Radiopaque filling material, method for producing radiopaque filling material, hardenable composition, and dental hardenable composition

Abstract

To provide an X-ray impermeable filler which facilitates production of a cured body excellent in both X-ray impermeability and transparency in the case of being blended with a curable composition, a method for producing the same, and a curable composition and a dental curable composition using the X-ray impermeable filler.SOLUTION: There are provided an X-ray impermeable filler which contains a particle body composed of organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix, wherein a full width at half maximum of a maximum intensity peak derived from the rare earth metal fluoride particles measured by an X-ray diffraction measurement method in a state after conversion into the organic-inorganic composite particles is 0.3° or more, a method for producing the same, and a curable composition and a dental curable composition using the X-ray impermeable filler.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a radiopaque filler, a method for producing a radiopaque filler, a hardenable composition, and a dental hardenable composition. [Background technology]

[0002] In dental treatment, after caries removal, a cavity is filled with a dental filling material, which is then hardened to seal the cavity. As such a dental filling material, a hardenable composition containing a polymerizable monomer, a filler, and a polymerization initiator as main components is generally used.

[0003] The filler used in this curable composition is generally an inorganic oxide filler, particularly a silica-based filler. However, silica-based fillers have low radiopacity. Therefore, the cured material in the cavity is not visualized during X-ray or CT scans during dental treatment, making it difficult to identify the treatment site.

[0004] On the other hand, as a means for improving the radiopacity of hardened products of hardenable compositions used for various applications, such as the dental hardenable compositions exemplified above, a method using a filler containing atoms with large atomic numbers is known. For example, Patent Document 1 proposes a technique using a filler made of a fluoride of a rare earth metal with atomic numbers of 57 to 71. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 3-17803 Summary of the Invention [Problem to be solved by the invention]

[0006] 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 1. 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.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radiopaque filler that, when incorporated into a hardenable composition, easily gives a hardened product that is excellent in both radiopacity and transparency; a method for producing the same; and a hardenable composition and a dental hardenable composition that use the radiopaque filler. [Means for solving the problem]

[0008] The above object is achieved by the present invention as follows: The radiopaque filler of the present invention contains a particle body consisting of organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix, and is characterized in that the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles after conversion into organic-inorganic composite particles, as measured by X-ray diffraction measurement, is 0.3° or more.

[0009] In one embodiment of the radiopaque filler of the present invention, the average particle size is preferably 22 μm to 70 μm.

[0010] In another embodiment of the radiopaque filler of the present invention, the average particle size is preferably 24 μm to 55 μm.

[0011] In another embodiment of the radiopaque filler of the present invention, the content of the rare earth metal fluoride particles contained in the organic-inorganic composite particles is preferably 60 mass % or more.

[0012] In another embodiment of the radiopaque filler of the present invention, the rare earth metal fluoride particles are preferably ytterbium fluoride particles.

[0013] The method for producing a radiopaque filler of the present invention is characterized by comprising at least the following steps: a mechanochemical treatment step of mechanochemically treating crystalline rare earth metal fluoride particles to obtain mechanochemically treated rare earth metal fluoride particles; a curing step of curing a raw material composition containing a polymerizable monomer and the mechanochemically treated rare earth metal fluoride particles to obtain a cured product; and a grinding step of grinding the cured product, thereby producing a radiopaque filler containing particle bodies made of organic-inorganic composite particles containing a resin matrix and the mechanochemically treated rare earth metal fluoride particles dispersed in the resin matrix, and in which the full width at half maximum of the maximum intensity peak derived from the mechanochemically treated rare earth metal fluoride particles after conversion into organic-inorganic composite particles is 0.3° or more as measured by X-ray diffraction measurement.

[0014] In one embodiment of the method for producing a radiopaque filler of the present invention, the polymerizable monomer is preferably a radical polymerizable monomer.

[0015] In another embodiment of the method for producing a radiopaque filler of the present invention, it is preferable that the crystalline rare earth fluoride particles are crystalline ytterbium fluoride particles, and the refractive index of the cured product of the polymerizable monomer at 25°C for sodium d-line is 1.45 to 1.60.

[0016] The curable composition of the present invention comprises a radiopaque filler, a polymerizable monomer, and a polymerization initiator, wherein the radiopaque filler contains a particle body made of organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix, and the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles measured by X-ray diffraction measurement after conversion into organic-inorganic composite particles is 0.3° or more.

[0017] The dental curable composition of the present invention comprises a radiopaque filler, a polymerizable monomer, and a polymerization initiator, wherein the radiopaque filler contains a particle body made of organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix, and is characterized in that the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles measured by X-ray diffraction measurement after conversion into organic-inorganic composite particles is 0.3° or more.

[0018] One embodiment of the dental curable composition of the present invention preferably further contains an inorganic oxide filler having an average primary particle size of 100 nm to 1000 nm.

[0019] In another embodiment of the dental curable composition of the present invention, the inorganic oxide filler preferably has an average primary particle size of 230 nm to 350 nm. [Effects of the Invention]

[0020] As described above, the present invention can provide a radiopaque filler that, when incorporated into a curable composition, easily gives a cured product that is excellent in both radiopacity and transparency; a method for producing the radiopaque filler; and a curable composition and a dental curable composition that use the radiopaque filler. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present inventors have conducted extensive research to solve a problem associated with conventional curable compositions that use a rare earth metal fluoride as the main component of a radiopaque filler, namely, the difficulty of obtaining a cured product that is excellent in both radiopacity and transparency. As a result, they have found that a curable composition using, as a radiopaque filler, a powder obtained by mechanochemically treating crystalline rare earth metal fluoride particles, such as crystalline ytterbium fluoride, for an extended period of time is effective in solving the above problem. As a result of further investigation, the inventors have found that (i) mechanochemical treatment reduces the crystallinity of crystalline rare earth metal fluoride particles, and (ii) when the index of the degree of crystallinity-amorphousness, i.e., the full width at half maximum (FWHM) of the maximum intensity peak measured in X-ray diffraction measurement of mechanochemically treated crystalline rare earth metal fluoride particles, is a certain value or more, it is particularly effective in solving the above problems. Based on these findings, the inventors have discovered the radiopaque filler of the present embodiment described below.

[0022] In this specification, unless otherwise specified, the expression "x to y" using the 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. Furthermore, 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."

[0023] 1. X-ray opaque filling material and its manufacturing method The radiopaque filler of this embodiment contains a particle body made of organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix, and the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles measured by X-ray diffraction measurement after conversion into the organic-inorganic composite particles is 0.3° or more.

