RU2807748C2 - Dental blank for milling and method of its production - Google Patents

Abstract

FIELD: dental materials.

SUBSTANCE: group of inventions concerns a dental workpiece for milling and a method of its manufacture. The following is proposed: a dental workpiece having a part to be milled, made of a polymer material, which includes a composite material containing inorganic particles dispersed in a polymer matrix. The polymer matrix is a cured product of at least one type of (meth)acrylic compound, which has a refractive index from 1.40 to 1.57. Inorganic particles include the following: at least one group of spherical particles of the same diameter (G-PID), including inorganic particles with a defined average primary particle diameter from 100 nm to 1,000 nm, having a narrow particle size distribution, and a group of ultra-fine particles (G-SFP), including inorganic particles with an average primary particle diameter of less than 100 nm. The particles forming the G-PID group or groups are particles of a complex oxide based on silicon dioxide and titanium group element oxide, which have a refractive index from 1.45 to 1.58; wherein the average diameters of the primary particles of different groups of G-PID particles differ from each other by 25 nm or more. The average diameter of G-SFP primary particles is 25 nm or more smaller than that of G-PID group particles with the smallest particle size. The total number of particles dispersed in the polymer matrix is as follows: for G-PID particles — from 100 to 800 parts wt., for G-SFP particles — from 0.1 to 5 parts wt., per 100 parts wt. including polymer matrix. The arrangement of all particles from G-PID groups in the polymer matrix has a short-range order structure that satisfies certain conditions. A method of producing the said preform involves mixing of an appropriate polymerizable monomer component (A), the above inorganic particles (B) and a polymerization initiator (C) to form a polymerizable curable composition; carrying out the casting and polymerization of the polymerizable curable composition to form a three-dimensional body of composite material, which forms all or a part of the target milling part in compliance with the above conditions.

EFFECT: group of inventions provides the following useful effects: the workpiece can have the desired color in a wide color range without the need to regulate the color using a pigment or dye; moreover, the blank provides restoration with an appearance that is in harmony with the color of the restored teeth, even when it is used to form a thick denture.

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Description

Technical field

The present invention relates to a dental milling workpiece comprising a composite material containing a polymer matrix and inorganic particles dispersed in the polymer matrix, and also relates to a method for producing such a workpiece. In particular, the present invention relates to a dental milling blank that has a structural color and a suitable level of contrast ratio to enable the formation of dentures with a color that matches well with the various colors of natural teeth, without the special use of pigments or dyes, and also relates to method for producing such a workpiece.

State of the art

Dental procedures are increasingly using digital technology to produce dental prosthetics such as inlays, onlays, crowns, bridges and implant superstructures. For example, as described in Patent Document 1, a computer-aided design (CAD) and computer-aided manufacturing (CAM) system that uses images of the oral cavity to perform milling of a dental workpiece for milling a non-metallic material using a CAD-CAM device based on CAD technology is increasingly being used. -CAM. As used herein, the term “dental milling blank” refers to a material that is capable of being attached to a milling machine in a CAD-CAM system and is to be milled (also referred to as a “milling blank”). Commonly known dental milling workpieces include (solid) blocks having a rectangular shape, a cylindrical shape or any other shape, and (hard) discs having a plate or disk shape. A dental workpiece for milling is often attached with a mounting pin so that it can be secured to the milling machine. This shape combined with a mounting pin is also called a dental milling blank. As used herein, the term “dental milling blank” also includes such a shape integrated with an attachment pin. The main part of the material to be milled (the main part of the dental workpiece to be milled) is also called the “milling target part”.

The target milling portion of the dental workpiece for milling can be made from any of a variety of materials such as glass ceramics, zirconia, titanium, and polymers. Among them, a polymer-based material consisting of a cured product of a curable composition containing an inorganic filler such as silica, a polymerizable monomer such as methacrylate polymer, and a polymerization initiator has attracted attention from the viewpoint of high machinability (millability), high aesthetic performance , strength and other properties.

During dental procedures, it is necessary to ensure the appearance of teeth as close as possible to the color of natural teeth. Proposals for satisfying this esthetic requirement include a single-component, single-layer dental milling blank, the color of which is controlled by adding a suitable type and amount of pigment or dye, and a multi-layer dental milling blank, which includes an array of layers of components of different colors.

For example, Patent Document 2 discloses a dental milling blank having high versatility, high productivity and high ability to reproduce the beauty of natural teeth, which is a resin-based dental block designed for CAD-CAM, containing an assembly of a dentin filling resin layer and a layer of enamel filling polymer, in which at least the dentin filling polymer layer contains light-scattering particles and provides a certain diffusion coefficient.

Patent Document 1: Unexamined Japanese Patent Application (PCT Application Translation), Publication No. 2016-535610

Patent Document 2: Unexamined Japanese Patent Application Publication No. 2017-213394.

Patent Document 3: Japan Patent No. 5274164.

Patent Document 4: PCT International Publication No. WO 2017/069274.

Brief description of the invention

Problems solved by the invention

Unfortunately, a dental prosthesis made from a dental milling blank containing a color-regulating pigment or dye may suffer from discoloration caused by aging or deterioration of the color of the pigment or dye such that the appearance of the restored portion may change in color and become incompatible with natural teeth over time after manipulation.

Therefore, it is an object of the present invention to provide a dental milling workpiece containing a resin-based material that is less vulnerable to such a problem, and to provide a method for producing such a workpiece.

Remedies

A first aspect of the present invention relates to a dental milling workpiece having a milling target portion including a polymer-based material, wherein

the polymer-based material includes at least one composite material containing a polymer matrix and inorganic particles dispersed in the polymer matrix,

inorganic particles include:

at least one group of spherical particles of uniform diameter (G-PID), including spherical inorganic particles with a defined average primary particle diameter from 100 nm to 1000 nm and having a size distribution in which 90% or more of all particles have diameters falling within range from mean primary particle diameter -5% mean primary particle diameter to mean primary particle diameter +5% mean primary particle diameter, and

group of ultrafine particles (G-SFP), including inorganic particles with an average diameter of primary particles less than 100 nm, while

for at least one group comprising one or more groups of spherical particles of the same diameter,

one or more groups of spherical particles of the same diameter are groups A, each of which is represented by G-PID _m , where A represents the number of groups, m is 1 when A is 1, or m is a positive integer from 1 to A, when A is 2 or more and the average diameter of the primary particles of the group increases with increasing m,

groups represented by G-PID _m have average diameters of primary particles that differ from each other by 25 nm or more,

the group of ultrafine particles has an average diameter of primary particles less than 25 nm or more than that of the group represented by G-PID ₁ ,

at least one composite material satisfies the relationship n _(Mx) < n _(G-PIDm) , where n _(Mx) represents the refractive index of the polymer matrix for light with a wavelength of 589 nm at 25°C, n _(G-PIDm) represents is the refractive index of the spherical inorganic particles of each group represented by G-PID _m for light with a wavelength of 589 nm at 25°C, and the relationship holds for each n _(G-PIDm) , and

at least one composite material has a short-range order structure in which spherical inorganic particles of all groups of spherical particles of the same diameter in the polymer matrix have an arrangement structure that satisfies:

condition 1, where the radial distribution function is plotted with r/r ₀ on the x-axis and the radial distribution function g(r) on the y-axis and shows the relationship between r/r ₀ and g(r) for r, where r/r ₀ represents is a normalized dimensionless number calculated by dividing the distance r from the center of any spherical inorganic particle in a composite material by the average diameter r of all spherical inorganic particles dispersed in the composite material, ag(r) represents the probability that the existence of any other spherical inorganic particle in point at a distance r from the center of any spherical inorganic particle has peaks, among which the peak closest to the origin provides the distance r ₁ between the nearest neighboring particles as the value of r corresponding to the top of the peak, and the distance r ₁ between the nearest neighboring particles 1-2 times the average diameter of all spherical inorganic particles dispersed in the composite material, and

condition 2, when the graph of the radial distribution function has peaks, among which the peak, the second closest to the origin, provides the distance r ₂ between the second nearest neighboring particles, since the value of r corresponds to the top of the peak, and the radial distribution function g(r) has a local minimum value from 0.56 to 1.10 between the distance r ₂ between the nearest neighboring particles and the distance r between the second nearest neighboring particles.

In the dental milling workpiece according to the present invention, the radial distribution function g(r) is preferably calculated by Formula (1): Where is the average density of spherical inorganic particles in the viewing plane, which is the inner surface of the composite material, wherein the average density is determined from a scanning electron microscopy image of the inner surface of the composite material, dn is the number of spherical inorganic particles in the area between the circle and the circle , spaced at a distance r from any spherical inorganic particle in the plane of observation, and a circle with a circle spaced at a distance r+dr from any spherical inorganic particle, and da is the area of the region where da=2πr × dr.

In the dental milling workpiece according to the present invention, the total amount of a group or groups of spherical particles of the same diameter dispersed in the resin matrix is preferably from 10 parts by mass to 1500 parts by mass based on 100 parts by mass of the resin matrix, and the amount of a group of ultrafine particles dispersed in polymer matrix, preferably ranges from 0.1 parts by weight to 50 parts by weight based on 100 parts by weight of the polymer matrix, the entire group or groups of spherical particles of the same diameter of inorganic particles preferably have an average primary particle diameter of from 230 nm to 1000 nm, and the group of ultrafine The particles preferably have an average primary particle diameter of from 3 nm to 75 nm, taking into account the block color and contrast ratio. Moreover, the difference between n _(MX) and n _(G-PIDm) (n _(G-PIDm) - n _(MX) ), which is represented by Δn, is preferably 0.001 to 0.1 for each n _(G-PIDm) .

In a dental milling workpiece, the at least one composite material in the target milling portion may include a plurality of composite materials having different compositions and bonded to each other.

A second aspect of the present invention relates to a method for manufacturing a dental milling workpiece of the present invention having a milling target portion of a specific shape, comprising:

mixing a polymerizable monomer component (A), inorganic particles (B) and a polymerization initiator (C) to form a polymerizable curable composition, wherein the polymerizable monomer component (A) is capable of forming a cured product having a refractive index of 1.40 to 1.57 for light with a wavelength of 589 nm at 25°C, inorganic particles (B) include: a group of spherical particles of the same diameter comprising a material having a refractive index higher than that of the cured product made from a polymerizable monomer component (A) for light with a wavelength 589 nm at 25 C, and a group of ultrafine particles, and

carrying out the casting and polymerization of the polymerizable curable composition with the formation of a three-dimensional body of composite material, which forms all or part of the target part of the milling, while

mixing is carried out to form a polymerizable curable composition capable of forming a cured product containing spherical inorganic particles that form an entire group or groups of spherical particles of the same diameter and have a short-range order structure satisfying conditions 1 and 2 as the arrangement structure.

In the production method of the present invention, at least a portion of the group or groups of spherical particles of the same diameter in the polymerizable curable composition are preferably in the form of an organic-inorganic composite filler comprising one group of spherical particles of the same diameter and a polymer having a refractive index lower than that of the spherical inorganic particles of one group of spherical particles of the same diameter for light with a wavelength of 589 nm at 25°C, and not containing any group of spherical particles of the same diameter other than one group of spherical particles of the same diameter, so that a short-range order structure can be reliably obtained.

In addition, for uniform polymerization and curing, the polymerization initiator (C) is preferably a thermal polymerization initiator, and casting and polymerization are preferably carried out at a temperature of 60°C to 200°C.

Effects of the Invention The dental milling workpiece of the present invention provides the following beneficial effects: (a) it does not require the inclusion of a dye or pigment and is thus less susceptible to the problem of discoloration over time; (b) it can have a desired color over a wide color range from blue transparent to yellow to red, which is the same as dentin, and (c) a group of ultrafine particles (G-SFP) in it provides a suitable level of transparency , so that it can form a relatively thick dental prosthesis with a color easily compatible with the color of the tooth being restored, and provides teeth with a wide range of colors allowing restoration of an appearance close to natural teeth. When a dental milling workpiece contains multiple groups of spherical particles of the same diameter (G-PID), each G-PID provides a structural color depending on the average diameter of the primary particles, and therefore the combination of groups (G-PID) provides the ability to control the color of the entire workpiece .

In the dental milling workpiece according to the present invention, the dispersion state of the spherical filler in the resin matrix of the composite material as part or all of the target milling part can be checked by observation under an electron microscope. Therefore, testing the correlation between the state of the dispersion and the production conditions, such as the mixing conditions to form a polymerizable curable composition as a starting material, allows one to determine the production conditions under which beneficial effects can be reliably obtained. The production method of the present invention using such conditions allows the dental milling workpiece of the present invention to be produced in high yield.

Brief Description of the Drawings FIG. 1A is a view showing an example of a plane image of a part of a cured product cut from the dental milling workpiece of Example 1, which is observed using a scanning electron microscope.

Fig. 1B is a view showing an example of coordinate data obtained from the scanning electron microscopy image of FIG. 1A.

