restorations. That is, in dental prostheses that include a relatively wide area from the vicinity of the cervical area to the incisal end where no natural teeth exist as a base, such as a front tooth crown, which is a dental prosthesis for restoring a front tooth, it was found that, as in the case of a white background, structural colors may not be observed and color adjustment effects may not be obtained.

The present invention aims to provide a resin blank for dental cutting that can harmonize with a wide variety of surrounding environments by taking full advantage of the color compatibility advantages of structural color resin blanks, even when producing a dental prosthesis that includes a portion where no natural teeth exist as a base.

The present inventors conducted research to solve the above problems. As a result, they discovered that when a colored hybrid resin layer is provided as a lower layer of a layer made of a hybrid resin that exhibits structural color, even when a dental prosthesis is fabricated that includes a portion where there is no natural tooth present as a base, the layer made of a hybrid resin that exhibits structural color has the effect of "being able to blend in with a wide variety of surrounding environments," and that when the color difference between the two layers is within a specific range, a natural gradation effect can be obtained, which led to the completion of the present invention.

That is, one embodiment of the present invention is a dental resin blank for cutting having a cutting part made of a composite material in which inorganic particles are dispersed in a resin matrix,
The composite material has a laminated structure in which a first layer and a second layer are bonded together,
the first layer is made of a first composite material that exhibits a structural color of a predetermined color tone independent of the angle of incidence of light,
the second layer is made of a second composite material having a color tone different from the color tone of the first composite material;
When the color tone of a composite material having a single color tone is expressed by the L ^* value, a ^* value, and b ^* value obtained by measuring a sample having a thickness of 1.0±0.1 mm against a white background using a spectrophotometer,
The following formula, which is an index of the difference between the color tone of the first composite material and the color tone of the second composite material, is ΔE ^* ={(L1 ^* -L2 ^* ) ² +(a1 ^* -a2 ^* ) ² +(b1 ^* -b2 ^* ) ² } ^1/2
(In the above formula, L1 ^* , a1 ^* , and b1 ^* are the L ^* value, a ^* value, and b ^* value in the first composite material, and L2 ^* , a2 ^* , and b2 ^* are the L ^* value, a ^* value, and b ^* value in the second composite material.)
The color difference: ΔE ^* defined as 2 to 30 ,
the total amount of pigment and colorant in the first composite material is 100 ppm by mass or less relative to the total mass of the first composite material, and the total amount of pigment and colorant in the second composite material is 500 to 7000 ppm by mass relative to the total mass of the second composite material;
The present invention relates to a laminated resin blank for dental cutting.

In the laminated resin-based blank for dental cutting of the above-mentioned form (hereinafter also referred to as "the blank of the present invention"), it is preferable that the first composite material satisfies all of the conditions (a) to (d) below.
(a) The inorganic particles are composed of an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 nm to 1000 nm, and include one or more groups of uniform-diameter spherical particles (G-PID) in which 90% or more of the total number of particles in a number-based particle size distribution of the aggregate are present within a 5% range around the predetermined average primary particle diameter.
(b) When the number of the uniform particle groups contained in the inorganic particles is a, and each uniform particle group is expressed in ascending order of average primary particle diameter as G-PID _m (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more), the average primary particle diameters of each G-PID _m when a is 2 or more differ from each other by 25 nm or more.
(c) When the refractive index of the resin matrix at 25° C. for light having a wavelength of 589 nm is n _(MX) and the refractive index of the inorganic spherical particles constituting each G-PID _m at 25° C. for light having a wavelength of 589 nm is n _(G-PIDm) , for each n _(G-PIDm) :
n _(MX) <n _(G-PIDm)
The relationship is established.
(d) A function expressing the probability that other inorganic spherical particles are present at a point distant r from the center of any inorganic spherical particle in the first composite material, which is determined based on a scanning electron microscope image in which an internal surface of the composite material is used as an observation plane, and is expressed by the following formula (1) based on the average particle density of the inorganic spherical particles in the observation plane: <ρ>, the number of inorganic spherical particles present in the region between a circle at a distance r from any inorganic spherical particle in the observation plane and a circle at a distance r+dr: dn, and the area of the region: da (where da = 2πr dr):
g(r)={1/〈ρ〉}×{dn/da}...(1)
When g(r) is a radial distribution function, the inorganic spherical particles constituting all of the "spherical particles of the same diameter" (G-PID) in the composite material are dispersed in the matrix material so as to have a short-range ordered structure that satisfies the following condition 1 and the following condition 2.
[Condition 1]: In a radial distribution function graph showing the relationship between r/r0 and the g(r) corresponding to r at that time, the x-axis is a dimensionless number (r/ _r0 ) obtained by dividing the distance r from the center of any inorganic spherical particle dispersed in the composite material by the average particle size _r0 of all the inorganic spherical particles dispersed in the composite material, _and the y-axis is the radial distribution function g(r), the nearest inter-particle distance _r1 , which is defined as the r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph, is a value that is 1 to 2 times the average particle size _r0 of all the inorganic spherical particles dispersed in the composite material.
[Condition 2]: When r corresponding to the peak top of the peak that is second closest to the origin among the peaks appearing in the radial distribution function graph is defined as the next nearest interparticle distance: _r2 , the minimum value of the radial distribution function: g(r) between the nearest interparticle distance: _r1 and the next nearest interparticle distance: _r2 is a value of 0.56 or more and 1.10 or less.

Furthermore, when the transparency of the composite material is expressed as an index of contrast ratio: CR, which is a value determined as a ratio of Y value: _YB / _YW on a black background to Y value: YW on a _white background, obtained by performing color difference measurement using a spectrophotometer on a sample having a thickness of 1.0±0.1 _mm , it is preferable that the contrast ratio: CR1 of the first composite material is 0.28 to 0.46, and the contrast ratio: CR2 of the second composite material is 0.50 to 0.65.

In the laminated dental cutting resin blank of the present invention, even when a dental prosthesis is produced that includes a relatively wide area from the vicinity of the cervical part to the incisal part where no natural tooth exists in the base layer, the incisal part is cut so that the first layer is made up of the first layer and the vicinity of the cervical part is made up of the second layer, so that the gradation from the cervical part to the incisal part of a natural tooth can be expressed to a high degree, and the color tone of a natural tooth can be reproduced more accurately. Moreover, since the first layer is made of a hybrid resin that expresses a structural color, the color tone naturally matches the color tone of the second layer. Therefore, it is sufficient to adjust the color tone using a pigment or dye only for the second layer that is located near the cervical part. Therefore, compared to the method disclosed in Patent Document 3, where the chromaticity difference and transparency difference between the three layers are highly adjusted and laminated, the labor required for adjustment and lamination is greatly reduced, and manufacturing efficiency is greatly improved. Furthermore, the labor required for shade taking during use can be reduced.

1. Overview of the Blank of the Present Invention The laminated resin blank for dental cutting of the present invention is a resin blank for dental cutting having a cuttable part made of a composite material (corresponding to a hybrid resin) in which inorganic particles are dispersed in a resin matrix, wherein the composite material (hybrid resin) constituting the cuttable part has a laminated structure in which a first layer and a second layer are bonded, the first layer is made of a first composite material which is a composite material that exhibits a structural color of a predetermined color tone independent of the angle of incidence of light, the second layer is made of a second composite material which is a composite material having a color tone different from that of the first composite material, and the color difference: ΔE ^* which is an index of the difference in color tone between the first composite material and the second composite material is within a specific range. The second composite material constituting the second layer of the laminated structure may be one which exhibits a structural color of a predetermined color tone independent of the angle of incidence of light, or one which does not exhibit such a structural color.

In addition, in the above laminated structure, the contrast ratio: CR1 of the first composite material is preferably 0.28 to 0.46, particularly 0.28 to 0.43, and the contrast ratio: CR2 of the second composite material is preferably 0.50 to 0.65, particularly 0.55 to 0.63, because the color matching resulting from the structural color of the first composite material is prominent.

The blank of the present invention is not particularly different from conventional hybrid resin-based dental cutting blanks, except that the part to be cut has the above-mentioned laminated structure, and may have a holding member for fixing it to a cutting machine, such as a holding pin, if necessary. The shape and size of the part to be cut are also not particularly limited, and may be a (solid) block formed into a rectangular or cylindrical shape, or a (solid) disk formed into a plate or board shape.

The cut part of the blank of the present invention may be a two-layer structure consisting of only the first and second layers, or may be a three or more layer structure with an additional layer, so long as it has the above-mentioned laminated structure. The thickness of each layer is not particularly limited, but is usually in the range of 1 to 13 mm, and preferably 2 to 12 mm.

When the composite material (hybrid resin) constituting the cut part has a laminated structure of three or more layers, it is preferable that the composite material (hybrid resin) has a three-layer or four-layer structure in which a layer of another composite material (hybrid resin) is bonded to the side opposite to the side of the first layer that is bonded to the second layer and/or the side opposite to the side of the second layer that is bonded to the first layer. In this case, when a layer (also called the "first layer side additional layer") made of another composite material (hybrid resin) is bonded to the side opposite to the side of the first layer that is bonded to the second layer, it is preferable that the composite material (hybrid resin) has a contrast ratio lower than CR1 and exhibits a structural color of a predetermined color tone independent of the angle of incidence of light. In addition, when a layer (also called the "second layer side additional layer") made of another composite material (hybrid resin) is bonded to the side opposite to the side of the second layer that is bonded to the first layer, it is preferable that the composite material (hybrid resin) has a contrast ratio higher than the contrast ratio of the second composite material: CR2, especially a composite material (hybrid resin) that does not exhibit a structural color. Furthermore, the color difference between the second layer and the second layer-side additional layer is preferably 1 to 10, and more preferably 2 to 8.

As described above, when a dental prosthesis for cavity repair in a relatively wide range from the vicinity of the cervical region to the incisal end is produced using the structural color resin blank described in Patent Document 4, the structural color is strongly affected by transmitted light, as in the case of a white background, and the structural color that is expressed may not be observed, and the color adjustment effect may not be obtained. On the other hand, when the cut part has the laminated structure as described above, the second layer is colored, so that the influence of transmitted light can be reduced, and the first layer can exhibit the inherent characteristics of the structural color resin blank. Therefore, even when a dental prosthesis is produced that includes a part in which natural teeth do not exist in the base layer, the dental prosthesis is produced by forming the vicinity of the cervical region with the second layer and the vicinity of the incisal end with the first layer, so that the part formed by the first layer can be matched to the surrounding color tone without particularly performing color adjustment using a pigment or dye. In addition, since the color difference: ΔE ^* between the first layer and the second layer is within a certain range, a natural gradation with a moderate blur can be seen between the two layers.