[0024] In the following description, the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles measured by X-ray diffraction measurement after conversion into organic-inorganic composite particles may be referred to as "full width at half maximum C." In contrast, the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles measured by X-ray diffraction measurement in the state of the rare earth metal fluoride particles alone (in other words, for the rare earth metal fluoride particles in a state before conversion into organic-inorganic composite particles) may be referred to as "full width at half maximum S." Furthermore, when referring to either or both of the full width at half maximum C and the full width at half maximum S, they may be simply referred to as "full width at half maximum." For reference, the full width at half maximum C is a characteristic value that specifies the radiopaque filler of this embodiment, while the full width at half maximum S is used as needed as a characteristic value for managing and controlling the manufacturing conditions when producing the radiopaque filler of this embodiment.

[0025] By setting the full width at half maximum C to 0.3° or more, when a curable composition containing the radiopaque filler of this embodiment 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 C 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 C is not particularly limited, but in practice, it is preferably 40° or less, more preferably 1° or less.

[0026] The full width at half maximum (FWHM) can be determined by performing X-ray diffraction on a powder sample to be measured. Specifically, an X-ray diffraction measurement is performed on the powder sample using an X-ray diffractometer over a 2θ range of 20° to 120° to obtain an X-ray diffraction pattern (chart) with 2θ (°) on the horizontal axis and diffraction intensity on the vertical axis. For the full width at half maximum (C), a powder sample in the form of organic-inorganic composite particles is prepared, while for the full width at half maximum (S), a powder sample in the form of rare earth metal fluoride particles alone is prepared. It is preferable to use a powder sample from which coarse particles have been removed, for example, by using a sieve with a mesh size of 100 μm, according to a standard method.

[0027] Next, peaks originating from 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 with the greatest intensity among the multiple peaks identified is determined. For example, in a specific example where the material of the rare earth metal fluoride particles is YbF3, the peak with the greatest intensity is a peak originating from the (111) plane and appears near 2θ = 28.0°. Here, the full width at half maximum is obtained by determining the peak width at an intensity that is 50% of the maximum intensity of the peak observed near 2θ = 28.0° (50% intensity). The peak width is determined 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 located at the 50% intensity.

[0028] Generally, there is a correlation between the full width at half maximum of the diffraction peak in X-ray diffraction measurements and the crystallite size, known as the Scherrer equation, and it is known that the crystallite size is inversely proportional to the full width at half maximum. The full width at half maximum is also affected by the distortion of the crystal lattice, and the greater the distortion, the wider the full width at half maximum tends to be. It is thought that the greater the distortion, the smaller the crystallite diameter, and the more the fine crystallites are oriented in various directions, which increases the amorphous nature, so the full width at half maximum can be said to be an indicator of the degree of crystallinity / amorphism of rare earth metal fluorides.

[0029] The radiopaque filler of this embodiment contains particle bodies composed of organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix. The form of the radiopaque filler is not particularly limited as long as it contains the particle bodies (organic-inorganic composite particles). Examples include (i) a form consisting solely of the particle bodies (organic-inorganic composite particles), (ii) a form containing the particle bodies and a surface treatment agent that chemically treats the surface of the particle bodies, (iii) a form containing the particle bodies and a coating agent that coats the surface of the particle bodies, and (iv) a form containing the particle bodies and external additive particles attached to the surface of the particle bodies. In form (i), the organic-inorganic composite particles may be used in their original state after granulation, or the organic-inorganic composite particles may be used after granulation, in which case the surface of the particle bodies has been subjected to physical surface treatment such as plasma treatment or mechanical surface treatment such as prolonged friction stirring. Furthermore, form (ii) refers to a form in which the particle body surface and the surface treatment agent are chemically bonded, and form (iii) refers to a form in which the coating agent simply covers the particle body surface so that it adheres physically without any gaps (a state in which it is not chemically bonded).

[0030] As the surface treatment agent, known surface treatment agents such as silane coupling agents and titanate coupling agents can be used as appropriate. Furthermore, known coating agents such as silicone oil can be used as appropriate as the coating agent. Furthermore, as the external additive particles, particles having a particle size sufficiently smaller than that of the particle itself can be used as appropriate. The silane coupling agent used as the surface treatment agent can improve the affinity between the X-ray opaque filler of this embodiment and the resin material constituting the cured body of the curable composition of this embodiment using the filler, as described below, and is therefore effective in improving the mechanical strength of the cured body. Therefore, it is particularly preferable that the organic-inorganic composite particles are particles surface-treated with a silane coupling agent.

[0031] The average particle size of the radiopaque filler is not particularly limited, but from the viewpoint of achieving a good balance between radiopacity and mechanical strength, it is preferably 22 μm to 70 μm, more preferably 24 μm to 55 μm. Furthermore, when ensuring mechanical strength is more important than radiopacity, the average particle size is preferably 3 μm to 38 μm, more preferably 8 μm to 25 μm. On the other hand, when ensuring radiopacity 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, it is preferably 110 μm or less.

[0032] The rare earth metal fluoride particles contained in the particle body (organic-inorganic composite particle) 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 C is 0.3° or more. When used for various purposes, the material of the rare earth metal fluoride particles is preferably, for example, lanthanum fluoride (LaF), cerium fluoride (CeF), or ytterbium fluoride (YbF), and among these, ytterbium fluoride (YbF) is more preferably.

[0033] Furthermore, when the radiopaque filler of this embodiment is used for dental purposes, from the viewpoint of easily ensuring a color tone and safety suitable for dental purposes, the material of the rare earth metal fluoride particles is preferably lanthanum fluoride (LaF3), cerium fluoride (CeF3), or ytterbium fluoride (YbF3), and further from the viewpoint of ensuring radiopaqueness, ytterbium fluoride (YbF3) is particularly preferable.

[0034] The rare earth metal fluoride particles contained in the particle body (organic-inorganic composite particles) can be shaped as follows: (i) a shape consisting of only rare earth metal fluoride particles; (ii) a shape containing rare earth metal fluoride particles and a surface treatment agent that chemically treats the surface of the rare earth metal fluoride particles; or (iii) a shape containing rare earth metal fluoride particles and a coating agent that coats the surface of the rare earth metal fluoride particles. In the shape (i), only rare earth metal fluoride particles may be used, or rare earth metal fluoride particles whose surfaces have been subjected to a physical surface treatment such as plasma treatment may also be used. Shape (ii) refers to a shape in which the surface of the rare earth metal fluoride particles is chemically bonded to the surface treatment agent, while shape (iii) refers to a shape in which the coating agent simply covers the surface of the rare earth metal fluoride particles so that there are no gaps between them (a state in which the coating agent is not chemically bonded).

[0035] As the surface treatment agent, known surface treatment agents such as silane coupling agents and titanate coupling agents can be used as appropriate. As the coating agent, known coating agents such as silicone oil can be used as appropriate.

