Dental-use curable composition, inorganic powder granular body, and method for producing same

Abstract

This dental-use curable composition contains: a polymerizable monomer (M); and a specific inorganic powder granular body (C) constituted from aggregated particles (c) composed of: inorganic particles (a) that constitutes an inorganic powder / granular body (A) having a specific average particle diameter and zeta potential; and inorganic particles (b) that constitutes an inorganic powder / granular body (B) having a specific average particle diameter and zeta potential. The dental-use curable composition further contains at least one selected from the inorganic powder / granular body (A) and a specific organic / inorganic composite powder / granular body (D), and the content of each of the powder / granular bodies is in a specific range.　The present invention successfully provides a dental-use curable composition that demonstrates high dispersibility of an inorganic powder granular body in the composition and good discharge properties from a syringe, that has adequate fluidity, that exhibits little change in fluidity over time and that has high mechanical strength after curing.

Description

Dental hardenable composition, inorganic powder and granules, and method for producing the same

[0001] The present invention relates to a dental curable composition, an inorganic powder and granules, and a method for producing the same.

[0002] Dental curable compositions contain, as their main components, a polymerizable monomer, an inorganic filler consisting of an aggregate of inorganic particles (inorganic powder), and a polymerization initiator. Among these, composite resins are one of the most widely used materials in dental treatment as materials for repairing cavities after removing tooth defects or caries.

[0003] Composite resins are required to have excellent properties such as ease of handling in a paste state before polymerization and hardening, aesthetics of the hardened product obtained after polymerization and hardening, and mechanical strength. In recent years, flowable composite resins have been developed in which a needle with a small hole called a needle tip is attached to a syringe containing composite resin paste, and the paste can be directly filled into a cavity from the tip of the needle. These resins are becoming more widely used in clinical settings because they allow for easier tooth restoration.

[0004] The flowable composite resin is required to have good operability when filling a cavity, specifically good ejection properties when ejected from a syringe equipped with a needle tip, and to have appropriate fluidity in a paste state depending on the case, etc. For example, if the fluidity in the paste state is too high, the paste will tend to drip and its formability (the ability to maintain its shape and not to deform due to natural flow when left standing) will be poor, so it is necessary for the resin to have appropriate fluidity.

[0005] Fullable composite resins have a relatively low inorganic powder content, which increases fluidity and improves dischargeability from a syringe, but the increased fluidity can sometimes make it difficult to achieve formability.

[0006] In response to such problems, Patent Document 1 discloses a technique for improving the physical properties of composite resins by using two types of inorganic powders in a specific ratio, each of which exhibits a zeta potential (in water) of opposite polarity and has a specific average particle size and specific surface area. In the examples, the technique uses a polymerizable monomer, a silica-based composite oxide having an average particle size of 50 nm to 1 μm, and a silica-based composite oxide having a specific surface area of ​​25 to 100 m. ２ It is described that a dental hardenable composition containing a crystalline rare earth metal fluoride having a fluoride content of 1000 ppm or more and a crystalline rare earth metal fluoride having a fluoride content of 1000 ppm or more has good ejectability (has a consistency suitable for ejection from a syringe) and exhibits appropriate fluidity that suppresses dripping of the paste.

[0007] International Publication No. 2023 / 085201 Pamphlet

[0008] As described above, Patent Document 1 discloses that a dental hardenable composition (paste-like) having appropriate fluidity can be obtained by using a silica-based composite oxide and a crystalline rare earth metal fluoride, which have different zeta potential polarities. However, Patent Document 1 does not discuss changes in the fluidity of the dental hardenable composition over time. According to the inventors' studies, the dental hardenable composition described in Patent Document 1 may become highly fluid and lose its appropriate fluidity when stored for a long period of time (for example, at 50°C for about one week).

[0009] Therefore, an object of the present invention is to provide a dental curable composition that has high dispersibility of inorganic powder particles in the composition, good dischargeability from a syringe, appropriate fluidity with little change in fluidity over time, and high mechanical strength after curing. Another object of the present invention is to provide an inorganic powder particle that has good dispersibility when blended in a dental curable composition, and a method for producing the same.

[0010] The present inventors have conducted extensive research to achieve the above-mentioned object, and as a result have found that the above-mentioned problems can be solved by a dental curable composition comprising a polymerizable monomer (M) and specific inorganic powder particles (C) constituted by agglomerated particles (c) consisting of inorganic particles (a) constituting inorganic powder particles (A) having a specific average particle size and zeta potential and inorganic particles (b) constituting inorganic powder particles (B) having a specific average particle size and zeta potential, and further comprising at least one kind selected from the inorganic powder particles (A) and specific organic-inorganic composite powder particles (D), wherein the contents of each powder particle are within specific ranges, and have thus completed the present invention.

[0011] The gist of the present invention is the following [1] to

[12] . [1] An inorganic powder granule (C) comprising: 100 parts by mass of a polymerizable monomer (M); and agglomerated particles (c) comprising: a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential when measured in water, and having an average primary particle diameter of 50 nm to 1 μm when measured by an electron microscope; and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, and having an average primary particle diameter of 1 to 300 nm when measured by an electron microscope, wherein the average value of the total mass of the inorganic particles (b) per 100 parts by mass of the total mass of the inorganic particles (a) contained in each of the agglomerated particles (c) constituting the inorganic powder granule (C) is within the range of 20 to 300 parts by mass. the inorganic powder particles (C) having an average agglomerated particle size of 1 to 50 μm, which is defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method; and 10 to 100 parts by mass of an inorganic powder particle (C), the inorganic powder particle (C) further comprising at least one of the inorganic powder particle (A) and an organic-inorganic composite powder particle (D), the organic-inorganic composite powder particle (D) being constituted by organic-inorganic composite particles (d) made of a composite material of the inorganic powder particle (A) and a resin, the content of the inorganic powder particle (A) in the composite material being 60 to 90 mass%, and the organic-inorganic composite powder particle (D) having an average particle size of 1 to 100 μm, which is defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method. [2] The dental curable composition according to the above [1], wherein the inorganic particles (b) are uniformly dispersed in the inorganic particles (a) in the individual agglomerated particles (c) constituting the inorganic powder granules (C).[3] The dental curable composition according to [1] or [2] above, wherein the inorganic particles (a) are made of a silica-based inorganic compound and the inorganic particles (b) are made of a crystalline rare earth metal fluoride. [4] The dental curable composition according to [1] to [3] above, wherein the full width at half maximum of the maximum intensity peak attributable to the crystalline rare earth metal fluoride in an X-ray diffraction pattern obtained by X-ray diffraction measurement of the inorganic powder granules (B) is 0.3° or more. [5] The dental curable composition according to [1] to [4] above, wherein the inorganic powder granules (C) are obtained by spray-drying a uniformly mixed slurry obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder granules (A) are dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder granules (B) are dispersed in a dispersion medium. [6] A method for producing the dental curable composition according to any one of [1] to [5] above, comprising mixing the polymerizable monomer (M), the inorganic powder (C), and at least one of the inorganic powder (A) and the organic-inorganic composite powder (D). [7] A method for producing the dental curable composition according to [6] above, comprising mixing the inorganic powder (C) with a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium and a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium, and spray-drying the resulting homogeneous mixed slurry. [8] A method for producing the dental curable composition according to [7] above, wherein the mixed slurry does not contain an ionic surfactant. [9] A method for producing the dental curable composition according to [7] or [8] above, wherein the mixed slurry has a concentration of less than 40% by mass.

[10] An inorganic powder / granule (C) comprising agglomerated particles (c) including a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential polarity when measured in water, and an average primary particle diameter measured by an electron microscope of 50 nm to 1 μm, and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential polarity when measured in water, and an inorganic powder / granule (B) comprising a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential polarity when measured in water, and an average primary particle diameter measured by an electron microscope of 1 to 300 nm, wherein the average value of the total mass of the inorganic particles (b) per 100 parts by mass of the total mass of the inorganic particles (a) contained in each agglomerated particle (c) constituting the inorganic powder / granule (C) is within a range of 20 to 300 parts by mass, An inorganic powder or granule having an average agglomerate particle size of 1 to 50 μm, defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method, and containing no ionic surfactant.

[11] A method for producing the inorganic powder or granule according to

[10] above, comprising a step of spray-drying a uniform mixed slurry obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder or granule (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder or granule (B) is dispersed in a dispersion medium, wherein the mixed slurry contains no ionic surfactant.

[12] A method for producing the inorganic powder or granule according to

[11] above, wherein the concentration of the mixed slurry is less than 40% by mass.

[0012] According to the present invention, it is possible to provide a dental curable composition that has high dispersibility of inorganic powder particles in the composition, good dischargeability from a syringe, appropriate fluidity with little change in fluidity over time, and high mechanical strength after curing. Furthermore, according to the present invention, it is possible to provide an inorganic powder particle that has good dispersibility when blended in a dental curable composition, and a method for producing the same.

[0013] 1 is a diagram showing a schematic diagram of inorganic powder particles (A) to (C) in the present invention. 2 is an image obtained by observing with a scanning electron microscope the cured product of the dental curable composition of Example 1. 3 is an image obtained by observing with a scanning electron microscope the cured product of the dental curable composition of Comparative Example 8.

[0014] [Dental curable composition] The dental curable composition of the present invention contains inorganic powder particles (C) composed of a polymerizable monomer (M) and agglomerated particles (c). Furthermore, the dental curable composition of the present invention contains at least one of inorganic powder particles (A) and organic-inorganic composite powder particles (D) as a powder particle other than the inorganic powder particles (C). Here, the agglomerated particles (c) are agglomerated particles composed of inorganic particles (a) constituting the inorganic powder particles (A) and inorganic particles (b) constituting the inorganic powder particles (B). Therefore, the dental curable composition of the present invention can contain the inorganic powder particles (A) and the inorganic powder particles (B) in specific forms, specifically, (A) in the form of (C), (A) as is, or (D), and (B) in the form of (C). Each component of the dental curable composition of the present invention will be described in detail below.

