Particle material and dental material

Abstract

The problem addressed is to provide a particle material that can be used for a filler of a dental material, and to provide a dental material using the particle material.　The particle material of the present invention that solves this problem is aggregates containing primary particles having a specific surface area particle size of 1-250 nm, the interior of which is composed of two or more metal elements with one or more of the metal elements being a heavy element having an atomic number of 38 or more, and the surface of which is composed of silica, wherein the specific surface area is 180 2 / g or less, the linseed oil absorption amount per unit volume (100 cm3) is 200 g or less, the linseed oil absorption amount per unit surface area (m2) is 0.02 g or less, the light transmittance exceeds 10%, and the mass of the heavy elements is 4-60% based on the total mass. Using these aggregates makes it possible to achieve optical performance similar to that of a small particle size while improving the strength.

Description

Particulate materials and dental materials

[0001] The present invention relates to a particulate material and a dental material using the particulate material.

[0002] Conventional dental materials commonly use resin compositions called composite resins, which contain inorganic particulate materials dispersed in a resin material (see, for example, Patent Document 1). Pre-hardened materials such as monomers are used as the resin material. Composite resins are polymerized and hardened by filling a missing tooth site with the resin and then irradiating it with external energy such as light. The present applicant has provided a filler to be filled into resin compositions that can be used for dental purposes.

[0003] Japanese Patent Application Publication No. 2021-155399 Japanese Patent Application Publication No. 2021-172577

[0004] Resin compositions that can be used in dental applications are applications that require aesthetics. For example, dental resin compositions are required to have high strength and excellent appearance, such as gloss when polished (hereinafter referred to as "polishability"). The inventors of the present application believed that the filler disclosed in Patent Document 2 did not achieve both polishability and filling ability. As a result of extensive research, they discovered that in order to achieve both strength and polishability, it is necessary to limit the upper limit of the specific surface area so that a large amount of filler can be filled, and to reduce the linseed oil absorption per surface area, thereby improving polishability.

[0005] Furthermore, when used as a dental material, imparting X-ray contrast is a desirable physical property. Here, (meth)acrylic acid-based resin materials commonly used in dental materials have a refractive index of around 1.50. Metal oxides (such as zirconia) with X-ray contrast have a high refractive index, and simply adding them as a filler does not easily adjust the refractive index to around 1.50. Furthermore, adding them while maintaining the refractive index does not provide sufficient X-ray contrast. Furthermore, the exposure of metal oxides with X-ray contrast on the surface raises concerns about deterioration in polishability, reactivity with silane coupling agents, and stability.

[0006] The present invention was completed in view of the above circumstances, and an object to be achieved is to provide a particulate material that can be used as a filler in dental materials, and a dental material that uses the particulate material.

[0007] The particulate material of the present invention, which solves the above-mentioned problems, is composed of a metal oxide having two or more kinds of metal elements inside, at least one of which is a heavy element having an atomic number of 38 or more, and is an aggregate of primary particles having a specific surface area particle size of 1 nm to 250 nm, and the surface of which is made of silica, and the specific surface area is 180 m ２ / g or less, unit volume (100 cm ３ ) linseed oil absorption per unit surface area (m ２ ) the linseed oil absorption per unit weight is 0.02 g or less, the light transmittance is more than 10%, and the mass of the heavy elements is 4% to 60% based on the total mass.

[0008] By using aggregates, it is possible to improve strength while achieving optical performance close to that of small particle sizes. Because the surface of the aggregate is made of silica, it is possible to introduce any functional group onto the surface by using a silane coupling agent, etc., and it is also possible to suppress the exposure of heavy elements, etc. to the surface.

[0009] The particulate material of the present invention having the above-mentioned configuration can achieve both polishing properties and filling properties when used in dental materials.

