Curable dental composition

Abstract

The present invention imparts X-ray opacity to "a curable dental composition with existing structural color system" without adversely affecting the desired structural color development and transparency in a cured body thereof, the composition containing a polymerizable monomer and specific inorganic spherical particles and being known as providing a cured body that develops a structural color of a predetermined tone regardless of the angle of incidence of light.　For this purpose, a preset amount of an X-ray opacifying filler is blended with the aforesaid "curable dental composition with existing structural color system". The X-ray opacifying filler comprises organic-inorganic composite particles in which a preset amount of rare earth metal fluoride particles are dispersed in a resin matrix, wherein: the full width at half maximum intensity peak assignable to the rare earth metal fluoride particles is 0.3° or more when measured by X-ray diffractometry; and the refractive index difference between the resin matrix and the polymerizable monomer in "the curable dental composition with existing structural color system" is 0.1 or less.

Description

dental curable composition

[0001] The present invention relates to dental hardenable compositions.

[0002] In dental treatment, after caries removal, a dental filling material called a dental composite resin (hereinafter simply referred to as "CR") is filled into the cavity, and then the cavity is sealed by hardening the dental filling material. Generally, a hardenable composition containing a polymerizable monomer, a filler, and a polymerization initiator as main components is used as such a dental filling material.

[0003] Restorations using dental composite resins (CR) (CR restorations) have rapidly become popular because they require less tooth removal, can achieve a color tone similar to natural tooth color, and are easy to operate. In recent years, due to their improved mechanical strength and adhesive strength to the teeth, they have been used not only for restoring anterior teeth, but also for restoring molars, which are subject to high occlusal pressure.

[0004] 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.

[0005] 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).

[0006] 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.

[0007] 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).

[0008] (A) The composition contains a polymerizable monomer (A), inorganic particles (B), and a photopolymerization initiator (C) as constituent components.

[0009] (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 ｍThe materials constituting the individual particles may be different from each other, and in this case, each G-PID ｍ 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 （ＭＸ） <n （Ｇ－ＰＩＤｍ） The above relationship must be satisfied.

[0010] (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):

[0011] [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 １is 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.

[0012] (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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] Meanwhile, as a means for improving the radiopacity of a cured product of a hardenable composition used for various applications, such as the dental hardenable compositions exemplified above, a method using a filler containing an atom with a large atomic number is known. For example, Patent Document 3 proposes a technique using a filler made of a fluoride of a rare earth metal with an atomic number of 57 to 71.

[0017] International Publication No. 2017 / 069274 Pamphlet International Publication No. 2020 / 050123 Pamphlet Japanese Patent Publication No. 3-17803

[0018] However, when a rare earth metal fluoride is used as a radiopaque filler to be blended into a curable composition, the transparency of the cured body decreases as the content of rare earth metal fluoride increases, as shown in Figure 2 of Patent Document 3. For this reason, with conventional curable compositions using rare earth metal fluorides, radiopaqueness must be sacrificed in order to obtain a cured body with high transparency, making it difficult to obtain a cured body with both excellent radiopaqueness and transparency.

[0019] Furthermore, according to the studies of the present inventors, when a rare earth metal fluoride is blended as an X-ray opaque filler in an existing structural color dental curable composition, not only is the color harmony impaired due to the decrease in transparency, but the expression of the desired structural color may also be adversely affected (see Comparative Examples 2 to 5 described below).

[0020] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a dental curable composition which has X-ray opacity when cured and can be suitably used as a structural color CR capable of aesthetic restoration.

[0021] The present invention solves the above-mentioned problems, and an embodiment of the present invention comprises: 100 parts by mass of a polymerizable monomer; 10 to 1,500 parts by mass of one or more "same-particle-size spherical particle groups" (G-PID) in total, which are composed of an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 to 1,000 nm, and in which the individual inorganic spherical particles constituting the aggregate are composed of substantially the same material, and in a number-based particle size distribution of the aggregate, 90% or more of the total number of particles are present within a 5% range around the predetermined average primary particle diameter; and a polymerization initiator, wherein when the number of the one or more "same-particle-size spherical particle groups" is defined as a, each "same-particle-size spherical particle group" is classified into G-PIDs in ascending order of their 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-PID ｍ The 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） | is 0 to 0.1.

[0022] In the dental curable composition (hereinafter also referred to as "dental curable composition of the present invention"), the content of the crystalline rare earth metal fluoride particles in the organic-inorganic composite particles constituting the radiopaque filler is preferably 60 to 90 mass % based on the total mass of the organic-inorganic composite particles, and the average particle size of the organic-inorganic composite particles is preferably 22 μm to 70 μm. Furthermore, the rare earth metal fluoride particles are preferably ytterbium fluoride particles.

[0023] Furthermore, it is preferable that the average primary particle size of all of the "spherical particles of the same particle size" (G-PID) contained in the dental hardenable composition of the present invention is within the range of 230 to 350 nm.

[0024] In addition, it is preferable that the dental curable composition of the present invention does not contain any rare earth metal fluoride particles other than the rare earth metal fluoride particles blended as the X-ray opaque filler, or that the content of such particles is 5 parts by mass or less per 100 parts by mass of the polymerizable monomer.

[0025] In addition, the Y value, which is an index of transparency of the cured product of the dental curable composition, is measured on a 1 mm thick cured product sample using a color difference meter against a black background. ｂ and Y, the Y value measured under a white background. ｗ Ratio to: Y ｂ / Y ｗ It is preferable that the cured product has a contrast ratio C defined as: 0.20 to 0.50.

[0026] The amount of the polymerization initiator to be blended relative to 100 parts by mass of the polymerizable monomer is preferably 0.01 to 0.5 parts by mass. Furthermore, the full width at half maximum is preferably 40° or less.

