Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K6/00—Preparations for dentistry
  • A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
  • A61K6/84—Preparations for artificial teeth, for filling teeth or for capping teeth comprising metals or alloys
  • A61K6/842—Rare earth metals
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K6/00—Preparations for dentistry
  • A61K6/15—Compositions characterised by their physical properties
  • A61K6/17—Particle size
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K6/00—Preparations for dentistry
  • A61K6/15—Compositions characterised by their physical properties
  • A61K6/16—Refractive index
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K6/00—Preparations for dentistry
  • A61K6/60—Preparations for dentistry comprising organic or organo-metallic additives
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K6/00—Preparations for dentistry
  • A61K6/70—Preparations for dentistry comprising inorganic additives
  • A61K6/71—Fillers
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K6/00—Preparations for dentistry
  • A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
  • A61K6/884—Preparations for artificial teeth, for filling teeth or for capping teeth comprising natural or synthetic resins
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K6/00—Preparations for dentistry
  • A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
  • A61K6/884—Preparations for artificial teeth, for filling teeth or for capping teeth comprising natural or synthetic resins
  • A61K6/887—Compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds

Definitions

• the present invention relates to a dental hardenable composition.
• CR dental composite resin
• a hardenable composition containing a polymerizable monomer, a filler, and a polymerization initiator as the main components is used as this type of dental filling material.
• CR restorations are rapidly gaining popularity because they require less tooth structure to be removed, can achieve a color tone equivalent to that of natural teeth, and are easy to use. In recent years, due to their improved mechanical strength and adhesive strength with teeth, they are used not only for restoring anterior teeth, but also for molars, which are subject to high occlusal pressure.
• CR is usually colored by mixing it with pigments or dyes, but these substances can fade or discolor over time in the hardened body after treatment due to deterioration over time, causing discoloration over time after restoration, and the appearance of the restored area can no longer match that of the natural tooth.
• CRs have been proposed that use a filler containing spherical inorganic particles with a specific average particle size and particle size distribution, and that have a refractive index greater than that of the resin portion that becomes the matrix when cured, thereby producing structural colors that develop in a specific color tone independent of the angle of incidence of light through light interference and scattering, etc.
• structural color CRs which have attracted attention
• the structural color system CR has the following excellent features: (1) it does not use dyes or pigments, so it is less susceptible to the problem of discoloration over time; (2) it produces a structural color of a specific tone that is independent of the angle of incidence of light, depending on the average particle size of the spherical inorganic particles used; in particular, when spherical inorganic particles with an average primary particle size of 230-350 nm are used, it can be colored yellow to red, which is similar to the color of dentin; and (3) since the hardened body has a moderate transparency, it easily matches the color of the tooth to be restored, and it is possible to use a single type of composite resin to restore a wide range of colors of teeth to be restored with an appearance close to that of natural teeth, without the need for complicated shade taking or shade selection of the composite resin.
• the polymerizable curable composition that constitutes the structural color system CR satisfies the following conditions (a) and (b), but it is known that when the following condition (c) is also satisfied, a cured product that more reliably exhibits the desired structural color is obtained (see Patent Document 2).
• A Contains polymerizable monomer (A), inorganic particles (B), and photopolymerization initiator (C) as constituents.
• the inorganic particles (B) are (A-1)
• the present invention is composed of an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 to 1000 nm, and each inorganic spherical particle constituting the aggregate is substantially composed of the same substance, and includes one or more "groups of spherical particles having identical diameters" (G-PIDs) in which 90% or more of the total number of particles in the number-based particle size distribution of the aggregate are present within a range of 5% around the predetermined average primary particle diameter, (A-2) when the number of the one or more "spherical particle groups of the same diameter" is a, and each "spherical particle group of the same diameter” is expressed as G-PID m (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more) in order of increasing average primary particle diameter, when a is 2 or more, the substances constituting the individual particles of each G-PI
• n (MX) the refractive index at 25° C. of the inorganic spherical particles constituting each G-PID m is n (G-PIDm) , for any n (G-PIDm) , n (MX) ⁇ n (G-PIDm)
• n (MX) the refractive index at 25° C. of the inorganic spherical particles constituting each G-PID m
• the x-axis is a dimensionless number (r/ r0 ) obtained by dividing the distance from the center of any inorganic spherical particle dispersed in the cured body by the average particle size r0 of all the inorganic spherical particles dispersed in the cured body
• the y-axis is the radial distribution function g(r)
• the nearest inter-particle distance r1 which is defined as the r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph, is a value that is 1 to 2 times the average particle size r0 of all the inorganic spherical particles dispersed in the cured body of the mixture.