The first composite material constituting the first layer, the composite material to be added as necessary to the first layer side additional layer, and the second composite material and the composite material to be added as necessary to the second layer side additional layer in the case where they exhibit structural color, and the above composite materials contain inorganic spherical particles having a predetermined average (primary) particle size and a predetermined particle size distribution, similar to the composite material used in the structural color resin blank described in Patent Document 4, and exhibit a predetermined structural color (hereinafter also referred to as "specific structural color") that is not dependent on the angle of incidence of light (corresponding to the average particle size of the spherical particle group of the same particle size contained). As described above, for composite materials (hybrid resins) that exhibit such specific structural colors, the conditions that must be met to exhibit specific structural colors are known (see Patent Document 5). As these first composite materials, etc. in the present invention, composite materials that satisfy such conditions, specifically all of the conditions (a) to (d) described below {hybrid resins that satisfy all of the conditions (a) to (d) described below and exhibit specific structural colors are hereinafter also referred to as "structural color hybrid resins"} can be used without any particular restrictions.

On the other hand, when the second composite material and the composite material that will be the second layer side additional layer added as necessary do not exhibit structural color, hybrid resins that do not satisfy the above conditions {that is, do not satisfy at least one of the conditions (a) to (d) described below}, or hybrid resins that contain a large amount of pigment, etc., so that the expression of a specific structural color cannot be visually confirmed (hereinafter, collectively referred to as "non-structural color hybrid resins").

In the blanks of the present invention, it is extremely important that the first and second composite materials constituting the first and second layers in the laminate structure each have specific characteristics. Therefore, first, these characteristics, namely, the structural color, the specific structural color, and the conditions for hybrid resins to exhibit the specific structural color, as well as the contrast ratio and color difference, will be explained, and then the raw materials of the first and second composite materials, etc., and the preparation method thereof, as well as the manufacturing method of the blanks of the present invention will be explained.

In this specification, unless otherwise specified, the notation "x~y" using the numerical values x and y means "greater than or equal to x and less than or equal to y." In such a notation, when a unit is added only to the numerical value y, the unit is also applied to the numerical value x. In addition, in this specification, the term "(meth)acrylic" means both "acrylic" and "methacrylic." Similarly, the term "(meth)acrylate" means both "acrylate" and "methacrylate," and the term "(meth)acryloyl" means both "acryloyl" and "methacryloyl."

2. Structural color and specific structural color Structural color is a phenomenon in which light incident on an object having a fine structure reflects light of a specific wavelength due to interference, diffraction, refraction, etc. of the light caused by the fine structure, and structural colors of different colors are observed depending on the angle of incidence (or viewing angle) of light in opals, oil films, etc. In contrast, the laminated resin-based blank for dental cutting of the present invention utilizes a specific structural color in which a predetermined color is observed regardless of the angle of incidence of light as described above.

The above-mentioned specific structural color is known to be manifested by dispersing fine particles of uniform particle size so that they have a specific short-range order structure while being amorphous overall. In dental materials, resin-based materials that utilize specific structural colors have also been developed, specifically, single-layer resin-based blocks for dental cutting that consist only of composite materials that manifest such structural colors (see Patent Document 4). Furthermore, the conditions necessary for manifesting specific structural colors in hybrid resins, which are resin-based materials in which inorganic particles are dispersed in a resin matrix, have been clarified.

3. Conditions that structural color hybrid resins must satisfy As disclosed in Patent Document 5, in order for a hybrid resin to exhibit a specific structural color, it is necessary to satisfy all of the following conditions (a) to (d).

(a) The inorganic particles are composed of an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 nm to 1000 nm, and include one or more groups of uniform-diameter spherical particles (G-PID) in which 90% or more of the total number of particles in a number-based particle size distribution of the aggregate are present within a 5% range around the predetermined average primary particle diameter.
(b) When the number of the uniformly-sized spherical particle groups contained in the inorganic particles is a, and each uniformly-sized spherical particle group is expressed in order of decreasing average primary particle diameter as G-PID _m (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more), the average primary particle diameters of each G-PID _m when a is 2 or more differ from each other by 25 nm or more.
(c) When the refractive index of the resin matrix to light having a wavelength of 589 nm at 25° C. is n( _MX) and the refractive index of the inorganic spherical particles constituting each G-PID _m to light having a wavelength of 589 nm at 25° C. is n ( _{G-PIDm) ,} the relationship n _(MX) < n _{(G-PIDm) is satisfied for any n(G-PIDm)} .
(d) A function representing the probability that other inorganic spherical particles are present at a point distant r from the center of any inorganic spherical particle in the composite material (hybrid resin) , which is determined based on a scanning electron microscope image with the inner surface of the composite material as the observation plane, and the average particle density of the inorganic spherical particles in the observation plane: <ρ>, and the number of inorganic spherical particles present in the region between a circle at a distance r from any inorganic spherical particle in the observation plane and a circle at a distance r + dr: dn, and the area of the region: da (where da = 2πr · dr), are expressed by the following formula (1):
g(r)={1/<ρ>}×{dn/da}...(1)
When g(r) is a radial distribution function, the inorganic spherical particles constituting all of the "spherical particles of the same diameter" (G-PID) in the composite material are dispersed in a matrix material so as to have a short-range ordered structure that satisfies the following conditions 1 and 2:

[Condition 1]: In a radial distribution function graph showing the relationship between r/r0 and the g(r) corresponding to r at that time, the x-axis is a dimensionless number (r/ _r0 ) obtained by dividing the distance r from the center of any inorganic spherical particle dispersed in the composite material by the average particle size _r0 of all the inorganic spherical particles dispersed in the composite material, _and the y-axis is the radial distribution function g(r), the nearest inter-particle distance _r1 , which is defined as the r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph, is a value that is 1 to 2 times the average particle size _r0 of all the inorganic spherical particles dispersed in the composite material.
[Condition 2]: When r corresponding to the peak top of the peak that is second closest to the origin among the peaks appearing in the radial distribution function graph is defined as the next nearest interparticle distance: _r2 , the minimum value of the radial distribution function: g(r) between the nearest interparticle distance: _r1 and the next nearest interparticle distance: _r2 is a value of 0.56 or more and 1.10 or less.

The radial distribution function g(r) is generally represented by a radial distribution function graph in which the distance r is plotted on the x-axis (distance axis) and the value of g(r) at that distance r (the calculation result of the above formula (1)) is plotted on the y-axis (vertical axis), or by a radial distribution function graph in which the distance axis is a dimensionless number normalized by dividing the r by the average particle diameter of the particles and the y-axis (vertical axis) is the value of g(r) at r corresponding to the x-axis value (the calculation result of the above formula).

For the reason that <ρ> and dn are easy and reliable to confirm, it is preferable to use <ρ> and dn determined based on a scanning electron microscope image in which the internal surface of the first composite material is used as the observation plane, and g(r) calculated according to the above formula (1) based on da (=2πr·dr) corresponding to the value of dr used when determining the above dn.

The determination of <ρ>, dn and da based on a scanning electron microscope image with the inner surface of the first composite material as the observation plane can be performed as follows. That is, first, a composite material is prepared by curing a polymerizable curable composition that is the raw material of the first composite material, and a plane (observation plane) on which the dispersion state of the inorganic spherical particles inside the composite material can be observed is exposed on the surface by means of polishing the surface of the obtained composite material. Next, the observation plane is observed by a scanning electron microscope, and a microscopic image of a region containing at least 500 inorganic spherical particles in the plane is obtained. After that, the coordinates of the inorganic spherical particles in the region are obtained by using an image analysis software (e.g., "Simple Digitizer ver3.2" free software) from the obtained scanning electron microscope image. The average particle density <ρ> (unit: particles/cm2) can be determined by selecting one coordinate of any inorganic spherical particle from the obtained coordinate data, drawing a circle with a radius of distance r centered on the selected inorganic spherical particle and containing at least 200 inorganic spherical particles, and counting the number of inorganic spherical particles contained within the ^circle .

Regarding dn, when the average particle diameter of the inorganic spherical particles is represented by _r0 , dr is set so that its length is about _r0 /100 to _r0 /10, and dn can be determined by counting the number of inorganic spherical particles contained within the region between a circle having a radius of the distance r from the center of one arbitrarily selected inorganic spherical particle as the central particle and a circle having a radius of r+dr and having the same center as said circle. Furthermore, da, which is the area of the region between the two circles, is determined as 2πr·dr based on the length of dr that is actually set.

In the first composite material, the x-axis represents a dimensionless number (r/ _r0) normalized by dividing the distance r from the center of any inorganic spherical particle dispersed in the composite material by the average particle size r0 of all inorganic spherical particles dispersed in the composite material, and the y-axis represents a radial distribution function g(r ₎ representing the probability that other inorganic spherical particles are present at a point a distance r away from the center of any inorganic spherical particle. In this graph, the relationship between r/ _r0 and the g(r) corresponding to r at that time is represented by a radial distribution function graph. The nearest inter-particle distance _r1 , which is defined as the r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph, must be 1 to 2 times the average particle size _r0 of all inorganic spherical particles dispersed in the composite material (Condition 1). When _r1 is less than 1 time _r0 ( _r1 / _r0 <1), there is a lot of overlap between particles in the plane, and when _r1 is more than twice _r0 ( _r1 / _r0 >2), there is no particle in the vicinity of the selected central inorganic particle, so that short-range order is lost and structural color is not expressed. In other words, from the viewpoint of maintaining short-range order and facilitating the expression of structural color, _r1 / _r0 is preferably 1.0 or more and 2.0 or less, particularly 1.0 or more and 1.5 or less.