[0027] According to the present invention, the structural color dental curable composition of the present invention, which is obtained by blending a predetermined amount of a specific radiopaque filler into a dental curable composition known to be used as a structural color CR, can impart high radiopacity to the cured product when used as a CR without impairing the excellent features of the structural color CR.

[0028] 1 shows X-ray contrast images of the cured products of the dental hardenable compositions of Examples 1, 13, and 19 and Comparative Examples 1 and 4, and aluminum materials having thicknesses of 1 mm, 2 mm, 3 mm, and 4 mm.

[0029] The present inventors have conducted extensive research to solve the problem that it is difficult to obtain a cured product that is excellent in both radiopacity and transparency when using conventional curable compositions that use a rare earth metal fluoride as the main component constituting a radiopaque filler.

[0030] As a result, they have found that the curable composition containing the powder of crystalline rare earth metal fluoride particles such as crystalline ytterbium fluoride can improve the X-ray opacity without reducing the transparency of the cured product.Then, based on this finding, they have further researched and found that this phenomenon occurs when (i) the crystallinity of crystalline rare earth metal fluoride particles is reduced by mechanochemical treatment, and (ii) the full width at half maximum (FWHM) of the maximum intensity peak of crystalline rare earth metal fluoride measured by X-ray diffraction measurement, which corresponds to the crystallite diameter as an index of crystallinity, becomes more than a certain value (when the degree of crystallinity is reduced to more than a certain level), and have already proposed a new X-ray opaque filler made of rare earth metal fluoride particles with this specific crystallinity (PCT / JP2022 / 031237).

[0031] The inventors further investigated the radiopaque filler and found that a relatively large amount is required to obtain sufficient radiopacity, and that when the filler is added to a structural color system CR, it tends to be difficult to achieve the desired structural color (see Comparative Examples 3 and 4 described below).

[0032] As a result of further investigation, it was found that when crystalline rare earth metal fluoride particles with a FWHM of a certain level or more are compounded with an organic resin in advance to form organic-inorganic composite particles (specific X-ray opaque filler), high X-ray opacity can be imparted even when the amount of rare earth metal fluoride particles compounded is small, and further, even when compounded with structural color CR, X-ray opacity can be imparted without significantly adversely affecting the expression of the desired structural color, which led to the completion of the present invention.

[0033] As described above, the dental curable composition of the present invention is characterized by the incorporation of a specific radiopaque filler. Therefore, the specific radiopaque filler and its manufacturing method will be explained first, followed by a detailed description of the dental curable composition of the present invention.

[0034] 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."

[0035] 1. Regarding the specific radiopaque filler (1) Overview of the specific radiopaque filler The specific radiopaque filler is composed of organic-inorganic composite particles in which a plurality of crystalline rare earth metal fluoride particles, each having a full width at half maximum (unit: °) of 0.3° or more when the crystallinity of each crystalline rare earth metal fluoride particle constituting a powder made of 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 performing X-ray diffraction measurement on the powder, are dispersed in a resin matrix.

[0036] The specific X-ray opaque filler is usually composed only of the organic-inorganic composite particles (hereinafter also referred to as "particle bodies"), but may also contain external additive particles such as silica or titanium oxide (fine particles). 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 a 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 been surface-treated with a known surface treatment agent such as a silane coupling agent or a titanate coupling agent.

[0037] 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.

[0038] 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 made of crystalline rare earth metal fluoride particles to determine the crystallinity of the individual crystalline rare earth metal fluoride particles constituting the powder.

[0039] Crystalline rare earth metal fluoride particles with a full width at half maximum of 0.3° or more do not significantly reduce the transparency of the dental curable composition cured product, even when incorporated directly into a dental curable composition without being composited with an organic resin to form organic-inorganic composite particles (see PCT / JP2022 / 031237 and Comparative Examples 3 and 4 described below). The reason for this effect is 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 amorphousize 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 with 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.

[0040] Even when a specific X-ray opaque filler is used as the polymerizable monomer of the dental hardenable composition, the refractive index of the hardened 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 cured product of the dental curable composition are integrated together), and the above-mentioned properties of crystalline rare earth metal fluoride particles having a full width at half maximum of 0.3° or more are exhibited.

[0041] As described above, by setting the full width at half maximum of the crystalline rare earth metal fluoride particles to 0.3° or more, when a curable composition containing the radiopaque filler of the present invention is cured, a cured product having excellent radiopacity and transparency can be easily obtained. In other words, even if the amount of the radiopaque filler of this embodiment blended into 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.

[0042] When crystalline rare earth metal fluoride particles having a full width at half maximum of less than 0.3° are blended in an amount necessary to impart radiopacity, either as they are 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 Comparative Examples 2 and 5 described below).

[0043] (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.

[0044] Next, peaks attributable to the rare earth metal fluoride particles 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, when the material of the rare earth metal fluoride particles 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.

[0045] The full width at half maximum of the crystalline rare earth metal fluoride particles 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 particles 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.

[0046] (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. When used for various purposes, the material of the rare earth metal fluoride particles can be, for example, lanthanum fluoride (LaF ３ ), cerium fluoride (CeF ３ ), or ytterbium fluoride (YbF ３ ) is preferable, and among these, ytterbium fluoride (YbF ３ ) is more preferred.

[0047] Furthermore, when the specific radiopaque filler is used for dental purposes, the material of the rare earth metal fluoride particles is preferably lanthanum fluoride (LaF), from the viewpoint of easily ensuring a color tone and safety suitable for dental purposes. ３ ), cerium fluoride (CeF ３ ), or ytterbium fluoride (YbF ３ ), and from the viewpoint of ensuring X-ray opacity, ytterbium fluoride (YbF ３ ) is particularly preferred.