[0015] In this specification, unless otherwise specified, the expression "x to y" using numerical values ​​x and y means "greater than or equal to x and less than or equal to y." In such an expression, when a unit is assigned only to the numerical value y, the unit also applies to the numerical value x. 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."

[0016] <Polymerizable Monomer (M)> The dental curable composition of the present invention contains a polymerizable monomer. As the polymerizable monomer, polymerizable monomers such as radical polymerizable monomers and cation polymerizable monomers used in conventional dental curable compositions can be used without any particular limitation. Among them, it is preferable to use commonly used (meth)acrylate polymerizable monomers, specifically acidic group-containing (meth)acrylate polymerizable monomers, hydroxyl group-containing (meth)acrylate polymerizable monomers, and monofunctional and polyfunctional (meth)acrylate polymerizable monomers that do not have these substituents.

[0017] Examples of suitable (meth)acrylate polymerizable monomers include the following: Acidic group-containing (meth)acrylate polymerizable monomers include (meth)acrylic acid, N-(meth)acryloyl-p-aminobenzoic acid, 2-(meth)acryloyloxybenzoic acid, 2-(meth)acryloyloxyethylphenylhydrogenphosphate, and 2-(meth)acryloyloxyethylphosphonic acid. Hydroxyl group-containing (meth)acrylate polymerizable monomers include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 2,2-bis[(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane, and 2,2-bis[4-(4-methacryloyloxy)-3-hydroxybutoxyphenyl]propane. Furthermore, examples of the monofunctional and polyfunctional (meth)acrylate polymerizable monomers not having the above-mentioned substituents include methyl (meth)acrylate, ethyl (meth)acrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,6-bis(methacrylethyloxycarbonylamino)trimethylhexane, and 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane.

[0018] Among these polymerizable monomers, bifunctional or higher functional polymerizable monomers, more preferably bifunctional to tetrafunctional polymerizable monomers, are preferred because of their high polymerizability and the particularly high mechanical strength of the cured product, etc. These polymerizable monomers may be used alone or in combination.

[0019] <Inorganic Powder and Particle (C)> The inorganic powder and particle (C) contained in the dental curable composition of the present invention is an inorganic powder and particle (C) composed of agglomerated particles (c) including a plurality of inorganic particles (a) that are made of the same material and that exhibit a negative zeta potential when measured in water, and that have an average primary particle diameter of 50 nm to 1 μm when measured with an electron microscope. The inorganic particles (a) that constitute inorganic powder and particle (A) are composed of a plurality of inorganic particles (b) that are made of the same material and that exhibit a positive zeta potential when measured in water, and that have an average primary particle diameter of 1 to 300 nm when measured with an electron microscope. The average value of the total mass of the inorganic particles (b) per 100 parts by mass of the total mass of the inorganic particles (a) contained in each of the aggregated particles (c) constituting the inorganic powder or granule (C) is in the range of 20 to 300 parts by mass, and the average aggregate particle diameter, defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method, is 1 to 50 μm. Each component constituting the inorganic powder or granule (C) will be described in detail below.

[0020] The inorganic powder (A) contained as the inorganic powder (C) in the dental curable composition of the present invention is composed of a plurality of inorganic particles (a), as shown schematically in FIG. 1 . The inorganic powder (A) is an aggregate of the inorganic particles (a), which are primary particles. Furthermore, the inorganic powder (A) composed of a plurality of inorganic particles (a) exhibits a negative zeta potential when measured in water, and the plurality of inorganic particles (a) are composed of the same material. Note that "composed of the same material" means that the plurality of inorganic particles (a) constituting the inorganic powder (A) have the same chemical structure.

[0021] The inorganic powder (B) contained as the inorganic powder (C) in the dental curable composition of the present invention is composed of a plurality of inorganic particles (b), as shown schematically in FIG. 1 . The inorganic powder (B) is an aggregate of the inorganic particles (b), which are primary particles. Furthermore, the inorganic powder (B) composed of a plurality of inorganic particles (b) exhibits a positive (plus) zeta potential measured in water, and the inorganic particles (b) are composed of the same material. "Composed of the same material" means that the plurality of inorganic particles (b) constituting the inorganic powder (B) have the same chemical structure. Here, the polarity of the zeta potential measured in water refers to the polarity (i.e., positive or negative) of the zeta potential measured by electrophoretic light scattering for inorganic powder dispersed in ion-exchanged water at pH 7.

[0022] As shown schematically in FIG. 1 , the inorganic powder (C) is composed of agglomerated particles (c) consisting of inorganic particles (a) constituting the inorganic powder (A) and inorganic particles (b) constituting the inorganic powder (B). The agglomerated particles (c) are composed of a plurality of inorganic particles (a) and a plurality of inorganic particles (b), and any inorganic particle constituting the agglomerated particle is in contact with any other inorganic particle constituting the agglomerated particle. The formation of agglomerated particles (c) can be confirmed using an electron microscope. The inorganic powder (C) is an aggregate of a plurality of agglomerated particles (c). When the inorganic powder (C) is incorporated into a dental curable composition, the generation of aggregates, particularly the generation of aggregates caused by the inorganic particles (b), is suppressed. For example, when a crystalline rare earth metal fluoride is used as the inorganic particle (b), aggregates of the crystalline rare earth metal fluoride are generally likely to be generated. However, when the inorganic powder (C) is incorporated into a dental curable composition, the generation of aggregates is suppressed. Therefore, the dental curable composition of the present invention exhibits good dispersibility of the inorganic powder and can minimize changes in fluidity over time. While the reason for this is unclear, it is presumed to be as follows. That is, since the inorganic powder (C) is composed of agglomerated particles (c), the inorganic particles (b) such as crystalline rare earth metal fluoride and the inorganic particles (a) such as silica-based inorganic compounds are dispersed and mixed at the primary particle level. This suppresses the formation of aggregates of the inorganic particles (b) such as crystalline rare earth metal fluoride, thereby improving dispersibility. It is believed that the suppression of the formation of aggregates of the inorganic particles (b) such as crystalline rare earth metal fluoride can minimize changes in the fluidity of the dental curable composition over time.

[0023] Furthermore, inorganic powder and granules (C) can be produced, for example, by spray-drying a mixed slurry containing inorganic powder and granules (A) and inorganic powder and granules (B), as described below. The use of inorganic powder and granules (C) can suppress an increase in the viscosity of the slurry used during production, making it easier to produce by spray-drying. The reason for this is unclear, but is presumed to be as follows. As described above, inorganic particles (a) exhibit a negative zeta potential in water, while inorganic particles (b) exhibit a positive zeta potential in water. In the present invention, the average primary particle diameters of inorganic powder and granules (A) composed of inorganic particles (a) and inorganic powder and granules (B) composed of inorganic particles (b) are each set within a specific range, and the content of inorganic particles (b) relative to inorganic particles (a) is set within a specific range. Therefore, it is presumed that in the slurry used for spray drying, units are formed in which inorganic particles (a) exhibiting a negative zeta potential are surrounded by inorganic particles (b) exhibiting a positive zeta potential, and the units repel each other due to their positive charge, thereby suppressing an increase in viscosity. The structure of the inorganic powder / granules (C) will be described in more detail below. First, inorganic powder / granules (A) and inorganic powder / granules (B), which are part of the inorganic powder / granules (C) and are used as raw materials for producing the inorganic powder / granules (C), will be described.

[0024] The inorganic powder (A) in the present invention is composed of a plurality of inorganic particles (a). The inorganic powder (A) has an average primary particle diameter of 50 nm to 1 μm. The average primary particle diameter is measured using a scanning or transmission electron microscope as follows. That is, n inorganic primary particles (a), which are 30 or more, preferably 100 or more, randomly selected from electron microscope images in which light and shade are clearly distinguishable and particle contours can be distinguished, are analyzed by image analysis to determine the circle-equivalent diameter (the diameter of a circle having the same area as the target particle) of each inorganic particle (a): X ｉ Find the first to nth X ｉ ３ Sum of: ΣX ｉ ３ Based on the formula: X = {(ΣX ｉ ３ ) / n} １／３ The average particle (volume) diameter: X calculated by

[0025] By setting the average primary particle size of the inorganic powder granules (A) to 50 nm to 1 μm and, as described below, setting the average primary particle size of the inorganic powder granules (B) and the mass ratio of the inorganic particles (a) to the inorganic particles (b) contained in the aggregate particles (c) within specific ranges, it becomes easier to adjust the viscosity of the slurry during the production of the inorganic powder granules (C) to a low value. Therefore, when the average primary particle size of the inorganic powder granules (A) is 50 nm to 1 μm, the inorganic powder granules (C) can be easily obtained by a spray drying method. From this perspective, as well as from the perspective of improving the polishability of the cured product when blended into a dental curable composition, the average primary particle size of the inorganic powder granules (A) is preferably 0.15 to 1.0 μm, and more preferably 0.15 to 0.8 μm.

[0026] The shape of the inorganic particles (a) constituting the inorganic powder and granules (A) is not particularly limited, and spherical, approximately spherical, or irregularly shaped particles can be used, but from the viewpoint of excellent abrasion resistance and surface smoothness of the cured product of the dental curable composition, spherical or approximately spherical is preferred. Note that the term "approximately spherical" refers to the longest length of each particle determined by image analysis of the n inorganic particles (a), which are 30 or more, preferably 100 or more, selected from the photographed image used when measuring the average particle diameter, as expressed by the major axis: L ｉ and the minimum width, which is the diameter in the direction perpendicular to the major axis: B ｉ Ratio to: B ｉ / L ｉ The sum of the first to nth items: ΣB ｉ / L ｉ Based on the formula: Pr = (ΣB ｉ / L ｉ ) / n: The average uniformity Pr is preferably 0.7 or more, and particularly preferably 0.8 or more. The upper limit of the average uniformity is 1.