In addition, in the first composite material, when the r corresponding to the peak top of the peak that is the second closest to the origin among the peaks appearing in the radial distribution function graph is taken as the next closest interparticle distance: _r2 , the minimum value of the radial distribution function: g(r ₎ between the nearest interparticle distance: _r1 and the next closest interparticle distance: r2 must be a value of 0.56 or more and 1.10 or less (condition 2). If the minimum value is less than 0.56, the long-range orderliness of the arrangement structure of the inorganic spherical particles is high, and not only does the dependency of the structural color on the incident angle of light increase, but the saturation of the composite material is also high, making it difficult to obtain color tone compatibility when used as a dental filling material. On the other hand, if the minimum value exceeds 1.10, the arrangement structure of the inorganic spherical particles becomes a random structure, making it difficult to obtain the desired reflective performance and difficult to express the desired structural color. That is, from the viewpoint of expressing a structural color and facilitating obtaining color compatibility as a dental filling material, the minimum value is preferably 0.56 or more and 1.10 or less, and more preferably 0.56 or more and 1.00 or less.

3. Color difference: ΔE ^* Color difference: ΔE ^* is an index that indicates the degree of difference between two colors, and the larger the value, the more different the color tones of the two colors are. In the present invention, color difference: ΔE ^* means ΔE* determined by the following formula using the difference (ΔL ^* , Δa ^* , and Δb ^* ) between the values (L ^* value, a ^* value, and b ^* value) of each coordinate axis in the L ^* a ^* b ^* color space (color system) in which lightness is represented by L ^* , hue is represented by a ^*, and ^{chroma is represented by b* .}
ΔE ^* = {(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² } ^1/2
In addition, the L ^* , a* and b* values for a composite material (hybrid resin) having a single color tone in this specification refer to the L ^* , a ^* and b* values obtained by measuring a sample having a thickness of 1.0±0.1 mm against a white background using a spectrophotometer. Specifically, they are determined by the L ^* , a ^* and b ^* values obtained by measuring the spectral reflectance of a white background (a standard white plate is placed over the cured product to block light) over a measurement area of 5 mmφ using a spectrophotometer (Tokyo Denshoku Co., Ltd., "TC-1800MKII", halogen lamp: 12V100W, measurement wavelength range 380-780nm) under the reflected _light 0 ^° d method (JIS ^Z8722) .

For example, the color difference ΔE ^* between the first composite material and the second composite material is calculated by measuring the color difference by a spectrophotometer using samples of the first composite material and the second composite material each having a thickness of 1.0±0.1 mm. If L ^* , a ^* , and b ^* in the first composite material are L1 ^* , a1 ^* , and b1 ^* , and L ^* , a ^*, and b ^* in the second composite material are L2 ^* , a2 ^*, and b2 ^* , then:
ΔL ^* = L1 ^* - L2 ^*
Δa ^* = a1 ^* - a2 ^*
Δb ^* = b1 ^* - b2 ^*
Therefore,
ΔE ^* = {(L1 ^* - L2 ^* ) ² + (a1 ^* - a2 ^* ) ² + (b1 ^* - b2 ^* ) ² } ^1/2
It becomes.

The color difference can be adjusted mainly by blending a pigment and a coloring matter into the second composite material to adjust its color tone (L2 ^* , a2 ^*, and b2 ^* ). In this case, the color tone (L1 ^* , a1 ^* , and b1 ^* ) may be adjusted by blending a pigment and a coloring matter into the second composite material within a range that does not impair the effect of the specific structural color expression of the first composite material. Note that if the difference in color tone is large, ΔE ^* increases, the lamination interface between the layers becomes clearly visible to the naked eye, and the gradation effect of naturally blurring the boundary tends to decrease.

The color difference ΔE* between the first composite material and the second composite material must be 2 to 30, preferably 2 to 25, and more preferably 2 to 20, because the first layer can exhibit the inherent characteristics of the structural color resin ^blank and can express a more natural gradation.

3. Contrast ratio: CR = _YB / _YW The contrast ratio: CR is an index of transparency of a composite material (resin-based material) in which inorganic particles are dispersed in a matrix resin, and in the present invention means a value determined as the ratio of the Y value: _YW when the background is white to the Y value: _YB / when the background is black, obtained when color difference measurement is performed on a sample with a thickness of 1.0±0.1 mm using a spectrophotometer. The smaller the contrast ratio: CR, the higher the transparency, and the larger the contrast _ratio : _CR , the lower the transparency.

Specifically, the contrast ratio is determined by measuring the spectral reflectance of a black background (light-shielded state) and a white background (light-shielded state with a standard white plate placed over the cured product) in a 5 mm diameter measurement area using the reflected light 0°d method (JIS Z8722) with a spectrophotometer (Tokyo Denshoku Corporation, "TC-1800MKII", halogen lamp: 12V 100W, measurement wavelength range 380-780nm).

The contrast ratio can be adjusted by adjusting the amount of ultrafine particles (G-SFP) made of inorganic particles with an average primary particle diameter of less than 100 nm, or coloring substances such as pigments and dyes.

In the laminated dental resin blank of the present invention, it is preferable that the contrast ratio values of the first and second composite materials constituting the first and second layers in the laminated structure included in the part to be machined are each within a predetermined range. That is, it is preferable that the contrast ratio of the first composite material: CR1 is 0.28 to 0.46, and the contrast ratio of the second composite material: CR2 is 0.50 to 0.65. If the value of CR1 is outside the above range, it becomes difficult to observe the specific structural color, and it tends to be difficult to achieve harmony with the surrounding color tone. In addition, if the value of CR2 is outside the above range, when a dental prosthesis is produced that includes a portion in the base layer where no natural teeth are present, it tends to be difficult to exert the "effect of being able to widely harmonize with various surrounding environments" possessed by the first layer that expresses structural color.

From the viewpoint of effectiveness, it is preferable that CR1 is 0.28 to 0.46, particularly 0.28 to 0.43, and CR2 is 0.50 to 0.65, particularly 0.55 to 0.63. Also, it is preferable that the difference from the contrast ratio: CR2-CR1=ΔCR=ΔY _B /Y _W is 0.10 or more, particularly 0.12 to 0.27.

5. Raw materials for structural color hybrid resin and its manufacturing method As described above, the first composite material constituting the first layer, the composite material to be the first layer side additional layer added as needed, and the second composite material and the composite material to be the second layer side additional layer added as needed, when they exhibit structural color, are structural color hybrid resins, and the second composite material and the composite material to be the second layer side additional layer added as needed, when they do not exhibit structural color, are non-structural color hybrid resins.

The structural color hybrid resin used in the present invention is no different from the composite material described in claim 1 of Patent Document 5, except that it does not require ultrafine particles (G-SFP) from inorganic particles with an average primary particle diameter of 100 nm. The raw materials and preparation method are no different from the raw materials and preparation method described in claim 9 of Patent Document 5, except for the above points.

In other words, a curable composition containing a polymerizable monomer, inorganic particles that satisfy certain conditions, and a polymerization initiator is used as a raw material composition (hereinafter referred to as a "structural color raw material composition"), and the inorganic particles in the structural color raw material composition are brought to a specific dispersion state before being cured, thereby producing a structural color hybrid resin such as a first composite material.

The conditions that the inorganic particles must satisfy are as follows: (i) to (iii).
(i) The particle is composed of an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within the range of 100 nm to 1000 nm, and in a number-based particle size distribution of the aggregate, 90% or more of the total number of particles contain uniform-diameter spherical particle groups (G-PID) existing within a 5% range around the predetermined average primary particle diameter, and the number of uniform-diameter spherical particle groups is one or more.
(ii) when the number of the uniformly-sized spherical particle groups contained in the inorganic particles is a and each uniformly-sized spherical particle group is expressed in order of decreasing average primary particle diameter as G-PID _m (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more), the average primary particle diameters of each G-PID _m differ from each other by 25 nm or more.
(iii) When the refractive index at 25° C. of the cured product of the polymerizable monomer is n _(MX) and the refractive index at 25° C. of the inorganic spherical particles constituting each G-PID _m is n _(G-PIDm) , for each n _(G-PIDm) ,
n _(MX) <n _(G-PIDm)
The relationship is established.

The conditions for the dispersion state that the structural color raw material composition must satisfy are shown in (I) and (II) below.
(I) In a radial distribution function graph showing the relationship between r/r0 and g(r) corresponding to r at that time, the x-axis is a dimensionless number (r/ _r0 ) obtained by dividing the distance r from the center of any inorganic spherical particle dispersed in the hardened body of the structural color raw material composition by _the average particle diameter _r0 of all inorganic spherical particles dispersed in the hardened body of the raw material composition, and the y-axis is a radial distribution function g(r) representing the probability that other inorganic spherical particles exist at a point distant by a distance r from the center of the any inorganic spherical particle, the nearest inter-particle distance _r1 , defined as the r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph, is 1 to 2 times the average particle diameter _r0 of all inorganic spherical particles dispersed in the hardened body of the mixture.
(II) When the r corresponding to the peak top of the peak that is second closest to the origin among the peaks appearing in the radial distribution function graph is defined as the next nearest interparticle distance _r2 , the minimum value of the radial distribution function g(r) between the nearest interparticle distance _r1 and the next nearest interparticle distance _r2 is a value of 0.56 to 1.10.

The above conditions (i) to (iii) correspond to the conditions (a) to (c) that the structural color hybrid resin must satisfy, and the cured product of the polymerizable monomer contained in the structural color raw material composition corresponds to the resin matrix of the structural color hybrid resin (e.g., the resin matrix in the first composite material), and the inorganic particles contained in the structural color raw material composition correspond to the inorganic particles dispersed in the resin matrix of the structural color hybrid resin (e.g., the inorganic particles dispersed in the resin matrix in the first composite material). Regarding the above condition (iii), from the viewpoint of the visibility and clarity of the structural color and the color tone compatibility when used as a dental cutting blank, Δn (=n _(G-PIDm) -n _(MX ) ), which is the difference between n _(G-PIDm) and n _(MX) , is preferably 0.001 or more and 0.1 or less, more preferably 0.002 or more and 0.1 or less, and most preferably 0.005 or more and 0.05 or less.

Furthermore, satisfying the above conditions (I) and (II) corresponds to condition (a) that structural color hybrid resins must satisfy.

The following describes the raw materials for the structural color raw material composition that serves as the raw material for the structural color hybrid resin of the first composite material, etc. (in other words, the hardened product becomes the structural color hybrid resin of the first composite material, etc.).