[0010] The particulate material of the present invention and a dental material using the particulate material will be described in detail below based on the following embodiments. The particulate material of this embodiment can provide a resin composition with high translucency by dispersing it in a transparent resin material. Resin compositions with high translucency are suitable for use in dental materials such as denture materials and dental filling materials. (Particle Material) The particulate material of this embodiment is an aggregate of primary particles whose interior (referred to as the "core") is composed of a metal oxide containing two or more metal elements, at least one of which is a heavy element with an atomic number of 38 or higher, and whose surface is composed of silica, with a specific surface area of ​​1 nm to 250 nm.

[0011] The particulate material is preferably an aggregate formed by aggregation of primary particles bonded by dehydration condensation or fused together. OH groups exist on the surface of the metal oxide constituting the primary particles, and dehydration condensation occurs between adjacent primary particles, or the metal oxide melts and fuses together.

[0012] The particle size of the aggregates is not particularly limited. Because the primary particles are bonded and fused together, they are firmly bonded together, improving the mechanical strength of the particulate material. Since the strength can be improved as the particle size increases, it is preferable to increase the particle size to the extent that it can be mixed. For example, when the particulate material is to be applied to a form that may be physically inaccessible, such as a thin film, the appropriate particle size distribution of the particulate material is determined so that it can physically penetrate the form of the part to which it is to be applied.

[0013] The volume average particle size of the aggregates is preferably 0.1 μm or more and 10 μm or less, with examples of lower limits being 0.2 μm, 0.3 μm, 0.5 μm, and 1.0 μm, and examples of upper limits being 8.0 μm, 5.0 μm, and 3.0 μm. These lower and upper limits can be arbitrarily combined. When the particle size of the aggregates is in the range equal to or greater than the above-mentioned lower limit, strength is improved when applied to a resin composition. Furthermore, when the particle size is in the range equal to or less than the above-mentioned upper limit, the particulate material can be properly dispersed in the resin material, etc. Note that by mixing large and small particle size aggregates as individual aggregates, the filling rate at which the aggregates can be filled into the resin composition can be improved.

[0014] The specific surface area of ​​the aggregate is 180 m ２ / g or less. In particular, the upper limit is 160m ２ / g, 150m ２ / g, 130m ２ / g, 100m ２ / g can be exemplified, with a lower limit of 10m ２ / g, 115m ２ / g, 20m ２ / g, 30m ２ / g is an example. These lower and upper limits can be combined arbitrarily. The specific surface area is a value measured by the BET method using nitrogen gas.

[0015] The specific surface area particle size of the primary particles constituting the aggregates can be exemplified as lower limit values ​​of 3 nm, 5 nm, 9 nm, 11 nm, and 14 nm, and as upper limit values ​​of 240 nm, 180 nm, 120 nm, 100 nm, 80 nm, 60 nm, 50 nm, 40 nm, and 30 nm. These lower and upper limit values ​​can be arbitrarily combined. The specific surface area particle size is a particle size calculated from the specific surface area of ​​the aggregates, and is calculated based on the specific surface area measured by the BET method using nitrogen gas, assuming that the primary particles constituting the aggregates are spherical. Specifically, (specific surface area particle size: nm) = 6 ÷ {(specific gravity: g / nm) × (specific surface area: nm ２ ))

[0016] The aggregates are composed of an interior containing two or more metal elements and a surface made of silica. The metal elements constituting the interior of the aggregates are not particularly limited, but are preferably those with high oxide stability. Examples include aluminum, zirconium, titanium, and silicon, which can form oxides that are particularly stable against moisture. The two or more metal elements can exist in the interior of the aggregates as a single metal oxide or as a composite oxide of two or more metal elements.

[0017] These two metal elements can be contained as a single compound in each of the primary particles constituting the aggregate, thereby aggregating primary particles having multiple compositions. It is also possible to contain multiple metal elements or multiple compounds in a single primary particle. The metal elements contained in the aggregate also include silicon. In other words, the present invention also includes cases in which a particle material consisting solely of silica is contained as primary particles. Furthermore, primary particles composed of compounds consisting of elements other than the contained metal element can also be contained. Elements other than the metal element can be contained up to the amount in which the metal element is the main component. Here, the amount in which the metal element is the main component means a content of 50 mass% or more, preferably 70% or more, and more preferably 90% or more.