[0027] The material of the inorganic particles (a) constituting the inorganic powder and granules (A) is not particularly limited as long as the polarity of the zeta potential is negative. Examples of materials that can be used include metal oxides such as amorphous silica, quartz, titania, zirconia, chromium oxide, iron oxide, and tungsten oxide, which are used as fillers in conventional dental curable compositions; and composite oxides such as silica-zirconia, silica-titania, silica-titania-barium oxide, silica-titania-zirconia, borosilicate glass, aluminosilicate glass, and fluoroaluminosilicate glass. Because of their general use and ease of availability, the material of the inorganic particles (a) is preferably a silica-based inorganic compound. By silica-based inorganic compound is meant an inorganic compound containing silica. Among silica-based inorganic compounds, silica-based composite oxides such as the silica-zirconia, silica-titania, silica-titania-barium oxide, and silica-titania-zirconia are particularly preferred, with silica-zirconia being more preferred. Many silica-based composite oxide particles have strong acid sites on their surfaces, and the negative degree of the zeta potential is often large. The zeta potential of the inorganic powder (A) in water is preferably −20 mV or less, more preferably −40 mV or less. The lower limit of the zeta potential is not particularly limited, but is generally −100 mV or more. The inorganic powder (A) may be a combination of multiple inorganic powders with different average primary particle sizes, and in that case, the zeta potentials of the multiple inorganic powders are preferably each within the above-mentioned range. The inorganic powder (A) may also be surface-treated with a silane coupling agent or the like, as long as the treatment does not change the polarity of the zeta potential.

[0028] The inorganic powder (B) in the present invention is composed of a plurality of inorganic particles (b). The average primary particle diameter of the inorganic powder (B) is 1 to 300 nm. By setting the average primary particle diameter of the inorganic powder (B) and the average primary particle diameter of the inorganic powder (A) within specific ranges, and by setting the amount of each inorganic powder within a specific range, the viscosity of the slurry used in producing the inorganic powder (C) of the present invention can be easily reduced. Furthermore, as described below, when producing the inorganic powder (B) by mechanochemical treatment, an average primary particle diameter of less than 1 nm is not preferred because it requires a long treatment time. Furthermore, by setting the average primary particle diameter of the inorganic powder (B) to 1 to 300 nm, the polishability and transparency of the cured product of the dental curable composition can be easily improved. From the viewpoint of reducing the slurry viscosity and improving the polishability and transparency of the cured product of the dental curable composition, the average primary particle diameter of the inorganic powder (B) is preferably 15 to 280 nm, more preferably 15 to 200 nm. The average primary particle size of the inorganic powder and particles (B) can be measured by the same method as the above-mentioned method for measuring the average primary particle size of the inorganic powder and particles (A).

[0029] The zeta potential of the inorganic powder or particle (B) is positive. The zeta potential of the inorganic powder or particle (B) is preferably 10 mV or more, preferably 20 mV or more, and preferably 60 mV or less.

[0030] As the material of the inorganic particles (b), rare earth metal compound particles are preferred in terms of color tone and safety. Among them, ytterbium fluoride (YbF ３ ), lanthanum fluoride (LaF ３ ), cerium fluoride (CeF ３ ), gadolinium fluoride (GdF ３ It is preferable to use a crystalline rare earth metal fluoride such as ytterbium fluoride, and from the viewpoint of X-ray opacity, it is most preferable to use ytterbium fluoride. Whether or not a material is crystalline can be determined by whether or not peaks based on crystal planes are confirmed when X-ray diffraction measurement is performed.

[0031] In the present invention, when inorganic powder (B) composed of a crystalline rare earth metal fluoride is used, it is preferable that the specific surface area has been increased by pulverization or the like. Increasing the specific surface area improves the formability of the dental curable composition, which is a paste. Here, formability means the property of the dental curable composition not to deform after being discharged from a syringe until it is cured (the property of being unlikely to deform due to natural flow when left standing and being able to maintain its shape). The specific surface area of ​​the inorganic powder (B) is preferably 10 to 100 m ２ / g, more preferably 10 to 80 m ２ / g, and more preferably 10 to 70 m ２ The specific surface area can be measured by a nitrogen adsorption method.

[0032] A method for increasing the specific surface area of ​​the inorganic powder (B) includes pulverizing the raw powder (B') of the inorganic powder (B). The pulverization method is not particularly limited, but mechanochemical treatment is preferred because it suppresses a decrease in transparency when blended into a dental curable composition and makes it easy to adjust the transparency to an appropriate level for a composite resin. Mechanochemical treatment increases the specific surface area and simultaneously produces a rare earth metal fluoride with enhanced amorphousness.

[0033] In addition, ytterbium fluoride (YbF ３ Although methyl methacrylate (MMA) is well known as an X-ray contrast filler, its incorporation into dental hardenable compositions such as composite resins is known to reduce the transparency of the cured product. This reduction in transparency can be suppressed by increasing the amorphous nature of the composition through mechanochemical treatment.

[0034] The mechanochemical treatment means a treatment of applying mechanical energy to the raw material powder, and means a treatment of performing at least one of mechanical grinding, pulverization, and dispersion. Because the specific surface area of ​​the inorganic powder or particle (B) can be reliably and efficiently increased, a wet method is preferably employed, and a treatment using a wet bead mill (wet bead mill treatment) is particularly preferred. Details of the wet bead mill treatment will be described later.

[0035] The conditions for mechanochemical treatment vary depending on the operating method of the wet bead mill used, the bead diameter, the type of inorganic powder and granules, the slurry concentration, etc. These conditions can be adjusted by conducting a preliminary experiment using the equipment and conditions that will actually be used for mechanochemical treatment, and checking the specific surface area of ​​the treated inorganic powder and granules versus the mechanochemical treatment time.

[0036] When the inorganic powder (B) composed of a crystalline rare earth metal fluoride is mechanochemically treated, in addition to the effect of increasing the specific surface area described above, the crystallinity of the crystalline rare earth metal fluoride is reduced, thereby suppressing a decrease in transparency when blended into a dental hardenable composition, making it easier to adjust the transparency to an appropriate level for a composite resin.

[0037] When an inorganic powder (B) composed of a crystalline rare earth metal fluoride is used, the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained by X-ray diffraction measurement of the inorganic powder (B) is preferably 0.3° or more. The crystallinity of the crystalline rare earth metal fluoride can be evaluated by the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern, and the smaller the full width at half maximum, the higher the crystallinity. Incidentally, the full width at half maximum of the maximum intensity peak of rare earth metal fluorides generally used as X-ray opaque materials and commercially available rare earth metal fluoride powders available as raw material powders is usually less than 0.3° (specifically, about 0.12° to 0.27°), and when such rare earth metal fluoride powder is incorporated, the transparency is reduced. To achieve the effect of suppressing the decrease in transparency, it is necessary to make the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern 0.3° or more, for example, by performing mechanochemical treatment. From the viewpoint of the effect of suppressing the decrease in transparency, the full width at half maximum of the maximum intensity peak is preferably 0.4° or more, particularly 0.5° or more. The full width at half maximum of the maximum intensity peak increases as the mechanochemical treatment time is increased, but the amount of increase varies depending on various conditions. Therefore, it is preferable to conduct preliminary experiments based on the equipment, conditions, etc. used to perform the mechanochemical treatment, and confirm the full width at half maximum derived from the crystalline rare earth metal fluoride relative to the mechanochemical treatment time. The upper limit of the full width at half maximum is not particularly limited, but in the case of mechanochemical treatment, it usually does not exceed 2.0°.

[0038] The full width at half maximum of the maximum intensity peak in the X-ray diffraction pattern can be determined by performing X-ray diffraction measurement on the inorganic powder / particle (B) composed of the crystalline rare earth metal fluoride of the present invention. Specifically, X-ray diffraction measurement is performed using an X-ray diffractometer in the 2θ range of 20 to 120°, and peaks attributable to the crystalline rare earth metal fluoride are identified in the resulting X-ray diffraction pattern (chart) with the horizontal axis representing 2θ (°) and the vertical axis representing the diffraction intensity. The peak with the maximum intensity among them (for example, YbF ３The peak width at 2θ of the peak corresponding to the (1,1,1) crystal plane, which appears around 2θ=28.0°, can be determined by calculating the full width at half maximum, i.e., the peak width at an intensity where the intensity is 50% of the peak intensity (maximum intensity) (the absolute value of the difference in 2θ between the two intersections of the intensity and the peak line: unit "(°)"). Note that, when measuring, it is preferable to use a powder from which coarse particles have been removed, for example, by using a sieve with a mesh size of 100 μm, as the measurement sample.

[0039] As described above, the inorganic powder and granules (C) used in the present invention are composed of agglomerated particles (c) consisting of the inorganic particles (a) constituting the inorganic powder and granules (A) and the inorganic particles (b) constituting the inorganic powder and granules (B).

[0040] The average total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) contained in the individual aggregate particles (c) constituting the inorganic powder granules (C) is within the range of 20 to 300 parts by mass. If the average total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) exceeds 300 parts by mass, dispersibility is poor and agglomerations are likely to occur when the inorganic powder granules (C) are blended into a dental curable composition. On the other hand, if the average total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) is less than 20 parts by mass, it becomes difficult to produce the inorganic powder granules (C) by spray drying. Even if the inorganic powder granules (C) can be produced, the effects of blending the inorganic particles (b) are likely to be reduced. For example, the formability of the dental curable composition is likely to be reduced, and if the inorganic particles (b) are radiopaque, the radiographic contrast properties are likely to be reduced. The average value of the total mass of the inorganic particles (b) relative to 100 parts by mass of the total mass of the inorganic particles (a) contained in each of the agglomerated particles (c) is preferably 22 to 280 parts by mass, more preferably 25 to 250 parts by mass. The total mass of the inorganic particles (b) relative to 100 parts by mass of the total mass of the inorganic particles (a) can be adjusted by the amounts of the inorganic powder particles (A) and the inorganic powder particles (B) used when producing the inorganic powder particles (C). That is, when producing the inorganic powder particles (C) by the spray drying method described below, the average value can be adjusted by the ratio of the amounts of the inorganic powder particles (A) and the inorganic powder particles (B) contained in the mixed slurry to be subjected to spray drying.