5-1. Polymerizable monomers as raw materials for structural color raw material compositions The polymerizable monomers in the structural color raw material composition are those whose hardened bodies become the resin matrix of structural color hybrid resins. As the polymerizable monomers, radically polymerizable monomers can be suitably used. The radically polymerizable monomers are not particularly limited, and can be appropriately selected from (meth)acrylic compounds, cationic polymerizable monomers such as epoxies and oxetanes, and the like. For example, in order to obtain a dental polymerizable hardening composition, it is preferable to use (meth)acrylic compounds. Examples of (meth)acrylic compounds that can be suitably used include methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylic acid, N-(meth)acryloylglycine, p-vinylbenzoic acid, 2-(meth)acryloyloxybenzoic acid, 6-(meth)acryloyloxyethylnaphthalene-1,2,6-tricarboxylic acid anhydride, 13-(meth)acryloyloxytridecane-1,1-dicarboxylic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, N-hydroxypropyl (meth)acrylate, 1 ... Examples of the alkyl group include ethyl (meth)acrylamide, N,N-(dihydroxyethyl)(meth)acrylamide, 2,2-bis(methacryloyloxyphenyl)propane, 2,2-bis[(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,6-bis(methacrylethyloxycarbonylamino)trimethylhexane, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, neopentyl glycol dimethacrylate, and 4,4-diphenylmethane diisocyanate.

If necessary, multiple types of these (meth)acrylate polymerizable monomers may be used in combination.

As the polymerizable monomer, multiple types of polymerizable monomers are generally used to adjust the physical properties (mechanical properties and adhesion to tooth tissue in dental applications) of the hardened body that becomes the resin matrix of the structural color hybrid resin. In this case, it is desirable to set the type and amount of the polymerizable monomer so that the refractive index of the polymerizable monomer composition (mixture) at 25°C is in the range of 1.38 to 1.55, from the viewpoint of easily satisfying the above-mentioned condition regarding the refractive index. That is, when a silica-titanium group element oxide-based composite oxide, which is easy to adjust the refractive index, is used as the inorganic spherical particle, the refractive index at 25°C is in the range of about 1.45 to 1.58 depending on the content of silica, but by setting the refractive index of the polymerizable monomer composition in the range of 1.38 to 1.55, the refractive index of the obtained hardened body can be adjusted to about 1.40 to 1.57, making it easy to satisfy the above-mentioned condition. The refractive index of the polymerizable monomer and the hardened body of the polymerizable monomer can be determined using an Abbe refractometer at 25°C.

5-2. Inorganic particles as raw materials for structural color raw material composition The structural color raw material composition contains inorganic particles in an amount of usually 100 to 900 parts by weight, preferably 150 to 700 parts by weight, per 100 parts by weight of the polymerizable monomer. The inorganic particles contained in the structural color raw material composition are also inorganic particles dispersed in the resin matrix of the structural color hybrid resin, and contain one or more "spherical particle groups of the same particle size" (G-PID). In order for the inorganic spherical particles constituting the G-PID to be dispersed in the matrix material so as to have a short-range order structure that satisfies the above conditions, it is preferable that the inorganic particles do not contain inorganic particles (regardless of their shape) having an average primary particle size in the range of 100 to 1000 nm other than the G-PID. However, the ultrafine particle group (G-SFP) having an average primary particle diameter of less than 100 nm is unlikely to affect the short-range ordered structure, and has the function of controlling the viscosity of the structural color raw material composition and the contrast ratio of the structural color hybrid resin depending on the amount of the ultrafine particle group (G-SFP) to 100 parts by mass of the polymerizable monomer, so it is preferable to mix it in the range of 0.1 to 40 parts by mass, especially 0.2 to 30 parts by mass.

When the structural color raw material composition does not substantially contain coloring substances such as dyes or pigments (for example, when the concentration of coloring substances is 100 mass ppm or less, preferably 50 mass ppm or less), by setting the amount of G-SFP in this range, the contrast ratio of the resulting structural color hybrid resin can be set to 0.28 to 0.46.

The amount of the spherical particles of the same particle size: G-PID is usually 100 to 900 parts by mass per 100 parts by mass of polymerizable monomer, as the total amount of all G-PID contained (i.e., the total amount of inorganic spherical particles). Since the structural color hybrid resin has a moderate transparency and has a high effect of expressing structural color, the amount of G-PID is preferably 100 to 900 parts by mass, and more preferably 150 to 700 parts by mass, per 100 parts by mass of polymerizable monomer when the structural color raw material composition does not contain ultrafine particles (G-SFP). In addition, when G-SFP is contained, it is preferable to use the amount obtained by subtracting the amount of G-SFP from the above amount.

When multiple types of G-PIDs are included, the amount of each G-PID may be appropriately allocated so that the total amount falls within the above range, taking into consideration the color tone of the structural color of each G-PID and the desired color tone of the dental cutting blank.

The inorganic spherical particles, G-PID, G-SFP, etc. that make up the inorganic particles are described in detail below.

(1) Inorganic spherical particles The inorganic spherical particles constituting the G-PID are not particularly limited in material as long as they satisfy the above-mentioned conditions for constituting the G-PID. Examples of materials that can be suitably used include amorphous silica, silica-titanium group element oxide composite oxide particles (silica-zirconia, silica-titania, etc.), quartz, alumina, barium glass, strontium glass, lanthanum glass, fluoroaluminosilicate glass, ytterbium fluoride, zirconia, titania, colloidal silica, etc. Among these, it is preferable to use particles made of silica-titanium group element oxide composite oxide, which is a composite oxide of silica and a titanium group element (group 4 element of the periodic table) oxide, because the refractive index can be easily adjusted. In the silica-titanium group element oxide composite oxide, the refractive index at 25°C can be changed within a range of about 1.45 to 1.58 depending on the content of the silica content. Specific examples of the silica-titanium group element oxide composite oxide particles include silica-titania, silica-zirconia, and silica-titania-zirconia.

The inorganic spherical particles may be surface-treated with a silane coupling agent.

(2) Group of spherical particles with the same particle size: G-PID
The uniform particle size spherical particle group (G-PID) is composed of an aggregate of inorganic spherical particles having a predetermined average primary particle size within the range of 100 to 1000 nm, and each inorganic spherical particle constituting the aggregate is The aggregate is substantially composed of the same material, and in the number-based particle size distribution of the aggregate, 90% or more of the total number of particles is present within a range of 5% around the predetermined average primary particle size. means...

The average primary particle diameter of inorganic spherical particles here means the average value obtained by taking a photograph of the G-PID using a scanning electron microscope, selecting 30 or more particles observed within a unit field of view of the photograph, and determining the primary particle diameter (maximum diameter) of each. In addition, spherical means that it is sufficient that the particles are approximately spherical, and do not necessarily have to be completely spherical. A photograph of the G-PID is taken using a scanning electron microscope, the maximum diameter of each particle (30 or more) within the unit field of view is measured, and the average uniformity obtained by dividing the particle diameter in the direction perpendicular to the maximum diameter by the maximum diameter is 0.6 or more, more preferably 0.8 or more.

In structural color hybrid resins such as the first composite material, the constituent inorganic particles of G-PID, which is an aggregate of inorganic particles with a narrow particle size distribution (number-based particle size distribution), are spherical, and each constituent particle of G-PID has a specific short-range order structure and is dispersed in the resin matrix, causing diffraction interference according to the Bragg condition, emphasizing light of a specific wavelength and generating colored light of a color tone according to the average primary particle size (structural color is expressed). In other words, in order for structural color to be expressed, 90% (by number) or more of the inorganic spherical particles that make up G-PID must be present within a range of 5% around the average primary particle size. In addition, in order to express a structural color with a specific color tone within a wide range of blue to yellow to red, the average primary particle size of the inorganic spherical particles that make up G-PID must be within the range of 100 to 1000 nm. When the average primary particle size is 230 to 800 nm, yellow to red structural colors (colored light) tend to appear, and when the average primary particle size is less than 150 nm to 230 nm, blue structural colors (colored light) tend to appear.

The average primary particle size of G-PID is preferably 230-800 nm, more preferably 240-500 nm, and particularly preferably 260-350 nm, because it produces a yellow to red structural color (colored light) that is favorable for restorative treatment of natural teeth. When G-PID with an average primary particle size in the range of 230 nm to 260 nm is used, the resulting colored light is yellowish, which is useful for restoring teeth in the B-type (reddish yellow) category of the shade guide ("VITA Classical", manufactured by VITA). When G-PID with an average primary particle size in the range of 260 nm to 350 nm is used, the resulting colored light is reddish, which is useful for restoring teeth in the A-type (reddish brown) category of the shade guide ("VITA Classical", manufactured by VITA). Since dentin often has a reddish hue, the embodiment using only G-PID with an average primary particle size in the range of 260 nm to 350 nm is the most preferable because it has a wide compatibility with various color tones of restored teeth. On the other hand, when only G-PID with a particle size in the range of 150 nm to less than 230 nm is used, as mentioned above, the obtained colored light is blue, and the color compatibility with the tooth structure tends to be poor for cavities formed from the enamel to the dentin, but it is useful for restoring enamel, especially incisal edges.

The inorganic particles contained in the structural color raw material composition (dispersed in the resin matrix in the structural color hybrid resin such as the first composite material) may contain one or more types of G-PID. The number of G-PIDs contained: a, is preferably 1 to 5, more preferably 1 to 3, and most preferably 1 or 2.

However, when multiple types of G-PID are contained in the inorganic particles, the average primary particle diameters of the respective G-PIDs _m must differ from each other by 25 nm or more. That is, when the number of G-PIDs contained in the inorganic particles is "a" (e.g., "3"), and each G-PID is expressed as G-PID _m (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more) in order of decreasing average primary particle diameter, the materials constituting the individual particles in each G-PID _m (e.g., G-PID ₁ , G-PID _2, and G-PID ₃ when a=3) may be different from each other, but when the average primary particle diameter of each G-PID _m in this case is d _m , each d _m must differ from each other by 25 nm or more (e.g., when a=3, |d ₁ - _{d 2} |≧25 nm, |d ₂ - _{d 3} |≧25 nm, and naturally |d ₁ - _{d 3} |≧25 nm). By satisfying this condition, for example, each G-PID can be dispersed in the form of an aggregate of a small number of inorganic spherical particles, not exceeding about 20, which are aggregated with a very loose binding force, and thus it is possible to disperse with a short-range ordered structure that can express a structural color for each G-PID, and as a result, it is possible to express a unique structural color (according to the average primary particle size) for each G-PID. On the other hand, if this condition is not satisfied, the particle size distribution of the inorganic spherical particles as a whole becomes broad, and probably the inorganic spherical particles constituting each G-PID are dispersed by mutual substitution, and it becomes difficult to express a structural color, which is probably due to the same phenomenon as when an aggregate of a single inorganic spherical particle that does not satisfy the condition of the number-based particle size distribution is used.