[0018] Metal elements may exist as metal oxides or may contain nitrides, carbides, etc. Specific internal compositions include aluminum oxide, zirconia, titania, silica, and composite oxides thereof. Examples of aluminum oxide include gamma alumina and boehmite.

[0019] At least one of the metal elements is a heavy element. A heavy element is an element with an atomic number of 38 or greater, and is preferably selected from the group consisting of zirconium, barium, and titanium, although not limited thereto. The content of the heavy element is 4% or more and 60% or less based on the total mass of the particulate material, with lower limits of 5%, 7%, 10%, and 14% being acceptable, and upper limits of 55%, 50%, 40%, and 30% being acceptable. These lower and upper limits can be combined arbitrarily.

[0020] The surface of the aggregate is composed of silica. "The surface of the aggregate is composed of silica" means that the lower limit of the area of ​​the portion of the aggregate surface covered with silica (hereinafter sometimes referred to as "silica portion" or "coating layer") is 50% or more, preferably 70%, 75%, or 80%, and more preferably completely covered with silica. The area of ​​the portion covered with silica can be measured from the exposed ratio of particles of heavy elements other than silica by direct observation with an electron microscope.

[0021] The particulate material preferably has a light transmittance of 10% or more, more preferably 15% or more, and even more preferably 20% or more.

[0022] Light transmittance was measured as follows. First, each test sample was placed in a test solution whose refractive index was adjusted in 0.005 increments. The OD values ​​were measured for five test solutions: the test solution with the highest visual transparency (the refractive index of this test solution was designated the refractive index of the test sample), and test solutions with refractive indices 0.005, 0.01, and 5. The refractive indexes of the obtained test solutions and their OD values ​​in the test solutions were plotted, and the light transmittance was calculated from the OD value at the apex of a quadratic curve approximated by a quadratic curve. The OD value was measured using a sample suspension (0.1 g of test sample suspended in 2 mL of test solution) in a 15 mm diameter hole using light with a wavelength of 589 nm.

[0023] The silica covering the surface is SiO ２ When converted to the total mass of the particulate material, the lower limit can be 40%, 50%, or 60%, and the upper limit can be 95%, 90%, or 85%. These lower and upper limits can be combined in any way.

[0024] The silica portion formed on the surface is a layer present on the surface of the aggregates. The thickness of the coating layer is not particularly limited, but it is preferable to coat the surface of the aggregates with almost no gaps. When a coating layer is present, it can be formed by coating the surfaces of the aggregated primary particles, resulting in direct aggregation of the primary particles (i.e., the coating layer is formed after the primary particles are aggregated), or it can be interposed between the aggregated primary particles (i.e., the coating layer is formed on the surfaces of the primary particles and then aggregated to form aggregates). The coating layer is preferably either covalently bonded to the surface of the primary particles or physically bonded via intermolecular bonding or the like. The organic substance constituting the coating layer is preferably a condensation product of a silane compound. A silane compound having two or more SiOR groups can form a coating layer composed of the condensation product. A method for producing a silane compound condensation product can be performed by condensing the aforementioned silane compound in contact with the surfaces of the primary particles (either before or after the formation of aggregates). The primary particles are typically made of an inorganic material and typically have OH groups on their surfaces. Therefore, the silane compound can react with the OH groups present on the surface of the primary particles to form covalent bonds.

[0025] A functional group may be introduced onto the surface of the silica portion. There are no particular limitations on the type of functional group to be introduced, but when dispersing in a resin material, it is preferable to introduce a functional group that has a high affinity with the resin material. For example, when acrylic acid and its esters, methacrylic acid and its esters, or epoxy resins are used as the resin material, introducing an acrylic group, a methacrylic group, an epoxy group, or the like can react with the resin material to form a strong bond.