Fig. 2 is a graph showing the radial distribution function g(r) calculated based on the parameters determined from the coordinate data in FIG. 1B.

Fig. 3 is a graph showing the radial distribution function for a portion of the cured product cut from the dental milling blank of Example 2.

Fig. 4 is a graph showing the radial distribution function for a portion of the cured product cut from the dental milling blank of Example 3.

Fig. 5 is a graph showing the radial distribution function for a portion of the cured product cut from the dental milling blank of Example 4.

Fig. 6 is a graph showing the radial distribution function for a portion of the cured product cut from the dental milling blank of Example 5.

Fig. 7 is a graph showing the radial distribution function for a portion of the cured product cut from the dental milling blank of Example 6.

Fig. 8 is a graph showing the radial distribution function of a part of the cured product cut from the dental milling workpiece of Comparative Example 2.

Preferred Mode for Carrying Out the Invention

A dental milling workpiece according to the present invention has a milling target portion including a resin-based material, wherein the resin-based material includes a certain composite material containing a resin matrix and inorganic particles dispersed in the resin matrix. Specifically, the entire target milling portion includes a specific composite material, or a portion of the target milling portion includes a specific composite material and the remainder thereof includes another polymer-based material. The part comprising a specific composite material may include several specific composite materials having different compositions and interconnected.

A certain composite material contains a polymer matrix and certain inorganic particles that are dispersed in the polymer matrix so as to satisfy specific dispersion conditions. Containing no specific pigment or dye, the specific composite material provides color based on a coloring mechanism called "structural color." The term “structural color” refers to the color that occurs when small particles in a medium cause reflection, interference, scattering, and transmission of light. Known technologies use a composite material to obtain a desired color, where the composite material contains inorganic particles dispersed in a medium such as a polymer (see Patent Documents 3 and 4).

For example, Patent Document 3 discloses a fine particle dispersion including first fine particles that are dispersed in a medium and have an average diameter of 50 nm to 1 μm and a particle diameter Cv of 10% or less, where the first fine particles are arranged so as to have an amorphous structure , and the dispersion of small particles has a short-range order structure that satisfies specific conditions determined by the radial distribution function g(r) in the plane. Patent Document 3 discloses that such a fine particle dispersion stably maintains a fine particle arrangement pattern and can reflect light of a certain wavelength and sufficiently reduce the angular dependence of reflected light having a maximum wavelength varying with the incident angle of the light.

Patent Document 4 discloses a curable composition containing a polymerizable monomer component (A), a spherical filler (B) including particles having an average diameter of 230 nm to 1000 nm, and a polymerization initiator (C), the curable composition satisfies the condition that 90 % or more of the particles have a diameter falling within the range of mean particle diameter -5% mean particle diameter to mean particle diameter +5% mean particle diameter, and at 25°C the spherical filler (B) has a refractive index nF greater than that of the product a polymerization reaction of a polymerizable monomer component (A), wherein the curable composition is capable of forming a 1 mm thick cured product that has a value (V) of less than 5 and a chromaticity (C) of 0.05 or more in the Munsell color system, measured with colored light on black background using a color difference meter, and has a value (V) of 6 or more and a chromaticity (C) of less than 2 in the Munsell color system, measured for colored light on a white background using a color difference meter.

Patent Document 4 states that a dental composite resin (CR) made from a curable composition has the following advantages: (1) it hardly causes the problem of discoloration over time because it contains no dye or pigment; (2) it can form a cured product with a yellow to red color that is the same as dentin, and (3) the cured product has a suitable level of transparency and thus has a color easily matched to the color of the tooth being restored, so that for dental fillings, only one type of composite resin can be used with a wide range of colors to create an appearance close to natural teeth, without the complex color matching or shade matching of composite resin.

Patent Document 3 suggests that fine particles of uniform diameter, dispersed to have a certain short-range order structure and to have an amorphous structure as a whole, can produce a constant structural color independent of changes in the angle of incidence of light. Patent Document 4 also shows that a cured product of a curable composition (or a CR made from a curable composition) has a portion with constituent particles collected relatively regularly, which interferes with the production of colored light, and also has a portion with constituent particles dispersed in an unregulated manner. in a manner that causes scattering when receiving colored light. This may indicate that in such a system the balance between long-range irregularity and short-range regularity in the spherical filler dispersion state is important for the benefits (1) - (3) stated above.

However, Patent Document 4 is silent on quantifying the balance of beneficial effects with respect to the curable composition. For example, it remains unknown how the addition of fine filler to control the viscosity of the cured composition or to control the contrast ratio of the cured product influences the beneficial effects. Regarding the spherical filler (B), Patent Document 4 discloses the use of only one group of spherical inorganic particles having a specific average primary particle diameter of 230 nm to 1000 nm and having a numerical size distribution in which 90% or more of all particles have diameters , falling within the range from an average primary particle diameter of -5% of an average primary particle diameter to an average primary particle diameter of +5% of an average primary particle diameter. Therefore, it remains unknown how the beneficial effects of using multiple groups of such particles with different average diameters of the primary particles are affected. Moreover, the invention of Patent Document 4 is mainly intended for the restoration of so-called shallow cavities with CR, and therefore it remains unknown whether the same beneficial effect can be obtained when forming a thick denture. In addition, it has been found that the desired beneficial effects cannot be obtained depending on the conditions of preparation of the curable composition by mixing the components, although the incidence of such a problem is not that high.

The unknown conditions mentioned above and changes in practical physical properties depending on the conditions of preparation of the curable composition can also be problems not only when the curable composition is used for CR, but also when the cured product of the composition is used as a denture.

The inventors of the present invention used the short-range order structure determination method based on the “in-plane radial distribution function g(r)” disclosed in Patent Document 3 to quantify the dispersion state of spherical particles. Based on such a method, the inventors of the present invention have determined the dispersion state of inorganic particles to obtain beneficial effects with respect to a system containing a polymer matrix and inorganic particles including a group of spherical particles of uniform diameter (G-PID) and a group of ultrafine particles (G-SFP), dispersed in a resin matrix which is similar to that disclosed in Patent Document 4. As a result, the inventors of the present invention have manufactured a dental milling workpiece using a composite material having a predetermined dispersion state from which unknown conditions and variations in practical physical properties are eliminated.

The inventors of the present invention have already proposed such a composite material (Japanese Patent Application No. 2018-165680). The present invention has been made based on the discovery that the short-range order structure of the composite material according to the proposal (also called “the composite material of the present invention”) to obtain beneficial effects can be successfully determined (in other words, beneficial effects can be obtained when conditions 1 and 2 are satisfied , defined above) in a system similar to that disclosed in Patent Document 4; the addition of ultrafine inorganic filler has virtually no effect on the mechanism for obtaining structural color; and as long as certain conditions are met, multiple groups of spherical fillers can be used, and even then, a short-range order structure is maintained to allow each group of spherical fillers to produce a structural color, and the structural colors produced by the groups combine to produce a specific structural color as a whole. The composite material of the present invention differs from the composite material disclosed in Patent Document 4 in that the cured product of Patent Document 4 contains only one group of spherical particles of uniform diameter (G-PID) with an average diameter of 230 nm to 1000 nm and does not contain any particular group of ultrafine particles (G-SFP), whereas the composite material of the present invention contains one or more groups of spherical particles of the same diameter (G-PID) with an average diameter from 100 nm to 1000 nm, and also contains a group of ultrafine particles (G-SFP) to control the contrast ratio of the cured product.

Moreover, the present invention has been made based on the discovery that the composite material according to the present invention, even when produced with a large thickness such as 10 mm, can also produce beneficial effects and is thus suitable for use as a dental workpiece for milling, and also based on new knowledge regarding the composite material according to the present invention.

Next, the present invention is described in detail, including the composite material of the present invention.

The composite material of the present invention constituting the dental milling workpiece of the present invention contains a resin matrix and inorganic particles dispersed in the resin matrix, and has the characteristics described below.

First, the inorganic particles include at least one group (or one or more groups) of spherical particles of uniform diameter (G-PID), including spherical inorganic particles with an average primary particle diameter of from 100 nm to 1000 nm and having a numerical size distribution , in which 90% or more of all particles have diameters falling within the range of mean primary particle diameter -5% mean primary particle diameter to mean primary particle diameter +5% mean primary particle diameter, and the group of ultrafine particles (G-SFP), including inorganic particles with an average primary particle diameter of less than 100 nm.

Second, one or more groups of spherical particles of the same diameter are groups A, each of which is represented by G-PID _m , where A represents the number of groups, m is 1 when A is 1, or m is a positive integer of 1 to A, when A is 2 or more, and the average diameter of the primary particles of the group increases with increasing m, the groups represented by G-PID _m have average diameters of the primary particles differing from each other by 25 nm or more, and the ultrafine particle group has an average primary particle diameter 25 nm or more smaller than that of the group represented by G-PID ₁ .

Third, the composite material satisfies the relationship n _(Mx) < n _(G-PIDm) , where n _(Mx) represents the refractive index of the polymer matrix for light with a wavelength of 589 nm at 25°C, n _(G-PIDm) represents is the refractive index of the spherical inorganic particles of each group represented by G-PID _m for light with a wavelength of 589 nm at 25°C, and the relationship holds for each P _(G-PIDm) .

Fourth, the composite material has a short-range order structure, in which spherical inorganic particles of all groups of spherical particles of the same diameter in the polymer matrix have an arrangement structure that satisfies conditions 1 and 2 below.

Condition 1: A graph of the radial distribution function plotted with r/r ₀ on the x-axis and the radial distribution function g(r) on the y-axis and showing the relationship between r/r ₀ and g(r) for r, where r/r ₀ represents is a normalized dimensionless quantity calculated by dividing the distance r from the center of any spherical inorganic particle in the composite material by the average diameter r of all spherical inorganic particles dispersed in the composite material, and g(r) represents the probability that the existence of any other spherical inorganic particle at a point removed by a distance r from the center of any spherical inorganic particle, has peaks, among which the peak closest to the origin provides the distance r ₁ between the nearest neighboring particles as the value of r corresponding to the top of the peak, and the distance r ₁ between the nearest neighbors particles 1-2 times larger than the average diameter of all spherical inorganic particles dispersed in the composite material.

Condition 2: The graph of the radial distribution function has peaks, among which the peak, the second closest to the origin, provides the distance r ₂ between the second nearest neighboring particles, since the value of r corresponds to the top of the peak, and the radial distribution function g(r) has a local minimum value from 0.56 to 1.10 between the distance r ₁ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles.

The composite material of the present invention having all four features allows incident light to undergo diffraction and interference in accordance with the Bragg condition, so that light of a certain wavelength is amplified without being influenced by the angle of incidence of light to obtain a structural color in accordance with the average diameter of the primary particles, which results in a specific structural color in accordance with the average diameter of the primary particles.

As noted above, the composite material of the present invention basically falls into the same category as the category of the cured product of the curable composition disclosed in Patent Document 4. However, the composite material of the present invention has the following new features: it has a predetermined dispersion state of spherical inorganic particles, which reliably produces beneficial effects; it contains an additional inorganic filler with particle sizes that do not adversely affect the beneficial effects, which corresponds to one of the “possible additives” for the curable composition disclosed in Patent Document 4, and it can contain several groups of spherical particles of the same diameter. The composite material of the present invention may have other features similar to those of the curable composition disclosed in Patent Document 4, such as a polymerizable monomer component as a starting material for the polymer matrix and the type of each group of spherical particles of the same diameter, more specifically, the average diameter of the primary particles and the numerical size distribution of the G-PID, the shape, material and refractive index of the spherical inorganic particles in the G-PID, and the polymerization initiator used to form the cured product.

Therefore, a fourth feature regarding said dispersion state of the spherical inorganic particles will first be described, and then what starting materials and methods should be used to form the composite material of the present invention will be described.

The dispersion state of spherical inorganic particles in the composite material according to the present invention is quantified by a short-range order structure determination method using the “in-plane radial distribution function g(r)” disclosed in Patent Document 3. The radial distribution function g(r) is a well-known function for determining the probability of the existence of a particle at a point at a distance r from any other particle, as also shown in Patent Document 3. The radial distribution function g(r) is given by Formula (1) below.

In formula (1), <p> represents the average density of particles in the plane, dn represents the number of particles in the region between a circle whose circumference is at a distance r from any particle in the plane at the center, and a circle with a circle at a distance r+dr from any spherical inorganic particle, and da is the area of the region where da=2πr × dr.

In general, the radial distribution function g(r) is expressed by the graph of the radial distribution function with distance r on the x-axis (distance axis) and g(r) (the result of the calculation by formula (1)) for z on the y-axis or expressed by the graph of the radial distribution function , plotted with a normalized dimensionless quantity calculated by dividing r by the average particle diameter on the distance axis and the value g(r) (calculated by the formula) for r corresponding to the value on the x-axis along the y-axis (vertical axis) (see Fig. .2-8).