When multiple G-PIDs are used, the average primary particle diameters _dm of the G-PIDs _m preferably differ from each other by 30 nm or more, particularly 40 nm or more (i.e., the difference between _dm and dm _-1 is 30 nm or more, particularly 40 nm or more). In addition, the difference between _dm and _dm-1 is preferably 100 nm or less, particularly 60 nm or less.

In addition, when multiple G-PIDs are contained in the structural color raw material composition, and further in the structural color hybrid resin such as the first composite material, each G-PID has an extremely sharp particle size distribution, and since there is a difference in the average primary particle diameter as described above, the particle size distributions of each G-PID are unlikely to overlap, and even if they overlap partially, it is possible to confirm the particle size distribution of each G-PID. In other words, the particle size distribution of inorganic particles has the same number of independent peaks as the number of G-PIDs contained in the range of 100 nm to 1000 nm, and even if each peak partially overlaps, the average primary particle diameter and number-based particle size distribution of each G-PID can be confirmed by performing waveform processing. In addition, the particle size distribution of inorganic particles contained in the structural color hybrid resin such as the first composite material can be confirmed, for example, by image processing of an electron microscope photograph of its internal surface.

(3) Organic-inorganic hybrid filler At least a part of the one or more "spherical particle groups of the same particle size" (G-PID) is preferably blended as an organic-inorganic hybrid filler that contains one type of "spherical particle groups of the same particle size" (G-PID) and a resin whose refractive index at 25°C is smaller than that of the inorganic spherical particles constituting the one type of "spherical particle groups of the same particle size" (G-PID), and does not contain any "spherical particle groups of the same particle size" (G-PID) other than the one type of "spherical particle groups of the same particle size" (G-PID), in other words, "an organic-inorganic hybrid filler containing only a single G-PID". Here, the organic-inorganic hybrid filler means a powder consisting of a complex in which an inorganic filler is dispersed in an (organic) resin matrix, or a filler consisting of an aggregate in which primary particles of an inorganic filler are bound together by an (organic) resin.

For example, when three types of G- PIDs having different average primary particle diameters, namely G-PID ₁ , G-PID _2, and G-PID _3, are included, it is preferable to blend all or a part of at least one of them as an "organic-inorganic composite filler containing only a single G-PID". When all of G-PID ₁ is blended into the structural color raw material composition as an organic-inorganic composite filler (composite filler ₁ ) containing only G-PID 1, the short-range ordered structure that expresses the structural color of G-PID ₁ is realized because only G-PID ₁ is contained in the composite filler 1, so that the structural color of G-PID ₁ is reliably expressed in the structural color hybrid resin such as the first composite material obtained by curing the structural color raw material composition. From the viewpoint of expecting such an effect and further facilitating adjustment of the viscosity of the structural color raw material composition, it is preferable that 10% to 90%, particularly 20% to 80%, and further 30% to 70% of each G-PID is blended as "an organic-inorganic composite filler containing only a single G-PID".

When G-PID is blended in a form other than "an organic-inorganic composite filler containing only a single G-PID", it is generally blended in the form of a powder (G-PID itself as an aggregate of inorganic spherical particles), but it is also possible to blend it as an organic-inorganic composite filler containing multiple types of G-PID.

When compounded as an organic-inorganic composite filler, it is important that the refractive index at 25°C of the resin constituting the (organic) resin matrix is smaller than that of the inorganic spherical particles contained in the organic-inorganic composite filler. The resin is not particularly limited as long as it satisfies such conditions, but is preferably a cured product of the polymerizable monomer in the raw material composition. In this case, it is not necessary to have exactly the same composition as the polymerizable monomer component of the raw material composition, but it is preferable to use one whose refractive index at 25°C is equivalent to that of the polymerizable monomer component at 25°C. In addition, when the refractive index of the resin at 25°C is n _(R) and the refractive index of the inorganic spherical particles at 25°C is n _(F) , in any organic-inorganic composite filler,
n _(R) < n _(F)
The relationship must be satisfied. When the organic-inorganic composite filler contains inorganic spherical particles having different refractive indices at 25° C., this relationship must be satisfied for all of the inorganic spherical particles. The difference between n _(F) and n _(R) , Δn (=n _(F) −n _(R) ), is preferably 0.001 or more and 0.01 or less, and more preferably 0.001 or more and 0.005 or less.

The average particle size of the organic-inorganic composite filler is not particularly limited, but from the viewpoint of improving the mechanical strength of the cured body and the operability of the curable paste, it is preferably 2 to 100 μm, more preferably 5 to 50 μm, and particularly preferably 5 to 30 μm.

The amount of organic-inorganic composite filler in the raw material composition may be determined by converting the amount of inorganic spherical particles contained in the organic-inorganic composite filler into the amount of G-PID, a group of spherical particles of the same particle size that is not made into an organic-inorganic composite filler and is contained in the raw material composition, so that the total amount of all G-PID contained (i.e., the total amount of inorganic spherical particles) is the amount described above.

(4) Ultrafine particle group: G-SFP
The ultrafine particle group (G-SFP) which may be contained in the inorganic particles is a particle aggregate consisting of inorganic particles having an average primary particle size of less than 100 nm, and is a precursor of the first composite material (when cured). It is blended for the purpose of adjusting the viscosity of the hardenable composition which is the material for obtaining the dental cutting blank, or for the purpose of adjusting the contrast ratio of the dental cutting blank. However, the average of G-SFP The primary particle diameter must be at least 25 nm smaller than the average primary particle diameter (d ₁ ) of G-PID _1, which has the smallest average primary particle diameter among the G-PIDs to be mixed with the inorganic particles. If the conditions are not satisfied, the dispersion state of the inorganic spherical particles is adversely affected, and it becomes difficult to express the specific structural color. The shape of the inorganic particles constituting the G-SFP is not particularly limited, and may be irregular. The lower limit of the average primary particle size is usually 2 nm.

The average primary particle size of G-SFP is preferably 3 nm to 75 nm, particularly preferably 5 nm to 50 nm, because it has little effect on the expression of structural color. For the same reason, it is preferably 30 nm or more, particularly preferably 40 nm or more smaller than the average primary particle size (d ₁ ) of G-PID ₁ .

The inorganic particles constituting G-SFP can be made of the same material as the inorganic spherical particles without any particular restrictions. In addition, surface treatment with a silane coupling agent can be performed as with the inorganic spherical particles. The preferred aspects are also basically the same as those of the inorganic spherical particles, except for the average primary particle size and shape.

5-3. Polymerization initiator as a raw material for structural color raw material composition The polymerization initiator as a raw material for structural color raw material composition is not particularly limited as long as it has the function of polymerizing and curing the polymerizable monomer. The polymerization method of the curable composition may be a reaction by light energy such as ultraviolet light or visible light (hereinafter referred to as photopolymerization), a chemical reaction between a peroxide and an accelerator, or a method by heat energy (hereinafter referred to as thermal polymerization), and any method may be used. Photopolymerization and thermal polymerization are preferred because the timing of polymerization can be freely selected by external energy such as light or heat, and the operation is simple. Thermal polymerization is particularly preferred because it is less likely to cause polymerization unevenness due to light irradiation and the polymerization reaction can be performed uniformly.

Photopolymerization initiators include benzoin alkyl ethers such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether; benzil ketals such as benzil dimethyl ketal and benzil diethyl ketal; benzophenones such as benzophenone, 4,4'-dimethylbenzophenone, and 4-methacryloxybenzophenone; α-diketones such as diacetyl, 2,3-pentanedione benzyl, camphorquinone, 9,10-phenanthraquinone, and 9,10-anthraquinone; 2,4-diethoxythioxanthone, 2- Thioxanthone compounds such as chlorothioxanthone and methylthioxanthone, bisacylphosphine oxides such as 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, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide can be used.

Reducing agents are often added to photopolymerization initiators. Examples of reducing agents include tertiary amines such as 2-(dimethylamino)ethyl methacrylate, ethyl 4-dimethylaminobenzoate, and N-methyldiethanolamine; aldehydes such as lauryl aldehyde, dimethylaminobenzaldehyde, and terephthalaldehyde; and sulfur-containing compounds such as 2-mercaptobenzoxazole, 1-decanethiol, thiosalicylic acid, and thiobenzoic acid.

Furthermore, in addition to the above photopolymerization initiator and reducing compound, a photoacid generator is often used. Examples of such photoacid generators include diaryliodonium salt compounds, sulfonium salt compounds, sulfonic acid ester compounds, halomethyl-substituted S-triazine derivatives, pyridinium salt compounds, etc.

Examples of thermal polymerization initiators include peroxides such as benzoyl peroxide, p-chlorobenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxydicarbonate, and diisopropylperoxydicarbonate; azo compounds such as azobisisobutyronitrile; boron compounds such as tributylborane, tributylborane partial oxide, sodium tetraphenylborate, sodium tetrakis(p-fluorophenyl)borate, and triethanolamine tetraphenylborate; barbituric acids such as 5-butylbarbituric acid and 1-benzyl-5-phenylbarbituric acid; and sulfinic acid salts such as sodium benzenesulfinate and sodium p-toluenesulfinate.

These polymerization initiators may be used alone or in combination of two or more. It is also possible to combine multiple initiators that use different polymerization methods.

The amount of polymerization initiator to be used may be selected according to the purpose, but is usually 0.01 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of polymerizable monomer.

When a thermal polymerization initiator is used, the polymerization temperature is preferably 60 to 200°C, more preferably 70 to 150°C, and even more preferably 80 to 130°C. If polymerization is carried out at a temperature below 60°C, the polymerization reaction will be insufficient, the strength of the dental cutting blank will be weakened, and cracks will occur. On the other hand, if polymerization is carried out at a temperature above 200°C, the structural color hybrid resin will be exposed to high temperatures during production, causing discoloration of the resin components, making it difficult to achieve the effect of the present invention of matching color with natural teeth.

5-4. Other additives that are the raw materials of the structural color raw material composition Other additives such as polymerization inhibitors and ultraviolet absorbers can be blended into the structural color raw material composition as long as they do not impair the effects of the composition.