[0026] The surface of the silica portion is provided with a compound represented by the formula (1): -OSiX １ X ２ X ３ and a functional group represented by formula (2): -OSiY １ Y ２ Y ３ In the formulas (1) and (2), X1 is a phenyl group, a vinyl group, an epoxy group, a methacryl group, an amino group, a ureido group, a mercapto group, an isocyanate group, or an acryl group; ２ , X ３ Ha-OSiR ３ and -OSiY ４ Y ５ Y ６ are each independently selected from the group consisting of: Y １ is R; Y ２ , Y ３ is R and -OSiY ４ Y ５ Y ６ are independently selected from the following: ４ is R; Y ５ and Y ６ is R and -OSiR ３ and R is independently selected from alkyl groups having 1 to 3 carbon atoms. ２ , X ３ , Y ２ , Y ３ , Y ５ , and Y ６ Any of the adjacent functional groups X ２ , X ３ , Y ２ , Y ３ , Y ５ , and Y ６ may be bonded to either of the above via —O—.

[0027] The refractive index of the particulate material can be controlled by adjusting the ratio of the amount of core to the amount of silica portion or by introducing functional groups into the silica portion. Because the particle size of the coated particles is small, the refractive index can be adjusted while maintaining transparency. When used in dental materials (described later), the difference in refractive index between the particulate material and the transparent resin material employed is preferably between -0.1 and 0.1.

[0028] The particulate material is packed into a unit volume (100 cm ３ The linseed oil absorption per unit area is 200 g or less, with particular upper limits of 170 g, 160 g, and 150 g being examples. This value can be reduced by increasing the packing rate of the particulate material or improving the sphericity. The unit volume is calculated by multiplying the apparent volume by 1 - porosity.

[0029] The unit surface area (m) calculated from the surface area of ​​the particulate material (measured by the BET method using nitrogen gas) ２ The linseed oil absorption per gram of powder is 0.02 g or less, with particular upper limits of 0.018 g, 0.016 g, and 0.014 g being examples of such values. This value can be reduced by increasing the packing density of the particulate material or by improving the sphericity. In particular, improving the sphericity is effective.

[0030] The particulate material may contain an inorganic particulate material having a volume average particle size of 1 nm to 200 nm and dispersed down to primary particles. The inorganic particulate material may be contained in an amount greater than 0% and not greater than 90% based on the total mass of the particulate material. Examples of lower limits for the content of the inorganic particulate material include 2%, 5%, and 10%, and examples of upper limits include 60%, 50%, and 40%. These lower and upper limits can be combined arbitrarily. By containing the inorganic particulate material in the above range, it is possible to reduce the viscosity of the resin composition and improve the toughness of the cured resin containing the inorganic particulate material.

[0031] The inorganic particle material is represented by the formula (1): —OSiX １ X ２ X ３ and a functional group represented by formula (2): -OSiY １ Y ２ Y ３and a functional group represented by the formula (1) are bonded to the surface of the silica particles. Formulas (1) and (2) are the same as those described above, and therefore description thereof will be omitted. (Method for producing particulate material) The method for producing particulate material of this embodiment is a method that can suitably produce the particulate material described above. The method for producing particulate material of this embodiment includes a dispersion step, a coating step, and other steps that can be selected as necessary. Examples of other steps include an aggregation step, a modification step, and a particle size distribution adjustment step.

[0032] The dispersion process is a process in which particles having the internal composition (core particles) are dispersed in a liquid dispersion medium to form a dispersion. Core particles can be obtained by a conventional method. For example, they can be produced by reacting a compound that serves as a precursor to the internal composition. For example, when zirconia is used as the internal composition, zirconia sol can be used. When boehmite is used, aluminum hydroxide, which has been milled to an appropriate particle size, can be used as a precursor, and then hydrothermal treatment can be performed to obtain core particles made of boehmite.

[0033] Furthermore, aluminum oxide with an appropriate particle size can be used as a precursor and heated in an acid or alkaline aqueous solution to obtain core particles. Colloidal silica can be considered as coated particles in which the surfaces of core particles made entirely of silica are coated with a surface composition made of silica, so adding colloidal silica is also included in the dispersion process. A mixture of multiple materials can be used as the core particles, or core particles made of multiple materials can be added sequentially.

