Method for producing radiopaque filler and method for producing dental curable composition

Abstract

The present invention provides a method for efficiently producing a radiopaque filler which can impart high radiopacity to a cured product of an existing structural-coloration-type dental curable composition without impairing the characteristics of the composition when blended with the composition.　By carrying out pulverization and particle size adjustment after kneading, polymerizing, and curing, at a pressure of 1.0 to 1.0×105 (Pa), a polymerizable monomer and particulates that are obtained by spray-drying slurry containing low crystalline rare earth metal fluoride particulates in which the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particulates is not less than 0.3° as measured by X-ray diffractometry, a radiopaque filler that is made of organic-inorganic composite particles in which the particulates are dispersed in a resin is produced.

Description

Method for producing radiopaque filling material and method for producing dental hardenable composition

[0001] The present invention relates to a method for producing a radiopaque filling material and a method for producing a dental hardenable composition.

[0002] In dental treatment, a cavity is formed by removing the carious portion of a carious tooth, and then a filling material called a composite resin (hereinafter simply referred to as "CR") made of a dental hardenable composition containing a polymerizable monomer, a filler, and a polymerization initiator as its main components is filled into the cavity, and then the filling material is hardened to seal the cavity (CR restoration). The CR restoration has the advantages of reducing the amount of tooth structure to be removed, being able to impart a color tone equivalent to natural tooth color, and being easy to operate. Furthermore, due to the improved mechanical strength of the CR hardened body and the improved adhesive strength to the tooth, it is used not only for restoring anterior teeth, but also for restoring molars, which are subject to high occlusal pressure.

[0003] In order to perform highly aesthetic restorations with CR restorations, it is common to determine the color (hue and tone) of the tooth to be restored (the tooth to be restored) (such color determination is sometimes called "shade taking") and select a CR of a color that matches the determined color for the restoration. To perform highly aesthetic restorations that faithfully reproduce the color variations depending on the part of the tooth, it was necessary to laminate multiple CRs of different colors. Furthermore, coloring of CRs is usually performed by blending pigments or dyes into the CR, but these substances can fade or discolor over time in the hardened body after treatment, causing discoloration over time after restoration, which can result in the appearance of the restored area no longer matching that of natural teeth.

[0004] In recent years, CRs have been proposed and have attracted attention. These CRs use a filler containing spherical inorganic particles having a specific average particle size and particle size distribution, and the refractive index of the spherical inorganic particles is made larger than the refractive index of the resin portion that becomes the matrix when cured. This allows the CRs to exhibit structural colors that develop in a predetermined color tone independent of the angle of incidence of light due to light interference, scattering, etc. (hereinafter, CRs that exhibit such structural colors are also referred to as "structural color CRs") (see Patent Documents 1 and 2).

[0005] The structural color system CR has the following excellent features: (1) it does not use dyes or pigments, and therefore is less susceptible to the problem of discoloration over time; (2) it exhibits a specific structural color tone that is independent of the angle of incidence of light, depending on the average particle size of the spherical inorganic particles used; in particular, when spherical inorganic particles with an average primary particle size of 230 to 350 nm are used, it can be colored in yellow to red, which is similar to the color of dentin; and (3) since the cured product has appropriate transparency, it easily blends with the color of the tooth to be restored, and it is possible to restore a wide range of colors of teeth to be restored with a single type of composite resin, resulting in an appearance similar to that of natural teeth, without the need for complicated shade-taking or composite resin shade selection.

[0006] The polymerizable curable composition constituting the structural color system CR satisfies the following conditions (A) and (B), but it is known that when the following condition (C) is further satisfied, a cured product that more reliably exhibits the desired structural color can be obtained (see Patent Document 2).

[0007] (A) The composition contains a polymerizable monomer (A), inorganic particles (B), and a photopolymerization initiator (C) as constituent components.

[0008] (A) The inorganic particles (B) satisfy the following conditions: (A-1) comprise an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 to 1000 nm, and the individual inorganic spherical particles constituting the aggregate are composed of substantially the same substance, and contain one or more "Group of spherical particles having identical diameter" (G-PID) in which 90% or more of the total number of particles in the number-based particle size distribution of the aggregate are present within a 5% range around the predetermined average primary particle diameter; (A-2) when the number of the one or more "Group of spherical particles having identical diameter" is defined as a, each "Group of spherical particles having identical diameter" is classified into G-PIDs in ascending order of average primary particle diameter. ｍ (However, m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more.) When a is 2 or more, each G-PID ｍ The materials constituting the individual particles may be different from each other, and in this case, each G-PIDｍ and (A-3) the refractive index at 25°C of the cured product of the polymerizable monomer component (A) is n （ＭＸ） and each G-PID ｍ The refractive index of the inorganic spherical particles at 25 ° C. is n （Ｇ－ＰＩＤｍ） When （Ｇ－ＰＩＤｍ） For n （ＭＸ） <n （Ｇ－ＰＩＤｍ） The above relationship must be satisfied.

[0009] (c) For a cured product obtained by curing a polymerizable curable composition, a radial distribution function g(r) representing the probability that other inorganic spherical particles are present at a point a distance r from the center of any inorganic spherical particle dispersed in the cured product is determined based on a scanning electron microscope image with the internal surface of the cured product as the observation plane, and is expressed by the formula g(r) = {1 / <ρ>} × {dn / da} based on the average particle density of the inorganic spherical particles in the observation plane: <ρ>, the number of inorganic spherical particles present in a region between a circle at a distance r from any inorganic spherical particle in the observation plane and a circle at a distance r + dr from the inorganic spherical particle, and the area of ​​the region: da (where da = 2πr dr), the dispersion state of the inorganic particles (B) in the cured product satisfies the following conditions (I) and (II):

[0010] [Conditions to be satisfied for the dispersion state] (I) The distance from the center of any inorganic spherical particle dispersed in the cured body: r is the average particle diameter of all inorganic spherical particles dispersed in the cured body: r ０ The dimensionless number (r / r ０ ) is the x-axis, the radial distribution function: g(r) is the y-axis, and the r / r ０ In a radial distribution function graph showing the relationship between g(r) and the r at that time, the nearest inter-particle distance is defined as r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph: r １ is the average particle size of all inorganic spherical particles dispersed in the cured product of the mixture: r ０ The value is between 1 and 2 times the value of the above.

[0011] (II) Among the peaks appearing in the radial distribution function graph, r corresponding to the peak top of the second closest peak from the origin is defined as the next nearest interparticle distance: r ２ When the distance between the nearest particles is r １ and the distance between the next nearest neighboring particles: r ２ The minimum value of the radial distribution function g(r) between is 0.56 or more and 1.10 or less.

[0012] According to Patent Document 2, colored light due to interference in the cured product occurs in areas where the constituent particles are relatively regularly accumulated, while colored light due to scattering occurs in areas where the constituent particles are randomly dispersed. １ Ga r ０ If the value is less than 1, the particles in the plane overlap each other more, and r １ Ga r ０ It is explained that if the minimum value exceeds twice the value of the minimum value, particles will no longer be present in the vicinity of the selected central inorganic particle, resulting in the loss of short-range order and the failure to exhibit structural color; and that, regarding the above condition (II), if the minimum value is less than 0.56, the long-range order of the arrangement structure of the inorganic spherical particles will be high, and not only will the dependency of the exhibited structural color on the angle of incidence of light increase, but the saturation of the cured product will also increase, making it difficult to achieve color compatibility when used as a dental filling material, while if the minimum value exceeds 1.10, the arrangement structure of the inorganic spherical particles will become random, making it difficult to achieve the desired reflective performance and the desired structural color will not be exhibited.

[0013] In a polymerizable curable composition satisfying these conditions (A) to (C) (hereinafter also referred to as an "existing structural color dental curable composition"), when it contains multiple spherical particles (G-PID) of the same particle size, each G-PID develops a structural color in the cured product with a color tone corresponding to its average primary particle size, and therefore it is possible to control the overall color tone by combining the G-PIDs. This is thought to be because when multiple G-PIDs are contained and there is a certain difference in the average primary particle size, inorganic spherical particles belonging to different G-PIDs can be dispersed in a short-range ordered structure that can develop a structural color for each G-PID without mutual substitution.

[0014] Incidentally, inorganic oxide fillers, particularly silica-based fillers, are generally used as fillers in hardenable compositions used as CRs, including existing structural color dental hardenable compositions. However, silica-based fillers have low radiopacity. Therefore, the hardened material in the cavity is not visualized in X-rays or CT scans during dental treatment, making it difficult to identify the treatment site.

[0015] Meanwhile, a known method for improving the radiopacity of a cured product of a hardenable composition used for various applications, such as the dental hardenable compositions exemplified above, is to use a filler made of a fluoride of a rare earth metal having an atomic number of 57 to 71 (see Patent Documents 3 and 4). Generally, the transparency of a cured product decreases as the content of rare earth metal fluoride increases (see Patent Document 3). However, when a radiopaque filler is used, the radiopacity can be improved without decreasing the transparency of the cured product (see Patent Document 4). The radiopaque filler is characterized by comprising a powder selected from the group consisting of a first powder containing crystalline rare earth metal fluoride particles as a main component and having an X-ray diffraction pattern in which the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride particles is 0.3° or more. The second powder is a surface-treated version of the first powder. According to Patent Document 4, the first powder, "a powder having a full width at half maximum of 0.3° or more in an X-ray diffraction pattern obtained when X-ray diffraction measurement is performed on a powder made of crystalline rare earth metal fluoride particles" (hereinafter also referred to as "low-crystalline rare earth metal fluoride powder"), is obtained by mechanochemically treating a powder having a full width at half maximum of less than 0.3° (hereinafter also referred to as "high-crystalline rare earth metal fluoride powder"). Furthermore, it is stated that the full width at half maximum of the low-crystalline rare earth metal fluoride powder is preferably 40° or less.

[0016] International Publication No. 2017 / 069274 Pamphlet International Publication No. 2020 / 050123 Pamphlet Japanese Patent Publication No. 3-17803 Pamphlet International Publication No. 2023 / 042598 Pamphlet

[0017] However, according to the investigations of the present inventors, when an X-ray opaque filler such as that disclosed in Patent Document 4 is blended with an existing structural color dental curable composition, the decrease in transparency is suppressed, but it has been confirmed that this may have an adverse effect on the expression of the desired structural color (see Reference Comparative Examples 2 to 4 described below).

[0018] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for efficiently producing a radiopaque filler that, when blended with an existing structural color dental hardenable composition (suitable as a structural color CR capable of aesthetic restoration), can impart high radiopacity to the cured product without impairing the characteristics of the composition.

[0019] The present invention solves the above-mentioned problems, and a first aspect of the present invention is a method for producing a radiopaque filler that imparts radiopacity to a dental hardenable composition containing a polymerizable monomer by blending the filler with the dental hardenable composition and a hardened product thereof, wherein when a powder made of crystalline rare earth metal fluoride particles is subjected to X-ray diffraction measurement, the powder has a full width at half maximum of less than 0.3° of the maximum intensity peak in an X-ray diffraction pattern obtained, and the powder has a full width at half maximum of 0.3° or more, and the powder has a full width at half maximum of 0.3° or more, and the powder is a "low-crystalline rare earth metal fluoride powder," the radiopaque filler mainly comprises organic-inorganic composite particles made of a composite material in which low-crystalline rare earth metal fluoride powder is dispersed in a resin matrix, and has an average particle size of 3 to 110 μm as measured by a laser diffraction / scattering method, and the method comprises: a secondary raw material powder particle preparation step of mechanochemically treating a raw material slurry in which a primary raw material powder particle consisting of a highly crystalline rare earth metal fluoride powder particle having an average primary particle diameter of 1 to 500 nm as measured by electron microscope observation is dispersed in a dispersion medium to obtain a treated slurry liquid in which a low-crystalline rare earth metal fluoride powder particle is dispersed in the dispersion medium, and spray-drying the obtained treated slurry to obtain a secondary raw material powder particle consisting of the low-crystalline rare earth metal fluoride powder particle; ５a curable raw material composition preparation step of kneading the components under a pressure of (Pa) to obtain a curable raw material composition; a curing step of curing the curable raw material composition to obtain an aggregate made of a composite material in which low-crystalline rare earth metal fluoride particles are dispersed in a resin matrix; and a granulation step of pulverizing the aggregate and then adjusting the particle size so that the average particle diameter is 3 to 110 μm.

[0020] In the manufacturing method of the above form (hereinafter also referred to as "the present X-ray opaque filler manufacturing method"), the amount of the secondary raw material powder and granules used in the curable raw material composition preparation step is preferably 230 to 900 parts by mass per 100 parts by mass of the polymerizable monomer.

[0021] The pressure during kneading in the curable raw material composition preparation step is preferably 100 to 35,000 (Pa).

[0022] A second aspect of the present invention is a filler comprising: 100 parts by mass of a polymerizable monomer; 1 to 100 parts by mass of an X-ray opaque filler mainly composed of organic-inorganic composite particles made of a composite material in which low-crystalline rare earth metal fluoride powder particles are dispersed in a resin matrix, the powder having an average particle size of 3 to 110 μm as measured by a laser diffraction / scattering method, calculated as the total mass of the low-crystalline rare earth metal fluoride powder particles; 10 to 1,500 parts by mass in total of one or more "same-particle-size spherical particle groups" consisting of an aggregate of inorganic spherical particles having a predetermined average primary particle size within a range of 100 to 1,000 nm as measured by electron microscope observation, wherein the individual inorganic spherical particles constituting the aggregate are made of substantially the same material and 90% or more of the total number of particles in the number-based particle size distribution of the aggregate are present within a 5% range around the predetermined average primary particle size; and 0.01 to 10 parts by mass of a polymerization initiator. A method for producing a dental hardenable composition that can express a structural color of a predetermined color tone independent of the angle of incidence of light and can provide a hardened product having X-ray contrast properties by mixing the above polymerizable monomers, further comprising the step of producing the X-ray opaque filler by the X-ray opaque filler production method, in which the refractive index of the hardened product of the polymerizable monomers at 25°C for sodium d-line is set to n （ＭＸ） The refractive index of the resin material constituting the resin matrix of the organic-inorganic composite particles constituting the X-ray opaque filler at 25° C. with respect to the sodium d line is n （F―ＭＸ） When the n of the polymerizable monomers actually mixed is （ＭＸ） and the n （F―ＭＸ） Absolute value of the difference between: |n （ＭＸ） -n （F―ＭＸ） the radiopaque filler is produced using a polymerizable monomer that is a raw material for the resin matrix, such that | satisfies the condition that | is 0 to 0.1.