With regard to the composite material according to the present invention, <p> and dn can be easily and reliably determined. Therefore, g(r) is preferably calculated by Formula (1) based on <p> and dn, which are determined from a scanning electron microscopy image of the inner surface of the composite material of the present invention in the observation plane, and da (=2πr × dr), which corresponds to the dr value used to determine dn.

<p>, dn and da can be defined as shown below. First, the composite material of the present invention is produced by subjecting the polymerizable curable composition as a starting material (also called “the polymerizable curable composition of the present invention”) to curing and other processes, and the resulting composite material is subjected to surface polishing or other processing so that the plane in which observes the state of dispersion of spherical inorganic particles in the composite material (observation plane), was opened on the surface. The viewing plane is then observed using a scanning electron microscope, and a microscopic image of a region containing at least 500 spherical inorganic particles is taken in the plane. The scanning electron microscopy image is then analyzed using image analysis software (e.g. Simple Digitizer version 3.2 (freeware)) to determine the coordinates of the spherical inorganic particles in the area. The coordinates of any of the spherical inorganic particles are selected from the coordinate data. A circle with a radius equal to the distance r is drawn with a selected spherical inorganic particle at the center so that it contains at least 200 spherical inorganic particles. The number of spherical inorganic particles inside the circle is counted and used to determine the average particle density <p> (in counting units per cm ² ).

dn can be determined by setting dr to a value from about r ₀ /100 to about r ₀ /10, where r ₀ is the average diameter of the spherical inorganic particles, drawing another circle that is concentric with the circle of radius r and has radius r+dr, and counting the number of spherical inorganic particles in the area between the two circles, da, that is, the area of the area between the two circles, is determined as 2πr⋅dr based on the actually determined length dr.

The composite material according to the present invention should be such that a radial distribution function plotted with r/r ₀ on the x-axis and radial distribution function g(r) on the y-axis, and showing the relationship between r/r ₀ and g(r) for r, where r/r ₀ is a normalized dimensionless quantity calculated by dividing the distance r from the center of any spherical inorganic particle in the composite material by the average diameter r of all spherical inorganic particles dispersed in the composite material, and g(r) represents the probability of the existence of any of another spherical inorganic particle at a point distant at a distance r from the center of any spherical inorganic particle, has peaks, among which the peak closest to the origin provides the distance r ₁ between the nearest neighboring particles as the value r corresponding to the top of the peak, and the distance r ₁ between the nearest neighboring particles is 1-2 times larger than the average diameter of the particles of all spherical inorganic particles dispersed in the composite material (condition 1). If r ₁ is less than 1 r ₀ (r ₁ /r ₀ < 1), many particles will overlap each other in the plane, so that structural color may not appear. If r ₁ is more than 2 times r ₀ (r ₁ /r ₀ >2), structural color may not be obtained because the particles will not exist near the selected central inorganic particle, so short-range order will be lost. Therefore, r ₁ /r ₀ should be from 1.0 to 2.0, preferably from 1.0 to 1.5, to maintain short-range order and facilitate the production of structural color.

The composite material of the present invention should also be such that the graph of the radial distribution function has peaks, among which the peak second closest to the origin provides the distance r ₂ between the second nearest neighboring particles as the value of r corresponding to the top of the peak, and the radial distribution function g(r) has a local minimum value from 0.56 to 1.10 between the distance r ₁ between the nearest neighboring particles and the distance Г2 between the second nearest neighboring particles (condition 2). If the local minimum value is less than 0.56, the spherical inorganic particles will have an arrangement structure with high long-range order, which will increase not only the dependence of the resulting structural color on the angle of incidence of light, but also the color saturation of the composite material, so that the composite material is less likely to have color matching when used as a dental filling material. On the other hand, if the local minimum value exceeds 1.10, the spherical inorganic particles will have a random arrangement structure, so that it is difficult to obtain the desired reflection characteristics, and it is difficult to create the desired structure color. Therefore, the local minimum value should be from 0.56 to 1.10, preferably from 0.56 to 1.00, to facilitate the development of structural color and to ensure color matching for the dental restorative material.

Through research, the inventors of the present invention have found that the curable composition disclosed in Patent Document 4 does not produce the desired beneficial effects depending on the formulation conditions (CR) by mixing the components, although the frequency of such a problem is very small, and such a system that cannot produce beneficial effects, does not satisfy condition 1 and/or condition 2 as a result of estimating the radial distribution function g(r) of the system. This means that the arrangement of spherical inorganic particles in a group of particles of the same diameter in the composite material of the present invention correlates with production conditions, such as the conditions for kneading the raw materials. In particular, if kneading is performed under conditions that can easily cause unevenness, such as hand kneading, unsatisfactory kneading conditions may occur with a certain probability, so that condition 1 or 2 may not be satisfied, which may result in the failure to obtain the desired color match and results in to a decrease in product yield. On the other hand, conditions 1 and 2 are reliably satisfied by appropriate measures such as kneading under controlled conditions using a kneader and degassing to prevent the presence of air bubbles in the composite material.

The following describes the starting materials for the composite material according to the present invention, production methods and other conditions.

Polymerizable monomer component (A)

The polymerizable monomer component (A) that is preferably used to form the polymer matrix may be, but is not limited to, one or more selected from radically polymerizable monomers such as (meth)acrylic compounds and cationically polymerizable monomers such as epoxy resins and oxetanes, etc. A (meth)acrylic compound is preferably used to form the polymerizable curable dental composition. Such a (meth)acrylic compound may be any of a monofunctional polymerizable monomer and a polyfunctional polymerizable monomer as disclosed in Patent Document 4. Such a (meth)acrylic compound may contain an acid group or a hydroxyl group in the molecule, or may be aromatic or aliphatic. Examples of a (meth)acrylic compound that is preferably used to form a dental polymerizable curable composition 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 anhydride, 13-(meth)acryloyloxytridecane-1,1-dicarboxylic acid, 2-(meth)acrylamido -2-methylpropanesulfonic acid, 2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate, N-hydroxyethyl(meth)acrylamide, N,N-(dihydroxyethyl)(meth)acrylamide, 2,2-bis((meth )acryloyloxyphenyl)propane, 2,2-bis[(3-(meth)acryloyloxy-2-hydroxypropyloxy)phenyl]propane, ethylene glycol di(meth)crylate, triethylene glycol di(meth)acrylate, 1,6-bis((meth)acrylethyloxycarbonylamino) trimethylhexane, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate and neopentyl glycol di(meth)acrylate.

If desired, two or more of these (meth)acrylic polymerizable monomers can be used in combination.

Typically, multiple polymerizable monomer components are used to control the physical properties (mechanical properties and adhesion to tooth substance in dental applications) of the cured product that forms the polymer matrix. In this case, the type and amount of polymerizable monomers are preferably selected so that the polymerizable monomer component (monomer mixture) has a refractive index of 1.38 to 1.55, so that the refractive index conditions specified above can be easily satisfied. In particular, when a complex oxide based on silica and titanium group oxides is used, which allows the refractive index of spherical inorganic particles to be easily adjusted, the resulting spherical inorganic particles have a refractive index of 1.45 to 1.58 depending on the silica content. Therefore, when the refractive index of the polymerizable monomer component is set to be in the range of 1.38 to 1.55, the refractive index of the resulting cured product can be adjusted to be in the range of about 1.40 to 1.57, making the conditions easier to achieve. The refractive indices of the polymerizable monomer component and the cured polymerizable monomer component product can be determined by measuring the refractive index of the sodium D-line (wavelength 589 nm) using an Abbe refractometer at 25°C. As used herein, the term “refractive index” means the refractive index of light with a wavelength of 589 nm at 25°C.

Inorganic particles (B)

In the composite material of the present invention, the inorganic particles (B) dispersed in the polymer matrix include one or more groups of spherical particles of uniform diameter (G-PID) and a group of ultrafine particles (G-SFP).

Group of spherical particles of the same diameter (G-PID)

The term "group of spherical particles of uniform diameter (G-PID)" means a group of spherical inorganic particles having a specific average primary particle diameter from 100 nm to 1000 nm and having a size distribution in which 90% or more of all particles have diameters falling within ranging from an average primary particle diameter of -5% of an average primary particle diameter to an average primary particle diameter of +5% of an average primary particle diameter. The individual spherical inorganic particles in a group are composed of essentially the same material.

As used herein, the term “average primary particle diameter of spherical inorganic particles” means the average of the primary particle diameters (maximum diameters) of 30 or more particles that are observed and sampled in a single field of view of a G-PID photograph taken with a scanning electron microscope. The term "spherical" can mean "substantially spherical" and does not always have to mean "completely spherical". The particles in the G-PID may have an average uniformity of 0.6 or more, preferably 0.8 or more, wherein the average uniformity is determined by photographing the G-PID using a scanning electron microscope, measuring the maximum diameter of each of the (30 or more) particles in a single field of view of the photograph, dividing by the maximum diameter of the particle diameter in the direction perpendicular to the maximum diameter, and averaging the resulting quotients.

In the composite material of the present invention, the component particles in the G-PID, which is a group of spherical inorganic particles with a narrow distribution (numerical size distribution), are dispersed in the polymer matrix in such a way that they have a certain short-range order structure that allows light to undergo diffraction and interference according to the Bragg condition, so that light of a specific wavelength is amplified to produce colored light having a color dependent on the average diameter of the primary particle (to produce structural color). Thus, to produce structural color, 90% or more (by number) of the spherical inorganic particles in the G-PID must have a primary particle diameter that falls within the range of an average primary particle diameter of -5% of an average primary particle diameter to an average primary particle diameter of +5 % average diameter of primary particles. Moreover, to obtain structural color with a hue ranging from blue to yellow to red, the spherical inorganic particles in G-PID must have an average primary particle diameter of 100 to 1000 nm. If spherical particles with an average primary particle diameter of less than 100 nm are used, it may be difficult to obtain visible light interference and hence structural color. If spherical particles with an average primary particle diameter greater than 1000 nm are used, the spherical particles may settle during the production of the composite material of the present invention or the grindability may be reduced, which is not preferable, although light interference may be expected to occur.

When the average diameter of the primary particles is between 230 and 800 nm, it is easy to obtain structural color (colored light) from yellow to red. When the average diameter of the primary particles is 150 nm or more but less than 230 nm, a structural color (color light) of blue color is easily obtained.

To produce a yellow to red structural color (colored light) that is preferred for restoring natural teeth, G-PID preferably has an average primary particle diameter of from 230 nm to 800 nm, more preferably from 240 nm to 500 nm, even more preferably from 260 nm to 350 nm. When G-PID with an average primary particle diameter of 230 nm to 260 nm is used, the resulting color light is yellow, which is useful for restoring teeth category B (reddish yellow) according to the shade scale (VITA Classical is available from VITA). When G-PID with an average primary particle diameter of 260 to 350 nm is used, the resulting color light is red, which is useful for restoring Category A (reddish brown) teeth according to the shade scale (VITA Classical is available from VITA). Dentin often has a red tint. Therefore, using only G-PID with an average primary particle diameter of 260 nm to 350 nm can provide a wide range of color matching to restore teeth of various shades and is therefore most preferred. When only G-PIDs with an average primary particle diameter of 150 nm or more to less than 230 nm are used, the resulting color light is blue, which may often not match the color of the tooth substance with a cavity extending from enamel to dentin, but is useful for restoring enamel , is particularly useful for restoring incisal areas.

In the composite material of the present invention, the inorganic particles dispersed in the polymer matrix may include one type of G-PID or multiple types of G-PID. The number A of groups represented by G-PIDs is preferably 1 to 5, more preferably 1 to 3, even more preferably 1 or 2. When the inorganic particles include multiple types of G-PIDs, the material of the inorganic particles may be the same or different for the plurality G-PID types.

In this regard, when the inorganic particles include a plurality of G-PID types, one of the plurality of G-PID types must have an average primary particle diameter that differs by 25 nm or more from the diameter of any other of the plurality of G-PID types. In other words, when inorganic particles include A types (eg, A=3) G-PID, each G-PID can be represented by G-PID _m , where m is 1, when A is 1 or m is a positive integer of 1 to A, when A is 2 or more and the average primary particle diameter of G-PID increases with increasing m, and one G-PID _m must have an average primary particle diameter d _m different by 25 nm or more from the diameter of any other G -PID _m . For example, when 25 nm and nm (automatically performed nm). When this condition is met, for example, each G-PID can produce a unique structural color (corresponding to each average diameter of the primary particles). This may be due to the fact that each G-PID may contain dispersed forms such as dispersed aggregates, each of which includes a small number (20 or less) of spherical inorganic particles that are held together by a very weak binding force, so that each G-PID may have a short-range order structure capable of producing a structural color. On the contrary, if this condition is not met, it is difficult to obtain a structural color. This may be due to the fact that all spherical inorganic particles may have a wide size distribution, so that spherical inorganic particles can be dispersed and replaced within multiple types of G-PIDs, causing a phenomenon similar to that which occurs when using the only group of inorganic particles that do not satisfy the condition of numerical size distribution.