[0034] The coating step is a step in which a precursor, which is a compound that becomes the surface composition (silica) by reaction, is added to the obtained dispersion to generate the surface composition, thereby coating and forming the surface of the core particles with the surface composition, thereby forming coated particles. When silica particles such as colloidal silica are added in the dispersion step, the colloidal silica acts as coated particles even without the coating step, because it is equivalent to coated particles in which the surface of core particles made of silica is coated with a surface made of silica.

[0035] The coating step may be carried out in one step or in multiple steps. Furthermore, when the dispersion step is carried out in multiple steps, the coating step may be carried out in the middle of the dispersion step. The ratio of the internal composition to the surface composition can be controlled by adjusting the amount of core particles and the amount of precursor added.

[0036] Any compound may be used as the precursor. For example, tetraethoxysilane can be used as the precursor. Tetraethoxysilane easily produces silica in the presence of water. A so-called sol-gel method can be used, in which tetraethoxysilane is hydrolyzed in an acidic or basic atmosphere.

[0037] The aggregation process is a process carried out after the coating process, in which the coated particles obtained in the coating process are heated to aggregate. Aggregates are formed in this process. The coated particles correspond to the primary particles of the aggregates. The obtained aggregates can be subjected to pulverization and classification to achieve the required particle size distribution. The heating temperature in the aggregation process is a temperature at which dehydration condensation and softening occur between the coated particles. Examples include temperatures above 250°C, 450°C or higher, and 500°C or higher. Heating within this temperature range can improve the strength of the obtained particulate material.

[0038] The modification step is a step carried out after the coating step, in which a silane compound is brought into contact with the surface of the coated particles obtained by the coating step to modify them. When combined with the aggregation step, the modification step can be carried out either before or after the aggregation step.

[0039] (Dental Material) The dental material of this embodiment includes the above-described particulate material and a transparent resin material that disperses the particulate material. The content of the particulate material is 10% or more and 80% or less by volume of the total material.

[0040] The particle materials that can be used are as described above, and further explanation will be omitted. The transparent resin material can be selected from ordinary resin materials such as thermoplastic resins and thermosetting resins. Examples include acrylic acid or acrylic acid esters and their derivatives, epoxy resins, polyimides, polycarbonates, polyethylene terephthalate, polybutylene terephthalate, polymethyl methacrylate, vinyl chloride, polypropylene, and polyethylene. The transparent resin material is a concept that includes not only polymeric materials but also precursors such as monomers before polymerization.

[0041] The method for dispersing the particulate material in the transparent resin material is not particularly limited. For example, when a thermoplastic resin is used as the transparent resin material, a transparent resin composition can be obtained by mixing and kneading a heated and melted transparent resin material with a particulate material, or by mixing a precursor of the transparent resin material (transparent resin precursor material: monomer, prepolymer, etc.) with a particulate material and then polymerizing the mixture. When the transparent resin material is a thermosetting resin, the transparent resin precursor and the particulate material can be mixed and then cured. Note that a mixture of a transparent resin precursor and a particulate material before polymerization is also included in the dental material of this embodiment. By using a photopolymerizable material as the transparent resin precursor material, a photopolymerizable transparent resin composition can be provided. The polymerized resin composition can be expected to have high transparency, a low coefficient of thermal expansion (CTE), and a high modulus of elasticity.

[0042] The particulate material of the present invention will be described in detail below based on examples. First, the production of the fillers used in the tests will be described. Fillers 1 to 8 are particulate materials of the present invention (Examples), and Fillers 9 to 13 are particulate materials outside the method of the present invention (Comparative Examples). (Sample Preparation) Filler 1: 300 g of isopropyl alcohol (IPA) and 50 g of tetraethoxysilane (Ethyl Silicate 28, Colcoat Co., Ltd.) were mixed, and then 500 g of zirconium sol (20% solids, Daiichi Kigenso Kagaku Kogyo Co., Ltd.: ZSL00014) was added and stirred, followed by standing at 25°C for 72 hours (dispersion process, coating process).