[0023] In the method for producing a dental curable composition of the above form (hereinafter also referred to as "the dental curable composition production method"), when the number of "spherical particle groups of the same particle size" in the one or more "spherical particle groups of the same particle size" is defined as a, each "spherical particle group of the same particle size" is classified into G-PID ｍ (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more), and each G-PID ｍ The refractive index of the inorganic spherical particles constituting the sodium d line at 25 ° C. is n （Ｇ－ＰＩＤｍ） When a is 2 or more, each G-PID ｍ The materials constituting the individual particles may be different from each other, and in this case, each G-PID ｍ The average primary particle diameters of n differ from each other by 25 nm or more, （Ｇ－ＰＩＤｍ） For （ＭＸ） <n （Ｇ－ＰＩＤｍ） It is preferable that the following relationship holds.

[0024] According to the present invention, by blending with an existing structural color dental curable composition, a novel radiopaque filler can be efficiently produced that can impart high radiopacity to the cured product without impairing the excellent features of the structural color CR.

[0025] The X-ray opaque filler (low-crystalline rare earth metal fluoride powder) disclosed in Patent Document 4 has the above-mentioned excellent features, but when the present inventors tried to incorporate it into structural color CR, they found that a large amount of X-ray opaque filler was required to achieve high X-ray opacity, and in that case, it was difficult to express the desired structural color (see Reference Comparative Examples 3 and 4 described below). Therefore, as a result of further investigations to solve this problem, it was found that when the low-crystalline rare earth metal fluoride powder was incorporated as a powder composed of organic-inorganic composite particles combined with an organic resin, rather than being incorporated directly, high X-ray opacity could be imparted even with a small amount of rare earth metal fluoride particles incorporated, and further, even when incorporated into structural color CR, X-ray opacity could be imparted without significantly adversely affecting the expression of the desired structural color (see Reference Examples described below), and this has already been proposed (Japanese Patent Application No. 2023-29645).

[0026] That is, a dental curable composition that can impart high X-ray opacity to a cured product when used as a CR without impairing the excellent characteristics of structural color CR, comprising: "a polymerizable monomer: 100 parts by mass; a total of 10 to 1,500 parts by mass of one or more "same-sized spherical particle groups" (G-PID) consisting of an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 to 1,000 nm, wherein the individual inorganic spherical particles constituting the aggregate are substantially made of the same material, and 90% or more of the total number of particles in the number-based particle size distribution of the aggregate are present within a 5% range around the predetermined average primary particle diameter; and a polymerization initiator: 0.01 to 0.5 parts by mass, wherein when the number of the one or more "same-sized spherical particle groups" is defined as a, each "same-sized spherical particle group" is classified into G-PIDs in ascending order of their average primary particle diameters. ｍ (However, m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more.) When a is 2 or more, each G-PID ｍ The materials constituting the individual particles may be different from each other, and in this case, each G-PID ｍThe average primary particle diameters of the polymerizable monomers differ from each other by 25 nm or more, and the refractive index of the cured product of the polymerizable monomers at 25°C with respect to the sodium d line is n （ＭＸ） and each G-PID ｍ The refractive index of the inorganic spherical particles constituting the sodium d line at 25 ° C. is n （Ｇ－ＰＩＤｍ） When （Ｇ－ＰＩＤｍ） For n （ＭＸ） <n （Ｇ－ＰＩＤｍ） The dental hardenable composition is capable of providing a cured product that exhibits a structural color of a predetermined color tone independent of the angle of incidence of light, and the dental hardenable composition comprises 1 to 100 parts by mass, calculated as the total mass of the crystalline rare earth metal fluoride particles, of an X-ray opaque filler (hereinafter also referred to as "specific X-ray opaque filler") characterized by comprising organic-inorganic composite particles in which a plurality of crystalline rare earth metal fluoride particles are dispersed in a resin matrix, the full width at half maximum (unit: °) of which is 0.3° or more when the crystallinity of each crystalline rare earth metal fluoride particle constituting a powder of the crystalline rare earth metal fluoride particles is expressed by the full width at half maximum (unit: °) of the maximum peak derived from the crystalline rare earth metal fluoride in an X-ray diffraction pattern obtained by X-ray diffraction measurement of the powder; and （ＭＸ） and the refractive index of the resin material constituting the resin matrix of the organic-inorganic composite particles constituting the X-ray opaque filler is n, （F―ＭＸ） Absolute value of the difference with: |n （ＭＸ） -n （F―ＭＸ） The present invention proposes a dental hardenable composition characterized in that | is 0 to 0.1.

[0027] The specific radiopaque filler has an absolute value of the difference: |n （ＭＸ） -n （F―ＭＸ）When incorporated into an existing structural color dental hardenable composition so as to satisfy the condition that | is 0 to 0.1, it can be said that this radiopaque filler can impart high radiopacity to the cured product without impairing the characteristics of the composition. However, as shown in the Reference Examples described below, in Japanese Patent Application No. 2023-29645, a treatment liquid (treatment slurry) containing a dispersion of low-crystalline rare earth metal fluoride powder obtained after mechanochemical treatment (treatment slurry) is dried using a rotary evaporator to produce a powder (secondary raw material powder) and a polymerizable monomer are kneaded in an agate mortar. The resulting hardenable composition is cured and the resulting hardened product is pulverized to obtain the specific radiopaque filler (on a laboratory scale). Therefore, it cannot be said that a method for efficiently producing a specific radiopaque filler on an industrial scale has been established.

[0028] Therefore, the present inventors attempted to prepare a curable composition by obtaining a secondary raw material powder by spray drying using a spray dryer or the like, and then kneading the obtained powder with a polymerizable monomer using a kneading device. As a result, it became clear that when the content of low-crystalline rare earth metal fluoride powder in the organic-inorganic composite particles constituting the specific radiopaque filler is increased in order to impart radiopacity, the kneaded product may not become a paste, and may become impossible to knead.

[0029] The present invention thus solves the above-mentioned problems that are specific to spray drying using a spray dryer and kneading using a kneading device, and by carrying out the kneading (mixing) under a specific reduced pressure, it makes it possible to efficiently produce a specific radiopaque filler even in the above-mentioned cases.

[0030] Since the specific radiopaque filler is a novel material discovered by the present inventors, the specific radiopaque filler will first be explained, and then the method for producing the radiopaque filler will be described in detail below.

[0031] In this specification, unless otherwise specified, the expression "x to y" using numerical values ​​x and y means "greater than or equal to x and less than or equal to y." In such an expression, when a unit is assigned only to the numerical value y, the unit also applies to the numerical value x. In addition, in this specification, the term "(meth)acrylic" means both "acrylic" and "methacrylic." Similarly, the term "(meth)acrylate" means both "acrylate" and "methacrylate," and the term "(meth)acryloyl" means both "acryloyl" and "methacryloyl." Furthermore, the term "(meth)acrylic resin" means a polymer polymerized using only (meth)acrylate monomers as polymerizable monomers used in the polymerization of the (meth)acrylic resin, or <ii> a polymer in which, when two or more types of polymerizable monomers including a (meth)acrylate monomer are used, the proportion of the (meth)acrylate monomers in all polymerizable monomers is 50 mol % or more.

[0032] 1. Regarding the specific radiopaque filler (1) Overview of the specific radiopaque filler The specific radiopaque filler is mainly composed of a powder or granule having an average particle size of 3 to 110 μm as measured by a laser diffraction / scattering method, the powder or granule being composed of organic-inorganic composite particles in which a plurality of crystalline rare earth metal fluoride particles having a full width at half maximum of 0.3° or more are dispersed in a resin matrix, when the crystallinity of each crystalline rare earth metal fluoride particle constituting the powder or granule is expressed by the full width at half maximum (unit: °) of the maximum peak derived from the crystalline rare earth metal fluoride in an X-ray diffraction pattern obtained when X-ray diffraction measurement is performed on the powder or granule.

[0033] Here, "mainly composed" means that the content of the organic-inorganic composite particles (hereinafter also referred to as "particle bodies") in the total mass of the specific radiopaque filler is 95% by mass or more, preferably 98% by mass or more. Examples of components that the specific radiopaque filler may contain in addition to the particle bodies include external additive particles such as silica and titanium oxide (fine particles). Furthermore, the organic-inorganic composite particles (particle bodies) may have their surfaces subjected to physical surface treatment such as plasma treatment, or mechanical surface treatment such as prolonged friction stirring, or may have been subjected to coating treatment using a known coating agent such as silicone oil. Furthermore, the crystalline rare earth metal fluoride particles in the organic-inorganic composite particles (particle bodies) may have their surfaces treated with a known surface treatment agent such as a silane coupling agent or a titanate coupling agent.

[0034] Generally, there is a correlation between the full width at half maximum of diffraction peak and crystallite size in X-ray diffraction measurement, known as Scherrer's formula, and it is known that crystallite size is inversely proportional to the full width at half maximum.In addition, the distortion of crystal lattice also affects the full width at half maximum (FWHM), and the full width at half maximum (FWHM) increases, and when the crystal lattice distortion increases, the full width at half maximum tends to widen.It is considered that the crystallite distortion is large, the crystallite diameter is small, and the fine crystallites are oriented in various directions, so that the crystallinity decreases, and therefore the full width at half maximum can be said to be an index of the crystallinity (more specifically, the perfection of crystal) of rare earth metal fluoride.

[0035] Unless otherwise specified, the term "full width at half maximum" used hereinafter in this specification means the full width at half maximum (unit: °) of the maximum peak derived from the crystalline rare earth metal fluoride in an X-ray diffraction pattern obtained when X-ray diffraction measurement is performed on a powder or granule made of the crystalline rare earth metal fluoride particles.

[0036] Crystalline rare earth metal fluoride powders (low-crystalline rare earth metal fluoride powders) having a full width at half maximum of 0.3° or more do not significantly reduce the transparency of the dental hardenable composition cured product, even when directly incorporated into a dental hardenable composition (see PCT / JP2022 / 031237 and Reference Comparative Examples 3 and 4 described below). The reasons for this effect are presumed to be as follows: First, the reduction in transparency in a system in which inorganic fine particles are dispersed in a resin matrix is ​​largely due to the diffuse reflection of light at the interface between the two. Meanwhile, the mechanochemical treatment is thought to gradually amorphize the surface vicinity of the crystalline rare earth metal fluoride particles from the surface toward the interior. When this phenomenon occurs, a layer (hereinafter also referred to as a "gradient refractive index layer") is formed near the surface of the crystalline rare earth metal fluoride particles, in which the refractive index gradually decreases with a constant gradient from the interior to the surface. The formed gradient refractive index layer contains a portion having a refractive index matching that of the resin matrix. As a result, it is believed that the proportion of reflected light is reduced overall (the proportion of transmitted light is increased), and the decrease in transparency is suppressed.

[0037] When the specific X-ray opaque filler containing the organic-inorganic composite particles (particle bodies) as a main component is used, the refractive index of the cured product of the polymerizable monomer at 25°C with respect to the sodium d line is n （ＭＸ） and the refractive index of the resin material constituting the resin matrix of the organic-inorganic composite particles constituting the specific X-ray opaque filler is the refractive index at 25°C for sodium d-line: n （F―ＭＸ） Absolute value of the difference with: |n （ＭＸ） -n （F―ＭＸ） The same effect can be obtained when the condition that | is 0 to 0.1, preferably 0 to 0.05 is satisfied. This is because the polymerizable monomer in the dental hardenable composition becomes a resin that constitutes the matrix of the hardened product of the dental hardenable composition, and its refractive index: n （F―ＭＸ） and the refractive index of the resin material constituting the resin matrix of the organic-inorganic composite particles: n （F―ＭＸ）are close to each other, diffuse reflection of light is less likely to occur on the surface of the organic-inorganic composite particles (in other words, the resin matrix of the organic-inorganic composite particles and the resin matrix of the hardened body of the dental hardenable composition are integrated together), and the above-mentioned properties of the low-crystalline rare earth metal fluoride powder are considered to be exhibited.

[0038] As described above, by setting the full width at half maximum of the crystalline rare earth metal fluoride powder to 0.3° or more, when a curable composition containing a specific radiopaque filler is cured, a cured product having excellent radiopacity and transparency can be easily obtained. In other words, even if the amount of the specific radiopaque filler blended in the curable composition is increased to improve the radiopacity of the cured product, a decrease in the transparency of the cured product can be suppressed. The full width at half maximum may be 0.3° or more, preferably 0.4° or more, and more preferably 0.5° or more. On the other hand, the upper limit of the full width at half maximum is not particularly limited, but in practice, it is preferably 40° or less, more preferably 1° or less.

[0039] When a crystalline rare earth metal fluoride powder having a full width at half maximum of less than 0.3° (highly crystalline rare earth metal fluoride powder) is blended in an amount necessary to impart radiopacity, either directly or after being converted into an organic-inorganic composite (as organic-inorganic composite particles similar to the organic-inorganic composite particles in the specific radiopaque filler), a decrease in the transparency of the cured product is unavoidable (see Reference Comparative Examples 2 and 5 described below).

[0040] (2) Method for Determining the Full Width at Half Maximum The full width at half maximum can be determined by performing X-ray diffraction measurement on a powder sample to be subjected to X-ray diffraction measurement. Specifically, X-ray diffraction measurement of the powder sample is performed using an X-ray diffractometer in a 2θ range of 20° to 120° to obtain an X-ray diffraction pattern (chart) in which the horizontal axis indicates 2θ (°) and the vertical axis indicates diffraction intensity. It is preferable to use a powder sample from which coarse particles have been removed in accordance with a standard method, for example, by using a sieve with a mesh size of 100 μm.

[0041] Next, peaks attributable to the rare earth metal fluoride in the X-ray diffraction pattern (chart) are identified, and the full width at half maximum of the peak having the greatest intensity among the multiple peaks identified is determined. For example, if the rare earth metal fluoride is YbF ３ To explain this case as a specific example, the peak with the highest intensity appears near 2θ = 28.0° as a peak due to the (111) plane. Here, the full width at half maximum is obtained by calculating the peak width at an intensity that is 50% of the maximum intensity of the peak observed near 2θ = 28.0° (50% intensity). Note that the peak width is calculated as the absolute value (unit: "deg [°]") of the difference between the 2θ value at one intersection point and the 2θ value at the other intersection point, where a convex peak line intersects with a straight line that is parallel to the horizontal axis of the X-ray diffraction pattern (chart) and is at the 50% intensity position.

[0042] The full width at half maximum of the crystalline rare earth metal fluoride powder in the organic-inorganic composite particles (particle bodies) constituting the specific radiopaque filler can be confirmed based on the X-ray diffraction pattern obtained by powder X-ray diffraction measurement of a powder sample consisting of the particle bodies. Furthermore, for the specific radiopaque filler obtained by the manufacturing method described below, the full width at half maximum of the crystalline rare earth metal fluoride powder in the particle bodies can also be confirmed based on the X-ray diffraction pattern obtained by powder X-ray diffraction measurement of a powder sample consisting of the secondary raw material powder (since the crystallinity of the secondary raw material powder does not change or substantially change during the mixing and grinding steps in preparing the raw material composition). Furthermore, the full width at half maximum of the crystalline rare earth metal fluoride particles in the specific radiopaque filler contained in the dental curable composition of the present invention can also be confirmed based on the X-ray diffraction pattern obtained by powder X-ray diffraction measurement of a powder sample containing organic-inorganic composite particles separated from these curable compositions or a powder sample obtained from a cured product of these curable compositions.