[0036] The content of the rare earth metal fluoride particles in the organic-inorganic composite particles is not particularly limited, but is preferably 60% by mass or more, more preferably 70% by mass or more, and the upper limit of the content is preferably 90% by mass or less, more preferably 80% by mass or less.

[0037] The resin material constituting the resin matrix contained in the particle body (organic-inorganic composite particle) is not particularly limited, and known resin materials can be appropriately selected, for example, (meth)acrylic resins, polyaryletherketone resins, etc. In the present specification, the term "(meth)acrylic resin" refers to a polymerizable monomer used in the polymerization of the (meth)acrylic resin, A polymer polymerized using only (meth)acrylate monomers, or <ii>In the case where two or more polymerizable monomers including a (meth)acrylate monomer are used, the polymer refers to a polymer in which the proportion of the (meth)acrylate monomer in the total polymerizable monomers is 50 mol % or more.

[0038] In the X-ray opaque filler of this embodiment, a suitable combination of materials constituting the particle body (organic-inorganic composite particles) includes a combination of at least one selected from the group consisting of lanthanum fluoride (LaF3), cerium fluoride (CeF3), and ytterbium fluoride (YbF3) as the material for the (A1) rare earth metal fluoride particles, and a (meth)acrylic resin as the resin material for the (B) resin matrix.A particularly suitable combination of materials constituting the particle body (organic-inorganic composite particles) includes a combination of at least one selected from the group consisting of ytterbium fluoride (YbF3) as the material for the (A2) rare earth metal fluoride particles, and a (meth)acrylic resin as the resin material for the (B) resin matrix.

[0039] The method for producing the radiopaque filler of this embodiment is not particularly limited, and any known method for producing organic-inorganic composite particles can be used as appropriate. In this case, the organic-inorganic composite particles are granulated using rare earth metal fluoride particles having a full width at half maximum S of 0.3° or more and a resin material or a resin material precursor (such as a polymerizable monomer).

[0040] When the full width at half maximum S of the rare earth metal fluoride particles used to manufacture the radiopaque filler is less than 0.3°, a mechanochemical treatment step is carried out in which rare earth fluoride particles having a full width at half maximum S of less than 0.3° (hereinafter sometimes referred to as "crystalline rare earth metal fluoride particles") are mechanochemically treated to obtain mechanochemically treated rare earth metal fluoride particles (rare earth metal fluoride particles having a full width at half maximum S of 0.3° or more). Conventionally, the full width at half maximum S 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, when producing the radiopaque filler of this embodiment, a mechanochemical treatment step is usually carried out in which crystalline rare earth metal fluoride particles obtained as raw materials are mechanochemically treated. Even if the full width at half maximum S of the rare earth metal fluoride particles is 0.3° or more, if the value of the full width at half maximum S is not particularly large, these rare earth metal fluoride particles may be used as raw material powder to carry out a mechanochemical treatment step in order to obtain a larger full width at half maximum S. Furthermore, in order to consider the treatment conditions when carrying out the mechanochemical treatment step, it is preferable to perform X-ray diffraction measurement as necessary to measure the full width at half maximum S of the crystalline rare earth metal fluoride particles or rare earth metal fluoride particles used as raw material powder having a full width at half maximum S of 0.3° or more.

[0041] Furthermore, as the crystalline rare earth metal fluoride particles or rare earth metal fluoride particles having a full width at half maximum S of 0.3° or more used as the 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.

[0042] In mechanochemical processing, depending on the processing conditions, prolonging the processing time can cause the particles contained in the raw material powder to be pulverized, resulting in the disintegration of secondary particles (agglomerated particles) and primary particles, resulting in a smaller particle size. However, a processing time of several hours does not significantly change the particle size of secondary particles or primary particles. For this reason, the raw material powder preferably has an average primary particle size of 1 nm to 500 nm, more preferably 5 nm to 300 nm, as measured by electron microscopy. The average primary particle size, as measured by laser diffraction / scattering, is preferably 0.1 μm to 0.6 μm, more preferably 0.1 μm to 0.3 μm. The average primary particle size is measured using a scanning electron microscope. Specifically, the powder was observed under an electron microscope at 100,000x magnification, and the average particle size of 100 primary particles in the obtained observation image was defined as the average primary particle size.

[0043] Here, mechanochemical treatment refers to a treatment that applies mechanical energy to 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 controlling the full width at half maximum (S), which indicates the degree of crystallinity-amorphousness 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 dispersibility of the raw material powder, a medium that is liquid at room temperature (15°C to 25°C) is preferred.

[0044] The mechanochemical treatment using a wet bead mill will be described in detail below.

[0045] In mechanochemical treatment using a wet bead mill, a slurry containing a mixture of raw material powder and a medium to be subjected to mechanochemical treatment is brought into contact with media (beads) that have been imparted with motion by stirring, vibration, or other means. 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 dental curable compositions.

[0046] 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.

[0047] 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. These bead separation methods can be selected depending on the particle size of the beads used, and any method can 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 will increase, which may make the mechanochemical treatment difficult.

[0048] 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.

[0049] 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 (FWHM) 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 the equipment that will actually perform the mechanochemical treatment and checking the FWHM S of the raw material powder after the mechanochemical treatment versus the mechanochemical treatment time. Furthermore, when mechanochemical treatment is performed, it is possible to obtain mechanochemically treated raw material powder with the desired FWHM S by appropriately sampling the slurry during the mechanochemical treatment as needed and checking the FWHM S as needed.

[0050] The raw powder (mechanochemically treated rare earth metal fluoride particles) adjusted to a full width at half maximum S of 0.3° or greater by mechanochemical treatment is typically subjected to appropriate post-treatment processes such as concentration, drying, and filtration. This process yields the raw powder (raw 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 powder and the polymerizable monomer) as needed before granulating the organic-inorganic composite particles. Furthermore, the raw 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. Surface treatment agents that can be used include commonly used compounds such as silane coupling agents and titanate coupling agents.

[0051] In granulating organic-inorganic composite particles, a granulation step is carried out using a raw material powder for granulation that has undergone at least a mechanochemical treatment step and a resin matrix raw material. The full width at half maximum (S) of the raw material powder for granulation may be 0.3° or more. However, from the viewpoint of more stably and reliably obtaining the radiopaque filler of this embodiment having a full width at half maximum (C) of 0.3° or more, a full width at half maximum (S) of 0.35° or more is preferred, and 0.4° or more is more preferred. The upper limit of the full width at half maximum (S) of the raw material powder for granulation is not particularly limited and can be selected appropriately according to the target full width at half maximum (C) of the radiopaque filler to be produced. In practice, a full width at half maximum (S) of 40° or less is preferred, and 1° or less is more preferred.