[0043] Thereafter, 2150 g of Snowtex OS (colloidal silica acidic sol, particle size 9 nm, solid content 20% by mass: Nissan Chemical Industries, Ltd.) was added, stirred, and allowed to stand at 44°C for 24 hours. 5% aqueous ammonia was added to adjust the pH to 8-9. The resulting liquid was a sol with good fluidity (dispersion step). The resulting sol was dried in a hot air dryer at 140°C for 14 hours (aggregation step).

[0044] The dried product was adjusted using a mixer and a dry jet mill so that D50 was 2 μm (particle size distribution adjustment step), and then calcined in an electric furnace at 1010 °C for 6 hours (calcination step). The BET specific surface area of ​​the calcined powder was 102 m ２ / g.

[0045] 10 parts by mass of 3-methacryloxypropyltrimethoxysilane (KBM503, manufactured by Shin-Etsu Chemical Co., Ltd.) was added to the powder obtained by firing and stirred with a mixer, thereby uniformly adhering the silane to the surface of the fired powder. Note that Fillers 1 to 11 shown in this example were prepared by adding 3-methacryloxypropyltrimethoxysilane to a powder having a surface area of ​​1 m. ２ 4 μmol per 1000g of zirconia was reacted. The mixture was then left to stand at 44°C for 24 hours, and then dried in a hot air dryer at 105°C for 6 hours to obtain Filler 1, the test sample for this test (modification step). The obtained Filler 1 is an aggregate formed by sintering coated particles in which zirconia core particles are coated with silica and silica particles (corresponding to coated particles in which silica is used as a core particle and is coated with silica), with 3-methacryloxypropyl groups introduced onto the surface. The introduction of 3-methacryloxypropyl groups is intended to enhance affinity with the adjusting resin described below, and the type of functional group that is preferably introduced varies depending on the type of resin to be mixed, and is selected appropriately. Filler 2: In the calcination step, the powder was calcined at 1020°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by calcination was 63m). ２Filler 2, a test sample for this test, was obtained in the same manner as Filler 1, except that 6 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder in the modification step. Filler 3: In the firing step, the powder was fired at 1040°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 25 m). ２ Filler 3, a test sample for this test, was obtained in the same manner as Filler 1, except that 3 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder in the modification step. Filler 4: In the firing step, the powder was fired at 850°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 159 m). ２ Filler 4, a test sample for this test, was obtained in the same manner as Filler 1, except that in the modification step, 16 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder. Filler 5: In the dispersion step, the amount of Snowtex OS was 1,525 g, and in the firing step, the powder was fired at 850°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 155 m). ２ Filler 5, a test sample for this test, was obtained in the same manner as Filler 1, except that in the modification step, 15 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder. Filler 6: In the dispersion step, the amount of Snowtex OS was 2750 g, and in the firing step, the powder was fired at 1010°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 47 m). ２ Filler 6, a test sample for this test, was obtained in the same manner as Filler 1, except that in the modification step, 5 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder. Filler 7: In the dispersion step, the amount of Snowtex OS was 3,660 g, and in the firing step, the powder was fired at 1,010°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 43 m). ２Filler 7, a test sample for this test, was obtained in the same manner as Filler 1, except that in