[0041] As described above, the inorganic powder (C) is an aggregate of a plurality of agglomerated particles (c) having different particle sizes. The inorganic powder (C) has an average agglomerated particle size (i.e., the average particle size of a plurality of agglomerated particles (c)) of 1 to 50 μm. An inorganic powder (C) having such an average agglomerated particle size is easy to handle. Furthermore, inorganic powders having an average agglomerated particle size of less than 1 μm or an average agglomerated particle size of more than 50 μm are difficult to prepare. From the viewpoint of improving handleability, the average agglomerated particle size of the inorganic powder (C) is preferably 3 to 30 μm, more preferably 5 to 25 μm. The average agglomerated particle size of the inorganic powder (C) can be adjusted to a desired range by adjusting production conditions such as the amount of dispersion medium used in the spray drying method described below. The average agglomerated particle size of the inorganic powder (C) can be measured by a laser diffraction-scattering method.

[0042] The inorganic powder and granules (C) preferably do not contain an ionic surfactant. When the inorganic powder and granules (C) do not contain an ionic surfactant, they do not cause curing inhibition due to the ionic surfactant, discoloration due to adsorption of a pigment to the ionic surfactant, or reduction in strength due to elution of the ionic surfactant when blended into a dental curable composition.

[0043] <Method for producing inorganic powder and granules (C)> The method for producing the inorganic powder and granules (C) is not particularly limited, but it is preferable to produce the inorganic powder and granules (C) by a spray drying method using a mixed slurry containing the inorganic powder and granules (A) and (B) described above. This will be described in detail below.

[0044] The inorganic powder (C) can be obtained by spray-drying a uniformly mixed slurry obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium. This production method, which includes a spray-drying step, can produce an inorganic powder (C) composed of agglomerated particles (c) in which inorganic particles (b) are uniformly dispersed within inorganic particles (a). Here, "uniformly dispersed" refers to a state in which inorganic particles (a) and inorganic particles (b) are dispersed and mixed at the primary particle level within agglomerated particles (c). For example, when the inorganic powder (C) is observed under an electron microscope, the brightness of each constituent particle (c) is uniform, and particles with a high overall brightness, such as particles having specifically high brightness regions or agglomerated particles composed only of inorganic particles (b), are not observed.

[0045] The mixed slurry is obtained by going through a step of preparing a slurry (Sa) and a step of preparing a slurry (Sb), and then mixing these slurries (Sa) and (Sb).

[0046] The step of preparing the slurry (Sa) is preferably carried out by subjecting a slurry obtained by mixing a dispersion medium and the inorganic powder / particles (A) to a dispersion treatment. Water is preferably used as the dispersion medium, but water to which an organic solvent has been added may also be used as needed. Examples of the organic solvent include ethanol, isopropyl alcohol, chloroform, and dimethylformamide. The amount of the dispersion medium used is usually 40 to 900 parts by mass per 100 parts by mass of the inorganic powder / particles (A). The dispersion treatment can be carried out using a mixing device such as a bead mill.

[0047] As the inorganic particles (a) constituting the inorganic powder and granules (A) contained in the slurry (Sa), silica-based inorganic compounds are preferred because they are widely used and easily available. Therefore, the slurry (Sa) is preferably a slurry in which inorganic particles (a) made of a silica-based inorganic compound are dispersed in water. Among the above silica-based inorganic compounds, silica-based composite oxides such as silica-zirconia, silica-titania, silica-titania-barium oxide, and silica-titania-zirconia are particularly preferred.

[0048] The step of preparing the slurry (Sb) is preferably carried out by subjecting a slurry containing a dispersion medium and the inorganic powder and granules (B) to a dispersion treatment. Water is preferably used as the dispersion medium, but water to which an organic solvent has been added may also be used as needed. Examples of the organic solvent include ethanol, isopropyl alcohol, chloroform, and dimethylformamide. The amount of the dispersion medium used is typically 40 to 900 parts by mass per 100 parts by mass of the inorganic powder and granules (B). The dispersion treatment can be carried out using a mixing device such as a bead mill.

[0049] From the viewpoints of color tone and stability, the inorganic particles (b) constituting the inorganic powder and granules (B) contained in the slurry (Sb) are preferably crystalline rare earth metal fluorides. Therefore, the slurry (Sb) is preferably a slurry in which inorganic particles (b) made of crystalline rare earth metal fluoride are dispersed in water. Among the above-mentioned crystalline rare earth metal fluorides, ytterbium fluoride (YbF ３ ), lanthanum fluoride (LaF ３ ), cerium fluoride (CeF ３ ), gadolinium fluoride (GdF ３ ) and the like are preferred, and from the viewpoint of X-ray opacity, it is most preferred to use ytterbium fluoride.

[0050] When inorganic powder (B) composed of a crystalline rare earth metal fluoride is used, the step of preparing the slurry (Sb) preferably involves treating the raw powder (B') with a wet bead mill using water as a medium (dispersion medium). The raw powder (B') is composed of crystalline rare earth metal fluoride particles, and the full width at half maximum of the maximum intensity peak attributable to the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained by X-ray diffraction measurement is less than 0.3°. By treating the raw powder (B') with a wet bead mill, it is possible to obtain the slurry (Sb) in which the inorganic powder (B) is dispersed, and the full width at half maximum of the maximum intensity peak attributable to the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained by X-ray diffraction measurement is 0.3° or more. The inorganic powder and granules of the present invention produced using such a slurry (Sb) in which the inorganic powder and granules (B) are dispersed suppresses a decrease in transparency when blended into a dental curable composition, and makes it easy to adjust the transparency to an appropriate level for a composite resin.

[0051] Wet bead milling is a type of mechanochemical treatment in which a slurry of powder to be treated mixed with a medium (dispersion medium) is brought into contact with media (beads) that have been imparted with movement by stirring, vibration, or the like, thereby imparting a pulverizing or crushing action to the powder. Materials used as the media include glass, alumina, zircon, zirconia, steel, and resin, but alumina or zirconia beads are preferred because of their excellent wear resistance and relatively low contamination. The size of the beads used can be selected according to the average particle size of the desired inorganic powder and granules (B), and is not particularly limited. However, in order to obtain inorganic powder and granules (B) suitable for incorporation into dental curable compositions, it is preferred to use beads with a diameter of 0.01 to 0.5 mm.

[0052] Wet bead mills are available in various operating modes, such as a batch mode in which the slurry and beads are directly charged into the device for processing, a circulation mode in which the slurry is circulated between a tank and the device, and a pass mode in which the slurry is passed through the device a predetermined number of times, and the operating mode can be selected depending on the amount of raw powder or grain (B') used for processing. It is preferable to use a circulation bead mill or a pass bead mill because they have good productivity and can process a relatively large amount of inorganic powder or grain.

[0053] Depending on the operating method, such as the circulation method or the pass method, it may be necessary to separate the slurry from the beads when carrying out the mechanochemical treatment. Examples of the bead separation method include a slit method, a screen method, and a centrifugal separation method. The bead separation method may be selected depending on the particle size of the beads used, and any method may be used without particular limitation. The concentration of the slurry to be subjected to the mechanochemical treatment is usually 40 to 900 parts by mass of the dispersion medium per 100 parts by mass of the raw material powder (B').

[0054] The inorganic powder and granules (B) contained in the slurry (Sb) are preferably 20 to 300 parts by mass, more preferably 22 to 280 parts by mass, and even more preferably 25 to 250 parts by mass, relative to 100 parts by mass of the inorganic powder and granules (A) contained in the slurry (Sa).

[0055] By mixing the slurry (Sa) and the slurry (Sb) prepared as described above, a uniform mixed slurry is obtained. Mixing can be performed using a stirrer or the like. The mixed slurry preferably does not contain an ionic surfactant. In the present invention, the viscosity of the mixed slurry can be reduced without using an ionic surfactant, resulting in a slurry suitable for spray drying, as described below. Furthermore, since the mixed slurry does not contain an ionic surfactant, an inorganic powder (C) that does not contain an ionic surfactant can be obtained. When such an inorganic powder (C) that does not contain an ionic surfactant is incorporated into a dental curable composition, it does not suffer from curing inhibition due to ionic surfactants, discoloration due to adsorption of dyes to the ionic surfactant, or a decrease in strength due to elution of the ionic surfactant. Here, examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. A surfactant is a compound that has a hydrophilic group and a hydrophobic group in one molecule. An anionic surfactant is a surfactant that can become an ion in an aqueous solution, and the hydrophilic group becomes an anion. A cationic surfactant is a surfactant that can become an ion in an aqueous solution, and the hydrophilic group becomes a cation. An amphoteric surfactant is a compound that, when dissolved in water, exhibits the properties of an anionic surfactant in the alkaline range and the properties of a cationic surfactant in the acidic range.

[0056] The mixed slurry may also contain a surface treatment agent, if necessary. The inorganic particles constituting the inorganic powder (A) or the inorganic powder (B) can be surface-treated using the surface treatment agent. Examples of such surface treatment agents include silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloyloxypropyltrimethoxysilane, κ-methacryloyloxydodecyltrimethoxysilane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, γ-chloropropyltrimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, and methyltriethoxysilane, as well as titanate-based coupling agents. The amount of the surface treatment agent to be added is, for example, 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass, per 100 parts by mass of the total of the inorganic powder particles (A) and the inorganic powder particles (B).