[0048] The resin material constituting the resin matrix of the organic-inorganic composite particles (particle bodies) is not particularly limited, and known resin materials can be appropriately selected, for example, (meth)acrylic resins, polyaryletherketone resins, etc. In this specification, "(meth)acrylic resin" means a polymer polymerized using only (meth)acrylate monomers as the polymerizable monomers used in the polymerization of the (meth)acrylic resin, or a polymer in which the proportion of (meth)acrylate monomers in all polymerizable monomers is 50 mol % or more when two or more types of polymerizable monomers including a (meth)acrylate monomer are used.

[0049] In the specific X-ray opaque filler, a suitable combination of materials constituting the organic-inorganic composite particles (particle body) is a combination of lanthanum fluoride (LaF) as the material of the (A1 group) rare earth metal fluoride particles. ３ ), cerium fluoride (CeF ３ ) and ytterbium fluoride (YbF ３ ) and (B) a (meth)acrylic resin as a resin material constituting the resin matrix. Particularly preferred combinations include (A2) a rare earth metal fluoride particle containing ytterbium fluoride (YbF ３ and (Group B) a (meth)acrylic resin as a resin material constituting the resin matrix.

[0050] The content of the rare earth metal fluoride particles in the organic-inorganic composite particles (particle bodies) is not particularly limited, but is preferably 60% by mass or more, more preferably 70% by mass or more, based on the total mass of the organic-inorganic composite particles, and the upper limit of the content is preferably 90% by mass or less, more preferably 80% by mass or less.

[0051] The average particle size of the organic-inorganic composite particles (particle bodies) is not particularly limited, but from the viewpoint of achieving a good balance between X-ray contrast properties and mechanical strength, it is preferably 22 to 70 μm, more preferably 24 to 55 μm. Furthermore, when ensuring mechanical strength is more important than X-ray contrast properties, 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 properties is more important than mechanical strength, the average particle size is preferably 38 μm or more, more preferably 70 μm or more. The lower limit is not particularly limited, but from the viewpoint of ensuring a certain level of mechanical strength or more, 110 μm or less is preferred.

[0052] 2. Method for Producing Specific Radiopaque Filler The method for producing the specific radiopaque filler (also referred to as the present production method) is not particularly limited as long as it is a method for granulating organic-inorganic composite particles using rare earth metal fluoride particles having a full width at half maximum of 0.3° or more and a resin material or a resin material precursor (polymerizable monomer, etc.), and any known method for producing organic-inorganic composite particles can be used as appropriate.

[0053] However, the full width at half maximum of rare earth metal fluorides generally used as radiopaque materials and commercially available rare earth metal fluoride powders available as raw material powders is usually less than 0.3° (specifically, about 0.17° to 0.27°). For this reason, it is preferable to employ the present manufacturing method because the specific radiopaque filler can be efficiently manufactured using such rare earth metal fluoride powder.

[0054] That is, it is preferable to adopt a manufacturing method including: a secondary raw material powder preparation step of mechanochemically treating a primary raw material powder consisting of a powder mainly composed of crystalline rare earth metal fluoride particles having a full width at half maximum of less than 0.3° to obtain a secondary raw material powder consisting of a powder mainly composed of rare earth metal fluoride particles having a full width at half maximum of 0.3° or more; a curing step of curing a raw material composition obtained by mixing raw materials including the polymerizable monomer that is a raw material of the resin matrix and the secondary raw material powder to obtain a cured product; and a pulverizing step of pulverizing the cured product.

[0055] Each step of the present production method will be described below. The hardening step and the pulverization step may be collectively referred to as a granulation step.

[0056] (1) Secondary Raw Material Powder Preparation Step In the secondary raw material powder preparation step, a primary raw material powder consisting of a powder mainly composed of crystalline rare earth metal fluoride particles having a full width at half maximum of less than 0.3° is mechanochemically treated to obtain a secondary raw material powder consisting of a powder mainly composed of rare earth metal fluoride particles having a full width at half maximum of 0.3° or more. Here, "mainly composed of" means that the powder may contain trace amounts of substances other than crystalline rare earth metal fluoride particles, such as surface treatment agents or additives that are physically attached to or chemically bonded to the surfaces of the crystalline rare earth metal fluoride particles, and the full width at half maximum of the crystalline rare earth metal fluoride particles must be less than 0.3° or 0.3° or more.

[0057] As the primary raw material powder, there can be used, without particular limitation, rare earth metal fluorides that are generally used as X-ray opaque materials, or commercially available rare earth metal fluoride powders that are available as raw material powders and have a full width at half maximum of less than 0.3° (specifically, about 0.17° to 0.27°). It is preferable to measure the full width at half maximum by X-ray diffraction measurement of the primary raw material powder as necessary.

[0058] 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.

[0059] In the mechanochemical treatment in the secondary raw material powder preparation process, depending on the treatment conditions, prolonging the treatment time can cause the particles contained in the raw material powder to be pulverized, resulting in the disintegration of secondary particles (aggregated particles) and primary particles, resulting in a smaller particle size. However, treatment times of several hours or so result in the disintegration of coarse aggregated particles, but do not significantly change the particle size of primary particles or submicron-level aggregated particles. For these reasons, the raw material powder preferably has an average primary particle size of 1 to 500 nm, more preferably 5 to 300 nm, as measured by electron microscopy. Furthermore, the average particle size measured by laser diffraction / scattering, which can also measure aggregate particle size, is preferably 0.1 to 0.6 μm, more preferably 0.1 to 0.3 μm. The average primary particle size is a value 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.

[0060] (2) Mechanochemical Treatment Mechanochemical treatment refers to a treatment that applies mechanical energy to a raw material powder, specifically at least one treatment 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 preferred as the mechanochemical treatment method, 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.