the modification step, 4 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder. Filler 8: In the dispersion step, the amount of Snowtex OS was 415 g, and in the firing step, the powder was fired at 850°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 150 m). ２ Filler 8, a test sample for this test, was obtained in the same manner as Filler 1, except that 15 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder in the modification step. Filler 9: In the firing step, the powder was fired at 1080°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 12 m). ２ Filler 9, a test sample for this test, was obtained in the same manner as Filler 1, except that 1 part by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder in the modification step. Filler 10: In the dispersion step and coating step, the amount of tetraethoxysilane was 105 g, and 500 g of Aluminum Sol 10A (solid content 10% by mass, manufactured by Kawaken Fine Chemical Co., Ltd., crystalline form: pseudoboehmite) was used instead of zirconia sol, the amount of Snowtex OS was 500 g in the dispersion step, and the firing step involved firing the powder at 1090°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 100 m ２ Filler 10, a test sample for this test, was obtained in the same manner as Filler 1, except that 10 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the fired powder in the modification step. Filler 11: In the firing step, the powder was fired at 1100°C for 6 hours using an electric furnace (the BET specific surface area of ​​the powder obtained by firing was 50 m). ２ / g), and the test sample Filler 11 for this test was obtained using the same process as Filler 8, except that 5 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to the calcined powder as a modification step. Filler 12: 0.4 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to 100 parts by mass of a particulate material made of silica (volume average particle size 2 μm, manufactured by Admatechs Co., Ltd., SO-C6) and stirred in a mixer. The mixture was then left to stand at 25°C for 72 hours and then dried in a hot air dryer at 105°C for 6 hours to obtain surface-treated Filler 12. Filler 13: 20 parts by mass of 3-methacryloxypropyltrimethoxysilane was added to 100 parts by mass of hydrophilic fumed silica (manufactured by Nippon Aerosil Co., Ltd., AEROSIL200) and stirred in a mixer. The mixture was then left to stand at 25°C for 72 hours and then dried in a hot air dryer at 105°C for 6 hours to obtain surface-treated Filler 13. (Linseed oil absorption and specific surface area) 5 to 10 g of each test sample was weighed out and measured. While adding linseed oil little by little, the mixture was stirred in a foam mixer at 2000 rpm at normal pressure for 1 minute, and then at 2000 rpm at 7.5 kPa for 1 minute, repeating this process. The amount of linseed oil required just before the mixture became paste-like was used to calculate the linseed oil absorption according to the following formula. The specific gravity was 2.38 g / cm for silica. ３ , zirconia 6.00 g / cm ３ , alumina 3.36 g / cm ３ The specific surface area was measured by the BET method using nitrogen gas. (linseed oil absorption [g / 100g]) = (total mass of added linseed oil) / (mass of filler used) × 100, (linseed oil absorption [g / 100cm ３ )=(linseed oil absorption amount [g / 100g])×specific gravity [g / cm ３ ], (linseed oil absorption [g / m ２ ]) = (linseed oil absorption [g / 100g]) / (specific surface area [m ２ / g] × 100), (Abrasiveness) 10 g of each test sample and 10 g of the prepared resin were mixed in a foam mixing mixer at 2000 rpm at normal pressure for 1 minute, and then at 2000 rpm at 3 kPa for 3 minutes. The resulting slurry-like resin composition was poured into a mold measuring 2.6 cm square and 6 mm high, and cured in a UV oven. For Fillers 6 and 9, a slurry-like resin composition could not be prepared.