[0043] (3) Organic-inorganic composite particles (particle body) The rare earth metal fluoride particles contained in the organic-inorganic composite particles (particle body) are not particularly limited in material, and known rare earth metal fluoride particles can be used as appropriate, as long as the full width at half maximum is 0.3° or more. From the viewpoint of easily ensuring a color tone suitable for dental use and safety, the rare earth metal fluoride is preferably lanthanum fluoride (LaF ３ ), cerium fluoride (CeF ３ ), or ytterbium fluoride (YbF ３ ), and further, from the viewpoint of ensuring X-ray opacity, ytterbium fluoride (YbF ３ ) is particularly preferred.

[0044] The resin material constituting the resin matrix of the organic-inorganic composite particles (particle bodies) is not particularly limited, and examples thereof include (meth)acrylic resins and polyaryl ether ketone resins.

[0045] However, when blended with an existing structural color dental curable composition, in order not to impair the structural color expression effect, the resin material constituting the resin matrix should be |n （ＭＸ） -n （F―ＭＸ） It is necessary to use a resin material such that | is 0 to 0.1. （ＭＸ） means the refractive index at 25°C of the cured product of the polymerizable monomer contained in the existing structural color dental curable composition with respect to the sodium d line, and n （F―ＭＸ） means the refractive index at 25°C for the sodium d line of the resin material that constitutes the resin matrix of the particle body.

[0046] The average particle size of the organic-inorganic composite particles (particle bodies) is 3 to 110 μm, preferably 8 to 100 μm. Here, the average particle size refers to the median diameter measured by laser diffraction / scattering. When the average particle size is outside the above range, from the viewpoint of achieving a better balance between X-ray contrast and mechanical strength, the average particle size is more preferably 22 to 70 μm, particularly 24 to 55 μm. Furthermore, when ensuring mechanical strength is more important than X-ray contrast, the average particle size is preferably 3 to 38 μm, more preferably 8 to 25 μm. On the other hand, when ensuring X-ray contrast is more important than mechanical strength, the average particle size is preferably 38 μm or more, more preferably 70 μm or more. The upper limit is preferably 110 μm or less, more preferably 100 μm or less, from the viewpoint of ensuring a certain level of mechanical strength.

[0047] The content of the rare earth metal fluoride particles in the organic-inorganic composite particles (particle bodies) is preferably 60 to 90 mass %, more preferably 70 to 80 mass %, based on the total mass of the organic-inorganic composite particles.

[0048] 2. The method for producing an X-ray opaque filler includes a secondary raw material powder preparation step of mechanochemically treating a raw material slurry in which a primary raw material powder comprising highly crystalline rare earth metal fluoride powder having an average primary particle diameter of 1 to 500 nm as measured by electron microscope observation is dispersed in a dispersion medium to obtain a treated slurry liquid in which low-crystalline rare earth metal fluoride powder is dispersed in the dispersion medium, and removing the dispersion liquid from the treated slurry to obtain a secondary raw material powder comprising low-crystalline rare earth metal fluoride powder; ５ The method is characterized by comprising: a curable raw material composition preparation step of kneading the raw material composition under a pressure (reduced pressure) of 100 Pa to obtain a curable raw material composition; a curing step of curing the curable raw material composition to obtain an aggregate of a composite material in which low-crystalline rare earth metal fluoride particles are dispersed in a resin matrix; and a granulation step of pulverizing the aggregate and then adjusting the particle size so that the average particle size is 3 to 110 μm. Each step will be described in detail below.

[0049] (1) Secondary Raw Material Powder and Particle Preparation Step In the secondary raw material powder and particle preparation step, a raw material slurry in which primary raw material powder particles consisting of highly crystalline rare earth metal fluoride powder particles with an average primary particle diameter of 1 to 500 nm as measured by electron microscope observation are dispersed in a dispersion medium is subjected to mechanochemical treatment to obtain a treated slurry liquid in which low-crystalline rare earth metal fluoride powder particles are dispersed in the dispersion medium, and the obtained treated slurry is spray-dried to obtain secondary raw material powder particles consisting of low-crystalline rare earth metal fluoride powder particles. Note that it is permissible for the primary and secondary raw material powder and particles to contain trace amounts of substances other than the crystalline rare earth metal fluoride particles, such as surface treatment agents or additives physically attached to or chemically bonded to the surfaces of the crystalline rare earth metal fluoride particles.

[0050] (1-1) Primary Raw Material Powder and Granules As the primary raw material powder and granules (highly crystalline rare earth metal fluoride powder and granules), rare earth metal fluorides generally used as X-ray opaque materials and commercially available rare earth metal fluoride powders having a full width at half maximum of less than 0.3° (specifically, about 0.17° to 0.27°) can be used without any particular restrictions. It is preferable to measure the full width at half maximum of the primary raw material powder and granules by X-ray diffraction measurement as necessary.

[0051] Furthermore, as the crystalline rare earth metal fluoride particles used as the primary raw material powder, particles whose surfaces are coated with nanosilica or the like, or particles whose surfaces are treated with a silane coupling agent or the like can also be used.

[0052] In the mechanochemical treatment used in the secondary raw material powder preparation process, depending on the treatment conditions, prolonging the treatment time can result in the pulverization of particles contained in the primary raw material powder, resulting in the disintegration of secondary particles (agglomerated particles) and primary particles, resulting in a reduction in their particle size. However, treatment times of several hours or so may result in the disintegration of coarse agglomerated particles, but do not significantly change the particle size of primary particles or submicron-level agglomerated particles. For these reasons, primary raw material powders should have an average primary particle size of 1 to 500 nm, preferably 5 to 300 nm, as measured by electron microscopy. Furthermore, laser diffraction / scattering methods, which can also measure agglomerated particle size, are preferred. Powders with an average particle size of 0.1 to 1 μm, particularly 0.1 to 0.6 μm, and more preferably 0.1 to 0.3 μm, are preferred. The average primary particle size is measured using a scanning electron microscope. Specifically, the powder was observed under an electron microscope at a magnification of 100,000 times, and the average primary particle diameter of 100 primary particles in the obtained observation image was determined.

[0053] (1-2) Mechanochemical Treatment Mechanochemical treatment refers to a process of applying mechanical energy to primary raw material powder particles, specifically at least one process selected from the group consisting of mechanical grinding, pulverization, and dispersion. From the viewpoint of easily and reliably and efficiently controlling the full width at half maximum (FWHM), which also indicates the degree of crystalline perfection of mechanochemically treated rare earth metal fluoride particles, to a desired value, a wet method is employed as the mechanochemical treatment, and a treatment method using a wet bead mill is particularly preferred. When mechanochemical treatment is performed by a wet method, solvents such as water or alcohol, or polymerizable monomers can be used as the medium, but from the viewpoint of the dispersibility of the raw material powder, a medium that is liquid at room temperature (15°C to 25°C) is preferred.

[0054] The mechanochemical treatment using a wet bead mill will be described in detail below.

[0055] In mechanochemical treatment using a wet bead mill, a slurry containing a mixture of raw material powder to be treated with a medium is brought into contact with media (beads) that have been imparted with motion by stirring, vibration, or the like. This pulverizes and disintegrates the raw material powder. Materials for the beads used as media include glass, alumina, zircon, zirconia, steel, and resin. However, alumina or zirconia is preferred due to their excellent wear resistance and relatively low contamination. The size of the beads used can be selected according to the particle size of the desired radiopaque filler, and there are no particular limitations. However, it is generally preferable to use beads with a diameter of 0.01 mm to 0.5 mm. Note that beads with such diameters are also suitable for obtaining a radiopaque filler with a particle size suitable for addition to a dental curable composition.

[0056] Wet bead mills come in various types depending on the operating method, such as a batch type in which the slurry and beads are directly charged into the device and processing is performed, a circulation type in which the slurry is circulated between a tank and the device, and a pass type in which the slurry is passed through the device a predetermined number of times. These operating methods can be selected depending on the amount of raw material powder used in the mechanochemical processing. It is preferable to use a circulation type bead mill because it has good productivity and can process a relatively large amount of raw material powder.

[0057] Depending on the operating method, such as the circulation method or pass method, it may be necessary to separate the slurry from the beads when carrying out the mechanochemical treatment. Examples of bead separation methods include slit, screen, and centrifugal separation methods. These bead separation methods may be selected depending on the particle size of the beads used, and any method may be used without particular restrictions. The concentration of the slurry used in the mechanochemical treatment is preferably 50 parts by mass or less of raw material powder per 100 parts by mass of medium. If the raw material powder in the slurry exceeds 50 parts by mass, the viscosity of the slurry increases, which may make the mechanochemical treatment difficult.

[0058] The increase in the viscosity of the slurry can be suppressed by adding a dispersant to the slurry. Therefore, adding a dispersant to the slurry makes it possible to mechanochemically treat a slurry with a higher concentration. Any known surfactant can be used as the dispersant without any particular limitation, and examples thereof include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and polymeric surfactants thereof. Specific examples include glycerin fatty acid esters and their alkylene glycol adducts, aliphatic monocarboxylic acid salts, alkylamine salts, and alkylbetaines. When the mechanochemically treated raw powder is mixed with the raw material constituting the resin matrix (resin matrix raw material) and granulated, it is preferable to use a cationic surfactant from the viewpoint of dispersibility during mixing.

[0059] The mechanochemical treatment conditions vary depending on the operating method and bead diameter of the wet bead mill used, the full width at half maximum of the raw material powder, the concentration of the slurry, and other conditions. These conditions can be appropriately selected after conducting a preliminary experiment using an apparatus that will actually perform the mechanochemical treatment and confirming the full width at half maximum of the raw material powder after the mechanochemical treatment versus the mechanochemical treatment time. Furthermore, when performing the mechanochemical treatment, it is possible to obtain mechanochemically treated secondary raw material powder having the desired full width at half maximum by appropriately sampling the slurry during the mechanochemical treatment as needed and appropriately checking the full width at half maximum.

[0060] The full width at half maximum of the secondary raw material powder granules may be 0.3° or more, but from the viewpoint of more stably and reliably obtaining the radiopaque filler of this embodiment, it is preferably 0.35° or more, and more preferably 0.4° or more. The upper limit of the full width at half maximum of the secondary raw material powder granules is not particularly limited and can be appropriately selected according to the target full width at half maximum of the radiopaque filler to be produced, but in practice it is preferably 40° or less, and more preferably 1° or less.

[0061] (1-3) Spray Drying and Secondary Raw Material Powder and Particles The slurry obtained by the mechanochemical treatment, in which the secondary raw material powder and particles (mechanochemically treated rare earth metal fluoride powder and particles) adjusted to have a full width at half maximum of 0.3° or more, is dispersed, is spray dried, and secondary raw material powder and particles made of low-crystalline rare earth metal fluoride powder are recovered.

[0062] Here, spray drying refers to a process in which a liquid raw material (slurry) is sprayed into hot air to instantly evaporate the water and obtain a dry powder (granules). For example, it refers to spray drying mechanochemically treated slurry using an atomizer disk type spray dryer to obtain secondary raw material powder and granules.

[0063] The secondary raw material powder particles that have been subjected to the mechanochemical treatment step and the post-treatment step may be subjected to a surface treatment to improve affinity with the resin matrix raw material used in granulating the organic-inorganic composite particles. Examples of surface treatment agents that can be used for the surface treatment include commonly used compounds such as silane coupling agents and titanate coupling agents.

[0064] (2) Curable Raw Material Composition Preparation Step In the curable raw material composition preparation step, 100 parts by mass of the polymerizable monomer that is the raw material of the resin matrix and 150 to 900 parts by mass of the secondary raw material powder and granules are mixed in a 1.0 to 1.0 × 10 ５ The hardenable raw material composition is obtained by kneading the materials under a pressure of 100 Pa. Furthermore, when the filling rate of the low-crystalline rare earth metal fluoride powder filled into the specific radiopaque filler is high, the specific radiopaque filler produced by the production method of the present invention is added to a dental hardenable composition for the purpose of imparting radiopaque properties. Therefore, the greater the amount of the secondary raw material powder added relative to 100 parts by mass of polymerizable monomer, the more effective the effect of the present invention. On the other hand, the greater the amount of the secondary raw material powder added relative to the polymerizable monomer, the longer the kneading time required for the hardenable raw material composition preparation step. Therefore, in the production method of the present invention, the amount of the secondary raw material powder added relative to 100 parts by mass of polymerizable monomer is, the more preferable it is. Therefore, the amount of the secondary raw material powder added in the production method of the present invention is preferably 233 to 900 parts by mass, particularly 250 to 567 parts by mass, relative to 100 parts by mass of polymerizable monomer.

[0065] (2-1) Regarding the polymerizable monomer serving as a raw material for the resin matrix As the polymerizable monomer serving as a raw material for the resin matrix of the organic-inorganic composite particles, known polymerizable monomers such as radical polymerizable monomers can be used. However, it is preferable to use radical polymerizable monomers such as (meth)acrylate monomers used in dental curable compositions.

[0066] The refractive index of the crystalline rare earth metal fluoride particles used as the first and second raw material powders at 25° C. with respect to the sodium d line: n Ｘ is usually in the range of 1.50 to 1.65, and in the case of crystalline ytterbium fluoride particles, it is 1.55. Therefore, the refractive index at 25°C for the sodium d line of the resin material that is the main component of the resin matrix that constitutes the organic-inorganic composite particles (particle body): n （F―ＭＸ） is preferably 1.45 to 1.60. Here, the "resin material that is the main component of the resin matrix" means a cured product of a polymerizable monomer (a cured product of a composition consisting of only a polymerizable monomer, or a cured product of a composition consisting of a polymerizable monomer and a small amount of a polymerization initiator). Ｘ and （F―ＭＸ） When and have similar values ​​as described above, it becomes easier to improve the transparency of the curable composition using the radiopaque filler.

[0067] From this viewpoint, it is preferable to satisfy the following formula (1A), it is more preferable to satisfy the following formula (2A), and it is even more preferable to satisfy the following formula (3A): Formula (1A) -0.02≦(n Ｘ -n （F―ＭＸ） )≦0.1 ・Formula (2A) 0.01≦(n Ｘ -n （F―ＭＸ） )≦0.07 ・Formula (3A) 0≦(n Ｘ -n （F―ＭＸ） )≦0.05.

[0068] Furthermore, when blended with an existing structural color dental hardenable composition, in order not to impair the structural color expression effect, the refractive index of the hardened product of the polymerizable monomer contained in the existing structural color dental hardenable composition at 25°C with respect to the sodium d line: n （ＭＸ）and the refractive index of the resin material constituting the resin matrix of the particle body is the refractive index at 25°C for the sodium d line: n （F―ＭＸ） Absolute value of the difference with: |n （ＭＸ） -n （F―ＭＸ） Since it is necessary to use a resin material such that | is 0 to 0.1, it is preferable to use a polymerizable monomer having the same or similar composition as the polymerizable monomer contained in the existing structural color dental curable composition.