[0052] As a method for granulating the organic-inorganic composite particles, any known granulation method can be used as appropriate, and the following two granulation methods are typically used. (1) First granulation method A granulation method comprising at least a curing step of obtaining a cured product by curing a raw material composition for granulation, the raw material composition including at least a raw material powder and a polymerizable monomer, and a pulverizing step of pulverizing the cured product. (2) Second granulation method A granulation method comprising at least a melt-kneading step of melt-kneading a granulation raw material composition containing at least a raw material powder and a thermoplastic resin to obtain a molten kneaded product, and a pulverizing step of pulverizing the solidified product obtained by cooling and solidifying the molten kneaded product.

[0053] As the polymerizable monomer used in the first granulation method, known polymerizable monomers such as radical 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 monomer, polymerization initiator, 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.

[0054] In addition, known thermoplastic resins such as polyaryl ether ketone resins can be used as the thermoplastic resin used in the second granulation method. Other additives can also be used in the granulation raw material composition as needed. Specific examples of other additives include those used in the curable composition of the present embodiment, which will be described later. Known melt-kneading methods can be used to melt-knead the granulation raw material composition, and the melt-kneading method disclosed in International Publication No. 2013 / 88921 can be used, for example. The resin matrix constituting 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.

[0055] The refractive index at 25°C of the crystalline rare earth metal fluoride particles used as the raw material powder with respect to the sodium d line 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 of the resin material that is the main component of the resin matrix that constitutes the organic-inorganic composite particles (particle body) with respect to the sodium d line is preferably 1.45 to 1.60. Here, the "resin material that is the main component of the resin matrix" refers to, in the first granulation method, a cured product of a polymerizable monomer ( In the second granulation method, the term "radio-opaque filler" refers to a cured product of a composition consisting only of a polymerizable monomer or a cured product of a composition consisting of a polymerizable monomer and a small amount of a polymerization initiator, and in the second granulation method, it refers to a thermoplastic resin. When the refractive index of the rare earth metal fluoride particles constituting the particle body (organic-inorganic composite particles) constituting the radiopaque filler and the refractive index of the resin material that is the main component of the resin matrix can be similar to each other as described above, it becomes easier to improve the transparency of the curable composition using the radiopaque filler.

[0056] From the same viewpoint, it is preferable that the following formula (1A) is satisfied, it is more preferable that the following formula (2A) is satisfied, and it is even more preferable that the following formula (3A) is satisfied. X means the refractive index at 25°C of the crystalline rare earth metal fluoride particles used in the production of organic-inorganic composite particles at the sodium d line, and n M means 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. ·Formula (1A) -0.02≦(n X -n M )≦0.1 ·Formula (2A) 0.01≦(n X -n M )≦0.07 ·Formula (3A) 0≦(n X -n M )≦0.05

[0057] In the first and second granulation methods, 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 needed, in order to be used as the radiopaque filler of any of the above-mentioned forms (i) to (iv).

[0058] 2. Hardenable composition and dental hardenable composition The curable composition of this embodiment contains the radiopaque filler of this embodiment, a polymerizable monomer, and a polymerization initiator.

[0059] As the polymerizable monomer, known polymerizable monomers can be used without any limitation. Specific examples include methyl (meth)acrylate, glycidyl (meth)acrylate, 2-cyanomethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, allyl (meth)acrylate, 2-hydroxyethyl mono(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate (3G), nonaethylene glycol di(meth)acrylate, propylene ... Examples of the polymerizable monomer include (meth)acrylate monomers such as acrylate, dipropylene glycol di(meth)acrylate, 2,2-bis[4-(meth)acryloyloxyethoxyphenyl]propane, 2,2-bis[4-(meth)acryloyloxyethoxyethoxyphenyl]propane, 2,2-bis{4-[3-(meth)acryloyloxy-2-hydroxypropoxy]phenyl}propane, 1,4-butanediol di(meth)acrylate, 1,3-hexanediol di(meth)acrylate, 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane (UDMA), and trimethylolpropane di(meth)acrylate. Two or more of these polymerizable monomers can be used in appropriate combination.

[0060] 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.

[0061] From the viewpoint of the transparency of the cured product of the curable composition, it is preferable that the refractive index of the cured product obtained by curing the polymerizable monomer used in the curable composition (or a composition consisting of the polymerizable monomer and a small amount of polymerization initiator) is the same as or similar to the refractive index of the resin material constituting the resin matrix of the organic-inorganic composite particles that constitute the X-ray opaque filler. 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 to produce the resin material constituting 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.

[0062] The amount of the radiopaque filler of this embodiment blended into the curable composition of this embodiment can be appropriately selected within a range that provides the radiopaqueness (radiographic contrast) and transparency of the cured product depending on the intended use of the curable composition. Furthermore, from the viewpoint of the handleability of the curable composition, the blending amount is preferably such that the curable composition becomes a paste. However, in general, the radiopaque filler is blended in an amount ranging from 1 to 400 parts by mass, and more preferably from 10 to 300 parts by mass, per 100 parts by mass of the polymerizable monomer contained in the curable composition.

[0063] As the polymerization initiator, any of chemical polymerization initiators, photopolymerization initiators, thermal polymerization initiators, etc., which are used as polymerization initiators capable of polymerizing the polymerizable monomers blended in the curable composition, can be used without any particular limitation. The type of polymerization initiator can be appropriately selected depending on the intended use of the curable composition.

[0064] Examples of photopolymerization initiators include 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 reducing agents include aromatic amines, aliphatic amines, aldehydes, and sulfur-containing compounds. Furthermore, trihalomethyltriazine compounds, aryliodonium salts, and the like can also be added as needed.

[0065] Examples of the thermal polymerization initiator 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.

[0066] The amount of the polymerization initiator to be added is not particularly limited as long as it is an amount that can initiate polymerization, but it is usually preferably in the range of 0.001 to 10 parts by mass per 100 parts by mass of the polymerizable monomer, and more preferably in the range of 0.05 to 5 parts by mass from the viewpoint of the polymerization rate and various physical properties of the resulting cured product (e.g., weather resistance and hardness).

[0067] The curable composition of this embodiment may contain other components, as needed, in addition to the radiopaque filler, polymerizable monomer, and polymerization initiator of this embodiment. Examples of such components include fillers other than the radiopaque filler (e.g., inorganic oxide fillers, organic fillers), polymerization inhibitors, UV absorbers, antistatic agents, fragrances, organic solvents, pigments, dyes, and thickeners, among other known additives. However, pigments and dyes may be used to the extent that they do not impair the transparency required for the intended use of the cured product obtained by curing the curable composition.