[0061] The mechanochemical treatment using a wet bead mill will be described in detail below.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] The secondary raw material powder (mechanochemically treated rare earth metal fluoride particles) adjusted to a full width at half maximum of 0.3° or more by mechanochemical treatment is typically subjected to appropriate post-treatment processes such as concentration, drying, and filtration. This results in a raw material powder (raw material powder for granulation) for granulating organic-inorganic composite particles. If a polymerizable monomer is used as a medium during mechanochemical treatment, the post-treatment process can be omitted. In this case, other components such as a polymerization initiator can be added to the mechanochemically treated slurry (a composition containing the raw material powder and the polymerizable monomer) as needed before granulating the organic-inorganic composite particles. Furthermore, the raw material powder that has undergone the mechanochemical treatment and post-treatment processes may be surface-treated to improve its affinity with the resin matrix raw material used to granulate the organic-inorganic composite particles. Commonly used surface treatment agents, such as silane coupling agents and titanate coupling agents, can be used.

[0068] (3) Granulation Process When granulating the organic-inorganic composite particles, a granulation process is carried out using a secondary raw material powder and a resin matrix raw material. The full width at half maximum of the secondary raw material powder 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 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.

[0069] In this manufacturing method, the granulation process for the organic-inorganic composite particles includes a curing process in which a raw material composition obtained by mixing a polymerizable monomer that is the raw material for the resin matrix of the organic-inorganic composite particles and raw materials including the secondary raw material powder is cured to obtain a cured product, and a crushing process in which the cured product is crushed.

[0070] As the polymerizable monomer serving as the raw material for the resin matrix of the organic-inorganic composite particles, known polymerizable monomers such as radically polymerizable monomers can be used, but it is particularly preferable to use (meth)acrylate monomers. Furthermore, various polymerization initiators such as chemical polymerization initiators, photopolymerization initiators, and thermal polymerization initiators, as well as other additives, can also be used in the granulation raw material composition as needed. Specific examples of the polymerizable monomers, polymerization initiators, and other additives are the same as those used in the curable composition of this embodiment, which will be described later. The resin matrix constituting the organic-inorganic composite particles (particle bodies) obtained by the first granulation method is composed of a material obtained by curing the remaining components (mainly polymerizable monomers) from the granulation raw material composition, excluding the raw material powder.

[0071] 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 can take similar values ​​as described above, it becomes easier to improve the transparency of a curable composition using a radiopaque filler.

[0072] 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.

[0073] The pulverization step can be performed by a known pulverization method using a ball mill, etc. 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.

[0074] In addition, when a thermoplastic resin such as a polyaryl ether ketone resin is used as the resin matrix of the organic-inorganic composite particles, the organic-inorganic composite particles can be produced as a specific X-ray opaque filler by adopting a granulation method that includes at least a melt-kneading step of melt-kneading a granulation raw material composition containing at least a secondary raw material powder and a thermoplastic resin to obtain a molten kneaded product, and a pulverization step of pulverizing the solidified product obtained by cooling and solidifying the molten kneaded product.

[0075] In this case, other additives can also be used in the granulation raw material composition as needed. Specific examples of other additives that can be used include those used in the dental curable composition of the present invention, which will be described later. As a method for melt-kneading the granulation raw material composition, known melt-kneading methods can be used, such as the melt-kneading method disclosed in International Publication No. 2013 / 88921. The resin matrix that constitutes the organic-inorganic composite particles (particle bodies) obtained by the second granulation method is composed of the remaining components (mainly thermoplastic resins) from the granulation raw material composition excluding the raw material powder.

[0076] 3. Dental hardenable composition of the present invention (1) Overview of the dental hardenable composition of the present invention The dental hardenable composition of the present invention is mainly characterized in that a predetermined amount of a specific radiopaque filler is blended into a dental hardenable composition used as a conventionally known structural color CR (existing structural color dental hardenable composition).

[0077] Here, the existing structural color dental curable composition refers to a dental curable composition that contains predetermined amounts of a polymerizable monomer, an inorganic filler, and a polymerization initiator, as already explained as the prior art, and that uses a filler that includes spherical inorganic particles having a specific average particle size and particle size distribution, i.e., one or more "groups of uniform particle size spherical particles" (G-PID), and that has a refractive index that is greater than the refractive index of a resin part that becomes a 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 wherein 90% or more of the total number of particles in the number-based particle size distribution of the aggregate are present within a range of 5% around the predetermined average primary particle diameter: 10 to 1500 parts by mass in total; and 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] The dental hardenable composition of the present invention is characterized in that, in addition to the above-mentioned existing structural color dental hardenable compositions, the following conditions 4 and 5 are satisfied:

[0082] Condition 4: Specific radiopaque filler: The radiopaque filler further contains 1 to 100 parts by mass, calculated as the total mass, of crystalline rare earth fluoride metal particles having a full width at half maximum of 0.3° or more.

[0083] Condition 5: Refractive index of the cured product of the polymerizable monomer at 25°C for sodium d line: n （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） | is between 0 and 0.1.

[0084] In other words, by further satisfying these conditions 4 and 5, it becomes possible to impart high radiopacity to the cured product without impairing the excellent features of existing structural color dental hardenable compositions, which are that "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 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 with an average primary particle size of 230 to 350 nm are used, it is possible to color the composition in yellow to red, which is similar to the color of dentin, and furthermore, (iii) since the cured product has appropriate transparency, it is easy to match 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."

[0085] The dental hardenable composition of the present invention has such a feature that the state of structural color expression in the cured product is almost the same as 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 of the present invention to that of the base existing structural color dental hardenable composition. １ / SR ２ This can be confirmed by comparing the above SR １ and S.R. ２ The 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.

[0086] 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.

[0087] The dental curable composition of the present invention that satisfies the above conditions 4 and 5 is made to exhibit high X-ray opacity in the cured product by blending a specific X-ray opaque filler into a base existing structural color dental curable composition, but is difficult to change the spectral reflectance ratio, and can maintain a spectral reflectance ratio of, for example, 0.9 or more without blending a toning agent such as a pigment.