[0069] Furthermore, a catalytic amount of a polymerization initiator is usually blended into the raw material composition for granulating the curable raw material composition. A thermal polymerization initiator is suitable as the polymerization initiator, and a chemical polymerization initiator and / or a photopolymerization initiator may be used in combination. Furthermore, other additives may be used as needed. Specific examples of the polymerizable monomer, polymerization initiator, and other additives include those used in the dental curable composition manufacturing method described below.

[0070] (2-1) Kneading Conditions In the curable raw material composition preparation step, in order to efficiently obtain the curable raw material composition, predetermined amounts of the polymerizable monomer and the secondary raw material powder and granules are kneaded at an absolute pressure of 1.0 to 1.0 × 10 (reduced pressure state) lower than 101,325 (Pa), which is considered to be atmospheric pressure. ５ It is necessary to knead the mixture under a pressure (reduced pressure) of 1.0 to 1.0 × 10 (Pa). Here, absolute pressure is different from the so-called gauge pressure and refers to a pressure defined based on a complete vacuum (absolute vacuum), and is an absolute pressure of 1.0 to 1.0 × 10 ５ Kneading under a pressure of 1.0 x 10 means that the atmospheric pressure during actual kneading is controlled within the above pressure range. If the kneading atmospheric pressure is less than 1.0 (Pa), the pressure will be too low, causing the polymerizable monomer and secondary raw material powder particles to scatter, making it impossible to knead the curable raw material composition. ５ If the pressure exceeds 100,000 (Pa) or 100 (kPa), the polymerizable monomer will not penetrate into the secondary raw material powder particles due to the high pressure, and the curable raw material composition will not be able to be kneaded. From the viewpoints of effectiveness and shortening the time required to adjust the atmosphere to the specified pressure, the kneading ambient pressure is preferably 100 to 35,000 (Pa), particularly 1,000 to 33,000 (Pa).

[0071] Such control of the atmospheric pressure during kneading can be achieved by using a kneading machine such as a planetary mixer that can perform kneading in a pressure-resistant, sealable space, charging the raw materials to be kneaded (to be mixed), and then using a vacuum pump or the like to adjust the pressure in the space to a predetermined pressure, sealing the space, and starting kneading. For example, this can be suitably achieved by using a two-shaft planetary kneading device such as a planetary mixer that employs a vacuum hood and vacuum shaft seals to enable kneading under reduced pressure.

[0072] The temperature during kneading is not particularly limited, but is preferably 25 to 60°C, and more preferably 30 to 40°C.

[0073] (3) Curing Step In the curing step, the curable raw material composition is cured to obtain a mass of a composite material in which low-crystalline rare earth metal fluoride particles are dispersed in a resin matrix. The curable raw material composition obtained in the kneading step is preferably cured by heat treatment. The heating temperature is preferably 50 to 500°C, and more preferably 80 to 200°C. In addition, in order to improve the polymerization rate of the resulting cured product and reduce polymerization inhibition due to oxygen, it is preferable to carry out the heat reaction under an inert gas such as nitrogen gas along with the heat treatment. The heat treatment time is preferably 10 to 500 minutes, and more preferably 20 to 200 minutes.

[0074] (4) Granulation Step In the granulation step, the aggregates are pulverized and then particle size adjustment is performed so that the average particle size is 3 to 110 μm. The method for pulverizing the aggregates is not particularly limited, and for example, a ball mill or the like can be used. When a ball mill is used as the pulverization method, zirconia is preferably used as the material for the balls used for pulverization in order to reduce contamination. The particle size of the zirconia balls used is preferably 1 to 100 mm, and more preferably 10 to 50 mm. The pulverization time in the ball mill is preferably 5 to 120 minutes, and more preferably 30 to 90 minutes.

[0075] The particle size adjustment performed after the pulverization step can be suitably performed using a sieve with openings corresponding to the target particle size (average particle diameter). Furthermore, the organic-inorganic composite particles (particle bodies) obtained after pulverization may be subjected to various surface treatments, coating treatments, external additive treatments, etc., as necessary.

[0076] 3. Dental curable composition manufacturing method (1) Overview of the dental curable composition manufacturing method The dental curable composition manufacturing method is a method for manufacturing a dental curable composition by adding |n （ＭＸ） -n （F―ＭＸ） The main feature of this composition is that it contains a predetermined amount of a specific radiopaque filler produced by this radiopaque filler production method, which is composed of organic-inorganic composite particles (particle bodies) made from a resin material such that | is 0 to 0.1.

[0077] (1-1) Existing Structural Color Dental Curable Composition Here, as already explained as the prior art, the existing structural color dental curable composition means a dental curable composition that contains predetermined amounts of a polymerizable monomer, an inorganic filler, and a polymerization initiator, and that uses a filler that contains spherical inorganic particles having a specific average particle size and particle size distribution, i.e., one or more “spherical particle groups of the same particle size” (G-PID), and that makes the refractive index of the spherical inorganic particles higher than the refractive index of the resin part that becomes the matrix when cured; specifically, when the amount of the polymerizable monomer contained in the dental curable composition is 100 parts by mass, the following conditions 1 to 3 are satisfied, thereby enabling the dental curable composition to exhibit a structural color that develops in a predetermined color tone that is independent of the angle of incidence of light due to light interference, scattering, etc.

[0078] Condition 1: The composition comprises an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 to 1000 nm, wherein the individual inorganic spherical particles constituting the aggregate are composed of substantially the same material, and the composition comprises one or more "same-diameter spherical particle groups" (G-PID) in total, in which 90% or more of the total number of particles in the number-based particle size distribution of the aggregate are present within a 5% range around the predetermined average primary particle diameter: 10 to 1500 parts by mass; and 0.01 to 0.5 parts by mass of a polymerization initiator.

[0079] Condition 2: When the number of the one or more "spherical particle groups of the same particle size" is defined as a, each "spherical particle group of the same particle size" is classified into G-PID ｍ (However, m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more.) When a is 2 or more, each G-PID ｍ The materials constituting the individual particles may be different from each other, and in this case, each G-PID ｍ The average primary particle diameters of the respective particles differ from each other by 25 nm or more.

[0080] Condition 3: The refractive index of the cured product of the polymerizable monomer at 25°C with respect to the sodium d line is n （ＭＸ） and each G-PID ｍ The refractive index of the inorganic spherical particles constituting the sodium d line at 25 ° C. is n （Ｇ－ＰＩＤｍ） When （Ｇ－ＰＩＤｍ） For n （ＭＸ） <n （Ｇ－ＰＩＤｍ） The following relationship holds.

[0081] In the method for producing a dental curable composition, the following components are mixed to satisfy the conditions 1 to 3: polymerizable monomer: 100 parts by mass; total amount of the one or more "spherical particle groups of the same particle size" (G-PID): 10 to 1500 parts by mass; |n （ＭＸ） -n （F―ＭＸ）The specific radiopaque filler produced by this radiopaque filler production method is constituted by organic-inorganic composite particles (particle bodies) using a resin material such that | is 0 to 0.1. The specific radiopaque filler is mixed with 1 to 100 parts by mass, calculated as the total mass of the low-crystalline rare earth fluoride metal particles, and 0.01 to 0.5 parts by mass of a polymerization initiator, to produce a dental curable composition that can give a cured product that exhibits a structural color of a predetermined color tone independent of the angle of incidence of light.

[0082] (1-2) Features of the Dental Curable Composition Obtained by the Present Dental Curable Composition Manufacturing Method The dental curable composition manufactured by the present dental curable composition manufacturing method can be made to have high radiopacity in the cured product without impairing the excellent features of existing structural color dental curable compositions, namely, "when used as a CR, (i) since no dye or pigment is used, the problem of discoloration over time after treatment is unlikely to occur, (ii) a structural color of a specific color tone that is independent of the angle of incidence of light is expressed depending on the average particle size of the spherical inorganic particles used, and in particular, when spherical inorganic particles having an average primary particle size of 230 to 350 nm are used, it can be colored to a yellow to red color similar to the color of dentin, and further, (iii) since the cured product has appropriate transparency, it can be easily matched with the color of the tooth to be restored, and therefore, it is possible to use a single type of composite resin to restore an appearance similar to that of natural teeth to teeth of a wide range of colors, without the need for complicated shade-taking or shade selection of the composite resin."

[0083] Such a feature is due to the fact that the state of structural color expression in the cured product is almost equivalent to that of a cured product of an existing structural color dental hardenable composition (also referred to as a base existing structural color dental hardenable composition) that does not contain a specific X-ray opaque filler or a filler that adversely affects the expression of structural color. Furthermore, such a property is due to the spectral reflectance ratio (SR) of the cured product of the dental hardenable composition obtained by the present dental hardenable composition production method to the cured product of the base existing structural color dental hardenable composition. １ / SR ２ Here, it can be confirmed by comparing the above SR １ and S.R. ２The maximum value of the spectral reflectance (SR) in the wavelength range of 600 nm to 750 nm (yellow to red region) is measured using a color difference meter on a 1 mm thick cured body obtained by curing the dental curable composition against a black background. １ ) and the maximum value of the spectral reflectance (SR) in the wavelength range of 400 nm to 500 nm (blue range) ２ ) where the smaller the spectral reflectance ratio, the more blue the structural color (colored light) of the cured body is, and the larger the spectral reflectance ratio, the more reddish the structural color (colored light) of the cured body is.

[0084] In the base existing structural color dental curable composition, the average primary particle diameter of the G-PID to be blended is usually controlled to obtain the desired structural color (desired spectral reflectance ratio: SR) of the cured product. １ / SR ２ The spectral reflectance ratio is typically set to a value that provides a spectral reflectance ratio (giving a spectral reflectance ratio). For example, in order to ensure excellent color matching when used to repair dentin or cavities formed from enamel to dentin, the spectral reflectance ratio is usually set to a range of 0.9 to 1.5. This is because, if the spectral reflectance ratio is less than 0.8, the yellow-to-red structural color (colored light) is weak, making it difficult to achieve color matching with natural teeth, which have a yellowish to reddish tinge, i.e., restored teeth containing dentin; and, if the spectral reflectance ratio exceeds 2.0, the yellowish to reddish tinge of the cured body is too strong compared to natural teeth, making it difficult to achieve good color matching.

[0085] The dental curable composition produced by the dental curable composition production method is such that the cured product exhibits high X-ray opacity by blending a specific X-ray opaque filler into a base existing structural color dental curable composition, yet the spectral reflectance ratio is difficult to change, and it is possible to maintain a spectral reflectance ratio of, for example, 0.9 or more without blending a toning agent such as a pigment.

[0086] Furthermore, in addition to point (iii) above, the dental curable composition produced by the dental curable composition production method can provide a cured product having a contrast ratio C of, for example, 0.20 to 0.50, preferably 0.25 to 0.45. Here, the contrast ratio C is the Y value measured against a black background using a color difference meter for a 1 mm-thick cured product sample, which serves as an index of the transparency of the cured product of the dental curable composition. ｂ and Y, the Y value measured under a white background. ｗ Ratio to: Y ｂ / Y ｗ The smaller the contrast ratio, the higher the transparency.

[0087] If the contrast ratio of the cured product of the dental hardenable composition is less than 0.20, the brightness (color density) of the cured product at the filled area will be low, the transmitted light will be strong at the filled area, and the colored light from the cured product will be weak. This is thought to make it difficult to achieve the color matching effect of the present invention when the composition is used to fill a deep cavity (e.g., a Class IV cavity). On the other hand, if the contrast ratio of the cured product exceeds 0.50, the brightness of the cured product will be high, making it difficult for light to penetrate to the underlying restoration. This will result in strong reflected light at the surface of the filled area and weak colored light from the cured product, making it difficult to achieve the color matching effect of the present invention. In other words, to achieve excellent color matching regardless of the depth of the cavity to be restored, the contrast ratio C of the cured product of the hardenable composition should be in the range of 0.20 to 0.50, and more preferably in the range of 0.20 to 0.45.

[0088] The reason why such an effect is obtained is not entirely clear, and the present invention is not limited to any particular theory, but the present inventors presume that the reason why high X-ray contrast can be obtained with a small amount of low-crystalline rare earth metal fluoride powder is that when low-crystalline rare earth metal fluoride powder is blended as is, the individual particles, which have weak X-ray opacity (areas with small X-ray opacity), are uniformly dispersed, causing the overall X-ray opacity to become blurred, whereas when blended as organic-inorganic composite particles, "regions with locally high density of rare earth metal fluoride particles" (regions with locally high X-ray opacity) are uniformly dispersed (scattered) throughout, making them clearly distinguishable when viewed as an image. Furthermore, with regard to the fact that blending it into structural color CR does not adversely affect the expression of the desired structural color, if low-crystalline rare earth metal fluoride powder is blended as is, the particles will penetrate between the particles of the group of spherical particles of the same particle size (G-PID) that form an ideal periodic structure, disrupting the periodic structure. On the other hand, by converting the low-crystalline rare earth metal fluoride powder into organic-inorganic composite particles, the absolute number of particles is reduced compared to when the low-crystalline rare earth metal fluoride powder is blended as is, reducing the frequency of disrupting the periodic structure of the G-PID. Furthermore, the organic-inorganic composite particle size increases, making it less likely for the particles to penetrate between the periodic structures of the G-PID. In other words, by using the low-crystalline rare earth metal fluoride powder as organic-inorganic composite particles, it becomes less likely to disrupt the periodic structure formed by the G-PID, and it is thought that this will not adversely affect the expression of the desired structural color.

[0089] (2) Raw materials used in the present dental curable composition manufacturing method Except for the incorporation of a predetermined amount of a specific radiopaque filler, the raw materials used in the present dental curable composition manufacturing method and their blending amounts are basically the same as the components and blending amounts of the existing structural color dental curable compositions disclosed in Patent Documents 1 and 2. Here, these will be briefly explained, and then the dental curable composition of the present invention will be described.

[0090] (2-1) Polymerizable Monomer As the polymerizable monomer, any of those usable in conventional dental hardenable compositions can be used without any particular limitation, but it is preferable to use a (meth)acrylate-based monomer. Specific examples of suitably usable (meth)acrylate-based monomers include methyl (meth)acrylate, glycidyl (meth)acrylate, 2-cyanomethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, allyl (meth)acrylate, 2-hydroxyethyl mono(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate (3G), nonaethylene glycol di(meth)acrylate, propylene ... Examples of suitable polymerizable monomers include acrylate, dipropylene glycol di(meth)acrylate, 2,2-bis[4-(meth)acryloyloxyethoxyphenyl]propane, 2,2-bis[4-(meth)acryloyloxyethoxyethoxyphenyl]propane, 2,2-bis{4-[3-(meth)acryloyloxy-2-hydroxypropoxy]phenyl}propane, 1,4-butanediol di(meth)acrylate, 1,3-hexanediol di(meth)acrylate, 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane (UDMA), trimethylolpropane di(meth)acrylate, etc. Two or more of these polymerizable monomers can be used in appropriate combination.