[0068] The material of the inorganic oxide filler is not particularly limited and any known material can be used as appropriate, including, for example, borosilicate glass, soda glass, glass containing heavy metals (barium, strontium, lanthanum, etc.), aluminosilicate glass, fluoroaluminosilicate glass, and other glasses; glass ceramics; silica; zirconia; quartz; and composite inorganic oxides such as silica-zirconia, silica-titania, and silica-alumina.

[0069] Among these inorganic oxide fillers, it is particularly preferable to use glass containing heavy metals (barium, strontium, lanthanum, etc.), silica, zirconia, silica-zirconia, and other composite oxides, from the viewpoint of the transparency and strength of the cured product of the curable composition.

[0070] Examples of organic fillers include particles made of organic polymers such as polymethyl methacrylate, polyethyl methacrylate, methyl methacrylate-ethyl methacrylate copolymer, cross-linked polymethyl methacrylate, cross-linked polyethyl methacrylate, ethylene-vinyl acetate copolymer, styrene-butadiene copolymer, acrylonitrile-styrene copolymer, and acrylonitrile-butadiene-styrene copolymer.

[0071] The inorganic oxide fillers and organic fillers described above can also be suitably used as fillers for dental hardenable compositions.

[0072] The particle size and shape of the inorganic oxide filler and organic filler are not particularly limited. The shape may be either spherical or amorphous, and the average primary particle size is within the range of 0.001 μm to 100 μm. The shape and average particle size may be selected appropriately depending on the intended use of the curable composition of this embodiment. The refractive index of these fillers is also not particularly limited, but is generally preferably about 1.4 to 2.6.

[0073] The amount of the filler (organic filler and / or inorganic oxide filler) contained in the curable composition of this embodiment is not particularly limited, but is preferably in a range that makes the curable composition paste-like. In this case, the total amount of the radiopaque filler and the filler (organic filler and / or inorganic oxide filler) is preferably 25 to 500 parts by mass, more preferably 40 to 400 parts by mass, per 100 parts by mass of the polymerizable monomer.

[0074] The required degree of transparency (or opacity) varies depending on the intended use of the curable composition. However, as described above, the curable composition of this embodiment basically has excellent transparency. Therefore, by further blending the curable composition of this embodiment with, for example, an additive that adjusts the transparency of the cured product, it is extremely easy to obtain the desired transparency (or opacity) depending on the intended use of the curable composition. That is, the curable composition of this embodiment ensures high X-ray opacity of the cured product while also allowing for extremely high design freedom in the degree of transparency (or opacity) depending on the intended use. Here, as the additive for adjusting the transparency of the cured product, for example, an inorganic oxide filler and / or organic filler having an average primary particle diameter of 100 nm to 1000 nm can be used. When mechanical strength is also required for the cured product, it is more preferable to use an inorganic oxide filler having an average primary particle diameter of 100 nm to 1000 nm.

[0075] The method for producing the curable composition of this embodiment is not particularly limited, and known methods for producing curable compositions may be appropriately adopted. Specifically, the curable composition of this embodiment can be prepared by weighing out and mixing predetermined amounts of each component constituting the curable composition in a dark place in the case of a photopolymerization-based curable composition, or at room temperature or a low temperature in the case of a thermal polymerization-based curable composition. In the case of a chemical polymerization-based curable composition, a curable composition composed of a combination of a first part and a second part is generally prepared so that the components constituting the polymerization initiator that generate active species when mixed can be maintained physically separated. The prepared curable composition is preferably in a paste form. The curable composition of this embodiment prepared in this manner is stored in an environment suitable for thermal polymerization, photopolymerization, or chemical polymerization systems (e.g., in the dark, at room temperature, at a low temperature, etc.) until use.

[0076] The curable composition of this embodiment can be cured by any known polymerization method suitable for the polymerization initiation mechanism of the polymerization initiator used. Specifically, light irradiation using a light source such as a carbon arc, xenon lamp, metal halide lamp, tungsten lamp, fluorescent lamp, sunlight, helium-cadmium laser, or argon laser, heating using a thermal polymerization apparatus, or a combination thereof, can be used without limitation. When polymerizing 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, so it can be determined in advance through preliminary experiments. When using the curable composition of this embodiment for dental purposes, it is generally preferable to adjust the blending ratio of the various components so that the irradiation time is within the range of approximately 5 to 60 seconds.

[0077] The curable composition of this embodiment can be used in a variety of applications, such as dental materials, adhesives, paints, and optical materials, but is particularly suitable for use as a dental curable composition. However, if the curable composition of this embodiment is used as a dental curable composition as is, the transparency of the cured product may be too high depending on the relationship with the treatment site to be treated. In such cases, it becomes difficult to perform dental treatment with excellent aesthetics. Therefore, when the curable composition of this embodiment is used as a dental curable composition, this dental curable composition may further contain, as necessary, an inorganic oxide filler having an average primary particle size of 100 nm to 1000 nm in addition to the radiopaque filler, polymerizable monomer, and polymerization initiator.

[0078] In the dental curable composition of this embodiment, the polymerizable monomer is preferably the above-mentioned (meth)acrylate monomer, and two or more types may be used in combination as needed.

[0079] Furthermore, the content of rare earth fluoride metal particles present in the form of organic-inorganic composite particles constituting the radiopaque filler in the dental curable composition is preferably 1% by mass or more, and more preferably 3% by mass or more, based on the total amount of the dental curable composition (100% by mass), from the viewpoint of ensuring radiographic contrast suitable for identifying the treatment site. On the other hand, from a practical viewpoint, the upper limit of the content of rare earth fluoride metal particles is preferably 80% by mass or less.

[0080] Furthermore, as the polymerization initiator used in the dental curable composition of this embodiment, a photopolymerization initiator is preferably used when the dental curable composition is used as a dental filling and restorative material that is hardened in the oral cavity, and a thermal polymerization initiator is preferably used when a bulk body obtained by hardening the dental curable composition is cut into a mill blank for use in a dental clinic, dental laboratory, etc. The blending amount of the polymerization initiator is preferably in the range of 0.001 to 10 parts by mass, and more preferably in the range of 0.05 to 5 parts by mass, per 100 parts by mass of the polymerizable monomer.

[0081] In the dental hardenable composition of this embodiment, an inorganic oxide filler having an average primary particle size of 100 nm to 1,000 nm can be used as needed to ensure the transparency of the cured product suitable for dental treatment, as described above. To ensure the transparency of the cured product suitable for dental use, the content of the inorganic oxide filler is preferably within the range of 20% to 80% by mass, and more preferably within the range of 40% to 70% by mass, based on the total amount of the dental hardenable composition (100% by mass). The average primary particle size of the inorganic oxide filler is not particularly limited as long as it is within the range of 100 nm to 1,000 nm. However, to impart a color tone closer to that of natural teeth (i.e., a yellowish or reddish color tone) to the cured product, it is preferably 230 nm to 350 nm, and more preferably 245 nm to 300 nm. The particle size distribution of the inorganic oxide filler is not particularly limited, but a narrower distribution is preferable from the viewpoint of facilitating control of the color tone imparted to the cured product. Specifically, it is preferable that 90% or more of the total number of particles in the number-based particle size distribution are within a range of ±5% of the reference value (100%), where the average primary particle diameter is the reference value. The shape of the inorganic oxide filler may be spherical or irregular.