[0088] Regarding point (iii), the dental curable composition of the present invention can provide a cured product having a contrast ratio C of 0.20 to 0.50, preferably 0.25 to 0.45. 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.

[0089] If the contrast ratio of the cured product of the dental hardenable composition of the present invention is less than 0.20, the brightness (color density) of the cured product at the filled area will be low, the transmitted light at the filled area will be strong, 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.

[0090] 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 rare earth metal fluoride particles is that when rare earth metal fluoride particles are blended as they are, the individual particles, which have weak X-ray opacity (small), are uniformly dispersed, causing the overall X-ray opacity to become blurred, whereas when they are 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 rare earth metal fluoride particles into structural color CR does not adversely affect the expression of the desired structural color, if rare earth metal fluoride particles are blended as they are, the particles will enter between the particles of a 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 rare earth metal fluoride particles into organic-inorganic composite particles, the absolute number of particles decreases compared to when rare earth metal fluoride particles are blended as they are, reducing the frequency of disrupting the periodic structure of the G-PID. Furthermore, the organic-inorganic composite increases the particle diameter, making it less likely for the particles to enter between the periodic structures of the G-PID. In other words, by converting rare earth metal fluoride particles into organic-inorganic composite particles, it becomes less likely to disrupt the periodic structure formed by the G-PID, and it is thought that this does not adversely affect the expression of the desired structural color.

[0091] (2) Regarding the Existing Structural Color Dental Curable Composition and Components of the Dental Curable Composition Except for the inclusion of a predetermined amount of a specific radiopaque filler, the components constituting the dental curable composition of the present invention and the amounts blended are basically the same as the components and amounts blended in the existing structural color dental curable compositions disclosed in Patent Documents 1 and 2. Therefore, we will briefly explain these components and then explain the dental curable composition of the present invention.

[0092] (2-1) Polymerizable Monomers Polymerizable monomers used in existing structural color dental curable compositions and dental curable compositions can be any polymerizable monomer that can be used in conventional dental curable compositions without any particular limitations, but it is preferable to use a (meth)acrylate-based monomer. Specific examples of suitable (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, 2,2,3,3-tetrafluoropropyl methacrylate (TFM), 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)acryloyloxypolyethoxyphenyl]propane (D-2,6E), 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.

[0093] 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.

[0094] 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.

[0095] In the dental hardenable composition of the present invention, from the viewpoint of not reducing the transparency of the cured product of the dental hardenable composition, |n （ＭＸ） -n （F―ＭＸ）| must be 0 to 0.1, preferably 0 to 0.07, more preferably 0 to 0.05, and particularly preferably 0 to 0.035. 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.

[0096] (2-2) Group of spherical particles of the same particle size: G-PID The group of spherical particles of the same particle size: G-PID used in the existing structural color dental curable composition and dental curable composition is composed of an aggregate of inorganic spherical particles having a predetermined average primary particle size within the range of 100 nm or more and 1000 nm or less (100 to 1000 nm), and refers to the aggregate in which the individual inorganic spherical particles constituting the aggregate are composed of substantially the same material and in which 90% or more of the total number of particles exists within a range of 5% around the predetermined average primary particle size in the number-based particle size distribution of the aggregate.

[0097] The average primary particle diameter of inorganic spherical particles referred to here means the average value obtained by taking a photograph of the 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) of each. Furthermore, "spherical" means that the particles are approximately spherical, and do not necessarily have 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.

[0098] In existing structural color dental curable compositions and cured products of dental curable compositions, the constituent particles of G-PID have a specific short-range order structure and are dispersed in a resin matrix, causing diffraction interference in accordance with the Bragg condition, emphasizing light of a specific wavelength and producing 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 structural colors with specific color tones 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.

[0099] 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.

[0100] The G-PID contained in the existing structural color dental curable composition and the dental curable composition 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 order of smallest to largest 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.) 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.

[0101] When existing structural color dental curable compositions and dental curable compositions contain multiple types of G-PIDs, each G-PID has an extremely sharp particle size distribution and differs in average primary particle diameter as described above, making it difficult for the particle size distributions of each G-PID to overlap. Even if they overlap partially, it is possible to confirm the particle size distribution of each G-PID. That is, the particle size distribution of the inorganic particles contained in the composite material according to this embodiment has the same number of independent peaks as the number of G-PIDs contained in the composite material in the 100 to 1,000 nm range. Even if the peaks partially overlap, the average primary particle diameter and number-based particle size distribution of each G-PID can be confirmed by performing waveform processing. Furthermore, the particle size distribution of the inorganic particles contained in the present invention can also be confirmed, for example, by image processing an electron microscope photograph of the inner surface of the composite material according to this embodiment.

[0102] 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.

[0103] (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.

[0104] 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%.

[0105] 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.

[0106] (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 composition 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 of the dental curable composition, 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

[0107] 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.

[0108] 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.

[0109] (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).

[0110] 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.

[0111] 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, it is preferable that the refractive index at 25°C of the cured product of the polymerizable monomer in the subsequent 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) is n, because the transparency of the cured product of the dental curable composition is unlikely to decrease.（ＭＸ） and the n' （F―ＭＸ） Absolute value of the difference with: |n （ＭＸ） -n' （F―ＭＸ） | must be between 0 and 0.1.

[0112] 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.

[0113] (2-6) G-PID Content The total content of G-PID in existing structural color dental curable compositions and the structural color dental curable composition of the present invention is 10 to 1,500 parts by mass per 100 parts by mass of the polymerizable monomer. Because the resulting composite material has appropriate transparency and a high structural color development effect, the total content is preferably 50 to 1,500 parts by mass, more preferably 100 to 1,500 parts by mass, even more preferably 100 to 450 parts by mass, and particularly preferably 150 to 400 parts by mass. When multiple types of G-PID are included, 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.