[0091] Among these polymerizable monomers, bifunctional to tetrafunctional polymerizable monomers are preferred because they have high polymerizability and the mechanical strength of the cured product is particularly high. From the viewpoint of the transparency of the cured product of the curable composition, it is more preferred to use any one of ethylene glycol di(meth)acrylate, 2,2-bis[4-(meth)acryloyloxyethoxyphenyl]propane, 2,2-bis{4-[3-(meth)acryloyloxy-2-hydroxypropoxy]phenyl}propane, and 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane (UDMA), or a combination of two or more of these polymerizable monomers.

[0092] From the viewpoint of easily satisfying the condition 3, it is desirable to set the type and amount of polymerizable monomer so that the refractive index of the polymerizable monomer composition (mixture) at 25°C relative to the sodium d line is in the range of 1.38 to 1.55. That is, when a silica-titanium group element oxide composite oxide, whose refractive index is easily adjustable, is used as the inorganic spherical particles, its refractive index at 25°C relative to the sodium d line is in the range of approximately 1.45 to 1.58 depending on the silica content. However, by setting the refractive index of the polymerizable monomer composition in the range of 1.38 to 1.55, the refractive index of the resulting cured product can be adjusted to approximately 1.40 to 1.57, making it easier to satisfy the condition 3. The refractive index of the polymerizable monomer and the cured product of the polymerizable monomer can be determined at 25°C using an Abbe refractometer.

[0093] Furthermore, from the viewpoint of not reducing the transparency of the cured product of the dental curable composition, |n （ＭＸ） -n （F―ＭＸ） | must be 0 to 0.1, and preferably 0 to 0.05. In order to adjust the refractive index in this way, for example, it is preferable to use the same type of polymerizable monomer as the polymerizable monomer used in the curable composition and the polymerizable monomer used in producing the resin material that constitutes the resin matrix of the organic-inorganic composite particles. Furthermore, when two or more types of polymerizable monomers are used in combination, it is also preferable that the blend ratios thereof are the same or similar.

[0094] (2-2) Group of uniformly sized spherical particles: G-PID Group of uniformly sized spherical particles: G-PID refers to an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within the range of 100 nm or more and 1000 nm or less (100 to 1000 nm), in which the individual inorganic spherical particles constituting the aggregate are composed of substantially the same substance, and in the number-based particle size distribution of the aggregate, 90% or more of the total number of particles are present within a range of 5% around the predetermined average primary particle diameter.

[0095] The average primary particle diameter of inorganic spherical particles referred to here means the average value obtained by photographing a G-PID using a scanning electron microscope, selecting 100 or more particles observed within a unit field of view of the photograph, and determining the primary particle diameter (maximum diameter) for each. Furthermore, "spherical" means that the particles are generally spherical, and do not necessarily need to be perfectly spherical. A photograph of the G-PID is taken using a scanning electron microscope, and the maximum diameter of each particle (100 or more) within the unit field of view is measured. The average uniformity obtained by dividing the particle diameter in the direction perpendicular to the maximum diameter by the maximum diameter is 0.6 or more, more preferably 0.8 or more. Since G-PID has the particle size distribution described above, the average primary particle diameter of G-PID from which a suspension of primary particles is obtained by ultrasonic irradiation closely matches the particle diameter (D50p value) at the cumulative 50% from the smallest diameter side, determined from the number particle size distribution measured for the suspension using a particle size distribution analyzer.

[0096] In the cured product of the dental curable composition obtained by the existing structural color dental curable composition and the present dental curable composition manufacturing method, the constituent particles of G-PID have a specific short-range ordered structure and are dispersed in the resin matrix, causing diffraction interference in accordance with the Bragg condition, emphasizing light of a specific wavelength and generating colored light of a color tone corresponding to the average primary particle diameter (structural color is expressed). That is, for structural color to be expressed, 90% or more (in number) of the inorganic spherical particles constituting G-PID must be present within a 5% range around the average primary particle diameter. In other words, if the "5% particle content" is defined as the percentage (%) of the "number of particles present within a 5% range around the average primary particle diameter" to the "total number of particles constituting G-PID," the 5% particle content must be 90% or more. Furthermore, in order to express a structural color with a specific color tone within a wide range from blue to yellow to red, the average primary particle diameter of the inorganic spherical particles constituting G-PID must be within a range of 100 to 1,000 nm. When spherical particles having an average primary particle size of less than 100 nm are used, the interference phenomenon of visible light is unlikely to occur and structural color is unlikely to appear.On the other hand, when spherical particles having an average primary particle size of more than 1000 nm are used, although the interference phenomenon of light can be expected to appear, settling of the spherical particles and a decrease in the polishability of the cured product occur, which is not preferred.

[0097] When the average primary particle size is 230 to 800 nm, a yellow to red structural color (colored light) is likely to be expressed, while when the average primary particle size is less than 150 to 230 nm, a blue structural color (colored light) is likely to be expressed. Because a yellow to red structural color (colored light) that is preferable for a dental filling and restorative material is expressed, the average primary particle size of G-PID is preferably 230 to 800 nm, more preferably 240 to 500 nm, and particularly preferably 260 to 350 nm. When G-PID having an average primary particle size in the range of 230 to 260 nm is used, the resulting colored light is yellowish, and is useful for repairing teeth that fall into the B-type (reddish-yellow) category in the shade guide ("VITA Classical," manufactured by VITA), and is particularly useful for repairing cavities formed from the enamel to the dentin. Furthermore, when G-PID with an average primary particle size in the range of 260 to 350 nm is used, the resulting colored light is reddish, making it useful for restoring teeth that fall into the A-type (reddish-brown) category in the shade guide (VITA Classical, manufactured by VITA), particularly for restoring cavities that extend from enamel to dentin. Because dentin often has a reddish hue, an embodiment using only G-PID with an average primary particle size in the range of 260 to 350 nm is most preferred, as it provides broad compatibility with restored teeth of various colors. On the other hand, when G-PID with a particle size in the range of 150 to less than 230 nm is used alone, as described above, the resulting colored light is blued, making it prone to poor color compatibility with cavities that extend from enamel to dentin, but is useful for restoring enamel, particularly incisal edges.

[0098] The G-PID used may be one type or multiple types. The number of G-PIDs contained: a, is preferably 1 to 5, particularly preferably 1 to 3, and most preferably 1 or 2. However, when multiple types of G-PIDs are contained in the inorganic particles, the average primary particle diameters of the respective G-PIDs must differ from each other by 25 nm or more. That is, when the number of G-PIDs contained in the inorganic particles is "a" (for example, "3"), the G-PIDs are sorted in ascending order of their average primary particle diameters. ｍ(However, m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more.) ｍ (For example, when a=3, G-PID １ , G-PID ２ and G-PID ３ ) The materials constituting the individual particles may be different from each other, but in this case, each G-PID ｍ The average primary particle diameter of each ｍ Then, each d ｍ are different from each other by 25 nm or more (for example, when a=3, |d １ -d ２ |≧25 nm, |d ２ -d ３ |≧25 nm and, naturally, |d １ -d ３ |≧25 nm). By satisfying this condition, for example, each G-PID is dispersed in the form of an aggregate of a small number of inorganic spherical particles, not exceeding about 20, agglomerated with very loose bonding forces, which is thought to be the reason why it becomes possible to disperse each G-PID with a short-range ordered structure that can express a structural color, and as a result, it becomes possible to express a unique structural color (corresponding to the average primary particle diameter) for each G-PID. On the other hand, if this condition is not satisfied, the particle size distribution of the inorganic spherical particles as a whole becomes broad, and the inorganic spherical particles constituting each G-PID are likely to disperse mutually replacing each other, which is thought to be due to the same phenomenon occurring as when an aggregate of a single inorganic spherical particle that does not satisfy the condition of the number-based particle size distribution is used, making it difficult to express a structural color. When multiple G-PIDs are used, ｍ Average primary particle diameter d ｍ are preferably different from each other by 30 nm or more, particularly 40 nm or more.

[0099] When a plurality of types of G-PID are used, each G-PID has an extremely sharp particle size distribution and has the above-described difference in average primary particle diameter, so that the particle size distributions of the G-PIDs are unlikely to overlap, and even if they partially overlap, it is possible to confirm the particle size distribution of each G-PID.

[0100] The G-PID is preferably formed by agglomerating inorganic spherical particles to form an aggregate particle size, because this facilitates the dispersion state of the inorganic spherical particles to obtain the short-range order structure described above. For example, the average aggregate particle size of the G-PID is preferably within the range of 5 to 200 μm, and more preferably within the range of 10 to 100 μm. The average aggregate particle size of the G-PID refers to the median diameter of volume statistics determined based on the results of measurement using a particle size distribution analyzer using a laser diffraction-scattering method.

[0101] (2-3) Inorganic spherical particles constituting G-PID The material of the inorganic spherical particles constituting G-PID is not particularly limited as long as it satisfies the above-mentioned conditions for constituting G-PID. Suitable examples of materials include amorphous silica, silica-titanium group element oxide composite oxide particles (silica-zirconia, silica-titania, etc.), quartz, alumina, barium glass, strontium glass, lanthanum glass, fluoroaluminosilicate glass, ytterbium fluoride, zirconia, titania, colloidal silica, and the like. Among these, it is preferable to use particles made of silica-titanium group element oxide composite oxides because the refractive index can be easily adjusted.

[0102] Here, silica-titanium group element oxide-based composite oxide particles refer to composite oxides of silica and titanium group element (Group 4 element of the periodic table) oxide, and their refractive index at 25°C relative to the sodium d-line can be varied within a range of approximately 1.45 to 1.58 depending on the silica content. Specific examples of silica-titanium group element oxide-based composite oxide particles include silica-titania, silica-zirconia, and silica-titania-zirconia, with silica-zirconia being preferred. The silica-zirconia composite ratio is not particularly limited, but from the viewpoints of imparting sufficient X-ray opacity and maintaining a refractive index within the preferred range described below, a silica content of 70 to 95 mol% and a titanium group element oxide content of 5 to 30 mol% are preferred. These silica-titanium group element oxide-based composite oxide particles may also contain small amounts of a composite of metal oxides other than silica and titanium group element oxide. Specifically, alkali metal oxides such as sodium oxide and lithium oxide may be contained in amounts up to 10 mol%.

[0103] Although there are no particular limitations on the method for producing such silica-titanium group element oxide composite oxide particles, a suitable method for obtaining spherical fillers is, for example, the so-called sol-gel method, in which a mixed solution containing a hydrolyzable organosilicon compound and a hydrolyzable organotitanium group metal compound is added to an alkaline solvent, and hydrolysis is carried out to precipitate a reaction product.These inorganic spherical particles made of silica-titanium group element oxide composite oxide are preferably surface-treated with a silane coupling agent such as γ-methacryloyloxyalkyltrimethoxysilane or hexamethyldisilazane.

[0104] (2-4) Relationship between the refractive index of the cured product of the polymerizable monomer and the refractive index of the inorganic spherical particles In the existing structural color dental curable compositions and the dental curable compositions obtained by the dental curable composition manufacturing method of the present invention, the refractive index at 25°C of the "cured product of the polymerizable monomer" (specifically, the cured product of the composition consisting of the polymerizable monomer and a small amount of polymerization initiator), which corresponds to the resin matrix in the cured product, is expressed as n （ＭＸ） and each G-PID ｍThe refractive index of the inorganic spherical particles constituting the sodium d line at 25 ° C. is n （Ｇ－ＰＩＤｍ） When （Ｇ－ＰＩＤｍ） The following relationship must also hold for

[0105] n （ＭＸ） <n （Ｇ－ＰＩＤｍ） If the above relationship is not satisfied, even if a structural color is expressed, light of short wavelengths is likely to be scattered in the resin matrix of the hardened product of the dental hardenable composition, making it difficult to confirm the expressed structural color. （Ｇ－ＰＩＤｍ） and （ＭＸ） The difference Δn is preferably 0.001 or more and 0.1 or less, more preferably 0.002 or more and 0.1 or less, and most preferably 0.005 or more and 0.05 or less.

[0106] As described above, by setting the refractive index of the polymerizable monomer composition at 25°C with respect to the sodium d line to the range of 1.38 to 1.55, the refractive index (n （ＭＸ） As described above, the refractive index (n （Ｇ－ＰＩＤｍ） ) can be changed in the range of about 1.45 to 1.58. Therefore, for example, by utilizing these relationships, Δn can be easily set in the above-mentioned preferred range.

[0107] (2-5) Preferred Form of Blending of G-PID For the reason that the above-mentioned short-range ordered structure can be obtained more simply and reliably, it is preferred that at least a part of the one or more uniform-particle-size spherical particle groups comprises one type of uniform-particle-size spherical particle group and a resin whose refractive index at 25°C to the sodium d line is smaller than the refractive index at 25°C of the inorganic spherical particles constituting the one type of uniform-particle-size spherical particle group, and that the organic-inorganic composite filler does not contain any uniform-particle-size spherical particle groups other than the one type of uniform-particle-size spherical particle group (i.e., an organic-inorganic composite filler containing only a single G-PID).

[0108] Here, the organic-inorganic composite filler means a powder consisting of a composite in which an inorganic filler is dispersed in an (organic) resin matrix, or a filler consisting of an aggregate in which primary particles of an inorganic filler are bound together by an (organic) resin. The preferred embodiment is, for example, three types of G-PID having different average primary particle diameters, i.e., G-PID １ , G-PID ２ , and G-PID ３ If the filler contains G-PID1, all or part of at least one of them is blended as an "organic-inorganic composite filler containing only a single G-PID". １ When the curable composition contains only an organic-inorganic composite filler (composite filler 1), the composite filler 1 contains only G-PID. １ Only G-PID is included. １ Therefore, the short-range ordered structure that exhibits the structural color of G-PID is realized, and the composite material obtained by curing the curable composition also exhibits the structural color of G-PID. １ The structural color of the material is revealed.

[0109] In order to expect such effects and to easily adjust the viscosity of the curable composition, it is preferable to blend 10 to 90%, preferably 20 to 80%, and more preferably 30 to 70% of each G-PID as an "organic-inorganic composite filler containing only a single G-PID." In this case, the refractive index of the resin matrix of the organic-inorganic composite filler at 25°C with respect to the sodium d line: n' （F―ＭＸ） is the refractive index (n （Ｇ－ＰＩＤｍ） ) must be smaller than the n （ＭＸ） Similarly, n （Ｇ－ＰＩＤｍ） and n' （F―ＭＸ） Furthermore, the refractive index at 25°C of the cured product of the polymerizable monomer in the structural color dental curable composition of the present invention (specifically, the cured product of the composition comprising the polymerizable monomer and a small amount of polymerization initiator) at the sodium d line: n（ＭＸ） and the n' （F―ＭＸ） Absolute value of the difference with: |n （ＭＸ） -n' （F―ＭＸ） | must be between 0 and 0.1.