When the composite material of the present invention includes a plurality of G-PIDs, the average primary particle diameters d _m of each G-PID _m preferably differ from each other by 30 nm or more, and more preferably differ from each other by 40 nm or more. In other words, the difference between d _m and d _m-1 is preferably 30 nm or more, more preferably 40 nm or more. The difference between d _m and d _m-1 is preferably 100 nm or less, more preferably 60 nm or less.

It should be noted that when the composite material of the present invention contains multiple types of G-PIDs, each of which has a very narrow size distribution and the average difference in primary particle diameters indicated above, the size distributions of the multiple types of G-PIDs are unlikely to overlap each other , or even if they partially overlap each other, each of the size distributions of multiple G-PID types can be identified. In other words, the inorganic particles in the composite material of the present invention will have the same number of size distribution peaks as the number of G-PID types in the composite material in the range from 100 nm to 1000 nm, and even if the peaks partially overlap each other, the average the primary particle diameter and numerical size distribution of each G-PID can be identified by waveform processing. The size distribution of inorganic particles can also be identified, for example, by image processing of an electron micrograph of the inner surface of the composite material of the present invention.

Spherical Inorganic Particles The inorganic particles in the G-PID can be made of any material as long as the conditions for the G-PID described above are met. Preferred examples of the material for inorganic particles include amorphous silica, complex oxides based on silica and titanium oxides (for example, silicon dioxide and zirconia, silicon dioxide and titanium), quartz, alumina, barium glass, strontium glass, lanthanum glass, fluoroaluminosilicate glass, ytterbium fluoride, zirconia, titanium dioxide and colloidal silica. Among them, composite oxide particles based on silica and titanium group oxide are preferably used to make it easier to adjust the refractive index.

As used herein, the term "silica-titanium composite oxide" means a composite oxide of silica and titanium element oxide (Group 4 element of the periodic table). The refractive index of the silica-titanium group element composite oxide may vary from about 1.45 to about 1.58 depending on the silica content. Specific examples of the silica-titanium group element composite oxide particles include silica-titanium particles, silica-zirconia particles, and silica-titanium-zirconium particles. Among them, silica and zirconia particles are preferred because they can provide high radiopacity. Although the silica and zirconia in the complex oxide may be present in any ratio, the complex oxide preferably has a silica content of from 70 to 95 moles. % and the oxide content of a titanium group element is from 5 to 30 mol. % to ensure sufficient radiopacity and refractive index in the preferred range shown below.

The silica-titanium oxide composite oxide particles may contain a small amount of a metal oxide other than silica and titanium oxide. In particular, the complex oxide particles based on silica-based oxide and titanium group element oxide may contain no more than 10 mol. % alkali metal oxides such as sodium oxide and lithium oxide.

The composite oxide particles based on silica and titanium group element oxide can be produced by any method. For example, a spherical filler of a complex oxide based on silicon dioxide and an oxide of a titanium element can be prepared using the so-called sol-gel method, which involves adding a mixed solution containing a hydrolyzable organosilicon compound and a hydrolyzable organometal compound of a titanium element to an alkaline medium, and implementing hydrolysis of the mixture to precipitate the reaction product.

The surface of spherical inorganic particles of a composite oxide based on silica and titanium group element oxide can be treated with a silane coupling agent. When an organic-inorganic composite filler is prepared as described below, treating the surface with a silane coupling agent can increase the strength of the interface with the organic polymer matrix of the organic-inorganic composite filler. Typical silane coupling agents include organosilicon compounds such as γ-methacryloyloxyalkyltrimethoxysilane and hexamethyldisilazane. When treating the surface, the silane coupling agent can be used in any amount. The optimal amount of silane coupling agent can be determined through a preliminary experiment to test the mechanical properties of the cured product of the polymerizable curable composition. For example, the silane coupling agent is preferably used in an amount of 0.1 parts by mass to 15 parts by mass based on 100 parts by mass of spherical inorganic particles.

Relationship between the refractive index of the polymer matrix and the refractive index of spherical inorganic particles

The composite material of the present invention must satisfy the relationship: n _(MX) < n _(G-PIDm) , where n _(MX) is the refractive index of the polymer matrix, an _(G-PIDm) is the refractive index of the spherical inorganic particles of each G-PID _m for each n _(G-PIDm) . If the ratio is not satisfied, short-wavelength light is easily scattered in the resin matrix even when a structure color is obtained, so that the resulting structure color is difficult to distinguish. For visibility and clarity of the resulting structural color and color matching of the dental workpiece for milling, the difference Δn between n _(G-PIDm) and n _(MX) (=n _(G-PIDm) - n _(MX) ) is preferably from 0.001 to 0.1 , more preferably from 0.002 to 0.1, even more preferably from 0.005 to 0.05.

As described above, the refractive index (n _(MX) ) of the cured product that forms the polymer matrix can be set to 1.40 to 1.57 when the refractive index of the polymerizable monomer component (which may be a mixture of polymerizable monomers) is set to range from 1.38 to 1.55. As described above, the refractive index n _(G-PIDm) can be varied from about 1.45 to about 1.58 by changing the silica content of the silica-titanium element oxide composite oxide. Therefore, Δn can be easily set to a preferred range using the relationships described above.

Group of ultra-fine particles (G-SFP) Group of ultra-fine particles (G-SFP) is a group of inorganic particles with an average primary particle diameter of less than 100 nm, which is added for the purpose of adjusting the viscosity of a polymerizable curable composition as a precursor to the composite material of the present invention or adjusting the coefficient contrast of the dental workpiece for milling according to the present invention. In this regard, G-SFP should have an average particle diameter 25 nm or more smaller than the average primary particle diameter (d ₁ ) of G-PID1, which is the smallest among the inorganic G-PID particles. If this condition is not satisfied, the dispersion state of the spherical inorganic particles may be disturbed, so that it is difficult to obtain a structural color. The inorganic particles in G-SFP may have any shape and may be spherical or indeterminate.

Typically, the average diameter of G-SFP primary particles may have a lower limit of 2 nm.

For less impact on structural color production, G-SFP preferably has an average primary particle diameter of 3 nm to 75 nm, more preferably 5 nm to 50 nm. For the same purpose, G-SFP preferably has an average primary particle diameter that is 30 nm or more, more preferably 40 nm or more, less than the average primary particle diameter (di) of G-PID 1.

The inorganic particles in G-SFP can be made of any material similar to the material of the spherical inorganic particles described above. The surface of inorganic G-SFP particles can also be treated with a silane coupling agent similar to that used for spherical inorganic particles. The preferred modes of producing inorganic particles for G-SFP are essentially the same as those for spherical inorganic particles, except with regard to the average diameter and shape of the primary particles.

Relationship between the composite material of the present invention and the polymerizable curable composition of the present invention

The composite material of the present invention is preferably produced by polymerizing and curing the polymerizable curable composition of the present invention as a starting material. The content of each component in the composite material of the present invention is almost uniquely determined in accordance with the composition of the polymerizable curable composition of the present invention. In addition, it is believed that the dispersion state of the spherical inorganic particles in the composite material of the present invention (dispersion structure) is substantially directly related to the dispersion state of the spherical inorganic particles in the polymerizable curable composition of the present invention (dispersion structure) immediately before curing. In other words, during curing, the state of the dispersion of spherical inorganic particles may be affected by polymerization, shrinkage, etc., but not to such an extent as to affect the fulfillment of conditions 1 and 2.

Polymerizable curable composition of the present invention

The polymerizable curable composition of the present invention contains a polymerizable monomer component (A), in particular, a polymerizable monomer component (A) capable of forming a cured product with a refractive index of 1.40 to 1.57; inorganic particles (B) including a group or groups of spherical inorganic particles of uniform diameter (G-PID) and a group of ultrafine particles (G-SFP), wherein the spherical inorganic particles of uniform diameter and ultrafine particles are made of a material or materials with a refractive index that is greater than that of a cured product made from a polymerizable monomer component (A) and a polymerization initiator (C). The polymerizable curable composition of the present invention is polymerized and cured to form a cured product that produces a structural color with a specific hue, independent of the angle of incidence of light, that corresponds to the composite material of the present invention.

Polymerizable monomer component (A) and inorganic particles (B)

The polymerizable monomer component (A) in the polymerizable curable composition of the present invention is the same as the polymerizable monomer component (A) described above as a starting material for the polymer matrix of the composite material of the present invention. G-PID, spherical inorganic particles constituting G-PID, G-SFP and inorganic particles constituting G-SFP are also the same as those described above as components of the composite material of the present invention.

As noted above, spherical inorganic G-PID particles have an average primary particle diameter of 100 nm to 1000 nm. For ease of formation of short-range order structure in the composite material of the present invention, G-PID preferably includes aggregate particles including aggregates of spherical inorganic particles. For example, G-PID preferably has an average aggregate particle diameter of 5 μm to 200 μm, more preferably 10 μm to 100 μm. In this regard, the average diameter of the aggregated G-PID particles can be calculated using the method described in the Examples section below.

The total content of G-PID in the polymerizable curable composition is typically from 10 parts by weight to 1500 parts by weight per 100 parts by weight of the polymerizable monomer component (A). The total content of G-PID in the polymerizable curable composition is preferably from 50 parts by mass to 1500 parts by mass, more preferably from 100 parts by mass to 1500 parts by mass, based on 100 parts by mass of the polymerizable monomer component (A), so that the resulting composite material has a suitable level transparency and effectively created structural color. The polymerizable curable composition may contain several types of G-PIDs. In such a case, the content of each G-PID can be suitably selected so that the total content of the G-PID falls within the above range, taking into account the shade of structural color produced by each G-PID and the desired color of the dental milling workpiece.

The content of G-SFP in the polymerizable curable composition can be suitably selected based on the viscosity of the polymerizable curable composition of the present invention, the contrast ratio of the dental milling workpiece of the present invention and other properties. The content of G-SFP in the polymerizable curable composition is generally from 0.1 parts by mass to 50 parts by mass, preferably from 0.2 parts by mass to 30 parts by mass, based on 100 parts by mass of the polymerizable monomer component (A).

Initiator (C) of polymerization

The polymerization initiator in the polymerizable curable composition of the present invention can be any material that performs the function of polymerizing and curing the polymerizable monomer component. Methods for polymerizing a polymerizable curable composition include a reaction using light energy such as ultraviolet or visible light (hereinafter referred to as "photopolymerization"), a chemical reaction between a peroxide and an accelerator, and a reaction using thermal energy (hereinafter referred to as "thermal polymerization"), any of which can be used. Photopolymerization and thermal polymerization are preferred because polymerization can be selected at any suitable time at which energy such as light or heat is added from outside, and the operation is simple. Thermal polymerization is preferred because it is less likely to cause uneven polymerization and provides uniform polymerization.

Examples of the photopolymerization initiator that can be used include benzoin alkyl ethers such as benzoin methyl ether, benzoin ethyl ether and benzoin isopropyl ether; benzyl ketals such as benzyl dimethyl ketal and benzyl diethyl ketal; benzophenone compounds such as benzophenone, 4,4'-dimethylbenzophenone and 4-methacryloxybenzophenone; α-diketones such as diacetyl, 2,3-pentadionebenzyl, camphorquinone, 9,10-phenanthraquinone and 9,10-anthraquinone; thioxanthone compounds such as 2,4-diethoxythioxanthone, 2-chlorothioxanthone and methylthioxanthone, and 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.

A reducing agent is often added to the photopolymerization initiator. Examples of such a reducing agent include tertiary amines such as 2-(dimethylamino)ethyl methacrylate, ethyl 4-dimethylaminobenzoate and N-methyldiethanolamine; aldehydes such as lauryl aldehyde, dimethylaminobenzaldehyde and terephthalicdehyde; sulfur-containing compounds such as 2-mercaptobenzoxazole, 1-decanethiol, thiosalicylic acid and thiobenzoic acid.

In many cases, a photopolymerization initiator and a reducing agent are used in conjunction with a photoacid generator. Examples of such a photoacid generator include a diaryliodonium salt compound, a sulfonium salt compound, a sulfonic acid ester compound, a halomethyl-S-triazine derivative and a pyridinium salt compound.

Examples of the thermal polymerization initiator include peroxides such as benzoyl peroxide, p-chlorobenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxydicarbonate and diisopropyl peroxydicarbonate; azo compounds such as azobiisobutyronitrile; boron compounds such as tributylborane, tributylborane partial oxide, sodium tetraphenylborate, sodium tetrakis(p-fluorophenyl)borate and triethanolamine tetraphenylboronic acid salt; 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 individually, or a mixture of two or more of these polymerization initiators may be used. A variety of initiators can also be used in combination for different types of polymerizations.