[0114] (2-7) Polymerization Initiator The polymerization initiator used in the existing structural color dental curable composition and the dental curable composition can be the same as the polymerization initiator used in the dental curable composition of the present invention. Because curing is often performed in the oral cavity, it is preferable to use a chemical polymerization initiator and / or a photopolymerization initiator. Photopolymerization initiators are more preferable because they do not require a mixing operation. These polymerization initiators may be used alone or in combination of two or more. The amount of polymerization initiator may be selected based on the intended purpose. The amount is typically 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, even more preferably 0.2 to 1.5 parts by weight, and even more preferably 0.01 to 0.5 parts by weight, per 100 parts by weight of polymerizable monomer.

[0115] 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.

[0116] 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.

[0117] (2-8) Specific Radiopaque Filler The specific radiopaque filler has already been described. The specific radiopaque filler to be blended in the dental hardenable composition of the present invention is a filler having a refractive index of n at 25°C for sodium d-line of the hardened product of the polymerizable monomer in the dental hardenable composition of the present invention. （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） | 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） is preferably 0 to 0.07, more preferably 0 to 0.05, and particularly preferably 0 to 0.035.

[0118] From the viewpoints of radiopacity, transparency, and structural color expression of the cured product, the amount of the specific radiopaque filler to be blended in the dental curable composition of the present invention is 1 to 100 parts by mass, preferably 15 to 75 parts by mass, and more preferably 28 to 80 parts by mass, per 100 parts by mass of the polymerizable monomer, calculated as the total mass of the crystalline rare earth fluoride metal particles having a full width at half maximum of 0.3° or more contained in the radiopaque filler of the present invention. If the amount is less than 1 part by mass (the lower limit), sufficient radiopacity cannot be obtained, and if the amount is more than 100 parts by mass (the upper limit), transparency and structural color expression are significantly reduced.

[0119] (2-9) Other Fillers The dental curable composition of the present invention may contain ultrafine particles (G-SFP), which are particle aggregates made of inorganic particles having an average primary particle diameter of less than 100 nm, for the purpose of adjusting the viscosity or the transparency of the cured product. 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 G-PIDs to be contained. 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.

[0120] Furthermore, the dental curable composition of the present invention may contain rare earth metal fluoride particles other than the rare earth metal fluoride particles incorporated as the specific radiopaque filler, as long as the effects of the present invention are not significantly impaired. The amount of such rare earth metal fluoride particles incorporated 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.

[0121] (2-10) Other Additives, etc. The dental curable composition of the present invention may contain other additives, such as polymerization inhibitors and ultraviolet absorbers, as long as they do not impair the effects of the composition. As described above, the cured product of the structural color dental curable composition of the present invention exhibits structural color without the use of coloring substances such as pigments. Therefore, it is not necessary to incorporate pigments that may discolor over time into the curable composition of this embodiment. However, this does not mean that the incorporation of pigments is prohibited, and pigments may be incorporated to the extent that they do not interfere with the colored light due to interference from the spherical filler. Specifically, approximately 0.0005 to 0.5 parts by mass, preferably approximately 0.001 to 0.3 parts by mass, of pigment may be incorporated per 100 parts by mass of polymerizable monomer.

[0122] 4. Method for Producing the Dental Curable Composition of the Present Invention The dental curable composition of the present invention contains the above-described components in predetermined amounts, and thereby can provide a cured product that exhibits a structural color of a predetermined color tone independent of the angle of incidence of light. From the viewpoint of ensuring the structural color, the dental curable composition is preferably prepared as follows.

[0123] That is, it is preferable that the dental curable composition of the present invention is prepared by a method that includes a mixing step of weighing out and mixing predetermined amounts of all components that are raw materials for the dental curable composition of the present invention, and that in the mixing step, the mixture obtained in the step is prepared by adopting 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):

[0124] [Conditions to be satisfied by 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.

[0125] (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.

[0126] 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):

[0127] 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.

[0128] 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).

[0129] In the above-mentioned manufacturing method, it is preferable to use g(r) calculated by the above formula (1) based on <ρ>, dn, and da (= 2πr · dr) corresponding to the value of dr used to determine dn, determined based on a scanning electron microscope image of the interior surface of the cured mixture as the observation plane, because <ρ> and dn are easily and reliably confirmed. <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 such as 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.

[0130] For dn, the average particle diameter of the inorganic spherical particles is ０ When expressed as , its length is r ０ / 100~r ０ dn 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.

[0131] 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 any inorganic spherical particle by a distance r is the y-axis, and r / r 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.

[0132] 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.

[0133] 5. Method for Curing the Dental Curable Composition of the Present Invention The dental curable composition of the present invention can be cured by any known polymerization method appropriate for the polymerization initiation mechanism of the polymerization initiator used. Specifically, the dental curable composition of the present invention can be cured by any known polymerization method, including, without limitation, light irradiation using a light source such as a carbon arc, xenon lamp, metal halide lamp, tungsten lamp, fluorescent lamp, sunlight, a helium-cadmium laser, or an argon laser; heating using a thermal polymerization apparatus; or a combination of these. 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 the present embodiment for dental purposes, it is generally preferable to adjust the blending ratio of the various components so that the irradiation time is in the range of about 5 to 60 seconds.

[0134] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0135] 1. Substance names and their abbreviations (1) Polymerizable monomers UDMA: 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane 3G: triethylene glycol dimethacrylate D-2,6E: 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane TFM: 2,2,3,3-tetrafluoropropyl methacrylate.

[0136] (2) Polymerization initiator CQ: camphorquinone (manufactured by Tokyo Chemical Industry Co., Ltd.) AIBN: azobisisobutyronitrile (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0137] (3) Additive (reducing agent) DMBE: ethyl p-N,N-dimethylaminobenzoate (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0138] (4) 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.