The hardened product of the structural color raw material composition, including the first composite material, becomes a structural color hybrid resin, and as described above, it expresses a specific structural color without using a coloring substance such as a pigment. Therefore, there is no particular need to blend coloring substances such as dyes and pigments that may discolor over time into the structural color hybrid resin, and it is preferable not to include coloring substances from the viewpoint of preventing discoloration and transparency. However, the blending of these coloring substances is not excluded, and they can be blended within a range that does not inhibit the effect of the specific structural color. Depending on the amount of inorganic particles, etc. contained in the structural color raw material composition that is the raw material of the first composite material, the (allowable) blending amount of the coloring substance based on the total mass of the structural color raw material composition (which is also the total mass of the first composite material) is usually 100 mass ppm or less, preferably 50 mass ppm or less. However, with regard to the structural color raw material composition that is the raw material of the composite material that becomes the second composite material and the second layer side additional layer formed as necessary, the effect of coloring takes precedence over the effect of the specific structural color, so it is necessary to blend the coloring substance so that the color difference from the first composite material is within a predetermined range, as described below.

5-5. Method for preparing raw material composition The raw material composition can be prepared by kneading and defoaming predetermined amounts of each of the above-mentioned components. In order to reliably satisfy the conditions (I) and (II) of the dispersion state, it is preferable to adjust as follows. That is, as for the kneading method, it is preferable to knead using a kneading device such as a planetary motion stirrer, because it is possible to satisfy the above-mentioned dispersion conditions in a short time and scale-up production is easy. In addition, as for the defoaming treatment, it is preferable to adopt a method of defoaming under reduced pressure, because it is possible to remove air bubbles in a short time even from a highly viscous composition.

In this method, the kneading and degassing treatment must be performed under kneading and degassing treatment conditions that have been confirmed to ensure that the dispersion state of the inorganic particles (b) in the hardened body obtained by hardening the resulting kneaded product satisfies the conditions (I) and (II).

It is preferable to determine such conditions by (1) preparing a curable composition having the same or substantially the same composition as the raw material composition to be actually produced in advance by changing the kneading conditions and degassing treatment conditions in multiple ways, and examining the radial-radial distribution function: g(r) of the cured product of the curable composition prepared under each condition to determine conditions that satisfy the conditions (I) and (II), and adopting the same conditions as the determined conditions. Since the desired first polymerizable curable composition can be reliably produced simply by setting the predetermined kneading conditions, it is not necessary to change the conditions each time when producing the same first polymerizable curable composition (same composition and same amount), and excessive kneading (kneading for an unnecessarily long time) can be prevented, which improves the efficiency of the work.

6. Non-structural color hybrid resin and its raw materials, etc. Non-structural color hybrid resin is a hybrid resin that does not satisfy at least one of the above conditions (a) to (d), or a hybrid resin that is blended with a large amount of pigment, etc., so that the expression of a specific structural color cannot be visually confirmed. It is used as a composite material when the second composite material and the composite material that becomes the second layer side additional layer added as needed do not express a structural color.

As described above, the second composite material has a different color tone from the first composite material, and the color difference must be within a specific range. The contrast ratio: CR2 of the second composite material is preferably 0.50 to 0.65. Since the first composite material is not usually colored by adding coloring materials such as dyes or pigments to obtain the effect of a specific structural color, the second composite material and the raw material composition from which it is made usually contain a coloring substance. This also applies to the composite material and raw material composition from which it is made that will be the second layer side additional layer that is added as necessary.

That is, the non-structural color hybrid resin, which is a composite material that becomes the second composite material and the second layer side additional layer added as necessary, is a composite material in which inorganic particles are dispersed in a resin matrix and a coloring material such as a dye or pigment is added so that the color difference from the first composite material is within a specific range, and is obtained by curing a polymerizable curable composition (hereinafter also referred to as "non-structural color raw material composition") containing a polymerizable monomer, inorganic particles, a polymerization initiator, and a coloring material. The non-structural color raw material composition may be a structural color raw material composition to which a coloring material has been added (in an amount such that the specific structural color cannot be visually confirmed), and the same polymerizable monomer and polymerization initiator as those in the structural color raw material composition can be used. There are no particular restrictions on the inorganic particles as in the structural color raw material composition, and those that are considered to be usable in conventional resin blanks for dental cutting processing can be used without any particular restrictions. The total amount of inorganic particles is usually 100 to 900 parts by weight, preferably 150 to 700 parts by weight, per 100 parts by weight of the polymerizable monomer. The amount of coloring material contained in the non-structural color raw material composition is usually 500 to 7000 mass ppm, preferably 600 to 6500 mass ppm, based on the total mass of the non-structural color raw material composition (which is also the total mass of the composite material that is the cured product). In addition, the composition may contain other additives such as ultrafine particles (G-SFP) for adjusting the color tone and contrast ratio of the cured product, polymerization inhibitors, and ultraviolet absorbers.

In the blank of the present invention, the second composite material and the non-structural color hybrid resin that forms the second layer side additional layer that is added as needed are often materials that make up the vicinity of the cervical part of the tooth in dental prostheses. Also, there are large individual differences in the color tone of the cervical part of the tooth, and it is necessary to prepare a color tone that suits each individual patient. By adding a coloring substance, it is possible to meet such requirements.

The coloring substance (colorant) may be a pigment or a dye. Representative pigments are inorganic pigments, and examples of such inorganic pigments include titanium oxide, zinc oxide, zirconium oxide, zinc sulfide, aluminum silicate, calcium silicate, carbon black, iron oxide, copper chromite black, chromium oxide green, chrome green, violet, chrome yellow, lead chromate, lead molybdate, cadmium titanate, nickel titanium yellow, ultramarine blue, cobalt blue, bismuth vanadate, cadmium yellow, and cadmium red. In the present invention, inorganic pigments also correspond to inorganic fillers. Organic pigments such as monoazo pigments, diazo pigments, diazo condensation pigments, perylene pigments, and anthraquinone pigments can also be used. Examples of dyes include red dyes such as KAYASET RED G (Nippon Kayaku) and KAYASET REDB (Nippon Kayaku); yellow dyes such as KAYASET Yellow 2G and KAYASET Yellow GN; and blue dyes such as KAYASET Blue N, KAYASET Blue G, and KAYASET Blue B. Considering color stability in the oral cavity, it is preferable to use water-insoluble pigments rather than water-soluble dyes.

7. Manufacturing Method of the Blank of the Present Invention The blank of the present invention can be manufactured by appropriately processing a laminate of the hybrid resin having the above-mentioned laminated structure into a part to be machined.

The hybrid resin laminate can be suitably manufactured by casting polymerization using a curable raw material composition that is the raw material of the hybrid resin (composite) that constitutes each layer. Here, casting polymerization means that a mold of a predetermined shape is filled with a polymerizable curable composition and then polymerized and cured. The volume of the mold may be appropriately selected according to the desired shape. Similarly, the shape of the mold may be a rectangular column, a cylindrical column, a square plate, a disk, or other irregular shape, and there is no particular restriction. During polymerization, pressure may be applied with an inert gas such as nitrogen, if necessary. A mold having the same or substantially the same shape as the part to be cut is prepared, and the curable raw material composition that will be each layer is filled in sequence to a predetermined thickness inside the mold, and then polymerized and cured, and the obtained bulk body (hybrid resin laminate) may be used as the part to be cut as it is, or it may be filled into a mold having a larger size to manufacture a bulk body, and this may be punched or cut to make the part to be cut. The filling method can be a known technique and is not particularly limited, but for example, the mold can be filled by injection, extrusion, pressing, etc.

The mold material may be metal, ceramic, resin, etc., depending on the purpose, and it is preferable to use a material that is more heat resistant than the polymerization temperature to be carried out. Examples of mold materials include SUS, high-speed tool steel, aluminum alloy, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), etc.

The obtained bulk body can be subjected to post-processing such as heat treatment, polishing, cutting, attachment of a holder, printing, etc., as necessary. Furthermore, a holding pin for fixing the dental cutting blank to the cutting machine can be attached as necessary. The shape of the holding pin is not particularly limited as long as it can fix the dental cutting blank to the cutting machine, and may not be provided depending on the shape of the dental cutting blank and the requirements of the processing machine. Examples of materials for the holding pin include stainless steel, brass, aluminum, etc. The method of fixing the holding pin to the part to be cut (dental cutting blank body) is not limited to adhesion, and may be a method such as fitting or screwing. There is also no particular limitation on the adhesion method, and various commercially available adhesives such as isocyanate-based, epoxy-based, urethane-based, silicone-based, and acrylic-based adhesives can be used.

Next, the multilayer mill blank of the present invention will be specifically described using examples. In each of the examples and comparative examples described below, various structural color raw material compositions and non-structural color raw material compositions are prepared, and the obtained compositions and their cured products are evaluated. In addition, these compositions are laminated in a predetermined combination and then cured to obtain a hybrid resin laminate that will become the cutting portion of the dental cutting blank, and the hybrid resin laminate is evaluated.

1. Raw materials for structural color raw material composition and non-structural color raw material composition The raw materials for the structural color raw material composition and non-structural color raw material composition used in the examples and comparative examples, as well as their physical properties, are described below.

1-1. Polymerizable monomer component As the polymerizable monomer component in the structural color raw material composition and the non-structural color raw material composition, a polymerizable monomer mixture M1 having the composition shown in Table 1 was used. The abbreviations in the polymerizable monomer column in Table 1 represent the compounds shown below, and the numbers in parentheses after the abbreviations represent the parts by mass used.
UDMA: 1,6-bis(methacrylethyloxycarbonylamino)trimethylhexane 3G: triethylene glycol dimethacrylate The viscosity of M1 and the refractive index of M1 (before curing) and its cured body were measured as follows. The results are shown in Table 1. That is, the viscosity was measured in a thermostatic room at 25°C using an E-type viscometer (Tokyo Seiki: VISCONIC ELD). The refractive index of M1 (before curing) and its cured body was measured in a thermostatic room at 25°C using an Abbe refractometer (Atago Co., Ltd.). At this time, the hardened sample was prepared by adding 0.2% by mass of camphorquinone (CQ) (as a photopolymerization initiator), 0.3% by mass of ethyl p-N,N-dimethylaminobenzoate (DMBE), and 0.15% by mass of hydroquinone monomethyl ether (HQME) per 100 parts by mass of polymerizable monomer, mixing the mixture uniformly, placing it in a mold having a through hole of 7 mmφ×0.5 mm, pressing polyester films on both sides, and then irradiating the mixture with light for 30 seconds using a halogen-type dental light irradiator (Demetron LC, manufactured by Cybron) with a light amount of 500 mW/cm ² to harden the mixture, and then removing it from the mold. When the hardened sample was set in the Abbe refractometer, bromonaphthalene, a solvent that does not dissolve the sample and has a higher refractive index than the sample, was dropped onto the sample in order to bring the hardened sample into close contact with the measurement surface.