[0082] In addition, the inorganic oxide filler may be surface-treated with a silane coupling agent to improve affinity with the resin matrix constituting the hardened body of the dental hardenable composition. As the silane coupling agent, the same silane coupling agent as that used for the surface treatment of the organic-inorganic composite particles constituting the X-ray opaque filler of this embodiment can be used.

[0083] Furthermore, the hardened product of the dental curable composition used in dental treatment is also required to have mechanical strength. From this viewpoint, the total amount of the radiopaque filler and inorganic oxide filler contained in the dental curable composition is preferably 40% by mass to 90% by mass, and more preferably 60% by mass to 80% by mass, based on the total amount of the dental curable composition (100% by mass).

[0084] In the curable composition of this embodiment, a suitable combination of materials constituting the curable composition includes a combination of the above-mentioned (Group A1) [or (Group A2)] and (Group B) as materials constituting the radiopaque filler, and (Group C) at least one (meth)acrylate monomer selected from the group consisting of ethylene glycol-based 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) as a polymerizable monomer. Furthermore, when the curable composition of the present embodiment further contains an inorganic oxide filler having an average primary particle diameter of 100 nm to 1000 nm, a combination of the above (Group A1) [or (Group A2)] with at least one inorganic oxide filler selected from the group consisting of (Group B), (Group C), and (Group D) glass containing at least one heavy metal selected from barium, strontium, and lanthanum, silica, zirconia, and silica-zirconia is particularly preferred.

[0085] In order to obtain a cured product having excellent radiopacity and appropriate transparency suitable for dental treatment, in addition to the dental curable composition of this embodiment using the radiopaque filler of this embodiment as the radiopaque filler, it is also possible to use a dental curable composition using rare earth metal fluoride particles or surface-treated particles thereof having a full width at half maximum S of 0.3° or more as the radiopaque filler instead of the radiopaque filler of this embodiment (hereinafter, this may be referred to as a "reference dental curable composition").

[0086] However, the dental hardenable composition of this embodiment is superior to the reference dental hardenable composition in not only the transparency and X-ray transmittance of the cured product but also the mechanical strength. In addition, the dental hardenable composition of this embodiment is more suitable than the reference dental hardenable composition in that it facilitates highly aesthetic dental treatment, as described below.

[0087] First, when dental treatment is performed using a dental hardenable composition, the dental hardenable composition (dental filling material) is filled into a Class III or Class IV cavity, and then the dental hardenable composition is hardened to seal the cavity with a hardened material. In this case, it is extremely important for aesthetic treatment that the difference in color between the restored area and the surrounding natural teeth is small. To meet this need, the simplest method is to incorporate a coloring material (pigment or dye) into the dental hardenable composition so that the color of the hardened material approximately matches the color of the natural teeth (yellowish or reddish). However, with this method, the coloring material in the hardened material located at the restored area fades or discolors due to aging, resulting in a deterioration in the aesthetics of the restored area over time.

[0088] To avoid deterioration of the color tone of the cured product over time due to such coloring materials, it is effective to use an inorganic oxide filler with an average primary particle size of 230 nm to 350 nm in the dental curable composition. However, even if an inorganic oxide filler with an average primary particle size of 230 nm to 350 nm is used, it is difficult to ensure sufficient X-ray contrast of the restored area.

[0089] On the other hand, the dental hardenable composition of this embodiment produces a cured product with a color shifted to a more yellowish or reddish hue compared to the reference dental hardenable composition. Therefore, the dental hardenable composition of this embodiment ensures X-ray contrast at the restoration site while facilitating highly aesthetic treatment without deterioration over time. While the reason for this effect is unclear, experimental data described below suggests that it is due to the synergistic effect of the rare earth metal fluoride particles having a full width at half maximum of 0.3° or more and the rare earth metal fluoride particles being dispersed in the cured product in the form of organic-inorganic composite particles.

[0090] The average primary particle size of the inorganic oxide filler used in the dental curable composition of this embodiment is preferably 230 nm to 350 nm, from the viewpoint of facilitating highly aesthetic dental treatment. [Example]

[0091] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0092] 1. Substance name and its abbreviation (1) Polymerizable monomer UDMA: 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane 3G: Triethylene glycol dimethacrylate

[0093] (2) Polymerization initiator CQ: Camphorquinone (Tokyo Chemical Industry Co., Ltd.) DMBE: Ethyl dimethylbenzoate (Tokyo Chemical Industry Co., Ltd.) AIBN: Azobisisobutyronitrile (Tokyo Chemical Industry Co., Ltd.)

[0094] (3) Polymerizable component M1: A liquid composition prepared by stirring and mixing a mixture of UDMA (80 parts by mass), 3G (20 parts by mass), CQ (0.2 parts by mass), and DMBE (0.35 parts by mass) for 6 hours. M2: A liquid composition prepared by stirring and mixing a mixture of UDMA (80 parts by mass), 3G (20 parts by mass), and AIBN (1 part by mass) for 6 hours. Table 1 shows the refractive indices of the polymerizable components M1 and M2 before and after curing.

[0095] (4) Crystalline rare earth metal fluoride particles YbF3-40: Ytterbium fluoride (manufactured by Sukgyung) with the following properties: ·Average primary particle diameter: approx. 40nm ·Average secondary particle size: 0.6μm Refractive index: 1.55

[0096] (5) Inorganic oxide filler PF-1: A silica-zirconia filler (composition: SiO2 / ZrO2 / Na2O = 89.8 / 9.0 / 1.2 (mol%)) with the properties shown below, surface-treated with a silane coupling agent (methacrylate-3-(trimethoxysilyl)propyl-3-(methacryloyloxy)propyltrimethoxysilane (Tokyo Chemical Industry Co., Ltd.)). ·Average primary particle diameter: 260nm Refractive index: 1.515 ·Symmetry: 0.90 Average particle size abundance: 92% Here, the uniformity refers to the ratio (D2 / D1) of the maximum diameter D1 of the filler particles to the particle diameter D2 in the direction perpendicular to the maximum diameter D1. The abundance of the average particle size refers to the proportion (%) of filler particles present within a particle size range of 100%±5% when the average primary particle size is taken as the reference (100%) in the particle size distribution based on the number of filler particles.