The effective amount of polymerization initiator can be selected depending on the purpose. The amount of the polymerization initiator is generally 0.01 parts by mass to 10 parts by mass, preferably 0.1 parts by mass to 5 parts by mass, based on 100 parts by mass of the monomer component to be polymerized.

Polymerization using a thermal polymerization initiator is preferably carried out at a temperature of from 60°C to 200°C, more preferably from 70°C to 150°C, even more preferably from 80°C to 130°C. If polymerization is carried out at a temperature less than 60°C, a dental milling workpiece with low strength may be obtained, in which cracking may occur. If polymerization is carried out at a temperature greater than 200° C., the resulting composite material of the present invention may be exposed to high temperature so that the resin component may become discolored, which may make it difficult to match the color of natural teeth.

Preferred modes of implementation of the polymerizable curable composition of the present invention

In the polymerizable curable composition of the present invention, at least some of the particles in one or more groups of spherical particles of the same diameter are preferably in the form of an organic-inorganic composite filler containing one group of spherical particles of the same diameter and a polymer with a refractive index lower than that of the spherical inorganic particles of one group and does not contain any other group of spherical particles of the same diameter than one group (in other words, the organic-inorganic composite filler contains only one type of G-PID).

As used herein, the term "organic-inorganic composite filler" means a filler made from a powder of a composite material containing an (organic) polymer matrix and an inorganic filler dispersed in the polymer matrix, or a coagulated material in which the primary particles of the inorganic filler are bound by an (organic) polymer.

According to a preferred mode, for example, when the composition contains three types of G-PID with different average diameters of the primary particles, namely G-PID ₁ , G-PID ₂ and G-PID ₃ , all or some of the particles of at least one of groups in the composition are an organic-inorganic composite filler containing only one G-PID. If all the particles in G-PID ₁ are in the form of an organic-inorganic composite filler containing only G-PID ₁ (composite filler 1) in a polymerizable curable composition, the composite filler 1 contains only G-PID ₁ and can provide a short-range order structure that gives a structural color specific to G-PID ₁ . Therefore, in this case, the composite material of the present invention, which is a cured product of the polymerizable curable composition of the present invention, reliably produces a structural color specific to G-PID ₁ . If G-PID ₁ is not part of the composite filler, it is mixed with G-PID ₂ and G-PID ₃ , which are added (not in the form of a composite material) at the same time as G-PID ₁ , so that a certain part of the particles in G-PID ₁ and G-PID ₂ are replaced by each other, and the nearest neighboring spherical inorganic particles in G-PID ₁ will form G-PID ₃ , which can destroy the short-range order structure in the region around such spherical inorganic particles. On the other hand, if all G-PID ₁ particles are in the form of composite filler 1, mutual replacement of particles does not occur and the short-range order structure is not disrupted. Therefore, the content of spherical inorganic particles not involved in creating the structural color can be reduced to the maximum extent possible, so that the resulting composite material reliably produces a structural color specific to G-PID ₁ . G-PID ₂ and/or G-PID ₃ may also be in the form of an organic-inorganic composite filler (composite filler 2) containing only G-PID ₂ and/or in the form of an organic-inorganic composite filler (composite filler 3), containing only G-PID ₃ so that their specific structural colors can be reliably created.

Preferably, from 10% to 90%, more preferably from 20% to 80%, even more preferably from 30% to 70% of the particles in each G-PID are in the form of an organic-inorganic composite filler containing only one G-PID, such that the above beneficial effect is expected, and the viscosity of the polymerizable curable composition according to the present description can be easily adjusted.

When G-PID is introduced into the mixture in a form other than "organo-inorganic composite filler containing only one G-PID", it is usually introduced into the mixture in the form of a powder (the G-PID itself as a group of spherical inorganic particles), but alternatively, spherical inorganic particles can be introduced into the mixture in the form of an organic-inorganic composite filler containing multiple types of G-PIDs. The following describes in detail the organic-inorganic composite filler, including this form.

Organic-inorganic composite filler

As noted above, the term "organo-inorganic composite filler" means a filler made from a powder of a composite material containing an (organic) polymer matrix and an inorganic filler dispersed in the polymer matrix, or a coagulated material in which the primary particles of the inorganic filler are interconnected ( organic) polymer.

In the polymerizable curable composition according to the present invention, the organic-inorganic composite filler includes spherical inorganic particles as an inorganic filler and a polymer having a refractive index lower than that of the spherical inorganic particles, which forms an (organic) polymer matrix. The polymer can be of any type satisfying the conditions specified above. Preferably, the polymer is a cured product of a polymerizable monomer component for use in forming the polymer matrix of the composite material of the present invention. Although the polymer need not include the same component as the polymerizable monomer component of the polymerizable curable composition of the present invention, the polymer preferably includes a component with the same refractive index as the polymerizable monomer component. Each organic-inorganic composite filler must satisfy the relationship n _(R) < n _(F) , where n _(R) is the refractive index of the polymer, an _(F) is the refractive index of the spherical inorganic particles. When the organic-inorganic composite filler contains different types of spherical inorganic particles with different refractive indices, the ratio must be maintained for each type of spherical inorganic particles. The Δn between n _(F) and n _(R) (=n _(F) - n _(R) ) is preferably 0.001 to 0.01, more preferably 0.001 to 0.005.

The content of spherical inorganic particles in the organic-inorganic composite filler is preferably from 30 wt. % up to 95 wt. %. When the content of spherical inorganic particles in the organic-inorganic composite filler is 30 wt. % or more, the polymerizable curable composition of the present invention can form a cured product that has sufficiently high mechanical strength and produces the desired colored light. From a practical point of view, it is difficult to obtain an organic-inorganic filler uniformly containing more than 95 wt. % spherical inorganic particles. The content of spherical inorganic particles in the organic-inorganic composite filler is more preferably from 40 wt. % up to 90 wt. %.

The organic-inorganic composite filler can be produced by a conventional production method, which includes mixing a specific amount of spherical inorganic particles, a polymerizable monomer component and a polymerization initiator; polymerizing the mixture by heating, irradiating light or other means, and then grinding the polymerization product. This production method produces an organic-inorganic composite filler having an indefinite shape and containing a composite material including a polymer matrix and spherical inorganic particles dispersed in the polymer matrix.

The organic-inorganic composite filler can also be produced by the method disclosed in WO 2011/115007 or WO 2013/039169, which, in particular, involves immersing aggregate particles, including aggregates of spherical inorganic particles, in a liquid composition containing a polymerizable monomer component, a polymerization initiator and organic solvent; then removing the organic solvent and polymerizing and curing the polymerizable monomer component by heat, light irradiation or other means. This method produces a porous organic-inorganic composite filler having a large number of small pores communicating with the outside, and including spherical inorganic primary particles that essentially remain in the form of aggregates, and a polymer that covers at least a portion of the surface of each of the primary particles. particles and connects primary particles with each other.

The average particle diameter of the organic-inorganic composite filler is preferably, but not limited to, 2 μm to 100 μm, more preferably 5 μm to 50 μm, even more preferably 5 μm to 30 μm, to provide high mechanical strength of the composite material according to the present invention or to ensure good processability of the polymerizable curable composition of the present invention.

Pigment, polymerization inhibitor, fluorescent whitening agent and other materials (generally in an amount of 0.0001 parts by mass to 5 parts by mass per 100 parts by mass of the organic-inorganic composite filler) can be added to the organic-inorganic composite filler, provided that its effect not broken. The organic-inorganic composite filler may also be subjected to washing or surface treatment with a silane coupling agent or the like.

The content of the organic-inorganic composite filler in the polymerizable curable composition of the present invention can be calculated and determined from the content of spherical inorganic particles in the organic-inorganic composite filler such that the total G-PID content (namely, the total content of spherical inorganic particles) falls within the above range, taking into account the content of a group of spherical particles of the same diameter not in the form of an organic-inorganic composite filler in the polymerizable curable composition.

Other Supplements

The polymerizable curable composition of the present invention may contain other additives such as a polymerization inhibitor and an ultraviolet absorber, provided that its effects are not impaired.

As described above, the composite material of the present invention obtained from the polymerizable curable composition of the present invention produces structural color even without any colorant such as pigment. Therefore, there is no need to add a pigment, which may discolor over time, to the polymerizable curable composition of the present invention. However, the addition of pigment is not prohibited, and the polymerizable curable composition may contain pigment in such an amount that it will not interfere with the colored light produced by the spherical filler. In particular, the polymerizable curable composition may contain pigment in an amount of from about 0.0005 parts by weight to about 0.5 parts by weight, preferably from about 0.001 parts by weight to about 0.3 parts by weight, based on 100 parts by weight of the polymerizable monomer component.

Method for producing a composite material according to the present invention and a dental workpiece for milling according to the present invention

Next, a method for producing a composite material according to the present disclosure and a method for producing a dental milling workpiece according to the present invention will be described.

The method for producing the composite material of the present invention also corresponds to one step in the method for producing the dental milling workpiece of the present invention. Specifically, a method for producing a dental milling workpiece of the present invention having a target milling portion of a certain shape includes mixing a polymerizable monomer component (A), inorganic particles (B) and a polymerization initiator (C) to form a polymerizable curable composition, in which the polymerizable monomer component (A) is capable of forming a cured product having a refractive index of from 1.40 to 1.57, the inorganic particles (B) include a group or groups of spherical particles of the same diameter comprising a material having a refractive index higher than that of the cured product obtained from a polymerizable monomer component (A), and a group of ultrafine particles, and molding and polymerizing a polymerizable curable composition to form a volumetric body of composite material that forms all or part of the target milling portion, wherein mixing is carried out to form a polymerizable curable composition capable of forming a cured product , containing spherical inorganic particles that form the entire group or groups of spherical particles of the same diameter and have a short-range order structure satisfying conditions 1 and 2 as an arrangement structure.

The polymerizable curable composition obtained in the mixing step has essentially the same composition as the polymerizable curable composition of the present invention described above. Kneading and degassing allow the inorganic particles (B) to be dispersed in the polymerizable monomer component (A), so that the composition can form a cured product containing spherical inorganic particles having a short-range order structure as an arrangement satisfying conditions 1 and 2 shown above. The kneading method is preferably carried out using a mixer such as a planetary centrifugal mixer, which can meet the required dispersion conditions in a short period of time and easily achieve large-scale production. Degassing preferably involves reduced pressure degassing, which can remove air bubbles in a short period of time from a high viscosity composition.

In this method, kneading and degassing should be performed under kneading and degassing conditions that have been confirmed as to whether the polymerizable curable composition (the polymerizable curable composition of the present invention) that is produced in the step can form a cured product in which the inorganic particles (B) dispersed in a state satisfying conditions 1 and 2 shown above.

The method for determining the kneading and degassing conditions is preferably method (1) or (2) described below.

(1) A method that includes pre-mixing under various sets of kneading and degassing conditions to form a polymerizable curable composition having a composition the same or substantially the same as that of the polymerizable curable composition actually produced; examining the radial distribution function g(r) for the cured product of the polymerizable curable composition obtained under each set of conditions to determine conditions that satisfy conditions 1 and 2 above; and acceptance of the same terms and conditions as certain terms.

(2) A method that includes collecting a portion of the composition obtained during kneading and degassing and/or after completion of kneading and degassing; checking whether the inorganic particles (B) dispersed in the curing reaction product of the selected composition are in a state satisfying conditions 1 and 2 above, and continuing kneading and/or degassing until the conditions are met.

When method (1) is used, for example, the kneading and degassing conditions can be determined as follows. First, numerous types of simulated kneading processes, each of which involve the use of a planetary centrifugal mixer (planetary mixer), which is an actual process device for mixing the starting materials for a curable composition having the same composition as the actual polymerizable composition. curable composition is performed under different conditions, such as different kneading speeds, different periods of kneading time and different degassing conditions after kneading. The radial distribution function g(r) is then examined for the cured product of the polymerizable curable composition obtained from each of the simulated kneading processes to determine the cured product satisfying conditions 1 and 2 above. Method (1) makes it possible to reliably obtain the required polymerizable curable composition only by setting certain mixing conditions. Therefore, method (1) can eliminate the need to change the conditions each time to produce the same polymerizable curable composition (same in composition and quantity) and prevent over-kneading (kneading for an unnecessarily long period of time) and thus can improve efficiency operations.

Method (2) is considered a particularly preferred method of obtaining a polymerizable curable composition, each time different in composition or quantity.