[0110] The amount of inorganic spherical particles blended into the organic-inorganic composite filler is preferably 30 to 95% by mass, particularly preferably 40 to 90% by mass. The average particle size is not particularly limited, but from the viewpoint of improving the mechanical strength of the composite material and the operability of the curable composition, the median diameter determined based on the results of measurement using a particle size distribution analyzer by a laser diffraction-scattering method is preferably 2 to 100 μm, more preferably 5 to 50 μm, and even more preferably 5 to 30 μm.

[0111] (2-6) Amount of G-PID Used The total amount of G-PID used is 10 to 1500 parts by mass relative to 100 parts by mass of the polymerizable monomer. Because the resulting composite material has appropriate transparency and a high structural color development effect, the amount is preferably 50 to 1500 parts by mass, and more preferably 100 to 1500 parts by mass. When multiple types of G-PID are used, the content of each G-PID may be appropriately set so that the total content falls within the above range, taking into consideration the color tone of the structural color due to each G-PID and the desired color tone of the composite material.

[0112] (2-7) Polymerization Initiator As the polymerization initiator in the dental curable composition of the present invention, since the composition is often cured in the oral cavity, it is preferable to use a chemical polymerization initiator and / or a photopolymerization initiator, and it is more preferable to use a photopolymerization initiator because a mixing operation is not required. These polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator to be added may be selected in an effective amount depending on the purpose, but it is usually used in a ratio of 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the polymerizable monomer.

[0113] Suitable photopolymerization initiators include, for example, benzoin alkyl ethers, benzil ketals, benzophenones, α-diketones, thioxanthone compounds, and bisacylphosphine oxides. A reducing agent is often added to the photopolymerization initiator. Examples of the reducing agent include aromatic amines, aliphatic amines, aldehydes, and sulfur-containing compounds. Furthermore, trihalomethyltriazine compounds, aryliodonium salts, and the like can also be added as needed.

[0114] Furthermore, examples of the thermal polymerization initiator that can be suitably used include peroxides such as benzoyl peroxide, p-chlorobenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxydicarbonate, and diisopropylperoxydicarbonate; azo compounds such as azobisisobutyronitrile; boron compounds such as tributylborane, tributylborane partial oxide, sodium tetraphenylborate, sodium tetrakis(p-fluorophenyl)borate, and tetraphenylborate triethanolamine 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.

[0115] (2-8) Specific radiopaque filler The specific radiopaque filler has already been explained, but |n （ＭＸ） -n （F―ＭＸ） | must be 0 to 0.1. If this condition is not satisfied, the transparency of the cured product of the structural color dental hardenable composition of the present invention will be significantly reduced. In order to satisfy the above condition, in the specific X-ray opaque filler blended in the structural color dental hardenable composition of the present invention, it is preferable to use a polymerizable monomer that is the raw material (of the matrix resin) of the specific X-ray opaque filler that has the same composition as or a composition similar to the polymerizable monomer in the structural color dental hardenable composition of the present invention. In addition, |n （ＭＸ） -n （F―ＭＸ） It is more preferable that | is 0 to 0.05.

[0116] From the viewpoint of X-ray opacity, transparency, and structural color expression of the cured product, the amount of the specific X-ray opaque filler used is 1 to 100 parts by mass, preferably 15 to 75 parts by mass, per 100 parts by mass of the polymerizable monomer, calculated as the total mass of the low-crystalline rare earth metal fluoride powder. If the amount is less than 1 part by mass (lower limit), sufficient X-ray opacity cannot be obtained, and if the amount is more than 100 parts by mass (upper limit), transparency and structural color expression are significantly reduced.

[0117] (2-9) Other Fillers For the purpose of adjusting the viscosity of the dental curable composition to be obtained or the transparency of the cured product, ultrafine particles (G-SFP), which are particle aggregates made of inorganic particles having an average primary particle diameter of less than 100 nm, may be blended. However, the average primary particle diameter of the G-SFP is smaller than that of the G-PID having the smallest average primary particle diameter among the blended G-PIDs. １ The average primary particle diameter (d １ ) must be at least 25 nm smaller than the inorganic spherical particles. If these conditions are not satisfied, it will have an adverse effect on the dispersion state of the inorganic spherical particles, making it difficult for the structural color to be expressed. The shape of the inorganic particles constituting the G-SFP is not particularly limited, and they may be amorphous or spherical. The lower limit of the average primary particle diameter is usually 2 nm. The average primary particle diameter of the G-SFP is preferably 3 to 75 nm, more preferably 5 to 50 nm, because this has little effect on the expression of the structural color. For the same reason, the average primary particle diameter of the G-SFP is preferably 3 to 75 nm, more preferably 5 to 50 nm, １ The average primary particle diameter (d １ ) is preferably at least 30 nm smaller, and more preferably at least 40 nm smaller. The inorganic particles constituting the G-SFP can be made of the same material as the inorganic spherical particles without any particular limitations. Furthermore, as with the inorganic spherical particles, they can also be surface-treated with a silane coupling agent. Except for the average primary particle diameter and shape, the preferred embodiments are also basically the same as those of the inorganic spherical particles. The content of the G-SFP may be appropriately determined taking into consideration the viscosity of the curable composition, the transparency of the cured product (or the contrast ratio serving as an index thereof), and the like, but is typically 0.1 to 50 parts by mass, and preferably 0.2 to 30 parts by mass, per 100 parts by mass of the polymerizable monomer.

[0118] Furthermore, rare earth metal fluoride particles other than the rare earth metal fluoride particles blended as the specific radiopaque filler may be included, as long as the effects of the present invention are not significantly impaired. The amount of such rare earth metal fluoride particles blended is preferably 5 parts by mass or less, and more preferably 0 to 3 parts by mass, per 100 parts by mass of the polymerizable monomer. In particular, the amount of crystalline rare earth fluoride metal particles having a full width at half maximum of less than 0.3° is preferably 0 to 0.5 parts by mass or less. When a specific radiopaque filler is used in combination with non-composite particles having a full width at half maximum of 0.3° or more, the total amount of the crystalline rare earth fluoride metal particles having a full width at half maximum of 0.3° or more contained in the specific radiopaque filler and the non-composite particles is preferably 0 to 100 parts by mass, more preferably 0 to 50 parts by mass, per 100 parts by mass of the polymerizable monomer.

[0119] (2-10) Other Additives, etc. Other additives, such as polymerization inhibitors and ultraviolet absorbers, can be blended to the extent that they do not impair the effects of the present invention. As described above, the resulting cured product of the dental curable composition exhibits structural color without the use of coloring substances such as pigments. Therefore, while there is no particular need to blend pigments that may discolor over time, the incorporation of pigments is not prohibited. Pigments may be blended to the extent that they do not interfere with the colored light due to interference from the spherical filler. Specifically, pigments may be blended in an amount of approximately 0.0005 to 0.5 parts by mass, preferably approximately 0.001 to 0.3 parts by mass, per 100 parts by mass of polymerizable monomer.

[0120] (3) Mixing Method The method for producing a dental curable composition includes a mixing step in which predetermined amounts of all raw material components are weighed and mixed. In the mixing step, it is preferable that the mixture obtained in the mixing step is prepared by a mixing method employing mixing conditions that have been confirmed to satisfy the following conditions (I) and (II) so that the dispersion state of the inorganic particles in the hardened product obtained by hardening the mixture satisfies the following conditions (I) and (II):

[0121] [Conditions to be satisfied for the dispersion state] (I) The distance from the center of any inorganic spherical particle dispersed in the cured body: r is the average particle diameter of all inorganic spherical particles dispersed in the cured body: r ０ The dimensionless number (r / r ０ ) is the x-axis, the radial distribution function: g(r) is the y-axis, and the r / r ０ In a radial distribution function graph showing the relationship between g(r) and the r at that time, the nearest inter-particle distance is defined as r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph: r １ is the average particle size of all inorganic spherical particles dispersed in the cured product of the mixture: r ０ The value is between 1 and 2 times the value of the above.

[0122] (II) Among the peaks appearing in the radial distribution function graph, r corresponding to the peak top of the second closest peak from the origin is defined as the next nearest interparticle distance: r ２ When the distance between the nearest particles is r １ and the distance between the next nearest neighboring particles: r ２ The minimum value of the radial distribution function g(r) between is 0.56 or more and 1.10 or less.

[0123] Here, the radial distribution function g(r) is a well-known function for determining the probability of the existence of another particle at a point a distance r away from any particle, and is defined by the following formula (1):

[0124] g(r)={1 / <ρ>}×{dn / da} (1) In the above formula (1), <ρ> represents the average particle density of particles in a plane, dn represents the number of particles present in a region between two circles whose centers are any particle in the plane and whose radii are r and r+dr, respectively, and da represents 2πr·dr, which is the area of ​​the region.

[0125] The radial distribution function g(r) is generally represented by a radial distribution function graph in which the x-axis (distance axis) represents the distance r and the y-axis (vertical axis) represents the value of g(r) at that r (the calculation result according to the above formula (1)), or by a radial distribution function graph in which the distance axis represents a dimensionless number normalized by dividing r by the average particle diameter of the particles and the y-axis (vertical axis) represents the value of g(r) at r corresponding to the value on the x-axis (the calculation result according to the above formula).

[0126] Because <ρ> and dn can be easily and reliably confirmed, it is preferable to use g(r) calculated using the above formula (1) based on <ρ>, dn, and da (= 2πr ⋅ dr), which are determined based on a scanning electron microscope image of the interior surface of the cured mixture as the observation plane, and the da corresponding to the dr value used to determine the dn. <ρ>, dn, and da can be determined as follows. First, the mixture is cured, and a plane (observation plane) on which the dispersion state of the inorganic spherical particles within the cured material can be observed is exposed by means of polishing the surface of the resulting cured material. Next, the observation plane is observed using a scanning electron microscope, and a microscopic image of a region containing at least 500 inorganic spherical particles within the plane is obtained. The obtained scanning electron microscope image is then analyzed using image analysis software (e.g., the free software "Simple Digitizer ver. 3.2") to determine the coordinates of the inorganic spherical particles within the region. One coordinate of any inorganic spherical particle is selected from the obtained coordinate data, and a circle is drawn with a radius of distance r, which is centered on the selected inorganic spherical particle and includes at least 200 inorganic spherical particles, and the number of inorganic spherical particles included in the circle is counted to determine the average particle density <ρ> (unit: particles / cm ２ ) can be determined.

[0127] For dn, the average particle diameter of the inorganic spherical particles is ０ When expressed as , its length is r ０ / 100~r ０dn can be determined by setting dr to a value of about / 10, using one arbitrarily selected inorganic spherical particle as the center particle, and counting the number of inorganic spherical particles contained in the region between a circle whose radius is the distance r from the center and a circle whose center is the same as the circle and has a radius of r + dr. Furthermore, da, which is the area of ​​the region between the two circles, is determined as 2πr dr based on the length of dr that is actually set.

[0128] The distance r from the center of any inorganic spherical particle dispersed in the cured body is then calculated as the average particle diameter r of all inorganic spherical particles dispersed in the composite material. ０ A dimensionless number (r / r ０ ) is the x-axis, and the radial distribution function g(r) representing the probability that another inorganic spherical particle is present at a point distant from the center of the arbitrary inorganic spherical particle by a distance r is the y-axis. ０ The relationship between g(r) and g(r) corresponding to r at that time is shown as a radial distribution function graph. From the viewpoint of maintaining short-range order and making it easier to express structural color, r １ / r ０ is 1.0 to 2.0, and preferably 1.0 to 1.5. From the viewpoint of developing a structural color and facilitating color matching as a dental filling material, the nearest interparticle distance r １ and the distance between the next nearest neighboring particles r ２ The minimum value of the radial distribution function g(r) between is a value of 0.56 to 1.10, and preferably a value of 0.56 to 1.00.

[0129] To facilitate satisfaction of these conditions, the inorganic spherical particles (G-PID) are preferably mixed in the mixing step as an organic-inorganic composite filler having a particle diameter of 5 to 50 μm, preferably 5 to 30 μm, or as aggregated particles having a particle diameter of 5 to 200 μm, preferably 10 to 100 μm. Furthermore, the incorporation of air bubbles during mixing not only makes it difficult to satisfy the above conditions but also leads to defects in the composite material. Therefore, it is preferable to perform a degassing treatment or the like to ensure that air bubbles do not remain at least after mixing. A degassing method using a decompression method is preferred because it can remove air bubbles in a short time, even from a highly viscous composition. When inorganic spherical particles are mixed while taking these points into consideration, sufficient stirring will generally satisfy the above conditions. However, even if a uniform state is visually determined, stirring may be insufficient from the perspective of satisfying the above conditions, making it difficult to determine the end point. Therefore, it is preferable to carry out the mixing step after or while determining the end point by the above method (a) or (b). (a) A method in which a curable composition having the same or substantially the same composition as the curable composition to be actually produced is mixed under multiple mixing conditions, and the radial distribution function g(r) of the cured product of the mixture obtained when mixed under each mixing condition is examined to determine mixing conditions that satisfy conditions (I) and (II), and the same mixing conditions as the determined mixing conditions are adopted. (b) A method in which a portion of the mixture obtained during and / or after the mixing step is sampled, and it is confirmed whether the dispersion state of the inorganic particles in the sampled cured product of the mixture satisfies conditions (I) and (II), and mixing is continued until these conditions are satisfied.

[0130] 4. Method for Curing Dental Curable Composition Obtained by the Dental Curable Composition Production Method The dental curable composition obtained by the dental curable composition production method may be cured by any known polymerization method appropriate for the polymerization initiation mechanism of the polymerization initiator used. Specifically, light irradiation using a light source such as a carbon arc, xenon lamp, metal halide lamp, tungsten lamp, fluorescent lamp, sunlight, helium-cadmium laser, or argon laser, heating using a thermal polymerization apparatus, or a combination thereof, can be used without any limitation. When polymerization is performed by light irradiation, the irradiation time varies depending on the wavelength and intensity of the light source and the shape and material of the cured product, and therefore can be determined in advance through preliminary experiments. When using the curable composition of this embodiment for dental purposes, it is generally preferable to adjust the blending ratios of the various components so that the irradiation time is in the range of about 5 to 60 seconds.

[0131] The present invention will be specifically explained below with reference to Reference Examples (Reference Examples and Reference Comparative Examples) and Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0132] 1. Substance names and their abbreviations (1) Polymerizable monomers UDMA: 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane 3G: Triethylene glycol dimethacrylate.