1-2. Group of spherical particles with the same particle size: G-PID
As G-PID, G-PID1 and G-PID2 shown in Table 2 were used. G-PID1 and G-PID2 were prepared in the same manner as the method (sol-gel method) disclosed in Patent Document 5. Both of them were surface-treated with γ-methacryloyloxypropyltrimethoxysilane. In addition, G-PID1 and G-PID2 were treated in the following manner in the same manner as described in the examples of Patent Document 5. The average primary particle diameter, the ratio of particles within ±5% [the ratio (%) of the number of particles present within 5% of the average primary particle diameter in the number-based particle size distribution to the total number of particles], the average uniformity The refractive index and the viscosity of the polymer were measured. The results are shown in Table 2. As shown in Table 2, both G-PID1 and G-PID2 were spherical particles having the same particle size that satisfied the above condition (a). It can be said that.

(1) Average primary particle diameter Photographs of powder were taken at magnifications of 5,000 to 100,000 times using a scanning electron microscope (manufactured by Philips, "XL-30S"). The photographed images were processed using image analysis software ("IP-1000PC", product name; manufactured by Asahi Kasei Engineering Corporation). The number of particles (30 or more) and primary particle diameter (maximum diameter) observed within a unit field of view of the photograph were measured, and the number average primary particle diameter was calculated based on the measured values (the sum of the measured values divided by the number of particles).

(2) Particle Proportion Within ±5% Among all particles (30 or more) in the unit field of view of the photograph, the number of particles having a primary particle diameter (maximum diameter) outside the particle diameter range of plus or minus 5% of the average primary particle diameter obtained above was counted, and this value was subtracted from the number of all particles to obtain the number of particles within the particle diameter range of plus or minus 5% of the average primary particle diameter in the unit field of view of the photograph, and calculated according to the following formula.

Percentage of particles within ±5% (%) = [(Number of particles within a particle size range of 5% around the average primary particle size in a unit field of view of a scanning electron microscope photograph) / (Total number of particles in a unit field of view of a scanning electron microscope photograph)] x 100

(3) Average uniformity A photograph of the powder was taken with a scanning electron microscope, and the number (n: 30 or more) of uniformly sized spherical particles (G-PID) observed within a unit field of view in the photograph was determined. The ratio (Bi/Li) of the maximum diameter of the particle (long diameter (Li)) to the diameter in the direction perpendicular to the long diameter (Bi) was calculated, and the sum of these ratios was divided by the number of particles to obtain the average uniformity.

(4) Refractive index The refractive index was measured by the immersion method using an Abbe refractometer (manufactured by Atago Co., Ltd.). That is, in a thermostatic room at 25° C., a group of uniform particle diameter spherical particles (G-PID) was dispersed in 50 ml of anhydrous toluene in a 100 ml sample bottle. 1-Bromotoluene was gradually added dropwise to this dispersion while stirring with a stirrer, and the refractive index of the dispersion at the point when the dispersion became most transparent was measured, and the obtained value was regarded as the refractive index of the group of uniform particle diameter spherical particles (G-PID).

1-3. Organic-inorganic composite filler (CF)
The organic-inorganic composite filler (CF) was also prepared as follows using G-PID2 shown in Table 2, in the same manner as in the examples of Patent Document 5. That is, first, a dispersion in which 100 g of G-PID2 was dispersed in 200 g of water was obtained using a circulation type grinder SC Mill (manufactured by Nippon Coke Engineering Co., Ltd.). Next, a mixed solution (pH 4) of 4 g of γ-methacryloyloxypropyltrimethoxysilane, 0.003 g of acetic acid, and 80 g of water, which had been separately prepared, was added to the dispersion and mixed until uniform. After that, the dispersion was lightly mixed and supplied onto a disk rotating at high speed to be granulated by a spray drying method, and then vacuum dried at 60° C. to obtain an aggregate having a roughly spherical shape. Thereafter, 50 g of the above aggregates were immersed in a polymerizable monomer solution prepared by mixing 10 g of a polymerizable monomer component M1, 0.025 g of azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and 5.0 g of methanol as an organic solvent. After thorough stirring, the organic solvent was removed, and the mixture was heated for 1 hour under conditions of a reduced pressure of 10 hectopascals and 100° C. to polymerize and harden the above polymerizable monomer component, thereby obtaining an organic-inorganic composite filler (CF) having a substantially spherical shape and an average particle size of 12 μm.

1-4. Ultrafine particles (G-SFP)
As the G-SFP, Reolosil QS-102 (average primary particle size 12 nm, manufactured by Tokuyama Corporation) was used.

1-5. Polymerization initiator A thermal polymerization initiator made of benzoyl peroxide (BPO) was used.

1-6. Pigments - Red pigment (Pigment Red 166)
・Yellow pigment (Pigment Yellow 95)
- Blue pigment (Pigment Blue 60).

2. Preparation of structural color raw material composition and non-structural color raw material composition and evaluation of the cured body 2-1. Preparation of structural color raw material composition (P1 to P6) Structural color raw material composition: P1 was prepared as shown below. That is, after mixing 100 parts by mass of M1 and 1.0 part by mass of BPO, G-PID1 and G-SFP were added so that the mass ratio of the two was G-PID1:G-SFP=95:5 and the inorganic filling rate, defined as the proportion of the mass of the total inorganic particles to the mass of the entire structural color raw material composition, was 72% by mass, and the mixture was mixed using a planetary mixer until it was uniform to form a paste, and structural color raw material composition: P1 was prepared.

In addition, structural color raw material compositions P2 to P6 were prepared in the same manner as above, except that the inorganic filling rate was set to the inorganic filling rate shown in Table 3.

The refractive index of the cured product of M1: n _(MX) is 1.509, and the refractive index of G-PID1 is n(G-PID1)=1.515, which is larger than n _(MX) , and therefore satisfies the above condition (c). Therefore, it can be said that the hybrid resins made of the cured products of these structural color raw material compositions: P1 to P6 all satisfy the above conditions (a) to (c) {P1 to P6 contain one type of G-PID, and also satisfy the above condition (b).}

2-2. Preparation of non-structural color raw material compositions (L1 to L6) After mixing 100 parts by mass of M1 and 1.0 part by mass of BPO, a mixture of 50% by mass of G-PID2 and 50% by mass of CF (organic-inorganic composite filler) was added so that the inorganic filling rate became 76%, and various pigments were added in the amounts shown in Table 4. Except for this, non-structural color raw material compositions: L1 to L6 were prepared in the same manner as in the preparation of P1.

2-3. Evaluation of the hardened body of each raw material composition 2-3-1. Confirmation that the hardened body of the structural color raw material composition (P1 to P6) is a structural color hybrid resin According to the method described in Patent Document 5, the hardened body of each structural color raw material composition (P1 to P6) was visually evaluated for coloring light, measured for the peak wavelength of coloring light, and evaluated for the radial distribution function of inorganic spherical particles by the methods shown in (1) to (3) below. The results are shown in Table 5.

(1) Visual Evaluation of Colored Light The structural color raw material compositions (P1 to P6) were vacuum degassed, filled into a 10 mm x 12 mm x 14 mm mold, and the upper surface was smoothed. Then, using a heating and pressure polymerization apparatus, they were subjected to heating and pressure polymerization under nitrogen pressure at a pressure of 0.4 MPa, 100°C, and 12 hours. Solid samples of 1 mm x 12 mm x 14 mm were cut out from the removed cured bodies, and polished to prepare solid samples for colored light measurement. Each solid sample for colored light measurement was placed perpendicular to the adhesive surface of a black tape (carbon tape) of about 10 mm square, and the color tone of the colored light was evaluated visually.

(2) Measurement method of peak wavelength of colored light For a solid sample for colored light measurement with black tape attached, prepared in the same manner as in (1), the spectral reflectance was measured against a black background using a spectrophotometer (Tokyo Denshoku Corporation, "TC-1800MKII", halogen lamp: 12V 100W, measurement wavelength range 380-780nm), and the maximum point of reflectance was taken as the wavelength of the colored light.

(3) Evaluation method of the radial distribution function of inorganic spherical particles A cured body was prepared in the same manner as in (1) except that the structural color raw material composition (P1 to P6) was filled into a mold of 5 mmφ×10 mm, and the radial distribution function was obtained by observing the dispersion state of the spherical particles in the cured body with a scanning electron microscope (manufactured by Philips, "XL-30S"), and the evaluation was performed. Specifically, the cross-section of the cured body was milled using an ion milling device (manufactured by Hitachi, Ltd., "IM4000") under conditions of 2 kV and 20 minutes to obtain an observation plane. A microscopic image of an area containing 1000 spherical particles in the plane of the observation plane was obtained with a scanning electron microscope, and the obtained scanning electron microscope image was analyzed with image analysis software ("Simple Digitizer ver. 3.2" free software) to obtain the coordinates of the spherical particles in the above area. From the obtained coordinate data, the coordinates of any one spherical particle were selected, and a circle was drawn with a radius of distance r around the selected spherical particle, containing at least 200 spherical particles, and the number of spherical particles contained within the circle was determined to calculate the average particle density <ρ> (unit: particles/cm ² ). dr is a value of about r ₀ /100 to r ₀ /10 (r ₀ indicates the average particle diameter of the spherical particles), and the number dn of particles contained within the region between the circle at distance r from the central spherical particle and the circle at distance r + dr, and the area da of the above region (where da = 2πr · dr) were determined. Using the values of <ρ>, dn, and da thus determined,
Formula: g(r)={1/<ρ>}×{dn/da}
A graph showing the relationship between the radial distribution function and r/ _r0 (r indicates an arbitrary distance from the center of the circle, and _r0 indicates the average particle diameter of the spherical particles) was then created, and the radial distribution function was evaluated as satisfying condition 1 and condition 2 with "S" and not satisfying condition with "N."

As shown in Table 5, it was confirmed that the hardened bodies of the structural color raw material compositions (P1 to P6) had a dispersion state of the inorganic spherical particles that satisfied the above-mentioned condition (d) and exhibited a specific structural color.