The polymerizable curable composition of the present invention is cast and polymerized to form a three-dimensional composite material body that forms all or part of the target milling portion. As used herein, the term "injection molding and polymerization" means a process that involves loading a polymerizable curable composition of the present invention into a mold of a particular configuration, and then polymerizing and curing the composition. The shape can have any volume suitably selected depending on the required configuration. The shape may have any configuration, such as a prismatic shape, a cylindrical shape, a rectangular plate shape, a disk shape, or any other irregular shape. During polymerization, if necessary, increased pressure can be created using an inert gas, such as nitrogen. A mold may be provided having a configuration similar to or substantially the same as that of the milling target portion into which the polymerizable curable composition of the present invention can be loaded and then polymerized and cured to form a three-dimensional body that can be used directly as the target milling parts. Alternatively, a mold may be provided having a size larger than the size of the milling target portion into which the composition can be loaded and then polymerized and cured to form a solid body that can be stamped or milled to form the milling target portion. Loading the composition into a mold can be accomplished using any known method such as injection molding, extrusion or compression molding. During the loading process, one polymerizable curable composition can be loaded, or a plurality of polymerizable curable compositions, varying in composition, can be loaded to form a multilayer material. The polymerizable curable composition of the present invention can also be loaded together with another polymerizable curable composition, as with any other polymer starting material, to form a multilayer material.

The mold can be made of metal, ceramic or polymer depending on the purpose and is preferably made of a heat-resistant material that is resistant to the temperature at which polymerization is carried out. Examples of mold material include stainless steel (SUS), high-speed tool steel, aluminum alloys, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS).

If necessary, the resulting solid body can also be subjected to subsequent steps such as heat treating, polishing, milling, attaching fasteners and printing. If necessary, a mounting pin can be attached to the solid body to secure the dental workpiece for milling to the milling machine. The fastening pin can have any shape that allows you to secure the dental workpiece for milling on the milling machine. The mounting pin may also be missing depending on the shape of the dental workpiece to be milled and the requirements of the processing machine. The fastening pin can be made, for example, of stainless steel, brass or aluminum. Methods for attaching the attachment pin to the milling target part (the main part of the dental workpiece for milling) include not only adhesive bonding, but also installation and fixation with screws. Bonding can be accomplished by any method using any commercially available adhesive such as isocyanate, epoxy, urethane, silicone or acrylic adhesive.

Examples

In the following, the present invention will be more specifically described with reference to examples, which are not intended to limit the present invention.

The dental milling blanks of the Examples and Comparative Examples were prepared by curing a polymerizable curable composition containing a polymerizable monomer component, inorganic particles and a polymerization initiator. First, each component used to form the polymerizable curable composition of each of the Examples and Comparative Examples is described.

1. Polymerizable monomer component Each of the mixtures M1 and M2 shown in Table 1, each of which is a mixture of polymerizable monomers, was used as a polymerizable monomer component. The abbreviations in the polymerizable monomers column of the table represent the following compounds, and each value in parentheses represents the content in parts by weight units.

UDMA: 1,6-bis(methacrylethyloxycarbonylamino)trimethylhexane

3G: triethylene glycol dimethacrylate

bis -GMA: 2,2-bis [(3-methacryloyloxy-2-hydroxypropyloxy)phenyl] propane Viscosities M1 and M2 were measured in a constant temperature room at 25°C using an E-type viscometer (VISCONIC ELD, manufactured by Tokyo Keiki Inc .).

The refractive index before curing (M1 or M2) and the refractive index after curing (cured product) were measured in a constant temperature room at 25°C using an Abbe refractometer (manufactured by Atago Co., Ltd.). A sample of the cured product was prepared by a method including adding 0.2 wt. to 100 parts by weight of M1 or M2. % camphorquinone (CQ), 0.3 wt. % ethyl p-N,N-dimethylaminobenzoate (DMBE) and 0.15 wt. % hydroquinone monomethyl ether (HQME) as photopolymerization initiators; their uniform mixing; adding the mixture to a mold with a through hole of 7 mm × 0.5 mm; then bringing the polyester films into pressing contact with both sides of the mixture; then curing the mixture by irradiation with light for 30 seconds using a dental halogen light irradiator (Demetron LC, manufactured by Sybron) with a light dose of 500 mW/cm ² and then removing the cured product from the mold. When a sample of a cured product was placed in an Abbe refractometer, a drop of a medium (bromonaphthalene) in which the sample was insoluble and which had a refractive index higher than that of the sample was placed on the sample so that the sample was in close contact with the measuring surface.

2. Inorganic particles

2-1. Group of spherical particles of the same diameter (G-PID)

G-PID1 to G-PID11 shown in Table 2 were used as G-PID. These groups of spherical particles of the same diameter were prepared in accordance with the method disclosed in Japanese Unexamined Patent Application Publication No. S58-110414 or S58-156524 (the so-called sol-gel method). Specifically, first, a mixed solution containing a hydrolyzable organosilicon compound (e.g., tetraethyl silicate) and a hydrolyzable organometallic titanium group metal compound (e.g., tetrabutyl zirconate, tetrabutyl titanate) in such a ratio as to provide the composition shown in the "composition" column of Table 2 is added to the ammonia solution. alcohol solution (eg, methanol, ethanol, isopropyl alcohol, isobutyl alcohol) and then hydrolyzed to obtain a precipitated reaction product. The precipitate was subsequently separated, then dried, possibly crushed, and then fired to produce a fired material. Then, 100 parts by mass of the calcined material was mixed and stirred with a stirrer with 4 parts by mass of γ-methacryloyloxypropyltrimethoxysilane and 3 parts by mass of n-propylamine in 500 parts by mass of methylene chloride. After removing the methylene chloride using an evaporator, the resulting product was dried by heating at 90°C to obtain a group of spherical particles of the same diameter as the treated surface. The average diameter of the primary particles, the average diameter of the aggregated particles, the average particle content, the average uniformity and the refractive index shown in Table 2 were measured as shown below.

(1) Average diameter of primary particles

A photograph of the powder was taken using a scanning electron microscope (XL-30S from Philips) at a magnification of 5000 to 100,000, and then it was subjected to image processing using image analysis software (IP-1000PC from Asahi Kasei Engineering Corporation), where the quantity particles (at least 30) and the diameters of the primary particles (maximum particle diameters) observed in a single field of view of the photograph. The average diameter of the primary particles was calculated from the determined values using the formula given below.

(n: number of particles, x _i : diameter of the primary i-th particle (maximum diameter))

(2) Average diameter of aggregated particles

A dispersion of 0.1 g G-PID) in 10 ml ethanol was prepared and thoroughly shaken by hand. The total volume-average diameter of the particles in the dispersion was determined using a laser diffraction-scattering particle size distribution analyzer (LS230, Beckrnan Coulter) and the Fraunhofer optical model. The resulting average diameter was used as the average diameter of the aggregated G-PID particles.

(3) Average particle size content (percentage (%) of particles with sizes falling within the average primary particle diameter range ±5% of the average primary particle diameter in the numerical size distribution for all particles)

The number of particles having a primary particle diameter (maximum dimensions) outside the range from the average primary particle diameter -5% of the average primary particle diameter to the average primary particle diameter +5% of the average primary particle diameter, which was determined as shown above, from all particles in single field of view of a photograph. The number of particles with a primary particle diameter falling within the range of an average primary particle diameter - 5% of the average primary particle diameter to an average primary particle diameter +5% of the average primary particle diameter was calculated by subtracting the counted number from the number of all particles. The content of average diameter particles was calculated using the formula below.

Content (%) of particles of average diameter = [(number of particles with a primary particle diameter falling within the range of the average diameter of primary particles ± 5% of the average diameter of a primary particle in a unit field of view in a scanning electron micrograph)/(number of all particles in a unit field microphotograph of a scanning electron microscope)] × 100

(4) Average uniformity

The photograph of the powder was taken using a scanning electron microscope. The number (n: at least 30) of particles in a group of spherical particles of the same diameter (G-PID) observed in a single photographic field of view was counted, as well as the long diameter (Li) (maximum size) and short diameter (Bi) (size in the direction , perpendicular to the long diameter) of each particle. The average particle uniformity was calculated using the formula below.

(5) Refractive index

The refractive index was measured by immersion method using an Abbe refractometer (manufactured by Atago Co., Ltd.). Specifically, a group of spherical particles of uniform diameter (G-PID) was dispersed in 50 mL of anhydrous toluene in a 100 mL sample vessel in a room kept at a constant temperature of 25 °C. While stirring the resulting dispersion using a stirrer, 1-bromotoluene was slowly added dropwise to the dispersion, during which the refractive index of the dispersion was determined when the dispersion reached its most transparent state. The resulting value was used as the refractive index of a group of spherical particles of the same diameter (G-PID).

2-2. Organic-inorganic composite filler (CF1)

To 200 g of water, 100 g of a group of spherical particles of the same diameter (G-PID5) shown in Table 2 was added. The particles were dispersed using an SC Mill circulating type atomizer (manufactured by Nippon Coke & Engineering Co., Ltd.) to form an aqueous dispersion.

Separately, 4 g (0.016 mol) of γ-methacryloyloxypropyltrimethoxysilane and 0.003 g of acetic acid were added to 80 g of water and stirred for 1 hour 30 minutes to form a homogeneous solution with pH 4. The solution was added to the aqueous dispersion and stirred until homogeneous. The lightly stirred dispersion was then fed to a disk rotated at high speed so that the dispersion was spray-dried to granulate. Spray drying was performed using a TSR-2W spray dryer (manufactured by Sakamoto Giken) having a rotating disk for centrifugal atomization. The disk rotation speed was 10,000 rpm, and the temperature of the drying atmospheric air was 200°C. The powder obtained by dry spray granulation was then dried in vacuum at 60° C. for 18 hours, obtaining 73 g of essentially spherical aggregates.

Then, 50 g of the aggregates were immersed in a polymerizable monomer solution consisting of a mixture of 10 g of polymerizable monomer component M1, 0.025 g of azobiisobutyronitrile (AIBN) as a thermal polymerization initiator, and 5.0 g of methanol as an organic solvent (containing 36 parts by weight of polymerizable monomer component per 100 parts by mass of organic solvent). The mixture obtained after thorough mixing was checked to see if it was in suspension form and then left for 1 hour.

The resulting mixture was transferred to a rotary evaporator. While stirring, the mixture was dried under a reduced pressure of 10 hPa under heating conditions at 40° C. (using a warm water bath) for 1 hour to remove the organic solvent. As a result of removing the organic solvent, a powder with high flowability was obtained. While stirring in a rotary evaporator, the resulting powder was heated under a reduced pressure of 10 hPa under conditions at 100° C. (using an oil bath) for 1 hour, so that the polymerizable monomer component in the powder was polymerized and cured. This process resulted in 45 g of a substantially spherical organic-inorganic composite filler (CF1) comprising spherical aggregates and an organic polymer coating the surface of the aggregates. The organic-inorganic composite filler had an average particle size of 33 μm.

2-3. Ultrafine particles (G-SFP)

Reolosil QS-102 (average primary particle diameter 12 nm, manufactured by Tokuyama Corporation) was used as G-SFP.

2-4. Inorganic particles of undefined shape

The inorganic particles F1 of undefined shape shown in Table 2 were used. The inorganic particles F1 of undefined shape were prepared in accordance with the method described, for example, in Japanese Unexamined Patent Application Publication No. H02-132102 or H03-197311, which involved dissolving an alkoxysilane compound in organic solvent; adding water to the solution for partial hydrolysis; then further adding to the partial hydrolysis product an alkoxide of another metal and an alkali metal compound, which were intended to form a composite material; allowing hydrolysis to continue to form a gel material; then drying the gel material, possibly grinding the dried material, and firing the dried material. As shown above for G-PID, the average primary particle diameter (meaning the average diameter of the crushed inorganic indeterminate particles), average particle content, and refractive index were measured for the inorganic undefined particles.

3. Polymerization initiator

A photopolymerization initiator consisting of a combination of camphorquinone (CQ) and ethyl p-N,N-dimethylaminobenzoate (DMBE) or a thermal polymerization initiator consisting of benzoyl peroxide (BPO) was used as the polymerization initiator.

Example 1

To 100 parts by weight of the polymerizable monomer component M1, 0.3 parts by weight of CQ and 1.0 parts by weight of DMBE were added and mixed to form a homogeneous polymerizable monomer composition. Then, 500 parts by weight of G-PID4 and 1.0 parts by weight of group of ultrafine particles (G-SFP) were weighed, to which the polymerizable monomer composition was gradually added under red light, while the mixture was thoroughly kneaded using a planetary mixer (manufactured by Inoue Mfg. Inc.) to form a homogeneous curable paste. The paste was degassed under reduced pressure to remove air bubbles, thereby obtaining a polymerizable curable composition. The resulting polymerizable curable composition was loaded into a prismatic mold (14 mm × 18 mm × 150 mm) made of polypropylene, while preventing air bubbles from entering the composition. Subsequently, after the top surface of the composition was leveled, the composition was irradiated for 1 minute with light from a dental LED polymerizer (α Light V manufactured by Morita Corporation). The resulting cured product was demolded to form a dental workpiece for milling.