[0133] (2) Polymerization initiators CQ: camphorquinone (manufactured by Tokyo Chemical Industry Co., Ltd.) DMBE: ethyl dimethylbenzoate (manufactured by Tokyo Chemical Industry Co., Ltd.) AIBN: azobisisobutyronitrile (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0134] (3) Polymerizable monomer composition (monomer composition) M1: A liquid composition prepared by stirring and mixing a mixture of UDMA (80 parts by mass), 3G (20 parts by mass), CQ (0.2 parts by mass), and DMBE (0.35 parts by mass) for 6 hours. M2: A liquid composition prepared by stirring and mixing a mixture of UDMA (80 parts by mass), 3G (20 parts by mass), and AIBN (1 part by mass) for 6 hours. The refractive indices before and after curing of curable components M1 and M2, measured according to the method described below, are shown in Table 1.

[0135]

[0136] (4) Highly crystalline rare earth metal fluoride powder YbF3-40: ytterbium fluoride (manufactured by Sukgyung Co., Ltd.) having the following properties: Corresponds to F-1 described below.

[0137] Average primary particle size: 40 nm Average secondary particle size: 0.6 μm Refractive index: 1.55 YbF in X-ray diffraction measurement ３ The full width at half maximum of the peak attributable to the (111) plane (the peak observed around 2θ=28°) having the greatest intensity: 0.17°. Note that these physical property values ​​were measured according to the method described later.

[0138] (5) Group of spherical particles of the same particle size (G-PID) PF-1: Silica-zirconia-based spherical particles (composition: SiO ２ / ZrO ２ / Na ２ O = 89.8 / 9.0 / 1.2 (mol %)) surface-treated with a silane coupling agent (methacrylate-3-(trimethoxysilyl)propyl-3-(methacryloyloxy)propyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.)). Average primary particle diameter: 260 nm Refractive index: 1.515 Uniformity: 0.90 5% particle content: 92% Here, uniformity refers to the ratio (D2 / D1) of the maximum diameter D1 of the spherical particles to the particle diameter D2 in the direction perpendicular to the maximum diameter D1. The average primary particle diameter and refractive index are values ​​measured according to the methods described below.

[0139] 2. Methods for measuring and evaluating the physical properties of raw materials (1) Measurement of refractive index (1-1) Refractive index of monomer compositions M1 and M2 (before curing) The refractive index of M1 and M2 (before curing) was measured as the refractive index for sodium d line at 25°C using an Abbe refractometer (DR-A1-Plus, manufactured by Atago Co., Ltd.).

[0140] (1-2) Refractive index of monomer compositions M1 and M2 (after curing) After the monomer composition was filled into a through-hole (diameter 7 mm, through-hole length 0.5 mm) provided in a mold, both openings of the through-hole were sealed by pressing with polyester film. Thereafter, for M1, a light intensity of 500 mW / cm was applied to the curable component M1 filled in the through-hole. ２ The resin was cured by irradiating it with light for 30 seconds using a halogen-type dental light irradiator (Demetron LC, manufactured by Cypron Co., Ltd.). For M2, instead of irradiating it with light, it was cured by heating it at 100°C for 30 minutes under nitrogen pressure using a nitrogen pressure heat polymerization apparatus, Polynar (manufactured by Towa Giken Co., Ltd.). The refractive index of the cured products M1 and M2 removed from the molds was then measured using the same procedure as in (1-1).

[0141] (1-3) Refractive Index of Rare Earth Metal Fluoride Particles and G-PID In a thermostatic chamber at 25° C., 1 g of the powder to be measured was suspended in 50 mL of anhydrous toluene in a 100 mL sample bottle. While stirring the resulting suspension with a stirrer, 1-bromotoluene was added dropwise little by little, and the refractive index of the suspension at the point when it became most transparent was measured in the same manner as in (1-1).

[0142] (2) Average Primary Particle Diameter of Rare Earth Metal Fluoride Particles and G-PID The average primary particle diameter of rare earth metal fluoride particles and G-PID was determined using a scanning electron microscope according to the following procedure. First, a measurement sample was prepared by fixing the rare earth metal fluoride particles or G-PID on a sample stage with carbon paste and then subjecting them to a conductive treatment (platinum vapor deposition). Next, this measurement sample was observed at a magnification of 100,000 times using an electron microscope (JSM-7800F PRIME, manufactured by JEOL Ltd.), and the average particle diameter of 100 primary particles in the obtained observation image was determined as the average primary particle diameter. Furthermore, for G-PID, the average value of uniformity was determined based on the primary particles (100 particles) in the obtained observation image.

[0143] (3) Measurement of the average secondary particle diameter of rare earth metal fluoride particles This was determined by particle size distribution measurement using the following procedure. First, a suspension was prepared by suspending 0.1 g of powder (rare earth metal fluoride particles) in 10 mL of ion-exchanged water. Next, this suspension was subjected to ultrasonic irradiation and particle size distribution measurement using a particle size distribution analyzer (LS13-320, manufactured by BECKMAN COULTER) to obtain a volumetric particle size distribution. The particle diameter (D50v value) corresponding to 50% cumulatively from the smallest diameter side of the volumetric particle size distribution was then taken as the average secondary particle diameter of the rare earth metal fluoride particles.

[0144] (4) Confirmation of the average primary particle diameter of G-PID by particle size distribution measurement The number particle size distribution was determined by particle size distribution measurement using the following procedure. First, a suspension was prepared by suspending 0.1 g of powder (G-PID) in 10 mL of ion-exchanged water. Next, this suspension was subjected to ultrasonic irradiation and particle size distribution measurement using a particle size distribution analyzer (LS13-320, manufactured by BECKMAN COULTER) to obtain the number particle size distribution. The particle diameter (D50p value) corresponding to 50% cumulative from the smallest diameter side of the number particle size distribution was determined, and this value agreed well with the average primary particle diameter determined by electron microscope observation.

[0145] 3. Reference Examples (Reference Examples 1 to 13 and Reference Comparative Examples 1 to 5) In order to confirm the hardening of the specific radiopaque filler, the above-mentioned raw materials were used to prepare small amounts of the specific radiopaque filler and other radiopaque fillers (which did not need to be manufactured using the radiopaque filler manufacturing method of the present invention), and these were evaluated, and curable compositions containing these radiopaque fillers were prepared and evaluated.

[0146] 3-1. Production of X-ray opaque filler (1) Mechanochemical treatment of crystalline rare earth metal fluoride powder 855 g of ion-exchanged water and 45 g of YbF3-40 (highly crystalline rare earth metal fluoride powder) were mixed to prepare a slurry. Next, the slurry was dispersed using a circulation type wet bead mill SC50 (manufactured by Mitsui Mining Co., Ltd.) with 100 g of zirconia beads (diameter: 0.3 mm) as media at a rotation speed of 3,000 rpm. The dispersion treatment conditions at this time are shown in Table 2.

[0147] The slurry after dispersion treatment was concentrated using a rotary evaporator at a bath temperature of 50°C to obtain a powder. This powder was dried under vacuum at 80°C for 15 hours to obtain mechanochemically treated rare earth metal fluoride powder. The average primary particle diameter of rare earth metal fluoride particles (crystalline rare earth metal fluoride powder YbF3-40 itself) F-1, which had a dispersion treatment time of 0 minutes, and mechanochemically treated rare earth metal fluoride powders F-3 to F-6 were measured by the method described in 2.(2), and the full width at half maximum S was measured by the method described below. The results are also shown in Table 2.

[0148] Measurement method of full width at half maximum S: A measurement sample was prepared by removing coarse particles from powder or granular material to be subjected to X-ray diffraction measurement using a sieve. Next, the measurement sample was loaded onto the sample stage of an X-ray diffractometer (Smartlab, manufactured by Rigaku Corporation) and X-ray diffraction measurement was performed to obtain an X-ray diffraction pattern (chart) with the horizontal axis representing 2θ (°) and the vertical axis representing diffraction intensity. Here, CuKα rays were used as the X-rays for the X-ray diffraction measurement. The rare earth metal fluoride was YbF ３ Therefore, the full width at half maximum of the peak attributable to the (111) plane (the peak observed at about 2θ = 28°) having the greatest intensity was determined. Note that by changing the powder to be measured to an X-ray opaque filler described below, the full width at half maximum C of the X-ray opaque filler can be determined in a similar manner.

[0149]

[0150] (2) Preparation of Curable Raw Material Composition and Curing / Pulverization Treatment 25 parts by mass of monomer composition M2 and 75 parts by mass of rare earth metal fluoride powder F-3 were weighed out and mixed in an agate mortar to prepare a paste-like curable raw material composition. The curable raw material composition thus obtained was thermally cured by heating at 100°C for 30 minutes under nitrogen pressure using a nitrogen pressure thermal polymerization apparatus (Poliner, manufactured by Towa Giken Co., Ltd.) to obtain a cured product. The obtained cured product and zirconia balls (diameter: 25 mm) were placed in a zirconia pot and subjected to a rotary pulverization treatment for 60 minutes to obtain a pulverized cured product. Coarse particles were removed from the pulverized product using a stainless steel sieve with 45 μm openings to obtain a radiopaque filler CF-1 (a specific radiopaque filler). The average particle size and full width at half maximum C of the radiopaque filler CF-1 were measured. The results are shown in Table 3. CF-1 to CF-4 and CF-1a to CF-1i other than RCF-1 obtained in Production Example 5 are specific radiopaque fillers.

[0151] The average particle size of the radiopaque filler was determined by particle size distribution measurement using the following procedure. That is, first, a suspension was prepared by suspending 0.1 g of powder (radiopaque filler) in 10 mL of ethanol. Next, this suspension was subjected to ultrasonic irradiation and particle size distribution measurement was performed using a particle size distribution meter (LS13-320, manufactured by BECKMAN COULTER) to obtain a volumetric particle size distribution. The particle diameter (D50v value) that is 50% cumulative from the small diameter side of the volumetric particle size distribution was then taken as the average particle size of the radiopaque filler. The full width at half maximum C was measured in the same manner as the full width at half maximum S. The results are also shown in Table 3.

[0152]

[0153] 3-2. Preparation of Curable Composition To monomer composition M1 (20 parts by mass), radiopaque filler (16 parts by mass) and G-PID:PF-1 (64 parts by mass) were added, and the mixture was mixed in an agate mortar to obtain a mixture. This mixture was then degassed under vacuum to remove air bubbles, yielding a paste-like curable composition. Note that, when preparing the curable compositions, the type of radiopaque filler was changed as shown in Table 4 to prepare the curable compositions of Reference Examples 1 to 13 and Reference Comparative Examples 1 to 5.

[0154] 3-3. Evaluation of cured products For each curable composition obtained by the above method, the X-ray contrast property, transparency, spectral reflectance ratio, and bending strength of the cured product were measured, and the dispersion state of the inorganic spherical particles (radial distribution function) was evaluated. The measurement and evaluation methods for each of the above physical properties are described below. The evaluation results are also shown in Table 5.

[0155] (1) Method for Measuring X-Ray Contrast Properties The X-Ray contrast properties of the cured product of the curable composition were measured using the following procedure. First, a through-hole (diameter 15 mm, through-hole length 1.0 mm) in a polytetrafluoroethylene mold was filled with the curable composition, and then both end openings of the through-hole were sealed by pressing with polypropylene film. Next, a dental light irradiator (TOKUSO POWER LIGHT, manufactured by Tokuyama Corporation) was positioned so as to be in close contact with the surface of the polypropylene film sealing the opening of the through-hole, and light was irradiated in this state. Light was irradiated at five locations on one opening side of the through-hole (one location in the center of the through-hole and four locations inside the outer edge of the through-hole) and five locations on the other opening side (one location in the center of the through-hole and four locations inside the outer edge of the through-hole). Light was then irradiated for 20 seconds at each light irradiation location to obtain a cured product. The thickness of the obtained cured product was measured using a micrometer. The cured product having a thickness of 1.0 mm±0.1 mm was used as a test piece for measuring the X-ray contrast property.

[0156] Next, an X-ray film (ultra-high sensitivity dental X-ray film, manufactured by Kodak) was placed on a 2.0 mm thick lead sheet, and then a test piece and an aluminum step wedge having five thicknesses (thickness: 1.0 ± 0.01 mm, 2.0 ± 0.01 mm, 3.0 ± 0.01 mm, 4.0 ± 0.01 mm, 5.0 ± 0.01 mm) were placed on the X-ray film. Subsequently, the test piece and step wedge were irradiated with X-rays from a height of 40 cm from the surface of the X-ray film using an X-ray irradiator (PANPAS-E, manufactured by YOSHIDA Corporation). The irradiation conditions were a tube voltage of 60 kVp and an irradiation time of 0.3 seconds. The X-ray film was then developed and printed onto photographic paper. Next, the optical densities of the test piece image and step wedge image on the photographic paper were measured. Next, a calibration curve was created based on the five step wedge thicknesses and the optical densities corresponding to these five thicknesses, and the thickness of the step wedge (i.e., aluminum material) at which the optical density of the test piece coincided with the optical density of the step wedge was determined based on this calibration curve. Then, when the optical density of an aluminum material with a thickness of 1 mm was taken as the reference (100 Al%), the value obtained by converting the determined aluminum material thickness into Al% was used as an evaluation index for X-ray contrast property.

[0157] (2) Transparency Measurement Method The transparency of the cured product of the curable composition was measured using the following procedure. First, the curable composition was filled into a hole (0.7 cm diameter, 0.1 cm length) in a polyacetal mold, and both end openings of the through-hole were sealed by pressure welding with polypropylene film. Next, a dental light irradiator (TOKUSO POWER LIGHT, manufactured by Tokuyama Corporation) was placed 0.5 cm away from the opening of the hole, and light was irradiated for 20 seconds to obtain a cured product. The thickness of the obtained cured product was confirmed using a micrometer. Cured products with a thickness within 1.0 mm ± 0.1 mm were used for transparency evaluation. Next, the Y value (a value related to brightness among the tristimulus values ​​of the XYZ color system defined in JIS Z8701) of the cured product was measured using a color difference meter (SE7700, manufactured by Nippon Denshoku Co., Ltd.) against a black background and a white background. The contrast ratio C calculated by the following formula was evaluated as an index of transparency. Note that the closer the contrast ratio C value is to 1, the more opaque the material is, and the closer the value is to 0, the more transparent the material is. Formula: C=Yb / Yw In the formula, Yb means the Y value when the cured product is measured against a black background, and Yw means the Y value when the cured product is measured against a white background.

[0158] (3) Method for Measuring Spectral Reflectance Ratio (SR1 / SR2 Against a Black Background) The spectral reflectance ratio of a cured product of a curable composition was determined by the following procedure. First, the spectral reflectance of the cured product used for the transparency evaluation was measured against a black background using a color difference meter (SE7700, manufactured by Nippon Denshoku Co., Ltd.) in a wavelength range of 380 nm to 780 nm. The spectral reflectance ratio R was then determined based on the following formula: R=SR1 / SR2 where SR1 represents the maximum reflectance in the yellow to red wavelength range (600 nm to 750 nm), and SR2 represents the maximum reflectance in the blue wavelength range (400 nm to 500 nm).