2-3-2. Evaluation of the lightness (L ^*) , hue (a ^*) , chroma (b ^*) and contrast ratio (CR) of each cured product of the raw material composition For the cured products of the structural color raw material compositions (P1 to P6) and the non-structural color raw material compositions (L1 to L6), L ^* , a ^* , b ^* and CR were measured by the methods shown in (4) and (5) below. The results are shown in Table 6.

(4) Measurement of lightness L ^* , hue a ^*, and chroma b ^* Each raw material composition was vacuum degassed, filled into a 10 mm x 12 mm x 14 mm mold, and the upper surface was smoothed. Then, using a heating and pressure polymerization apparatus, heating and pressure polymerization was carried out under nitrogen pressure at a pressure of 0.4 MPa, 100°C, and 12 hours. A solid sample of 14 mm x 12 mm x 1 mm was cut out from the removed cured body to prepare a solid sample for color difference measurement. For this solid sample, the spectral reflectance of a black background (light-shielded state) and a white background (light-shielded state with a standard white plate placed over the cured product) in a measurement area of 5 mmφ was measured using a spectrophotometer (manufactured by Tokyo Denshoku Corporation, "TC-1800MKII", halogen lamp: 12V 100W, measurement wavelength range 380 to 780 nm) in a reflected light 0° d method (JIS Z8722) to determine the L ^* value, a ^* value, and b ^* value.

(5) Measurement of Contrast Ratio (CR) Using the above color difference meter, the contrast ratio CR= _YB / _YW of the above sample was calculated based on _YB , which is the Y value when the background color is black, and YW, which is the Y value when the background color is _white .

3. Examples and Comparative Examples Using the above P1-6 and L1-6 pastes in the combinations shown in Table 7, a machined part was produced as follows, which was a hybrid resin laminate having a two-layer structure in which a hybrid resin layer made of a hardened product of the raw material composition for the first layer and a hybrid resin layer made of a hardened product of the raw material composition for the second layer were bonded to the same layer thickness.

That is, the raw material composition for the first layer was filled into the mold up to half the height of the mold (5 mm) and left to stand until the surface became flat, and then the raw material composition for the second layer was filled into the mold so as to fill it, taking care not to disturb the interface. Except for this, hardening was carried out in the same manner as in the preparation of samples for measuring L ^* , a ^* and b ^* , and the above-mentioned machined processed part was prepared.

The lamination interface of the obtained machined portion was evaluated, and a retaining pin was attached to the machined portion to prepare a dental machining resin blank, which was then used to fabricate a dental restoration (crown) for which the lamination interface condition and natural tooth approximation were evaluated. The specific evaluation method is shown below. The evaluation results are shown in Table 7 together with the color difference between the first and second layers: ΔE ^* and the contrast ratio difference: ΔCR (=CR2-CR1).

(1) Evaluation of Lamination Interface The laminate was visually observed to confirm whether the laminate interface was visible. The evaluation criteria are as follows:
5: The interface between the upper and lower layers is completely invisible.
4: The interface between the upper and lower layers is not visible.
3: The interface between the upper and lower layers is barely visible.
2: The interface between the upper and lower layers is barely visible.
1: The interface between the upper and lower layers is clearly visible.

(2) Evaluation of the lamination interface of a dental mock restoration The crown of the upper right first tooth was machined using a cutting machine (Roland, "DWX-50") to prepare a dental restoration (restoration), which was then bonded to a resin abutment (equivalent to A3 color) using Estacem II (Tokuyama Dental, adhesive resin cement), polished, and a mock restoration was performed. The state of the lamination interface after restoration was visually confirmed. The evaluation criteria are as follows:
5: The interface between the upper and lower layers is completely invisible, and the color is natural.
4: The interface between the upper and lower layers is barely visible, and the color is natural.
3: The interface between the upper and lower layers is difficult to see.
2: The interface between the upper and lower layers is faintly visible.
1: The interface between the upper and lower layers is clearly visible, and the color is unnatural.

(3) Evaluation of the similarity of the dental simulation restoration to the natural tooth The simulation restoration prepared in the same manner as in (2) was visually inspected to see whether the color tone from the cervical part to the incisal part was similar to that of the natural tooth. The evaluation criteria are as follows:
5: Natural color, like natural teeth.
4: The color is similar to that of natural teeth.
3: The color is somewhat similar to that of natural teeth.
2: The color is not very similar to natural teeth and feels slightly unnatural.
1: The color is unnatural and not at all similar to natural teeth.

As shown in Table 7, the "Natural Tooth Similarity Evaluation" of Comparative Example 1, which is a single-layer structural color resin blank (of P1 hardened body), and Comparative Example 2, which is a single-layer non-structural color resin blank (of L1 hardened body), is "1". That is, in Comparative Example 1, although the color tone of the cervical part being dark and the incisal part being light and transparent was reproduced, the color of the crown was white, so it was rated low in the visual evaluation of similarity to natural teeth. In addition, in Comparative Example 2, since the entire crown is non-structural color, the color tone of the cervical part being dark and the incisal part being light was not reproduced, so it was rated low in the visual evaluation of similarity to natural teeth. In contrast, the "Natural Tooth Similarity Evaluation" of Examples 1 to 11, although to a certain extent, are all rated higher than the evaluations of Comparative Examples 1 and 2. In particular, for Examples 1, 2, and 8-10, where ΔE ^* , CR1, CR2 and ΔCR were all within the suitable range (ΔE ^* = 2 to 20, CR1 = 0.28 to 0.43, CR1 = 0.55 to 0.63, ΔCR = 0.12 to 0.27), the evaluations of "Evaluation of the laminate interface,""Evaluation of the laminate interface of dental simulation restorations" and "Evaluation of similarity to natural teeth" were all rated "4" or higher.

Claims (3)

A dental resin blank for machining having a machining part made of a composite material in which inorganic particles are dispersed in a resin matrix,
The composite material has a laminated structure in which a first layer and a second layer are bonded together,
the first layer is made of a first composite material that exhibits a structural color of a predetermined color tone independent of the angle of incidence of light,
the second layer is made of a second composite material having a color tone different from the color tone of the first composite material;
When the color tone of a composite material having a single color tone is expressed by the L ^* value, a ^* value, and b ^* value obtained by measuring a sample having a thickness of 1.0±0.1 mm against a white background using a spectrophotometer,
The following formula, which is an index of the difference between the color tone of the first composite material and the color tone of the second composite material, is ΔE ^* ={(L1 ^* -L2 ^* ) ² +(a1 ^* -a2 ^* ) ² +(b1 ^* -b2 ^* ) ² } ^1/2
(In the above formula, L1 ^* , a1 ^* , and b1 ^* are the L ^* value, a ^* value, and b ^* value in the first composite material, and L2 ^* , a2 ^* , and b2 ^* are the L ^* value, a ^* value, and b ^* value in the second composite material.)
The color difference: ΔE ^* defined as 2 to 30 ,
the total amount of pigment and colorant in the first composite material is 100 ppm by mass or less relative to the total mass of the first composite material, and the total amount of pigment and colorant in the second composite material is 500 to 7000 ppm by mass relative to the total mass of the second composite material;
A laminated resin-based blank for dental cutting, characterized in that 2. The laminated resin-based blank for dental cutting according to claim 1, characterized in that the first composite material satisfies all of the following conditions (a) to (d):
(a) The inorganic particles are composed of an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 nm to 1000 nm, and include one or more groups of uniform-diameter spherical particles (G-PID) in which 90% or more of the total number of particles in a number-based particle size distribution of the aggregate are present within a 5% range around the predetermined average primary particle diameter.
(b) When the number of the uniform particle groups contained in the inorganic particles is a, and each uniform particle group is expressed in ascending order of average primary particle diameter as G-PID _m (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more), the average primary particle diameters of each G-PID _m when a is 2 or more differ from each other by 25 nm or more.
(c) When the refractive index of the resin matrix at 25° C. for light with a wavelength of 589 nm is n _(MX) and the refractive index of the inorganic spherical particles constituting each G-PID _m at 25° C. for light with a wavelength of 589 nm is n ( _G-PIDm) , for each n _(G-PIDm) :
n _(MX) <n _(G-PIDm)
The relationship is established.
(d) A function expressing the probability that other inorganic spherical particles are present at a point distant r from the center of any inorganic spherical particle in the first composite material, which is determined based on a scanning electron microscope image in which the inner surface of the composite material is used as an observation plane, and is expressed by the following formula (1) based on the average particle density of the inorganic spherical particles in the observation plane: <ρ>, the number of inorganic spherical particles present in the region between a circle at a distance r from any inorganic spherical particle in the observation plane and a circle at a distance r + dr: dn, and the area of the region: da (where da = 2πr · dr).
g(r)={1/<ρ>}×{dn/da}...(1)
When g(r) is a radial distribution function, the inorganic spherical particles constituting the group of uniform particle diameter spherical particles (G-PID) in the composite material are dispersed in the matrix material so as to have a short-range ordered structure that satisfies the following condition 1 and the following condition 2:
[Condition 1]: In a radial distribution function graph showing the relationship between r/r0 and the g(r) corresponding to r at that time, the x-axis is a dimensionless number (r/ _r0 ) obtained by dividing the distance r from the center of any inorganic spherical particle dispersed in the composite material by the average particle size _r0 of all the inorganic spherical particles dispersed in the composite material, _and the y-axis is the radial distribution function g(r), the nearest inter-particle distance _r1 , which is defined as the r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph, is a value that is 1 to 2 times the average particle size _r0 of all the inorganic spherical particles dispersed in the composite material.
[Condition 2]: When r corresponding to the peak top of the peak that is second closest to the origin among the peaks appearing in the radial distribution function graph is defined as the next closest interparticle distance: _r2 , the minimum value of the radial distribution function: g(r) between the nearest interparticle distance: _r1 and the next nearest interparticle distance: _r2 is a value of 0.56 or more and 1.10 or less. The transparency of the composite material is expressed as a contrast ratio (CR) index, where the ratio of the Y value ( _YB /YW) on a black background to the Y value (YW ₎ on a white background is determined by measuring the color difference of a sample having a thickness of 1.0±0.1 mm using a spectrophotometer, and the ratio is determined as _YB / _YW .
The first composite material has a contrast ratio CR1 of 0.28 to 0.46, and the second composite material has a contrast ratio CR2 of 0.50 to 0.65.
A laminated resin-based blank for dental machining according to claim 1 or 2 .