The resulting dental milling workpiece was subjected to (1) visual evaluation of color light, (2) measurement of the wavelength of color light, (3) evaluation of color matching using a colorimeter, (4) visual evaluation of color matching, (5) evaluation of the radial distribution function of spherical inorganic particles, (6) visual assessment of appearance, and (7) assessment of flexural strength. Tables 3-5 show the composition of each dental milling workpiece (note: the matrix column indicates the polymerizable monomer component used to form the polymer matrix) and the evaluation results. In fig. 1A shows an example of a plane image of a portion of a cured product cut from the dental milling blank of Example 1, which was observed using a scanning electron microscope. In fig. 1B shows an example of coordinate data obtained from the image in FIG. 1A, obtained using scanning electron microscopy. In fig. 2 is a graph showing the radial distribution function g(r) calculated based on the parameters determined from the coordinate data in FIG. 1B. In Example 1, a dental milling workpiece was successfully obtained that satisfied conditions 1 and 2 regarding the radial distribution function, which were reproduced 10 out of 10 times, and was judged to have a uniform appearance without cracks. Each assessment and measurement was carried out using the method shown below.

(1) Visual assessment of colored light

A portion of the cured product having a length of at least 7 mm and a thickness of 1 mm was cut from the dental milling blank of each of the Examples and Comparative Examples and used as an evaluation sample. The resulting evaluation sample was mounted vertically on the adhesive surface of a square black tape (carbon tape) measuring approximately 10 mm and the color of the colored light from the sample was visually observed.

(2) Wavelength of colored light

The evaluation sample was prepared as in section (1). The spectral reflectance of the sample was measured against a black background and against a white background using a color difference meter (TC-1800 MCP, manufactured by Tokyo Denshoku Co., Ltd.). The wavelength at the point of local maximum reflectance, measured against a black background, was defined as the wavelength of colored light.

(3) Color matching evaluation using a colorimeter

A sham restoration was performed on hard resin teeth with a Class II cavity (5 mm diameter, 3 mm depth) reproduced in the lower right sixth tooth. The dental workpiece for milling each of the Examples and Comparative Examples was milled to form a dental prosthesis corresponding to the missing part. The denture was bonded to the cavity using EsteCem II (adhesive resin cement, manufactured by Tokuyama Dental Corporation) and then polished to complete the filling. The color match of the simulated restored part was assessed using a two-dimensional colorimeter (RC-500, manufactured by PaPaLab Co., Ltd.). Hard resin teeth with high color intensity (corresponding to A4) and hard resin teeth with low color intensity (corresponding to A1) falling into category A (reddish brown) according to the shade scale (VITA Classical from VITA) were used as hard resin teeth ), as well as hard resin teeth with high color intensity (corresponding to B4) and hard resin teeth with low color intensity (corresponding to B1), falling into category B (reddish-yellow) according to the shade scale (VITA Classical from VITA) .

The hard resin teeth were placed in a 2D colorimeter and imaged. The resulting image was analyzed using image analysis software (RC Series Image Viewer, manufactured by PaPaLab Co., Ltd.). The color difference (ΔE* for CIELab) between the measured color values of the restored portion and the non-restored portion of the hard resin teeth was determined and evaluated for color consistency.

ΔE*={(ΔL*) ² +(Δa*) ² +(Δb*) ² } ^1/2

ΔL*=L1* - L2*

Δa*=a1* - a2*

Δb*=b1* - b2*

In the formula, L1* represents the brightness index of the restored part of the hard resin teeth, a1* and b1* represents the color index of the restored part of the hard resin teeth, L2* represents the brightness index of the non-restored part of the hard resin teeth, a2* and b2* represents the color value of the unrestored part of hard resin teeth, and ΔE* represents the amount of color change.

(4) Visual assessment of color matching

As shown in section (3), a restoration simulation was carried out, and the color match of the restored part was assessed visually. The evaluation criteria are the following.

Criteria for evaluation

5: The color of the filling is indistinguishable from the color of hard resin teeth.

4: The color of the filling matches well with the color of the hard resin teeth.

3: The color of the filling resembles the color of hard resin teeth.

2: The color of the filling resembles the color of hard resin teeth, but does not match the color well.

1: The color of the filling does not match the color of the hard plastic teeth.

(5) Estimation of the radial distribution function of spherical inorganic particles

A portion of the cured product with a diameter of 5 mm×10 mm was cut from the dental workpiece for milling each of the Examples and Comparative Examples. The dispersion state of the spherical particles in a portion of the cured product was observed using a scanning electron microscope (XL-30S, manufactured by Philips), where the radial distribution function of the particles was determined and evaluated. Specifically, a portion of the cured product was subjected to cross-cutting under 2 kV conditions for 20 minutes using an ion grinding system (IM4000 manufactured by Hitachi, Ltd.) so that an observable plane (observation plane) was formed. An area of the observation plane containing 1000 spherical particles was imaged using a scanning electron microscope. The resulting scanning electron microscopy image was analyzed using image analysis software (Simple Digitizer ver. 3.2 (freeware)) and the coordinates of the spherical particles in the area were determined. The coordinates of any of the spherical particles were selected from the obtained coordinate data. A circle of radius r was drawn centered on the selected spherical particle, where r represents the distance covering an area containing at least 200 spherical particles from the center. The number of spherical particles in the circle was counted and used to calculate the average particle density <p> (in counting units per cm ² ). The number dn of particles in the region between a circle whose circumference is spaced at a distance r from the spherical particle in the center and a circle whose circumference is at a distance r + dr from the spherical particle in the center was counted, and the area da of the region in which dr was the value in range from about r ₀ /100 to about r ₀ /10, where r ₀ was the average diameter of the spherical particles. The obtained values of <р>, dn and da were used to calculate the radial distribution function g(r) according to formula (1) below.

A graph is constructed showing the relationship between the radial distribution function and r/r ₀ , where r represents any distance from the center of the circle and r ₀ represents the average diameter of the spherical particles. The resulting radial distribution function was scored as “S” when it satisfied conditions 1 and 2, and as “N” when it did not satisfy either condition 1 and 2.

(6) Visual assessment of appearance

The appearance of the dental milling workpiece of each of the Examples and Comparative Examples was observed visually and rated as "S" if there were no cracks or other defects and as "N" if there was a crack.

(7) Evaluation of flexural strength

Test pieces with a width of 2 mm and a length of 25 mm were cut from the dental milling workpiece of each of the Examples and Comparative Examples. The test specimens were polished in the longitudinal direction with waterproof polishing paper No. 1500 to obtain test specimens with a thickness of 2 mm ± 0.1 mm. The resulting test specimens were subjected to three-point bending testing using a universal tensile testing machine (Autograph, manufactured by Shimadzu Corporation) under the conditions of a span of 20 mm and a crosshead speed of 1 mm/min in a room temperature atmosphere. The flexural strengths of five specimens were measured and used to calculate the average flexural strength.

Example 2

A dental milling blank was prepared as in Example 1, except that the composition of the dental milling blank was changed as shown in Table 3. As in Example 1, the resulting dental milling blank was subjected to (1) visual evaluation of colored light, ( 2) measuring the wavelength of colored light, (3) assessing color match with a colorimeter, (4) visual assessing color match, (5) assessing the radial distribution function of spherical inorganic particles, (6) visual assessing appearance, and (7) assessing strength to bend. Tables 3-5 show the evaluation results. In fig. 3 is a graph of the radial distribution function with respect to a portion of the cured product cut from the dental milling workpiece of Example 2. In Example 2, a dental milling workpiece satisfying conditions 1 and 2 regarding the radial distribution function was also successfully obtained, which were reproduced 10 times out of 10 and was judged to have a uniform appearance with no cracks.

Example 3

To 200 parts by weight of polymerizable monomer component M1, 0.6 parts by weight of CQ and 2.0 parts by weight of DMBE were added and mixed to form a homogeneous polymerizable monomer composition. Then, 200 parts by mass of G-PID4, 200 parts by mass of G-PID7, 200 parts by mass of G-PID10, and 1.0 parts by mass of group of ultrafine particles (G-SFP) were weighed and mixed with 100 parts by mass of the polymerizable monomer composition under red light. The mixture was thoroughly mixed using a planetary mixer (manufactured by hioue Mfg. Inc.) to form a homogeneous curable paste 1. Separately, 200 parts by weight G-PID4, 200 parts by weight G-PID9, 200 parts by weight G-PID11 and 1.0 parts by weight group ultrafine particles (G-SFP) were weighed and mixed with 100 parts by weight of the polymerizable monomer composition under red light. The mixture was thoroughly mixed using a planetary mixer (manufactured by Inoue Mfg. Inc.) to form a homogeneous curable paste 2. The resulting curable pastes 1 and 2 were degassed under reduced pressure so that air bubbles were removed, thereby obtaining polymerizable curable compositions 1 and 2. Each From the resulting polymerizable curable compositions 1 and 2, they were loaded into a prismatic mold (14 mm × 18 mm × 10 mm) made of polypropylene, while preventing air bubbles from entering the composition. Subsequently, after leveling the top surface of each composition, curable compositions 1 and 2 in molds were placed on top of each other (14 mm × 18 mm × 20 mm) so that their leveled surfaces were in close contact with each other, and then they were irradiated at for 1 minute under the light of a dental LED polymerizer (a Light V, manufactured by Morita Corporation). The resulting cured product was removed from the molds to form a dental blank for milling.

As in Example 1, the resulting dental milling workpiece was subjected to (1) color light visual evaluation, (2) color light wavelength measurement, (3) color match evaluation using a colorimeter, (4) color match visual evaluation, (5) evaluation of the radial distribution function of spherical inorganic particles, (6) visual evaluation of appearance, and (7) evaluation of flexural strength. Tables 3-5 show the evaluation results. In fig. 4 shows a graph of the radial distribution function for a portion of the cured product cut from the dental milling workpiece of Example 3. Example 3 also successfully produced a dental milling workpiece satisfying conditions 1 and 2 regarding the radial distribution function, which were reproduced 10 times out of 10 , and was assessed to have a uniform appearance without cracks.

Example 4

A dental milling blank was prepared as in Example 1, except that the composition of the dental milling blank was changed as shown in Table 3. As in Example 1, the resulting dental milling blank was subjected to (1) visual evaluation of colored light, ( 2) measuring the wavelength of colored light, (3) assessing color match with a colorimeter, (4) visual assessing color match, (5) assessing the radial distribution function of spherical inorganic particles, (6) visual assessing appearance, and (7) assessing strength to bend. Tables 3-5 show the evaluation results. FIG. 5 is a graph of the radial distribution function for a portion of the cured product cut from the dental milling blank of Example 4. Example 4 also successfully produced a dental milling blank satisfying conditions 1 and 2 regarding the radial distribution function, which were reproduced by 10 times out of 10 and was judged to have a uniform appearance with no cracks.

Example 5

To 100 parts by weight of the polymerizable monomer component Ml, 0.5 parts by weight of BPO were added and mixed to form a homogeneous polymerizable monomer composition. Then, 500 parts by weight of G-PID4 and 1.0 parts by weight of group of ultrafine particles (G-SFP) were weighed, to which the polymerizable monomer composition was gradually added under red light, while the mixture was thoroughly kneaded using a planetary mixer (manufactured by Inoue Mfg. Inc.) to form a homogeneous curable paste. The paste was degassed under reduced pressure to remove air bubbles, thereby obtaining a polymerizable curable composition. The resulting polymerizable curable composition was loaded into a prismatic mold (14 mm × 18 mm × 150 mm) made of polypropylene, while preventing air bubbles from entering the composition. Subsequently, after leveling the top surface of the composition, the composition was subjected to heat-pressure polymerization using a pressure polymerizer under pressurized conditions at a nitrogen pressure of 0.4 MPa and a temperature of 100°C for 12 hours. The resulting cured product was removed from the mold to form a dental blank for milling.

As in Example 1, the resulting dental milling workpiece was subjected to (1) color light visual evaluation, (2) color light wavelength measurement, (3) color match evaluation using a colorimeter, (4) color match visual evaluation, (5) evaluation of the radial distribution function of spherical inorganic particles, (6) visual evaluation of appearance, and (7) evaluation of flexural strength. Tables 3-5 show the evaluation results. In fig. 6 is a plot of the radial distribution function for a portion of the cured product cut from the dental milling workpiece of Example 5. Example 5 also successfully produced a dental milling workpiece satisfying conditions 1 and 2 regarding the radial distribution function, which were reproduced 10 times out of 10 , and was assessed to have a uniform appearance without cracks.

Example 6

A dental milling blank was prepared as in Example 5, except that the composition of the dental milling blank was changed as shown in Table 3. As in Example 1, the resulting dental milling blank was subjected to (1) color light visual evaluation, ( 2) measuring the wavelength of colored light, (3) assessing color match with a colorimeter, (4) visual assessing color match, (5) assessing the radial distribution function of spherical inorganic particles, (6) visual assessing appearance, and (7) assessing strength to bend. Tables 3-5 show the evaluation results. In fig. 7 is a graph of the radial distribution function for a portion of the cured product cut from the dental milling blank of Example 6. Example 6 also successfully produced a dental milling blank satisfying conditions 1 and 2 regarding the radial distribution function, which were reproduced 10 times out of 10 , and was assessed to have a uniform appearance without cracks.