[0097] 2. Preparation of Radiopaque 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.

[0098] 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. Table 2 shows the average primary particle diameter and full width at half maximum S of rare earth metal fluoride particles (crystalline rare earth metal fluoride particles YbF3-40 themselves) F-1, which had a dispersion treatment time of 0 minutes, and mechanochemically treated rare earth metal fluoride particles F-2 to F-6.

[0099] (2) Preparation of raw material composition and hardening / pulverization treatment <Production Example 1> A paste-like raw material composition was prepared by weighing out 25 parts by weight of polymerizable component M2 and 75 parts by weight of rare earth metal fluoride particles F-3 and mixing them in an agate mortar. This raw material composition was then thermally cured under nitrogen pressure at 100°C for 30 minutes using a nitrogen pressure thermal polymerization apparatus (Poliner, manufactured by Towa Giken Co., Ltd.) to obtain a cured product. The cured product and zirconia balls (diameter: 25 mm) were placed in a zirconia pot and subjected to a rotary grinding process for 60 minutes to obtain a pulverized cured product. The pulverized product was then used to remove coarse particles using a 45 μm stainless steel sieve to obtain radiopaque filler CF-1. The average particle size and full width at half maximum (FWHM) C of radiopaque filler CF-1 are shown in Table 3.

[0100] <Production Examples 2 to 14> Radiopaque fillers CF-2 to CF-4, RCF-1, and CF-1a to CF-1i were obtained in the same manner as in Production Example 1, except that the type of rare earth metal fluoride particles, grinding time, and / or sieve openings used in preparing the raw material composition were changed as shown in Table 3. The average particle size and full width at half maximum C of these radiopaque fillers are shown in Table 3.

[0101] 3. Preparation of Curable Composition To polymerizable component M1 (20 parts by mass), radiopaque filler (16 parts by mass) and inorganic oxide filler PF-1 (64 parts by mass) were added, and the mixture was mixed in an agate mortar to obtain a mixture. This mixture was then degassed under vacuum to remove air bubbles, yielding a paste-like curable composition. The curable compositions of Examples 1 to 13 and Comparative Examples 1 to 5 were prepared by varying the type of radiopaque filler as shown in Table 4. The cured products of the obtained curable compositions were measured for radiographic contrast, transparency, spectral reflectance ratio, and bending strength. The results are shown in Table 4.

[0102] 4. Various measurement and evaluation methods (1) Measurement of full width at half maximum The full width at half maximum was measured using the following procedure. First, a measurement sample was prepared by removing coarse particles from the powder (rare earth metal fluoride particles or X-ray opaque filler) 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, thereby obtaining 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.

[0103] When the material of the rare earth metal fluoride particles or the rare earth metal fluoride particles that make up the X-ray opaque filler is YbF3, the peak with the greatest intensity is the peak due to the (111) plane (the peak observed around 2θ = 28°), so the full width at half maximum of this peak was determined.

[0104] (2) Refractive index measurement (2-1) Refractive index of polymerizable monomer and polymerizable components M1 and M2 (before curing) The refractive index of the polymerizable monomer and polymerizable components M1 and M2 (before curing) was measured as the refractive index for sodium d line at 25°C using an Abbe refractometer (DR-A1-Plus, manufactured by Atago Co., Ltd.).

[0105] (2-2) Refractive index of polymerizable components M1 and M2 (after curing) The polymerizable component M1 was filled into a through-hole (diameter 7 mm, through-hole length 0.5 mm) provided in the mold, and then both openings of the through-hole were sealed by pressing with polyester film. Thereafter, the polymerizable component M1 was irradiated with a light intensity of 500 mW / cm 2 onto the polymerizable component M1 filled in the through-hole. 2 The polymerizable components M1 and M2 were cured by irradiating them with light for 30 seconds using a halogen-type dental light irradiator (Demetron LC, manufactured by Cypron Co., Ltd.). Polymerizable component M2 was cured by heating under nitrogen pressure at 100°C for 30 minutes using a nitrogen pressure heat polymerizer, Polynar (manufactured by Towa Giken Co., Ltd.), instead of irradiating them with light. The refractive indexes of the cured products of polymerizable components M1 and M2 were then measured using the same procedure as in (2-1).

[0106] (2-3) Refractive index of radiopaque fillers and inorganic oxide fillers In a thermostatic chamber at 25°C, 1 g of radiopaque filler or inorganic oxide filler 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 where it became most transparent was measured using the same procedure as in (2-1), and the obtained value was taken as the refractive index of the radiopaque filler or inorganic oxide filler.

[0107] (3) Average primary particle size 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, rare earth metal fluoride particles were fixed on a sample stage with carbon paste, and then subjected to a conductive treatment (platinum vapor deposition) to prepare a measurement sample. 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.

[0108] (4) Average primary particle size of inorganic oxide filler The average primary particle size of the inorganic oxide filler was determined by particle size distribution measurement using the following procedure. First, 0.1 g of powder (inorganic oxide filler) 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 size (D50p value) at the cumulative 50% point from the smallest diameter side of the number particle size distribution was then taken as the average primary particle size.

[0109] (5) Measurement of the average secondary particle size of rare earth metal fluoride particles The average secondary particle size of the rare earth metal fluoride particles was determined by particle size distribution measurement using the following procedure. First, 0.1 g of powder (rare earth metal fluoride particles) was suspended in 10 mL of ion-exchanged water to prepare a suspension. Next, while irradiating this suspension with ultrasound, particle size distribution measurement was performed using a particle size distribution analyzer (LS13-320, manufactured by BECKMAN COULTER) to obtain a volumetric particle size distribution. The particle size (D50v value) corresponding to the cumulative 50% from the smallest diameter side of the volumetric particle size distribution was then taken as the average secondary particle size of the rare earth metal fluoride particles.

[0110] (6) Measurement of the average particle size of radiopaque filler The average particle size of the radiopaque filler was determined by particle size distribution measurement using the following procedure. First, 0.1 g of powder (radiopaque filler) was suspended in 10 mL of ethanol 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 volumetric particle size distribution. The particle size (D50v value) that was 50% cumulative from the smallest diameter side of the volumetric particle size distribution was then taken as the average particle size of the radiopaque filler.

[0111] (7) Measurement of X-ray contrast The X-ray contrast properties of the cured product of the curable composition were measured using the following procedure. First, a through-hole (15 mm diameter, 1.0 mm length) 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 that it was in close contact with the surface of the polypropylene film sealing the opening of the through-hole, and light was irradiated. Light was irradiated at five locations on one opening side of the through-hole (one location in the center of the through-hole and four locations inside the outer edge of the through-hole) and five locations on the other opening side (one location in the center of the through-hole and four locations inside the outer edge of the through-hole). Light was 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. Cured products with a thickness of 1.0 mm ± 0.1 mm or less were used as test specimens for measuring X-ray contrast properties.