[0139] FM1: 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. FM2: A liquid composition prepared by stirring and mixing a mixture of D-2,6E (100 parts by mass) and AIBN (1 part by mass) for 6 hours. FM3: A liquid composition prepared by stirring and mixing a mixture of D-2,6E (50 parts by mass), 3G (50 parts by mass), and AIBN (1 part by mass) for 6 hours. FM4: A liquid composition prepared by stirring and mixing a mixture of D-2,6E (20 parts by mass), 3G (80 parts by mass), and AIBN (1 part by mass) for 6 hours. FM5: A liquid composition prepared by stirring and mixing a mixture of UDMA (70 parts by mass), TFM (30 parts by mass), and AIBN (1 part by mass) for 6 hours. FM6: A liquid composition prepared by stirring a mixture of UDMA (40 parts by mass), TFM (60 parts by mass), and AIBN (1 part by mass) for 6 hours. The refractive indices of curable component M1 and FM1 to FM6 before and after curing, measured according to the method described below, are shown in Table 1.

[0140]

[0141] In the monomer composition M1 shown in Table 1, the content of the polymerization initiator relative to 100 parts by mass of the monomer is 0.2 parts by mass.

[0142] (5) Crystalline rare earth metal fluoride particles YbF3-40: ytterbium fluoride (manufactured by Sukgyung Co., Ltd.) having the following properties: Average primary particle diameter: 40 nm Average secondary particle diameter: 0.6 μm Refractive index: 1.55 These physical property values ​​were measured according to the method described below.

[0143] (6) Group of spherical particles of the same particle size (G-PID) PF-1: Silica-zirconia-based spherical particles (composition: SiO ２ / ZrO ２ / Na ２O = 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.

[0144] 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 FM1 to FM6 (before curing) The refractive index of M1 and FM1 to FM6 (before curing) was measured as the refractive index for the sodium d line at 25°C using an Abbe refractometer (DR-A1-Plus, manufactured by Atago Co., Ltd.).

[0145] (1-2) Refractive index of monomer composition M1 and FM1 to FM6 (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 FM1 to FM6, which were then removed from the molds, was measured using the same procedure as in (1-1).

[0146] (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).

[0147] (2) Average Primary Particle Diameter of Rare Earth Metal Fluoride Particles The average primary particle diameter of rare earth metal fluoride particles was determined using a scanning electron microscope according to the following procedure. First, a measurement sample was prepared by fixing rare earth metal fluoride particles 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 100,000x magnification 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.

[0148] (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.

[0149] (4) Average Primary Particle Diameter of G-PID This was determined by particle size distribution measurement using the following procedure. First, 0.1 g of powder (G-PID) was suspended in 10 mL of ion-exchanged water to prepare a suspension. 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 number particle size distribution. The particle diameter (D50p value) at 50% cumulative from the smallest diameter side of the number particle size distribution was then taken as the average primary particle diameter.

[0150] 3. Preparation of X-ray Opaque Filler (1) Mechanochemical Treatment of Crystalline Rare Earth Metal Fluoride Particles The mechanochemical treatment of crystalline rare earth metal fluoride particles was carried out as follows. First, 855 g of ion-exchanged water and 45 g of crystalline rare earth metal fluoride particles 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 are shown in Table 2.

[0151] 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 particles. For rare earth metal fluoride particles F-1 (crystalline rare earth metal fluoride particles YbF3-40 themselves) with a dispersion treatment time of 0 minutes and mechanochemically treated rare earth metal fluoride particles F-3 to F-6, the average primary particle diameter was 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.

[0152] Measurement method of full width at half maximum S: A measurement sample was prepared by removing coarse particles from powder (rare earth metal fluoride particles) 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 particles were 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.

[0153]

[0154] (2) Preparation of Raw Material Composition and Curing / Crushing Treatment <Production Example 1> 25 parts by mass of monomer composition FM1 and 75 parts by mass of rare earth metal fluoride particles F-3 were weighed out and mixed in an agate mortar to prepare a paste-like raw material composition. Next, this raw material composition 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. This pulverized product was then subjected to a 45 μm stainless steel sieve to remove coarse particles from the pulverized product, thereby obtaining a radiopaque filler CF-1. 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.

[0155] 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. Then, the particle diameter (D50v value) that is 50% cumulative from the small diameter side of the volumetric particle size distribution was 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.

[0156] <Production Examples 2 to 22> Radiopaque fillers CF-2 to CF-4, RCF-1, CF-1a to CF-1i, CF-1-50 to 90w, and CF-1FM2 to FM6 were obtained in the same manner as in Production Example 1, except that the monomer composition and the type of rare earth metal fluoride particles used in preparing the raw material composition were changed as shown in Table 3, and the amount of rare earth metal fluoride particles, the grinding time, and / or the mesh size of the sieve were appropriately changed. The average particle size and full width at half maximum C of these radiopaque fillers were measured. The results are shown in Table 3.

[0157]

[0158] Examples 1 to 27 and Comparative Examples 1 to 5 (1) Preparation of Curable Compositions 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 then 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 Examples 1 to 27 and Comparative Examples 1 to 5.

[0159] (2) 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.

[0160] (2-1) 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) provided 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 at 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 at 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.

[0161] 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.

[0162] Furthermore, to obtain X-ray angiograms, the test pieces of Examples 1, 13, and 19 and Comparative Examples 1 and 4, as well as the aluminum materials (thicknesses of 1, 2, 3, and 4 mm), were observed using a tabletop X-ray transmission inspection device (μB1300, manufactured by Matsusada Precision Co., Ltd.). The X-ray irradiation conditions were tube voltage: 55 kV, tube current: 0.30 mA. The observed images were imported into dedicated image capture software (μRayVision, manufactured by Matsusada Precision Co., Ltd.), and the X-ray angiograms were saved as digital images. The X-ray angiograms (digital images) obtained by this method are shown in Figure 1.