[0057] The inorganic powder and granule (C) can be obtained by spray-drying the mixed slurry. Spray-drying methods include a method in which the mixed slurry is atomized into fine droplets using a high-speed airflow, sprayed, and dried (also known as a nozzle-type spray-drying method), or a method in which the mixed slurry is dropped onto a disk-shaped rotor rotating at a rotation speed of 1,000 to 50,000 rpm, and then atomized and dried by centrifugal force (also known as a disk-type spray-drying method). The resulting inorganic powder and granule (C) is composed of agglomerated particles (c). From the perspective of obtaining agglomerated particles (c) with a uniform particle size, a disk-type spray-drying method is preferred, in which the atomized mixed slurry is immediately dried with hot air or an inert gas. The temperature of the gas used for drying is preferably 60 to 300°C, particularly 80 to 250°C. Furthermore, disk-type spray-drying methods allow for appropriate spray drying even when the mixed slurry has a relatively high concentration.

[0058] The concentration of the mixed slurry used in spray drying is preferably less than 40% by mass, more preferably 38% by mass or less, and even more preferably 35% by mass or less, from the viewpoint of enabling proper spray drying and obtaining desired agglomerated particles, and is preferably 10% by mass or more, from the viewpoint of improving the productivity of the inorganic powder or granule (C). The concentration of the mixed slurry means the concentration (% by mass) of the inorganic powder or granule in the mixed slurry.

[0059] The inorganic powder (C) obtained by spray drying is preferably subjected to vacuum drying after spray drying, in order to remove any remaining dispersion medium. Vacuum drying is generally carried out at a reduced pressure of 0.01 to 100 hectopascals at 20 to 150°C for 1 to 48 hours. The inorganic powder obtained by spray drying may be pulverized as necessary to adjust the average particle size to an appropriate value. Examples of pulverization methods that can be used include a vibration ball mill, a bead mill, and a jet mill.

[0060] <Inorganic powder particles (A), organic-inorganic composite powder particles (D)> The dental curable composition of the present invention further contains at least one of inorganic powder particles (A) and organic-inorganic composite powder particles (D) as a powder particle other than the inorganic powder particles (C) from the viewpoint of improving the mechanical strength of the cured product, etc. The details of the structure of the inorganic powder particles (A) are as described above, and therefore will not be described here.

[0061] The organic-inorganic composite powder (D) is composed of a plurality of organic-inorganic composite particles (d). The organic-inorganic composite particles (d) are a composite material of inorganic powder (A) and a resin, in which the content of the inorganic powder (A) in the composite material is 60 to 90 mass%. The content of the inorganic powder (A) in the composite material is preferably 65 to 90 mass%, more preferably 70 to 90 mass%. When the organic-inorganic composite powder (D) is used, the inorganic powder (A) can be blended into the composition as the organic-inorganic composite powder (D). Because the inorganic powder (A) in the organic-inorganic composite powder (D) is coated with a resin, it tends to be less likely to interact with the inorganic powder (B).

[0062] The resin in the composite material is not particularly limited, but is preferably a cured product obtained by polymerizing a polymerizable monomer. As the polymerizable monomer, those described above as the polymerizable monomer (M) can be used without any particular limitation.

[0063] The organic-inorganic composite powder and granules (D) have an average particle size of 1 to 100 μm. If the average particle size is less than 1 μm, the dental curable composition will have poor ejection properties when ejected from a syringe. If the average particle size is more than 100 μm, the mechanical strength, such as bending strength, of the cured product of the dental curable composition will tend to decrease. The average particle size of the organic-inorganic composite powder and granules (D) corresponds to the average value of the particle sizes of a plurality of organic-inorganic composite particles (d), and is an average particle size defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method.

[0064] The organic-inorganic composite powder (D) may be obtained by polymerizing a mixture of inorganic powder (A), a polymerizable monomer, and a polymerization initiator, followed by pulverization. Alternatively, the organic-inorganic composite powder (D) may be a microporous organic-inorganic composite powder obtained by immersing an agglomerated powder composed of inorganic agglomerated particles formed by agglomeration of the inorganic particles (a) constituting the inorganic powder (A) in a polymerizable monomer solution containing a polymerizable monomer, a polymerization initiator, and an organic solvent, removing the organic solvent, and then polymerizing and curing the polymerizable monomer. The agglomerated powder can be obtained, for example, by spray-drying an aqueous dispersion containing the inorganic powder (A). The polymerizable monomer may be any of the polymerizable monomers described above as the polymerizable monomer (M) without particular limitation, and the polymerization initiator may be any of the polymerization initiators described below as being suitable for addition to the dental curable composition without particular limitation.

[0065] <Contents of inorganic powder particles (A) and inorganic powder particles (B) regardless of their inclusion form> As described above, inorganic powder particles (C) are composed of a plurality of agglomerated particles (c), organic-inorganic composite powder particles (D) are composed of a plurality of organic-inorganic composite particles (d), and inorganic powder particles (A) are composed of a plurality of inorganic particles (a) as described above. On the other hand, when producing inorganic powder particles (C) and organic-inorganic composite powder particles (D), inorganic powder particles (A) are used as a raw material as described above, and therefore inorganic powder particles (C) and organic-inorganic composite powder particles (D) each contain inorganic powder particles (A). Therefore, when inorganic powder particles (A) are blended as a powder particle other than inorganic powder particles (C) and organic-inorganic composite powder particles (D), inorganic powder particles (A) of different inclusion forms will be present in the dental curable composition. For this reason, the term "total content of inorganic powder particles (A) regardless of their form of inclusion" will be used to represent the content of all inorganic powder particles (A) in the dental curable composition (i.e., the total amount of inorganic powder particles (A) including the amount of inorganic powder particles (A) contained in inorganic powder particles (C) and the amount of inorganic powder particles (A) contained in organic-inorganic composite powder particles (D) that are blended as needed).

[0066] In the dental curable composition, the total content of the inorganic powder and granules (A), regardless of their content form, is 170 to 270 parts by mass, and more preferably 180 to 250 parts by mass, per 100 parts by mass of the polymerizable monomer (M). If the total content of the inorganic powder and granules (A), regardless of their content form, is less than 170 parts by mass, the dental curable composition is likely to experience significant changes in flowability over time, and the mechanical strength of the cured product is likely to decrease. If the total content of the inorganic powder and granules (A), regardless of their content form, is more than 270 parts by mass, the dischargeability is poor.

[0067] Furthermore, when producing inorganic powder particles (C), inorganic powder particles (B) are used as a raw material, and therefore inorganic powder particles (C) contains inorganic powder particles (B). Furthermore, the dental curable composition of the present invention may contain inorganic powder particles (B) as a powder particle other than inorganic powder particles (C). In such a case, the dental curable composition contains inorganic powder particles (B) in different inclusion forms. For this reason, the term "total content of inorganic powder particles (B) regardless of their inclusion form" is used, which represents the content of all inorganic powder particles (B) in the dental curable composition (i.e., the total amount of inorganic powder particles (B) contained in inorganic powder particles (C) and the amount of inorganic powder particles (B) in other inclusion forms that are blended as necessary).

[0068] In the dental curable composition, the total content of the inorganic powder and granules (B), regardless of their content form, is 5 to 50 parts by mass, preferably 8 to 45 parts by mass, per 100 parts by mass of the polymerizable monomer (M), from the viewpoint of improving the mechanical strength of the cured product. If the total content of the inorganic powder and granules (B), regardless of their content form, is less than 5 parts by mass, the fluidity will change significantly over time, and the shapability will be poor. If the total content of the inorganic powder and granules (B), regardless of their content form, is more than 50 parts by mass, the dischargeability will be poor.

[0069] <Polymerization initiator> A polymerization initiator may be added to the dental curable composition of the present invention. The polymerization initiator is not particularly limited as long as it has the function of polymerizing the polymerizable monomer. However, it is preferable to use a photopolymerization initiator or a chemical polymerization initiator used in direct dental filling and restoration applications, which are often cured in the oral cavity, and it is more preferable to use a photopolymerization initiator from the viewpoint of simplicity, as it does not require a mixing operation.

[0070] Examples of the polymerization initiator used in photopolymerization include benzoin alkyl ethers such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether; benzil ketals such as benzil dimethyl ketal and benzil diethyl ketal; benzophenones such as benzophenone, 4,4'-dimethylbenzophenone, and 4-methacryloxybenzophenone; α-diketones such as diacetyl, 2,3-pentanedione benzyl, camphorquinone, 9,10-phenanthraquinone, and 9,10-anthraquinone; and 2,4-diethoxythioxanthracene. Examples of suitable phosphine compounds that can be used include thioxanthone, 2-chlorothioxanthone, and methylthioxanthone; and bisacylphosphine oxides such as bis-(2,6-dichlorobenzoyl)phenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide.

[0071] Incidentally, a reducing agent is often added to the photopolymerization initiator, and examples thereof include tertiary amines such as 2-(dimethylamino)ethyl methacrylate, ethyl 4-dimethylaminobenzoate, and N-methyldiethanolamine; aldehydes such as lauryl aldehyde, dimethylaminobenzaldehyde, and terephthalaldehyde; and sulfur-containing compounds such as 2-mercaptobenzoxazole, 1-decanethiol, thiosalicylic acid, and thiobenzoic acid.

[0072] Furthermore, in addition to the photopolymerization initiator and reducing agent, a photoacid generator is often used. Examples of such photoacid generators include diaryliodonium salt compounds, sulfonium salt compounds, sulfonate ester compounds, halomethyl-substituted S-triazine derivatives, and pyridinium salt compounds.

[0073] These polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator to be added may be selected to be an effective amount depending on the purpose, but is usually 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the polymerizable monomer. <Other Additives> The dental curable composition of the present invention may contain additives such as polymerization inhibitors, pigments, ultraviolet absorbers, and fluorescent agents, as long as they do not impair the effects of the composition.