[0159] (4) Measurement Method of Flexural Strength The flexural strength of the cured product was measured by the following procedure. First, a through-hole (length 25 mm, width 2 mm, through-hole length 2 mm) provided in a stainless steel mold was filled with the curable composition, and both end openings of the through-hole were sealed by pressure welding with a polypropylene film. Next, a dental light irradiator (TOKUSO POWER LIGHT, manufactured by Tokuyama Corporation) was positioned so as to be in close contact with the surface of the polypropylene film sealing the opening of the through-hole, and light was irradiated in this state. Light was irradiated at three locations on one opening side of the through-hole (one location in the center of the through-hole and two locations inside the outer edges at both ends of the length direction of the through-hole) and three locations on the other opening side (one location in the center of the through-hole and two locations inside the outer edges at both ends of the length direction of the through-hole). Then, light was irradiated for 20 seconds at each light irradiation location to obtain a cured product. The obtained cured body was adjusted with #1500 waterproof abrasive paper to have dimensions of 25 mm ± 2 mm in length, 2 mm ± 0.1 mm in width, and 2 mm ± 0.1 mm in thickness. The adjusted dimensions of the cured body were used as a test piece to measure bending strength. This test piece was mounted on a precision universal testing machine (Autograph AG5000D, manufactured by Shimadzu Corporation), and the three-point bending fracture strength was measured under conditions of a branch distance of 20 mm and a crosshead speed of 1 mm / min, to obtain a load-deflection curve. The bending strength was then calculated based on the following formula: σB = (3PS) / (2WB ２ ) Here, the symbols in the formula represent σB: bending strength (Pa), P: load (N) at the time of fracture of the test piece, S: distance between supports (m), W: width (m) of the test piece, and B: thickness (m) of the test piece.

[0160] (5) Evaluation Method of Dispersion State (Radial Distribution Function) of Inorganic Spherical Particles The dispersion state (radial distribution function) of inorganic spherical particles in a curable composition was evaluated by the following procedure. A cured product prepared in the same manner as in the transparency evaluation above was subjected to cross-sectional milling using an ion milling device (IM4000, manufactured by Hitachi, Ltd.) at 2 kV for 20 minutes to obtain an observation plane. The cured product was then fixed to a sample stage with carbon paste, and the observation plane was subjected to a conductive treatment (platinum vapor deposition) to prepare a measurement sample. Next, this measurement sample was observed at 10,000x magnification using an electron microscope (JSM-7800F PRIME, manufactured by JEOL Ltd.), and the coordinates of 1,000 inorganic spherical particles in the obtained observation image were determined using image analysis software (Simple Digiizer ver. 3.2, free software). One coordinate of an inorganic spherical particle is arbitrarily selected from the obtained coordinate data, and a circle is drawn with a radius of distance t, which is centered on the selected inorganic spherical particle and includes at least 200 inorganic spherical particles, and the number of spherical particles included in the circle is determined to obtain the average particle density <ρ> (unit: particles / cm ２ ) was calculated. dr is calculated by ０ / 100~r ０ / 10 (r ０ The value is about the average primary particle diameter of the inorganic spherical particles, and the number dn of particles contained in the region between the circle at a distance r from the central inorganic spherical particle and the circle at a distance r + dr from the central inorganic spherical particle, and the area da of the region are calculated. Using the values ​​of <ρ>, dn, and da thus calculated, the following formula was calculated: g(r) = {1 / <ρ>} × {dn / da} to find the radial distribution function g(r). Then, the radial distribution function and r / r ０ (r indicates an arbitrary distance from the center of the circle, r ０ A graph showing the relationship between the average primary particle diameter of the inorganic spherical particles and the particle diameter (r) was created, and based on the graph obtained, an evaluation was made as to whether the following conditions (I) and (II) were satisfied. In Table 5, "A" means that both conditions (I) and (II) are satisfied, and "B" means that both conditions (I) and (II) are not satisfied. (I) The nearest inter-particle distance: r, which is defined as the r corresponding to the peak top of the peak that is closest to the origin among the peaks appearing in the radial distribution function graph. １is the average particle diameter: r ０ (II) The next nearest neighbor particle distance: r, which is defined as the r corresponding to the peak top of the second nearest peak from the origin among the peaks appearing in the radial distribution function graph. ２ and the nearest particle distance: r １ The minimum value of the radial distribution function g(r) between is 0.56 or more and 1.10 or less.

[0161]

[0162]

[0163] Reference Comparative Example 1 is an example of a dental hardenable composition based on an existing structural color, which was prepared to have a spectral reflectance of 1.16 so as to exhibit excellent color compatibility (expressing a structural color in the yellow to red range) when used as a CR for restoring cavities formed in dentin or from enamel to dentin. However, since no radiopaque filler was blended, it did not exhibit sufficient radiographic contrast.

[0164] As can be seen from the results of Reference Comparative Examples 2 to 4, when crystalline rare earth metal fluoride particles are incorporated without being organic-inorganic composited, an improvement in X-ray contrast is observed, but as described above, the crystalline rare earth metal fluoride particles penetrate between the G-PIDs, preventing the formation of a periodic structure, and the condition I in the evaluation of the radial distribution function is not satisfied, resulting in a low spectral reflectance ratio (compared to the value of Comparative Example 1 which does not contain crystalline rare earth metal fluoride particles).

[0165] As can be seen from the results of Reference Comparative Example 5, when crystalline rare earth metal fluoride particles having a full width at half maximum of less than 0.3° are compounded into an organic-inorganic composite and incorporated, the X-ray contrast property and bending strength are improved, and conditions I and II in the evaluation of the radial distribution function are satisfied. However, due to light refraction and scattering between the crystalline rare earth metal fluoride particles and the matrix, the cured body becomes opaque and the spectral reflectance ratio decreases compared to when crystalline rare earth metal fluoride particles are not incorporated (Comparative Example 1).

[0166] As can be seen from the results of Reference Examples 1 to 4, when crystalline rare earth metal fluoride particles having a full width at half maximum of 0.3° or more are combined with an organic-inorganic composite and blended (with a specific X-ray opaque filler), improvements in X-ray contrast and bending strength are observed, as in Reference Comparative Example 5, and further, the decrease in the spectral reflectance ratio is suppressed, maintaining a relatively high spectral reflectance ratio.

[0167] As can be seen from the results of Reference Examples 5 to 13, there is a tendency that the smaller the particle size of the radiopaque filler to be added, the lower the X-ray contrast property and the higher the bending strength, but it is clear that the particle size of the radiopaque filler does not affect the evaluation of transparency, spectral reflectance ratio, or radial distribution function.

[0168] 4. Examples and Comparative Examples Examples 1-10 and Comparative Examples 1-2 (1) Secondary Raw Material Powder Preparation Step In accordance with the method described in "3-1. Production of X-ray Opaque Filler" and "(1) Mechanochemical Treatment of Crystalline Rare Earth Metal Fluoride Powder," a highly crystalline rare earth metal fluoride powder (YbF3-40) was subjected to wet mechanochemical treatment under the conditions shown in Table 6. The resulting slurry was spray-dried using a disk-type spray dryer at a slurry concentration of 30-40 wt %, a rotation speed of 18,000-20,000 rpm, and an inlet temperature of 200-300°C, yielding secondary raw material powders SF-1 to SF-5. The average primary particle diameter and full width at half maximum of the secondary raw material powders thus obtained were measured in the same manner as in the Reference Example. The results are shown in Table 6.

[0169]

[0170] (2) Step of preparing curable raw material composition Using a two-axis planetary kneading machine capable of vacuum and pressure reduction operation, 100 parts by mass of monomer composition M1 and the secondary raw material powder and granules were kneaded in the amount ratio and under the conditions shown in Table 7, with the temperature inside the kneading machine maintained at 25 to 50°C. Table 7 also shows the results of whether kneading was possible without any problems (kneadability). In Table 7, "A" means that kneading was possible, and "B" means that kneading was not possible.

[0171]

[0172] As shown in Table 7, Comparative Example 1 was an example in which kneading was performed under atmospheric pressure without reducing the pressure. However, when kneading was performed under atmospheric pressure, the polymerizable monomer did not penetrate the secondary raw material powder particles, and the mixture did not become a paste, making it impossible to knead the curable raw material composition. Furthermore, as can be seen from the results of Comparative Example 2, when the degree of vacuum was high, the powder and polymerizable monomer scattered during decompression, making it impossible to knead the curable raw material composition. As can be seen from the results of Example 1, kneading the curable raw material composition under reduced pressure was possible. Furthermore, as can be seen from the results of Examples 1 to 5, increasing the pressure made the curable raw material composition more easily aggregated and shortened the kneading time. Furthermore, as can be seen from the results of Examples 7 to 10, kneading was possible under reduced pressure when 70 to 90 parts by mass of secondary raw material powder particles were used per 100 parts by mass of polymerizable monomer.

[0173] (2) Curing and Granulation Steps Next, for systems that could be kneaded, the resulting curable raw material composition was cured using a nitrogen pressure heat polymerization reactor (Poliner, manufactured by Towa Giken Co., Ltd.) to form a mass, which was then heated under nitrogen pressure at 100°C for 30 minutes to form a mass. The resulting cured product and zirconia balls (diameter: 25 mm) were then placed in a zirconia pot and rotary ground for 60 minutes to obtain a pulverized cured product. Further, coarse particles were removed from the pulverized product using a stainless steel sieve with 45 μm openings, yielding a powder (radiopaque filler) with the average particle size shown in Table 7.

[0174] Using the radiopaque filler thus obtained, a curable composition was prepared and evaluated in the same manner as in Reference Example, and the same results as in Reference Example were obtained.

Claims

1. A method for producing an X-ray opaque filler that imparts X-ray opacity to a dental curable composition and its cured form by incorporating a polymerizable monomer into the dental curable composition, When X-ray diffraction measurements are performed on granular materials consisting of crystalline rare-earth metal fluoride particles, granular materials with a full width at half maximum (FMAX) of the maximum intensity peak in the obtained X-ray diffraction pattern are defined as "highly crystalline rare-earth metal fluoride granular materials" if the FMAX is less than 0.3°, and granular materials with a FMAX of 0.3° or more are defined as "lowly crystalline rare-earth metal fluoride granular materials." The aforementioned X-ray opaque filler is mainly composed of organic-inorganic composite particles made of a composite material in which low-crystalline rare-earth metal fluoride powders are dispersed in a resin matrix, and whose average particle size, as measured by laser diffraction and scattering, is 3 to 110 μm. The aforementioned method, A secondary raw material powder preparation step involves mechanochemically treating a raw material slurry in which primary raw material powders consisting of highly crystalline rare earth metal fluoride powders having an average primary particle size of 1 to 500 nm as measured by electron microscope observation are dispersed in a dispersion medium to obtain a treated slurry liquid in which low-crystalline rare earth metal fluoride powders are dispersed in the dispersion medium, and then spray-drying the obtained treated slurry liquid to obtain secondary raw material powders consisting of low-crystalline rare earth metal fluoride powders; 100 parts by mass of polymerizable monomer to be used as raw material for the resin matrix, and 150 to 900 parts by mass of the secondary raw material powder / granules, in a ratio of 1.0 to 1.0 × 10 ５ A process for preparing a curable raw material composition, which involves kneading under a pressure of (Pa) to obtain a curable raw material composition; A curing step of curing the curable raw material composition to obtain a lump made of a composite material in which low-crystalline rare-earth metal fluoride particles are dispersed in a resin matrix; and A granulation process in which the aggregate is crushed and then the particle size is adjusted so that the average particle size is 3 to 110 μm; including, A method for producing an X-ray opaque filler, characterized by the following features.

2. The method for producing an X-ray opaque filler according to claim 1, wherein the amount of the secondary raw material powder used in the curable raw material composition preparation step is 230 to 900 parts by mass per 100 parts by mass of the polymerizable monomer.

3. A method for producing an X-ray opaque filler according to claim 1, wherein the kneading in the curable raw material composition preparation step is performed at 100 to 35,000 (Pa).

4. Polymerizable monomer: 100 parts by mass, An X-ray opaque filler mainly composed of organic-inorganic composite particles made of a composite material in which low-crystallinity rare-earth metal fluoride powders are dispersed in a resin matrix, with an average particle size of 3 to 110 μm as measured by laser diffraction and scattering: in terms of the total mass of the low-crystallinity rare-earth metal fluoride powders: 1 to 100 parts by mass, One or more "groups of spherical particles of the same particle size" consisting of an aggregate of inorganic spherical particles having a predetermined average primary particle size, the average primary particle size measured by electron microscopy being within the range of 100 to 1000 nm, wherein the individual inorganic spherical particles constituting the aggregate are composed of substantially the same substance, and in the particle size distribution based on the number of particles of the aggregate, 90% or more of the total number of particles are located within 5% before or after the predetermined average primary particle size: 10 to 1500 parts by mass in total, and Polymerization initiator: 0.01 to 10 parts by mass A method for producing a dental curable composition that, by mixing, can produce a cured body exhibiting a predetermined structural color regardless of the angle of incidence of light and having X-ray contrast properties, The step of preparing the aforementioned radiopaque filler further includes the step of manufacturing the radiopaque filler by the manufacturing method described in claim 1, In this process, the refractive index of the cured polymerizable monomer with respect to sodium d lines at 25°C is set to n （ＭＸ） The refractive index of the resin material constituting the resin matrix of the organic-inorganic composite particles constituting the X-ray-impermeable filler is set to n at 25°C for sodium d rays. （F―ＭＸ） In this case, the polymerizable monomer that is actually mixed is the n （ＭＸ） and the aforementioned n （F―ＭＸ） The absolute value of the difference: |n （ＭＸ） -n （F―ＭＸ） The X-ray opaque filler is manufactured using a polymerizable monomer that serves as a raw material for the resin matrix, such that the condition that | is between 0 and 0.1 is satisfied. A method for producing a dental hardening composition characterized by the above.

5. When the number of "spherical particle groups with the same particle size" in the one or more "spherical particle groups with the same particle size" is set as a, each "spherical particle group with the same particle size" is represented as G-PID in ascending order of its average primary particle size ｍ (However, m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more.) and each of the above G-PID ｍ The refractive index of the inorganic spherical particles constituting the sodium d line at 25 ° C is n （Ｇ－ＰＩＤｍ） When it is set as, Each G-PID when a is 2 or more ｍ The materials that make up each individual particle may be different from each other. In the case of each G-PID ｍ The average primary particle diameters differ from each other by more than 25 nm. Which n （Ｇ－ＰＩＤｍ） Even for n （ＭＸ） <n （Ｇ－ＰＩＤｍ） The relationship holds true. A method for producing the dental curable composition according to claim 4.