[0046] The resulting cured product was polished for 2 minutes with #400 polishing paper using a pressure polishing machine (Doctor-lap, manufactured by Maruto) under the polishing conditions of LOAD ADJUST 0.35, BALANCER 0.35, HEAD SPEED 3.2, SPEED 20.

[0047] Thereafter, polishing was carried out under the same polishing conditions except that the polishing paper was replaced with #2000, and the sample was checked every 10 seconds to measure the time until gloss was observed on the entire polished surface.

[0048] The adjusting resin used was a mixture of 60 parts by mass of urethane dimethacrylate (Sigma-Aldrich), 40 parts by mass of triethylene glycol dimethacrylate (Shin-Nakamura Chemical Co., Ltd.), 0.3 parts by mass of camphorquinone (Sigma-Aldrich), and 1 part by mass of ethyl 4-dimethylaminobenzoate (Tokyo Chemical Industry Co., Ltd.). (Refractive Index and Light Transmittance) The refractive index and light transmittance are measured by the methods described in the embodiments. Hereinafter, the above operations will be specifically explained using a filler adjusted to a refractive index of 1.51 as an example.

[0049] The filler adjusted to a refractive index of 1.51 has the highest transparency when immersed in a test liquid with a refractive index of 1.51, so test liquids with refractive indices of around 1.51, 0.005, 0.010, and 1.500, 1.505, 1.510, 1.515, and 1.520 were prepared using cyclohexane, toluene, and bromonaphthalene.

[0050] 0.1 g of test sample was placed in 2 mL of this test solution and placed in a 15 mm diameter hole, and the optical density (OD value) was measured in the vertical direction at a wavelength of 589 nm. The OD value and refractive index in each test solution were plotted and approximated to a quadratic curve, and the light transmittance was calculated from the OD value at the apex (the point with the lowest OD value). (Results) The refractive index, specific surface area, linseed oil absorption, zirconium (element with 38 or more elements) content, zirconia content (converted to simple Zr), light transmittance, and polishability are shown in Table 1.

[0051] As is clear from Table 1, the unit volume (100 cm ３ It was found that Fillers 10 and 13, which have a linseed oil absorption per unit mass (m) of more than 200 g, do not form a slurry even when mixed with the adjusting resin at a mass ratio of 1:1, and are unable to exhibit sufficient filling properties in the resin material. ２ When the polishing properties of Fillers 9 and 12, which have a linseed oil absorption of more than 0.02 g per particle, were examined, it was found that Filler 9 required 120 seconds, which was longer than the other fillers, until gloss appeared, while Filler 12 did not appear glossy after polishing.

[0052] Fillers 1, 2, 3, 4, and 9 were produced by almost the same procedure except that the temperature in the firing process was changed. It was found that the specific surface area decreased as the firing temperature increased. As the specific surface area decreased, the linseed oil absorption per surface area increased to 0.02 g / m. ２ It was found that the filler 9 exceeding this value had a reduced light transmittance and abrasiveness.

Claims

1. An aggregate consisting of a metal oxide having two or more kinds of metal elements, at least one of which is a heavy element with an atomic number of 38 or more, a specific surface area of ​​primary particles having a particle size of 1 nm to 250 nm, and a surface of silica, and a specific surface area of ​​180 m ２ / g or less, unit volume (100 cm ３ The linseed oil absorption per unit surface area (m ２ a linseed oil absorption of 0.02 g or less per particle; a light transmittance of more than 10%; and a mass of the heavy elements of the particulate material of 4% to 60% based on the total mass.

2. The particulate material according to claim 1, wherein the volume average particle size is 0.1 μm to 10 μm, and the primary particles are bonded or fused together by dehydration condensation.

3. The particulate material according to claim 1, comprising an inorganic particulate material having a volume average particle size of 1 nm to 200 nm and dispersed into primary particles.

4. The inorganic particulate material has the formula (1): -OSiX １ X ２ X ３ and a functional group represented by formula (2): -OSiY １ Y ２ Y ３ The particle material according to claim 3, wherein the functional group represented by the formula (1) or (2) is bonded to the surface of the silica particle. ２ , X ３ Ha-OSiR ３ and -OSiY ４ Y ５ Y ６ are each independently selected from the group consisting of: １ is R; Y ２ , Y ３ is R and -OSiY ４ Y ５ Y ６ are each independently selected from the following: ４ is R; Y ５ and Y ６ is R and -OSiR ３ R is independently selected from alkyl groups having 1 to 3 carbon atoms. ２ , X ３ , Y ２ , Y ３ , Y ５ , and Y ６ Either of the X of the adjacent functional group ２ , X ３ , Y ２ , Y ３ , Y ５ , and Y ６ may be bonded to any one of the above via -O-.) 5. The particulate material according to claim 1, which is dispersed in a transparent resin material and used in a dental material.

6. The particulate material according to claim 5, wherein the difference in refractive index between said particulate material and said transparent resin material is -0.01 to 0.

01.

7. A dental material comprising: a particulate material according to any one of claims 1 to 4; and a transparent resin material in which the particulate material is dispersed, wherein the content of the particulate material is 10% to 80% based on the total volume.

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