[0074] The dental curable composition of the present invention can be prepared by mixing the polymerizable monomer (M), inorganic powder and granules (C), inorganic powder and granules (A), and / or organic-inorganic composite powder and granules (D), as well as any optional components, in predetermined amounts to obtain a paste, and then degassing the paste under reduced pressure to remove air bubbles. The dental curable composition of the present invention exhibits good syringeability, moderate fluidity, minimal change in fluidity over time, and high mechanical strength after curing. Therefore, it can be suitably used as a flowable composite resin.

[0075] [Inorganic Powder and Particles (C)] In the present invention, the inorganic powder and particles (C) can be provided as inorganic powder and particles that have good dispersibility when blended in a dental curable composition. The inorganic powder granules (C) are composed of agglomerated particles (c) including: inorganic particles (a) constituting inorganic powder granules (A) which are made of a plurality of inorganic particles (a) made of the same material and which exhibit a negative zeta potential polarity when measured in water, and which have an average primary particle diameter of 50 nm to 1 μm as measured by an electron microscope; and inorganic particles (b) constituting inorganic powder granules (B) which are made of a plurality of inorganic particles (b) made of the same material and which exhibit a positive zeta potential polarity when measured in water, and which have an average primary particle diameter of 1 to 300 nm as measured by an electron microscope; wherein the inorganic powder granules (C) are composed of agglomerated particles (c) which include: a total mass of the inorganic particles (a) contained in each agglomerated particle (c) constituting the inorganic powder granules (C): the average value of the total mass of the inorganic particles (b) per 100 parts by mass is within a range of 20 to 300 parts by mass; The inorganic powder (C) has an average agglomerated particle size, defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method, of 1 to 50 μm, and does not contain an ionic surfactant. Details of the inorganic powder (C) and its production method are as explained for the inorganic powder (C) contained in the dental curable composition described above, and therefore will not be explained here.

[0076] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these examples. First, in the examples and comparative examples, the substances used as raw materials for the compositions prepared and their abbreviations, as well as the methods for evaluating the raw materials and the prepared compositions, will be described.

[0077] 1. Raw materials and their abbreviations (1) Polymerizable monomers ・UDMA: 1,6-bis(methacrylethyloxycarbonylamino)-2,2-4-trimethylhexane ・3G: Triethylene glycol dimethacrylate ・GMA: 2,2-bis[(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane ・D-2.6E: 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane

[0078] (2) Inorganic Powder and Particles The average primary particle size and average uniformity of each inorganic powder and particle are values ​​determined based on the evaluation method described below. (2)-1 Inorganic powders and granules composed of silica-based inorganic compounds ・FA-1: Inorganic powder and granules composed of spherical silica-zirconia particles produced by the sol-gel method (average primary particle diameter 150 nm, average uniformity: 0.95) ・FA-2: Inorganic powder and granules composed of spherical silica-zirconia particles produced by the sol-gel method (average primary particle diameter 260 nm, average uniformity: 0.95) ・FA-3: Inorganic powder and granules composed of spherical silica-zirconia particles produced by the sol-gel method (average primary particle diameter 400 nm, average uniformity: 0.9) ・FA-4: Inorganic powder and granules composed of amorphous silica-zirconia particles produced by the sol-gel method (average primary particle diameter 1000 nm) ・FA-5: Inorganic powder and granules composed of silica (average primary particle diameter 300 nm, manufactured by Nippon Shokubai Co., Ltd.) FA-6: Inorganic powder composed of spherical silica-zirconia particles produced by the sol-gel method (average primary particle diameter 40 nm, average uniformity: 0.90) FA-7: Inorganic powder composed of amorphous silica-zirconia produced by the sol-gel method (average primary particle diameter 4000 nm).

[0079] (2)-2 Inorganic powder composed of crystalline rare earth fluoride particles: YbF ３ -40:3 Inorganic powder composed of ytterbium fluoride (average primary particle diameter 46 nm, manufactured by Treibacer). YbF ３ -200: Inorganic powder and granules composed of ytterbium trifluoride (average primary particle diameter 200 nm, manufactured by Treibacer). YbF ３-300: Inorganic powder composed of ytterbium trifluoride (average primary particle diameter 270 nm, manufactured by Treibacer).

[0080] (3) Polymerization initiators: CQ: camphorquinone; DMBE: N,N-dimethyl-p-ethyl benzoate.

[0081] 2. Manufacturing Method, Evaluation Method, and Evaluation Results of Inorganic Powder and Particles (1) Inorganic Powder and Particle (A) Made of Silica-Based Inorganic Compound The average primary particle size and zeta potential of the inorganic powder and particles FA-1 to FA-7 were determined as follows. The results are shown in Table 1. Using a wet bead mill SC50 (manufactured by Mitsui Mining Co., Ltd.), 400 parts by mass of each inorganic powder and particle were mixed with 600 parts by mass of ion-exchanged water to prepare a slurry. This slurry was then subjected to a dispersion treatment using 100 g of φ0.3 mm zirconia beads as a medium at a rotation speed of 3,000 rpm for 10 minutes to prepare slurries (SA-1 to SA-7) in which inorganic powder and particles made of silica-based inorganic compounds were dispersed. The slurry in which inorganic powder FA-1 is dispersed is SA-1, the slurry in which inorganic powder FA-2 is dispersed is SA-2, the slurry in which inorganic powder FA-3 is dispersed is SA-3, the slurry in which inorganic powder FA-4 is dispersed is SA-4, the slurry in which inorganic powder FA-5 is dispersed is SA-5, the slurry in which inorganic powder FA-6 is dispersed is SA-6, and the slurry in which inorganic powder FA-7 is dispersed is SA-7.

[0082] <Method for measuring average primary particle diameter> Photographs of the powder were taken with a scanning electron microscope ("XL-30S" manufactured by Philips) at magnifications of 5,000 to 100,000 times, and the photographed images were processed using image analysis software ("IP-1000PC", product name; manufactured by Asahi Kasei Engineering Corporation). The average primary particle diameter was determined based on the measured value of the number of particles (100 or more) observed within a unit field of view of the photograph.

[0083] <Method for measuring the zeta potential of inorganic powder particles> The inorganic powder particles were suspended in ion-exchanged water at pH 7 and dispersed in water by irradiating with ultrasound for 30 minutes so that the suspension concentration became 1.0% by mass. The zeta potential of this suspension was measured using a zeta potential measuring device ("ELSZ-2000" manufactured by Otsuka Electronics Co., Ltd.). Each sample was measured three times, and the average was taken as the zeta potential.

[0084]

[0085] (2) Inorganic powder (B) made of crystalline rare earth metal fluoride The inorganic powder (B) made of each of the above-mentioned crystalline rare earth metal fluorides (YbF ３ -40, YbF ３ -200 and YbF ３ The inorganic powder particles (B) were dispersed in a wet bead mill SC50 (manufactured by Mitsui Mining Co., Ltd.) to obtain slurries (SB-1 to SB-5) containing the inorganic powder particles (B). The mechanochemical treatment was carried out by using a wet bead mill SC50 (manufactured by Mitsui Mining Co., Ltd.) to mix 600 parts by mass of ion-exchanged water with 400 parts by mass of each crystalline rare earth fluoride, and dispersing the resulting slurry at 3,000 rpm using 100 g of φ0.3 mm zirconia beads as media for the treatment time shown in Table 2. The resulting slurry was dried under reduced pressure using an evaporator to prepare inorganic powder particles (B); FB-1 to FB-5, using the crystalline rare earth metal fluoride particles with the materials and dispersion treatment times shown in Table 2. The average primary particle size and zeta potential of the obtained inorganic powder were measured in the same manner as in (1) above, and the 2θ and full width at half maximum (°) of the peak of the crystal plane (1,1,1) in the X-ray diffraction pattern were measured as follows. The results are shown in Table 2.

[0086] <Method for measuring 2θ and full width at half maximum (°) of crystal plane (1,1,1)> The powder was filled on a sample stage and measured using an X-ray diffractometer ("Smartlab" manufactured by Rigaku Corporation) to obtain an X-ray diffraction pattern (chart) with 2θ (°) on the horizontal axis and diffraction intensity on the vertical axis. Here, CuKα rays were used as X-rays for the X-ray diffraction measurement. When the material of the crystalline rare earth metal fluoride particles was YbF３ In this case, the peak with the greatest intensity is the peak due to the (1,1,1) plane (the peak observed around 2θ=28°), and the full width at half maximum (°) of this peak was therefore determined.

[0087]

[0088] (3) Preparation of Inorganic Powder (C) Composed of Agglomerated Particles (FC-1 to FC-16) 100 g of the slurry SA-2 and 25 g of the slurry SB-2 were mixed to obtain a mixed slurry. Next, 1.6 g (0.006 mol) of γ-methacryloyloxypropyltrimethoxysilane and 20 g of water were added, followed by addition of acetic acid to adjust the pH to 4, and the mixture was stirred for 1 hour and 30 minutes to obtain a uniform solution. This solution and ion-exchanged water (50 g) for adjusting the concentration were added to the mixed slurry and mixed uniformly. Thereafter, while gently mixing the dispersion, the inorganic powder dried by spray drying was collected from the cyclone collection section and the collection section below the main body. The spray dryer used was a spray dryer (Spray Dryer "FOC-20", manufactured by Okawara Kakoki). The disk rotation speed was 26,000 rpm, and the temperature of the drying atmosphere air was 200°C. The inorganic powder recovered from the cyclone recovery unit was then vacuum dried at 80°C for 17 hours to obtain inorganic powder (C): FC-1. The inorganic powder recovered from the recovery unit below the main body was similarly vacuum dried to obtain inorganic powder (C): FC-2.