[0163] (2-2) 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 through-hole length) provided 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 this cured product was measured using a color difference meter (SE7700, manufactured by Nippon Denshoku Co., Ltd.) against a black background and against 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.

[0164] (2-3) 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).

[0165] (2-4) 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. The light irradiation positions were three positions on one opening side of the through-hole (one position in the center of the through-hole and two positions inward from the outer edges at both ends in the length direction of the through-hole) and three positions on the other opening side (one position in the center of the through-hole and two positions inward from the outer edges at both ends in the length direction of the through-hole). Then, light irradiation was performed for 20 seconds at each light irradiation position 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 where the symbols in the formula represent σB: bending strength (Pa), P: load at fracture of the test piece (N), S: distance between supports (m), W: width of the test piece (m), and B: thickness of the test piece (m).

[0166] (2-5) 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 was created, and based on the graph obtained, an evaluation was made as to whether the following conditions (I) and (II) were satisfied (◯) or not (×). (I) The nearest inter-particle distance: r, which is defined as 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. １ is 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.

[0167]

[0168]

[0169] 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.

[0170] As can be seen from the results of 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 and prevent the formation of a periodic structure, and 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).

[0171] As can be seen from the results of 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 blended, 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 blended (Comparative Example 1).

[0172] As can be seen from the results of Examples 1 to 4 and 22 to 27, when crystalline rare earth metal fluoride particles having a full width at half maximum of 0.3° or more were combined with an organic-inorganic composite and blended (with a specific X-ray opaque filler), improvements in X-ray contrast and bending strength were observed, as in Comparative Example 5, and further, the decrease in the spectral reflectance ratio was suppressed, maintaining a relatively high spectral reflectance ratio.

[0173] As can be seen from the results of 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.

[0174] As can be seen from the results of Examples 14 to 18, the greater the difference in refractive index between the resin matrix of the organic-inorganic composite particles constituting the X-ray opaque filler to be blended and the cured product of the monomer composition, the more opaque the cured product becomes, and the spectral reflectance ratio decreases slightly. However, the transparency and spectral reflectance ratio are within a range that does not impair the characteristics of structural color CR, and 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. It can be seen that these compositions have the characteristics of structural color CR.

[0175] As can be seen from the results of Examples 19 to 21, the lower the content of crystalline rare earth metal fluoride particles in the organic-inorganic composite particles that make up the radiopaque filler to be blended, the lower the X-ray contrast property and the more transparent the cured product tends to be, and the higher the content, the higher the X-ray contrast property and the more opaque the cured product tends to be. However, it can be seen that the content of crystalline rare earth metal fluoride particles in the organic-inorganic composite particles that make up the radiopaque filler does not affect the evaluation of the spectral reflectance ratio or the radial distribution function.

Claims

1. Polymerizable monomer: 100 parts by mass; the composition comprises: 10 to 1,500 parts by mass in total of one or more "same-size 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 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 range of 5% around the predetermined average primary particle diameter; and a polymerization initiator; 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 particles differ from each other by 25 nm or more, The refractive index of the cured product of the polymerizable monomer at 25°C for 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） Also, n （ＭＸ） <n （Ｇ－ＰＩＤｍ） The relationship is established, A dental hardenable composition capable of providing a hardened product that exhibits a structural color of a predetermined color tone regardless of the angle of incidence of light, The powder is made of a crystalline rare earth metal fluoride, and the crystallinity of the individual crystalline rare earth metal fluoride particles constituting the powder 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. The X-ray opaque filler comprises organic-inorganic composite particles dispersed in a resin matrix, the full width at half maximum of the crystalline rare earth metal fluoride particles being 0.3° or more, in an amount of 1 to 100 parts by mass, calculated as the total mass of the crystalline rare earth metal fluoride particles; Refractive index of the cured product of the polymerizable monomer at 25°C for sodium d line: n （ＭＸ） and the refractive index at 25°C of the resin material constituting the resin matrix of the organic-inorganic composite particles constituting the X-ray opaque filler with respect to the sodium d line: n （F―ＭＸ） Absolute value of the difference with: |n （ＭＸ） -n （F―ＭＸ） | is between 0 and 0.1; A dental hardenable composition comprising:

2. 2. The dental curable composition according to claim 1, wherein the content of the crystalline rare earth metal fluoride particles in the organic-inorganic composite particles constituting the radiopaque filler is 60 to 90 mass % based on the total mass of the organic-inorganic composite particles.

3. 2. The dental curable composition according to claim 1, wherein the organic-inorganic composite particles constituting the radiopaque filler have an average particle size of 22 to 70 μm.

4. 2. The dental hardenable composition according to claim 1, wherein the rare earth metal fluoride particles are ytterbium fluoride particles.

5. 2. The dental curable composition according to claim 1, wherein the average primary particle size of all of the contained "spherical particles of the same particle size" (G-PID) is within the range of 230 to 350 nm.

6. 2. The dental curable composition according to claim 1, wherein the dental curable composition does not contain any rare earth metal fluoride particles other than the rare earth metal fluoride particles blended as the X-ray opaque filler, or the content of such particles is 5 parts by mass or less per 100 parts by mass of the polymerizable monomer.

7. Y value, which is an index of transparency of the cured product of the dental curable composition, is measured on a 1 mm thick cured product sample using a color difference meter against a black background. ｂ and Y, the Y value measured under a white background. ｗ Ratio to: Y ｂ / Y ｗ 2. The dental hardenable composition according to claim 1, which gives a cured product having a contrast ratio C defined as: C = 0.20 to 0.

50.

8. 2. The dental curable composition according to claim 1, wherein the amount of the polymerization initiator blended is 0.01 to 0.5 parts by mass based on 100 parts by mass of the polymerizable monomer.

9. The dental hardenable composition according to claim 1 , wherein the full width at half maximum is 40° or less.