[0112] Next, an X-ray film (ultra-sensitive dental X-ray film, manufactured by Kodak) was placed on a 2.0 mm thick lead sheet. Then, a test specimen and an aluminum step wedge with five thicknesses (thicknesses: 1.0 ± 0.01 mm, 2.0 ± 0.01 mm, 3.0 ± 0.01 mm, 4.0 ± 0.01 mm, and 5.0 ± 0.01 mm) were placed on top of the X-ray film. The test specimen and step wedge were then irradiated with X-rays from a height of 40 cm above the surface of the X-ray film using an X-ray irradiator (PANPAS-E, manufactured by YOSHIDA). The irradiation conditions were a tube voltage of 60 kVp and an exposure time of 0.3 seconds. The X-ray film was then developed and printed onto photographic paper. The optical densities of the test specimen and step wedge images on the photographic paper were then 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 properties.

[0113] (8) Transparency assessment The transparency of the cured product of the curable composition was measured using the following procedure. First, the curable composition was filled into a hole (0.7 cm diameter, 0.1 cm length) in a polyacetal mold, and both end openings of the through-hole were sealed by pressure 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 measured 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 specified 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 a white background. The contrast ratio C calculated using the following formula was used as an index of transparency. The contrast ratio C indicates that the material is more opaque as the value approaches 1, and that the material is more transparent as the value approaches 0. ·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.

[0114] (9) Evaluation of spectral reflectance ratio (SR1 / SR2 against a black background) The spectral reflectance ratio of the cured product of the 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 the wavelength range of 380 nm to 780 nm. Then, the spectral reflectance ratio R was calculated according to the following formula. ·Formula R=SR1 / SR2 In the formula, SR1 means the maximum value of reflectance in the yellow to red wavelength range (600 nm to 750 nm), and SR2 means the maximum value of reflectance in the blue wavelength range (400 nm to 500 nm).

[0115] (10) Bending strength measurement The bending strength of the cured product of the curable composition was measured using the following procedure. First, the curable composition was filled into a through-hole (25 mm long, 2 mm wide, 2 mm long) provided in a stainless steel mold, and both end openings of the through-hole were sealed by pressing with a polypropylene film. Next, light was irradiated while 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 through-hole opening. Light was irradiated at three locations on one opening side of the through-hole (one location in the center of the through-hole and two locations inside the outer edges at both ends of the length direction of the through-hole) and three locations on the other opening side (one location in the center of the through-hole and two locations inside the outer edges at both ends of the length direction of the through-hole). Then, light was irradiated for 20 seconds at each light irradiation location to obtain a cured product. The resulting cured product was polished with #1500 waterproof abrasive paper to a length of 25 mm ± 2 mm, width of 2 mm ± 0.1 mm, and thickness of 2 mm ± 0.1 mm. The cured product was then used as a test specimen for measuring bending strength. This test specimen was mounted on a precision universal testing machine (Autograph AG5000D, manufactured by Shimadzu Corporation) and the three-point bending fracture strength was measured at a support distance of 20 mm and a crosshead speed of 1 mm / min, obtaining a load-deflection curve. The bending strength was then calculated using the following formula: ·Formula σB=(3PS) / (2WB 2 ) Here, the symbols in the formula are, σB: bending strength (Pa), P: load at the time of fracture of the test piece (N), ,S: distance between supports (m), W: width of test piece (m), B: thickness of test piece (m).

[0116] [Table 1]

[0117] [Table 2]

[0118] [Table 3]

[0119] Table 4 < / ii>

Claims

1. The particle body comprises organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix, the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles measured by X-ray diffraction measurement after being made into organic-inorganic composite particles is 0.3° or more; An X-ray opaque filler characterized by having an average particle size of 38 μm to 110 μm.

2. 2. The radiopaque filler according to claim 1, wherein the average particle size is 38 μm to 70 μm.

3. 3. The radiopaque filler according to claim 1, wherein the average particle size is 38 μm to 55 μm.

4. 4. The radiopaque filler according to claim 1, wherein the content of the rare earth metal fluoride particles in the organic-inorganic composite particles is 60% by mass or more.

5. 5. The radiopaque filler according to claim 1, wherein the rare earth metal fluoride particles are ytterbium fluoride particles.

6. a mechanochemical treatment step of mechanochemically treating crystalline rare earth metal fluoride particles to obtain mechanochemically treated rare earth metal fluoride particles; a curing step of curing a raw material composition containing a polymerizable monomer and the mechanochemically treated rare earth metal fluoride particles to obtain a cured product; and a grinding step of grinding the cured product, A method for producing an X-ray-opaque filler, comprising: a particle body made of organic-inorganic composite particles including a resin matrix and mechanochemically treated rare earth metal fluoride particles dispersed in the resin matrix; wherein the X-ray-opaque filler has a full width at half maximum of 0.3° or more of the maximum intensity peak derived from the mechanochemically treated rare earth metal fluoride particles measured by X-ray diffraction measurement after being converted into organic-inorganic composite particles; and an average particle size of 38 μm to 110 μm.

7. 7. The method for producing a radiopaque filler according to claim 6, wherein the polymerizable monomer is a radical polymerizable monomer.

8. the crystalline rare earth fluoride particles are crystalline ytterbium fluoride particles, 8. The method for producing an X-ray-opaque filler according to claim 6, wherein the refractive index of the cured product of the polymerizable monomer at 25° C. to sodium d-line is 1.45 to 1.

60.

9. The composition comprises an X-ray opaque filler having an average particle size of 38 μm to 110 μm, a polymerizable monomer, and a polymerization initiator; the radiopaque filler contains a particle body made of organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix; A curable composition characterized in that the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles after being made into organic-inorganic composite particles is 0.3° or more, as measured by X-ray diffraction measurement.

10. The composition comprises an X-ray opaque filler having an average particle size of 38 μm to 110 μm, a polymerizable monomer, and a polymerization initiator; the radiopaque filler contains a particle body made of organic-inorganic composite particles containing a resin matrix and rare earth metal fluoride particles dispersed in the resin matrix; A dental curable composition characterized in that the full width at half maximum of the maximum intensity peak derived from the rare earth metal fluoride particles after being made into organic-inorganic composite particles, as measured by X-ray diffraction measurement, is 0.3° or more.

11. 11. The dental curable composition according to claim 10, further comprising an inorganic oxide filler having an average primary particle size of 100 nm to 1000 nm.

12. 12. The dental curable composition according to claim 11, wherein the inorganic oxide filler has an average primary particle size of 230 nm to 350 nm.

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