[0089] Inorganic powders (C): FC-3 to FC-13 were prepared in the same manner as FC-1, except that the types and ratios of the silica-based inorganic compound slurry and the crystalline rare earth metal fluoride slurry used in the preparation of inorganic powders (C) and the amount of ion-exchanged water added for concentration adjustment were changed as shown in Table 3. Note that when slurries (SA-6, SA-7) containing dispersed inorganic powders (FA-6, FA-7) composed of silica-based composite oxides that do not satisfy the requirements of the present invention were used, or when the amount of crystalline rare earth metal fluoride was small and the viscosity of the slurry was high, the slurry clogged the nozzle during spray drying, making spraying impossible (FC-14 to FC-16). The average agglomerated particle size (median diameter in the volume-based particle size distribution) of the obtained inorganic powders (C) was measured as follows. The formation of agglomerated particles in inorganic powders (C) was confirmed using a scanning electron microscope.

[0090] (FC-17) 100 g of the slurry SA-2 and 100 g of the slurry SB-2 were mixed to obtain a mixed slurry. Next, 1.6 g (0.006 mol) of γ-methacryloyloxypropyltrimethoxysilane and 20 g of water were added, and then acetic acid was added to adjust the pH to 4. The mixture was stirred for 1 hour and 30 minutes to obtain a uniform solution. 100 g of the mixed slurry and ion-exchanged water for adjusting the concentration were added to this solution and mixed uniformly. Thereafter, while gently mixing the dispersion, the inorganic powder (C) dried by a spray drying method was collected from the cyclone collection section and the collection section below the main body. The spray dryer used was a spray dryer (Spray Dryer "RL-8", manufactured by Okawara Kakoki). The spray pressure was 0.20 MPa, and the temperature of the drying atmosphere air was 200°C. The inorganic powder recovered from the cyclone recovery section was then vacuum-dried at 80°C for 17 hours to obtain 65 g of inorganic powder (C): FC-17 composed of agglomerated particles. The average agglomerated particle diameter (median diameter in the volume-based particle size distribution) of the obtained inorganic powder (C) was measured as follows. The formation of agglomerated particles in the inorganic powder (C) was confirmed using a scanning electron microscope.

[0091] <Method for measuring average agglomerated particle diameter> 0.1 g of inorganic powder composed of agglomerated particles was dispersed in 10 mL of ethanol and thoroughly shaken by hand. The median diameter of the volume statistics was determined using a particle size distribution analyzer (LS230, manufactured by Beckman Coulter) based on the laser diffraction-scattering method and the optical model "Fraunhofer."

[0092] The average total mass of the crystalline rare earth metal fluoride (inorganic particles (b)) relative to 100 parts by mass of the total mass of the silica-based inorganic compound (inorganic particles (a)) contained in the individual agglomerated particles constituting the obtained inorganic powder granule (FC-1) was 25 parts by mass, which corresponds to the value shown in Table 3. Similarly, the average total mass of the crystalline rare earth metal fluoride (inorganic particles (b)) relative to 100 parts by mass of the total mass of the silica-based inorganic compound (inorganic particles (a)) for the other inorganic powder granules (FC-2 to FC17) corresponds to the value shown in Table 3. The concentration (% by mass) shown in Table 3 means the concentration (% by mass) of the inorganic powder granule in the mixed slurry used for spray drying.

[0093]

[0094] (4) Regarding organic-inorganic composite powder (D) composed of organic-inorganic composite particles composed of a composite material of inorganic powder (A) composed of silica-based composite oxide and resin, 100 g of the inorganic powder (FA-2) was added to 200 g of ion-exchanged water, and an aqueous dispersion (dispersion of inorganic powder) was obtained using a circulation type mill SC Mill (manufactured by Nippon Coke Engineering Co., Ltd.). Next, 4 g (0.016 mol) of γ-methacryloyloxypropyltrimethoxysilane and 0.003 g of acetic acid were added to 80 g of water and stirred for 1 hour and 30 minutes to obtain a homogeneous solution with a pH of 4. This solution was added to the dispersion of the inorganic powder and mixed until homogeneous. Thereafter, while gently mixing the dispersion, it was supplied onto a rotating disk at high speed and granulated by spray drying. Spray drying was performed using a spray dryer TSR-2W (manufactured by Sakamoto Giken Co., Ltd.) equipped with a rotating disk and atomizing by centrifugal force. The disk rotation speed was 10,000 rpm, and the temperature of the drying atmosphere air was 200°C. The powder obtained by spray drying was then vacuum-dried at 60°C for 18 hours to obtain 73 g of powder (agglomerated powder) composed of approximately spherical aggregated particles. Next, 30 g of the aggregated powder was immersed in a polymerizable monomer solution containing 7 g of UDMA as a polymerizable monomer, 0.015 g of azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and 12.4 g of ethanol as an organic solvent. After thorough stirring, the mixture was allowed to stand for 1 hour after confirming that it had become a slurry. The mixture was then dried for 1 hour using a vacuum dryer at a reduced pressure of 10 hectopascals and heated to 40°C to remove the organic solvent. After removing the organic solvent, a powder with no aggregation and high fluidity was obtained. The powder was heated for 20 minutes under conditions of a reduced pressure of 10 hectopascals and 140°C to polymerize and harden the polymerizable monomer in the powder. Then, the mixture was sieved through a 100 μm mesh to obtain 26 g of organic-inorganic composite powder (D): FD-1, which was composed of approximately spherical organic-inorganic composite particles in which the surfaces of the obtained spherical aggregates were coated with an organic polymer.

[0095] Organic-inorganic composite powder FD-2 was obtained in the same manner as FD-1, except that the amount of polymerizable monomer UDMA used was changed to 4.1 g. Organic-inorganic composite powder FD-3 was obtained in the same manner as FD-1, except that the amount of polymerizable monomer UDMA used was changed to 16 g. Organic-inorganic composite powder FD-4 was obtained in the same manner as FD-1, except that the amount of polymerizable monomer UDMA used was changed to 1.6 g. Organic-inorganic composite powder FD-5 was obtained in the same manner as FD-1, except that the amount of polymerizable monomer UDMA used was changed to 22.6 g. The powder recovered from the sieve during the sieving process in the production of FD-1 was designated organic-inorganic composite powder FD-6. Organic-inorganic composite powder FD-7 to FD-9 with different average particle sizes were obtained by pulverizing FD-6 using a vibration ball mill. The average particle diameter (median diameter in the volume-based particle size distribution) of the obtained organic-inorganic composite powder (D) was determined as follows. The results are shown in Table 4.

[0096] <Evaluation of the average particle size of organic-inorganic composite powder particles> 0.1 g of organic-inorganic composite powder particles (D) was dispersed in 10 mL of ethanol and ultrasonically irradiated for 20 minutes. Using a particle size distribution analyzer "LS230" (manufactured by Beckman Coulter) based on the laser diffraction-scattering method, the average particle size was determined from the median diameter of volume statistics using the optical model "Fraunhofer."

[0097]

[0098] 3. Examples and Comparative Examples Example 1 A polymerizable monomer solution was prepared by completely dissolving 0.20 parts by mass of CQ and 0.5 parts by mass of DMBE as polymerization initiators in a polymerizable monomer mixture consisting of 60 parts by mass of UDMA and 40 parts by mass of 3G. Subsequently, 140 parts by mass of inorganic powder (A) FA-2, 93 parts by mass of inorganic powder (C) FC-4, and the polymerizable monomer solution were kneaded in a mortar until homogeneous to form a paste, and the mixture was degassed to prepare a dental curable composition paste. The prepared dental curable composition paste was filled into a cylindrical syringe, and a plunger for expelling the contents of the syringe and a cap were attached. One of the syringes filled with the prepared dental curable composition was then stored in an incubator at 50°C for one week. The dental curable compositions obtained were evaluated for flowability in a paste state, consistency, dispersibility of the crystalline rare earth metal fluoride in the curable composition, contrast ratio, bending strength, and discharge feeling by the following methods. The flowability evaluation was performed on the dental curable compositions immediately after preparation and after one week of storage at 50°C. The evaluation result immediately after preparation was defined as the "initial" value (initial value), and the evaluation result after one week of storage at 50°C was defined as the "post-storage" value (post-storage value). The results are shown in Table 5.

[0099] <Method for Measuring Flowability> A 20G needle tip was attached to the tip of a syringe filled with the prepared paste-like dental curable composition. After allowing the composition to stand for 30 minutes in a thermostatic chamber at 25°C, a circle with a diameter of 5 mm was drawn on a glass plate. 0.1 g of the dental curable composition was dispensed into the circle, and the plate was then allowed to stand horizontally in an incubator at 37°C for 2 minutes. The vertical and horizontal diameters of the paste were measured for spread, and the average of both values ​​was calculated. This evaluation was performed twice, and the average value was used as the flowability of the paste. Regarding fluidity, the degree of change due to storage was evaluated by calculating {(value after storage - initial value) / initial value} x 100 as the rate of change (%).

[0100] <Method for Measuring Consistency> The prepared dental curable paste composition was left to stand in an incubator at 45°C for 1 day, and then left to stand at 25°C for 30 minutes. The consistency of the paste was measured using the following method. 0.2 g of paste was weighed out onto a polypropylene film, with the center raised. A polypropylene film, a glass plate, and a weight (50 g in total) were placed on top of the paste in this order. After 10 seconds, the glass plate and weight were removed. The vertical and horizontal diameters of the paste were measured through the polypropylene film, and the average of both measurements was calculated. The above evaluation was performed twice, and the average value was used as the consistency of the paste.