Comparative examples 1 and 3-5

A dental milling blank was prepared as in Example 1, except that the composition of the dental milling blank was changed as shown in Table 3. As in Example 1, the resulting dental milling blank was subjected to (1) visual evaluation of colored light, ( 2) measuring the wavelength of colored light, (3) assessing color match using a colorimeter, (4) visual assessing color match, (6) visual assessing appearance, and (7) assessing flexural strength. Tables 3-5 show the evaluation results.

Comparative example 2

To 100 parts by weight of the polymerizable monomer component M1, 0.3 parts by weight of CQ and 1.0 parts by weight of DMBE were added and mixed to form a homogeneous polymerizable monomer composition. Then, 400 parts by weight of G-PID2 and 1.0 parts by weight of group of ultrafine particles (G-SFP) were weighed, to which the polymerizable monomer composition was gradually added under red light while the mixture was kneaded in a mortar to form a curable paste. The paste was degassed under reduced pressure to remove air bubbles, thereby obtaining a polymerizable curable composition. The resulting polymerizable curable composition was loaded into a prismatic mold (14 mm × 18 mm × 150 mm) made of polypropylene, while preventing air bubbles from entering the composition. Subsequently, after leveling the top surface of the composition, the composition was irradiated for 1 minute with light from a dental LED polymerizer (a Light V, manufactured by Morita Corporation). The resulting cured product was removed from the mold to form a dental blank for milling.

As in Example 1, the resulting dental milling workpiece was subjected to (1) color light visual evaluation, (2) color light wavelength measurement, (3) color match evaluation using a colorimeter, (4) color match visual evaluation, (5) assessment of the radial distribution function of spherical inorganic particles and (6) visual assessment of appearance. Tables 3-5 show the evaluation results. In comparative example 2 the rating was unsatisfactory (1 point out of 5). These evaluation results are shown in the table. In Comparative Example 2, the flexural strength could not be assessed because cracking was observed upon visual evaluation of the appearance.

The results of Examples 1-6 demonstrate that cured products meeting the conditions of the present invention exhibit colored light on a black background and have good color consistency.

The results shown in FIG. 1A, 1B and 2 demonstrate that the dental milling workpiece obtained in Example 1 has a short-range order structure according to the present invention, since the radial distribution function g(r) has a first maximum peak observed at the position where the distance r ₁ between the nearest neighbors particles 1.03 times larger than the particle size r ₀ (r ₁ /r ₀ is 1.03), and since the radial distribution function g(r) has a local minimum value of 0.60 between the distance r ₁ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles.

The results shown in FIG. 3 demonstrate that the dental milling workpiece obtained in Example 2 has a short-range order structure according to the present invention, since the radial distribution function g(r) has a first maximum peak observed at the position where the distance r ₁ between the nearest adjacent particles is 1 .24 times the particle size r ₀ (r ₁ /r ₀ is 1.24) and since the radial distribution function g(r) has a local minimum value of 0.62 between the distance r ₁ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles.

The results shown in FIG. 4 demonstrate that the dental milling workpiece obtained in Example 3 has a short-range order structure according to the present invention, since the radial distribution function g(r) has a first maximum peak observed at the position where the distance r ₁ between the nearest adjacent particles is 1 .41 times the particle size r ₀ (r ₁ /r ₀ is 1.41) and since the radial distribution function g(r) has a local minimum value of 0.88 between the distance r ₁ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles.

The results shown in FIG. 5 demonstrate that the dental milling workpiece obtained in Example 4 has a short-range order structure according to the present invention, since the radial distribution function g(r) has a first maximum peak observed at the position where the distance r ₁ between the nearest adjacent particles is 1 .04 times the particle size r ₀ (r ₁ /r ₀ is 1.04) and since the radial distribution function g(r) has a local minimum value of 0.80 between the distance r ₂ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles.

The results shown in FIG. 6 demonstrate that the dental milling workpiece obtained in Example 5 has a short-range order structure according to the present invention, since the radial distribution function g(r) has a first maximum peak observed at the position where the distance r ₁ between the nearest adjacent particles is 1 .24 times the particle size r ₀ (r ₁ /r ₀ is 1.24) and since the radial distribution function g(r) has a local minimum value of 1.00 between the distance r ₁ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles.

The results shown in FIG. 7 demonstrate that the dental milling workpiece obtained in Example 6 has a short-range order structure according to the present invention because the radial distribution function g(r) has a first maximum peak observed at the position where the distance r ₁ between the nearest adjacent particles is 1 .68 times the particle size r ₀ (r ₁ /r ₀ is 1.68) and since the radial distribution function g(r) has a local minimum value of 0.86 between the distance r ₁ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles.

The results of Comparative Examples 1 and 3-5 demonstrate that cured products not satisfying any of the conditions according to the present invention do not have the desired color (n _(MX) < n _(G-PIDm is not satisfied in Comparative Example 1), do not show color light on a black background (G-PID has an average particle diameter of 80 nm in comparative example 3; the filler has an undefined shape in comparative example 4; the difference between the average diameters of the primary particles of the individual groups represented by G-PID _m has a size of less than 25 nm in comparative example 5) and have low color matching.

The results of Comparative Example 2 demonstrate that the composition resulting from heterogeneous kneading does not satisfy the spherical inorganic particle structure conditions of the present invention and provides poor color matching to the tooth substance.

The results shown in FIG. 8 demonstrate that the dental milling workpiece obtained in Comparative Example 2 does not have a short-range order structure according to the present invention because the radial distribution function g(r) has a first maximum peak observed at the position where the distance r ₁ between the nearest neighboring particles is 1.58 times the size r ₀ (r ₁ /r ₀ is 1.58), and since the radial distribution function g(r) has a local minimum value of 0.18 between the distance r ₁ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles.

Claims (25)

1. A dental milling workpiece comprising a milling target portion including a polymer-based material, wherein the polymer-based material includes at least one composite material comprising a polymer matrix and inorganic particles dispersed in the polymer matrix, wherein the polymer matrix is a cured product of at least one kind of (meth)acrylic compound, and the cured product has a refractive index of 1.40 to 1.57; And inorganic particles include: at least one group of spherical particles of uniform diameter (G-PID), including spherical inorganic particles with a defined average primary particle diameter from 100 nm to 1000 nm and having a size distribution in which 90% or more of all particles have diameters falling within range from average primary particle diameter -5% average primary particle diameter to average primary particle diameter +5% average primary particle diameter, where spherical inorganic particles forming a group or groups of spherical particles of the same diameter (G-PID) are composite oxide particles of silica and titanium element oxide, wherein the composite oxide particles of silica and titanium element oxide have a refractive index of 1.45 to 1.58; And group of ultrafine particles (G-SFP), including inorganic particles with an average diameter of primary particles less than 100 nm, while for at least one group comprising one or more groups of spherical particles of the same diameter, one or more groups of spherical particles of the same diameter are groups A, each of which is represented by G-PIDm, where A is the number of groups, m is 1 when A is 1, or m is a positive integer from 1 to A when A is 2 or more, and the average diameter of the primary particles of the group increases with increasing m, groups represented by G-PIDm have average primary particle diameters that differ from each other by 25 nm or more, the group of ultrafine particles has an average diameter of primary particles less than 25 nm or more than that of the group represented by G-PID ₁ , wherein the total number of group or groups of spherical particles of the same diameter (G-PID) dispersed in the polymer matrix is from 100 to 800 parts by mass based on 100 parts by mass of the polymer matrix, and the number of group of ultrafine particles (G-SFP) dispersed in polymer matrix, ranges from 0.1 to 5 parts by weight per 100 parts by weight of the polymer matrix; at least one composite material satisfies the relationship n _(Mx) < n _(G-PIDm) , where n _(Mx) represents the refractive index of the polymer matrix for light with a wavelength of 589 nm at 25°C, n _(G-PIDm) represents is the refractive index of spherical inorganic particles of each group represented by G-PIDm for light with a wavelength of 589 nm at 25°C, and the relationship holds for each n _(G-PIDm) , and at least one composite material has a short-range order structure in which spherical inorganic particles of all groups of spherical particles of the same diameter in the polymer matrix have an arrangement structure that satisfies: condition 1, where the radial distribution function is plotted with r/r ₀ on the x-axis and the radial distribution function g(r) on the y-axis and shows the relationship between r/r ₀ and g(r) for r, where r/r ₀ represents is a normalized dimensionless number calculated by dividing the radius r centered on a selected spherical particle, where r is the distance covering an area containing at least 200 spherical particles from the center by the average diameter _r0 of all spherical inorganic particles dispersed in the composite material, and g(r) represents the probability that the existence of any other spherical inorganic particle at a point distant r from the center of any spherical inorganic particle has peaks, among which the peak closest to the origin provides the distance r ₁ between its nearest neighbors particles as the r value corresponding to the top of the peak, and the distance r ₁ between the nearest neighboring particles is 1-2 times larger than the average diameter r ₀ of all spherical inorganic particles dispersed in the composite material, and condition 2, when the graph of the radial distribution function has peaks, among which the peak, the second closest to the origin, provides the distance r ₂ between the second nearest neighboring particles, since the value of r corresponds to the top of the peak, and the radial distribution function g(r) has a local minimum value of 0.56 to 1.10 between the distance r ₁ between the nearest neighboring particles and the distance r ₂ between the second nearest neighboring particles, where the radial distribution function g(r) is calculated by formula (1): g(r) = {1/<ρ >} × {dn/da}, where <ρ> represents the average density of spherical inorganic particles in the viewing plane, which is the inner surface of the composite material, the average density being determined from a scanning electron microscopy image of the inner surface of the composite material, dn is the number of spherical inorganic particles in the region between a circle with a circle at a distance r from any spherical inorganic particle in the viewing plane and a circle with a circle at a distance r+dr from any spherical inorganic particle, and da is the area of the region , where da = 2πr × dr, in which dr is a value in the range from r ₀ /100 to r ₀ /10. 2. The dental workpiece for milling according to claim 1, wherein the entire group or groups of spherical particles of the same diameter of inorganic particles have an average primary particle diameter of from 230 nm to 1000 nm, and the group of ultrafine particles have an average primary particle diameter of from 3 nm to 75 nm. 3. The dental workpiece for milling according to claim 1 or 2, where the difference between n _(MX) and n _(G-PIDm) (n _(G-PIDm) - n _(MX) ), which is represented by Δn, is from 0.001 to 0 ,1 for each n _(G-PIDm) . 4. The dental workpiece for milling according to any one of claims 1 to 3, wherein the at least one composite material in the target milling portion includes a plurality of composite materials having different compositions and bonded to each other. 5. A method for manufacturing a dental workpiece for milling according to any one of claims. 1-4, having a target milling part of a certain shape, including: mixing a polymerizable monomer component (A), inorganic particles (B) and a polymerization initiator (C) to form a polymerizable curable composition, wherein the polymerizable monomer component (A) is at least one type of (meth)acrylic compound and is capable of forming a curable product having a refractive index of 1.40 to 1.57 for light of wavelength 589 nm at 25°C, inorganic particles (B) include a group or groups of spherical particles of the same diameter (G-PID), wherein the spherical inorganic particles represent are particles of a complex oxide based on silicon dioxide and an oxide of a titanium group element, and the particles of a complex oxide based on silicon dioxide and an oxide of a titanium group element have a refractive index of 1.45 to 1.58, and a group of ultrafine particles; And carrying out the casting and polymerization of a polymerizable curable composition with the formation of a volumetric body of composite material, which forms all or part of the target milling part, while the total number of a group or groups of spherical particles of the same diameter (G-PID) in the polymerizable curable composition is from 100 to 800 mass parts based on 100 parts by mass of the polymerizable monomer component (A), and the amount of the group of ultrafine particles (G-SFP) in the polymerizable curable composition is from 0.1 to 5 parts by mass based on 100 parts by mass of the polymerizable monomer component (A), wherein mixing is carried out to form a polymerizable curable composition capable of forming a cured product containing spherical inorganic particles that form an entire group or groups of spherical particles of the same diameter and have a short-range order structure satisfying conditions 1 and 2 as the arrangement structure. 6. The method of claim 5, wherein at least a portion of the group or groups of spherical particles of the same diameter in the polymerizable curable composition are in the form of an organic-inorganic composite filler including one group of spherical particles of the same diameter, and a polymer having a lower refractive index, than spherical inorganic particles of one group of spherical particles of the same diameter for light with a wavelength of 589 nm at 25°C, and not containing any group of spherical particles of the same diameter, except for one group of spherical particles of the same diameter, and the polymer included in the composition organic-inorganic composite filler, is a cured product of at least one type of (meth)acrylic compound, and the cured product has a refractive index of 1.40 to 1.57. 7. The method according to claim 5 or 6, wherein the polymerization initiator (C) is a thermal polymerization initiator, and casting and polymerization are carried out at a temperature of 60°C to 200°C.