[0101] <Method for Evaluating the Dispersibility of Crystalline Rare Earth Metal Fluoride Particles in a Dental Curable Composition> The prepared dental curable composition was placed in a mold with a 7 mm diameter x 1 mm through-hole, and polyester films were pressed onto both sides. Then, one side of the polyester film was peeled off, and the peeled surface was irradiated with light from a dental light irradiator (Eliper Deep Cure, manufactured by 3M) at a distance of 3 mm for 20 seconds. After curing, the dental curable composition was removed from the mold, placed in 10 mL of ethanol, and ultrasonically treated for 20 minutes. The resulting cured product was fixed with carbon tape on a sample stage with the irradiated surface facing up, and a conductive treatment (platinum vapor deposition) was performed to prepare a measurement sample. A backscattered electron image of this measurement sample was observed at 1,000x magnification using a scanning electron microscope (JEOL Ltd., "JSM-7800F PRIME"), and the number of bright particles of 3 μm or larger observed within a unit field of view of the photograph was counted. A: No highly bright particles of 3 μm or more are observed within the unit field of view of the scanning electron microscope. B: Highly bright particles of 3 μm or more are observed within the unit field of view of the scanning electron microscope.

[0102] <Method for evaluating the contrast ratio (Yb / Yw) of the dental curable composition cured product> The prepared dental curable composition was placed in a mold having a through-hole of 7 mmφ×1 mm, and polyester films were pressed onto both sides. Then, the irradiation intensity on the surface of the polyester film was 1000 mW / cm ２The distance was adjusted so that the curable dental composition was 1 / 3 the same as that of the original, and both surfaces were irradiated with light for 20 seconds each using a dental light irradiator (Eliper Deep Cure, manufactured by 3M). After the dental curable composition was cured, it was removed from the mold, and the tristimulus Y value (background colors: black and white) of the cured product was measured using a color difference meter (TC-1800MKII, manufactured by Tokyo Denshoku). The contrast ratio (Yb / Yw) was calculated based on the following formula: Contrast ratio (Yb / Yw) = Y value when background color is black / Y value when background color is white.

[0103] <Method for Measuring "Flexural Strength"> A dental curable composition paste was filled into a stainless steel mold and pressed against a polypropylene film. Using a visible light irradiator (Eliper Deep Cure, manufactured by 3M), the paste was irradiated from one side for 30 seconds x 3 times, with the polypropylene film being attached to the mold in different positions so that the entire surface was exposed to light. The other side was then similarly attached to the polypropylene film and irradiated for 30 seconds x 3 times to obtain a cured product. The cured product was trimmed into a 2 x 2 x 25 mm rectangular column using #1500 waterproof abrasive paper. This sample was mounted on a testing machine (Shimadzu Corporation, "Autograph AG5000D") and the three-point bending fracture strength was measured at a support distance of 20 mm and a crosshead speed of 1 mm / min. A load-deflection curve was obtained, and the bending strength was calculated using the following formula. Five test pieces were evaluated, and the average value was taken as the bending strength. Formula: σB = (3PS) / (2WB ２ ) The symbols in the above represent σB: bending strength (Pa), P: load at fracture of the test piece (N), S: distance between supports (m), W: width of the test piece (m), and B: thickness of the test piece (m).

[0104] <Evaluation of Discharge Feel> A 20G needle tip was attached to the tip of the syringe container, and 0.2 g of paste was discharged from the tip of the needle tip onto a glass plate (5 cm x 10 cm) by pressing the plunger. The ease of pressing the plunger at this time was confirmed, and the discharge feel of the paste was evaluated according to the following evaluation criteria. A discharge feel of 1 to 3 was considered to be acceptable. 1: Paste can be discharged even with weak pressure, and dischargeability is very good. 2: Paste can be discharged without difficulty, and dischargeability is good. 3: Paste can be discharged by pressing a little harder, and dischargeability is acceptable. 4: Paste can be discharged by pressing hard, but dischargeability is poor. 5: Paste cannot be discharged at all.

[0105] Examples 2 to 28, Comparative Examples 1 to 8 Paste-like dental curable compositions were prepared in the same manner as in Example 1, except that the polymerizable monomer (M), inorganic powder and granules (A), inorganic powder and granules (B), inorganic powder and granules (C), and organic-inorganic composite powder and granules (D) used were changed as shown in Tables 5 to 8, and the obtained compositions were evaluated in the same manner as in Example 1. The results are shown in Tables 5, 6, 7, and 8.

[0106]

[0107]

[0108]

[0109]

[0110] As can be seen from the results of Examples 1 to 28, when inorganic powders and organic-inorganic composite powders satisfying the requirements of the present invention are used, the crystalline rare earth metal fluoride is sufficiently dispersed in the hardenable composition, and the change in fluidity over time is small. Figure 2 shows a photograph of the cured product of the dental hardenable composition of Example 1 observed with a scanning electron microscope. No bright particles of 3 μm or more were observed, demonstrating good dispersibility of the crystalline rare earth metal fluoride. As can be seen from the results of Comparative Examples 1 and 2, when the amount of inorganic powder (B), regardless of its content form, does not satisfy the requirements of the present invention, a decrease in strength and a worsening of the discharge feeling are observed, and significant changes in fluidity over time are observed upon storage. As can be seen from the results of Comparative Example 3, when the inorganic powder (C) does not satisfy the requirements of the present invention, the crystalline rare earth fluoride particles are not sufficiently dispersed in the hardenable composition, and significant changes in fluidity over time are observed upon storage. As can be seen from the results of Comparative Examples 4 to 7, when the organic-inorganic composite powder (D) does not satisfy the requirements of the present invention, the strength of the cured product of the dental curable composition decreases or the feeling of discharging becomes poor. Figure 3 shows a photograph of the cured product of the dental curable composition of Comparative Example 8, observed with a scanning electron microscope. High-brightness particles of 3 μm or more were observed, indicating poor dispersibility of the crystalline rare earth metal fluoride. As can be seen from these results, when the inorganic powder (B) is directly added, aggregated particles remain in the curable composition, which is not sufficiently dispersed, and the fluidity changes significantly over time.

Claims

1. Polymerizable monomer (M): 100 parts by mass; and inorganic powder granule (C) composed of agglomerated particles (c) including a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential polarity when measured in water, and an average primary particle diameter measured by an electron microscope of 50 nm to 1 μm constituting inorganic powder granule (A), and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential polarity when measured in water, and an average primary particle diameter measured by an electron microscope of 1 to 300 nm constituting inorganic powder granule (B), wherein the total mass of the inorganic particles (a) contained in each of the agglomerated particles (c) constituting the inorganic powder granule (C): the average value of the total mass of the inorganic particles (b) relative to 100 parts by mass is within the range of 20 to 300 parts by mass, the inorganic powder particles (C) having an average agglomerated particle size of 1 to 50 μm, defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method; and 10 to 100 parts by mass of an inorganic powder particle (C), the inorganic powder particle (C) further comprising at least one of the inorganic powder particle (A) and an organic-inorganic composite powder particle (D), the organic-inorganic composite powder particle (D) being constituted by organic-inorganic composite particles (d) made of a composite material of the inorganic powder particle (A) and a resin, the content of the inorganic powder particle (A) in the composite material being 60 to 90 mass%, and the organic-inorganic composite powder particle (D) having an average particle size of 1 to 100 μm, defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method; A dental curable composition, characterized in that a total content of the inorganic powder and granules (A) in the composition, regardless of the form of inclusion, is 170 to 270 parts by mass, and a total content of the inorganic powder and granules (B), regardless of the form of inclusion, is 5 to 50 parts by mass.

2. The dental hardenable composition according to claim 1, wherein in each aggregate particle (c) constituting the inorganic powder (C), the inorganic particles (b) are uniformly dispersed in the inorganic particles (a).

3. The dental hardenable composition according to claim 1, wherein the inorganic particles (a) are made of a silica-based inorganic compound, and the inorganic particles (b) are made of a crystalline rare earth metal fluoride.

4. A dental hardenable composition according to claim 3, wherein the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained when X-ray diffraction measurement is performed on the inorganic powder / grain (B) is 0.3° or more.

5. The dental curable composition according to claim 1, wherein the inorganic powder (C) is obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium, to obtain a uniform mixed slurry, and then spray-drying the mixture.

6. A method for producing a dental hardenable composition according to claim 1, comprising mixing the polymerizable monomer (M), the inorganic powder (C), and at least one of the inorganic powder (A) and the organic-inorganic composite powder (D).

7. A method for producing a dental curable composition according to claim 6, wherein the inorganic powder (C) is produced by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium to obtain a uniform mixed slurry, and spray drying the resulting mixture.

8. The method for producing a dental hardenable composition according to claim 7, wherein the mixed slurry does not contain an ionic surfactant.

9. The method for producing a dental hardenable composition according to claim 7, wherein the concentration of the mixed slurry is less than 40% by mass.

10. An inorganic powder / granule (C) comprising agglomerated particles (c) including a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential when measured in water, the inorganic particles (a) constituting an inorganic powder / granule (A) having an average primary particle diameter of 50 nm to 1 μm when measured by an electron microscope, and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, the inorganic particles (b) constituting an inorganic powder / granule (B) having an average primary particle diameter of 1 to 300 nm when measured by an electron microscope, the inorganic particles (c) being agglomerated particles (c) including a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, the inorganic particles (b) being agglomerated particles (c) comprising an inorganic powder / granule (C) having an average total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) contained in each agglomerated particle (c) constituting the inorganic powder / granule (C), the average value of the total mass of the inorganic particles (b) is within the range of 20 to 300 parts by mass, An inorganic powder or granule having an average agglomerated particle size, defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method, of 1 to 50 μm, and containing no ionic surfactant.

11. A method for producing inorganic powder or granules according to claim 10, comprising a step of spray-drying a uniform mixed slurry obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder or granules (A) are dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder or granules (B) are dispersed in a dispersion medium, wherein the mixed slurry does not contain an ionic surfactant.

12. The method for producing inorganic powder or granules according to claim 11, wherein the concentration of the mixed slurry is less than 40% by mass.

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