• the colored light due to interference in the hardened body occurs in the part where the constituent particles are relatively regularly accumulated, and the colored light due to scattering occurs in the part where the constituent particles are randomly dispersed.
• the above condition (I) when r1 is less than 1 time of r0 , the overlap between the particles in the plane increases, and when r1 is more than 2 times of r0 , the particles do not exist near the selected central inorganic particle, so that the short-range order disappears and the structural color does not appear.
• the minimum value is less than 0.56
• the long-range order of the arrangement structure of the inorganic spherical particles increases, and not only does the incidence angle dependency of the structural color that appears increase, but the saturation of the hardened body increases, making it difficult to obtain color tone compatibility when used as a dental filling material, but when the minimum value is more than 1.10, the arrangement structure of the inorganic spherical particles becomes a random structure
• each G-PID develops a structural color in the hardened form with a color tone that corresponds to its average primary particle size, so it is also possible to control the overall color tone by combining the G-PIDs that are blended.
• inorganic spherical particles belonging to different G-PIDs can be dispersed with a short-range ordered structure that can express a structural color for each G-PID without mutual substitution.
• inorganic oxide fillers are generally used as fillers to be mixed into hardenable compositions used as CR, including existing structural color dental hardenable compositions.
• silica-based fillers have low X-ray opacity. For this reason, the hardened material in the cavity is not imaged during X-ray or CT scan photography during dental treatment, making it difficult to identify the treatment site.
• Patent Document 3 proposes a technology that uses a filler made of a fluoride of a rare earth metal with atomic numbers of 57 to 71.
• the present invention was made in consideration of the above circumstances, and aims to provide a dental hardenable composition that is X-ray opaque when cured and can be suitably used as a structural color CR for aesthetic restorations.
• the present invention solves the above problems, and the present invention provides the following aspects: Polymerizable monomer: 100 parts by mass; the aggregate is made of inorganic spherical particles having a predetermined average primary particle diameter in the range of 100 to 1000 nm, the individual inorganic spherical particles constituting the aggregate being made of substantially the same material, and 90% or more of the total number of particles in the number-based particle size distribution of the aggregate are present within a range of 5% around the predetermined average primary particle diameter, the aggregate comprising: 10 to 1500 parts by mass in total; and a polymerization initiator;
• G-PID m where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more
• a dental hardenable composition capable of giving a hardened product exhibiting a structural color of a predetermined color tone independent of the angle of incidence of light The powder is made of crystalline rare earth metal fluoride particles, and the crystallinity of the individual crystalline rare earth metal fluoride particles constituting the powder is expressed by the full width at half maximum (unit: °) of the maximum peak derived from the crystalline rare earth metal fluoride in an X-ray diffraction pattern obtained by performing X-ray diffraction measurement on the powder, and the X-ray opaque filler (hereinafter also referred to as "specific X-ray opaque filler”) is the X-ray opaque filler.
• the dental hardenable composition is characterized in that
• the content of the crystalline rare earth metal fluoride particles in the organic-inorganic composite particles constituting the X-ray opaque filler is preferably 60 to 90 mass% based on the total mass of the organic-inorganic composite particles, and the average particle size of the organic-inorganic composite particles is preferably 22 ⁇ m to 70 ⁇ m.
• the rare earth metal fluoride particles are preferably ytterbium fluoride particles.
• the average primary particle size of all of the "spherical particles of the same particle size" (G-PID) contained in the dental hardenable composition of the present invention is within the range of 230 to 350 nm.
• the dental hardenable composition of the present invention does not contain rare earth metal fluoride particles other than the rare earth metal fluoride particles blended as the X-ray opaque filler, or that the content of rare earth metal fluoride particles other than the rare earth metal fluoride particles is 5 parts by mass or less per 100 parts by mass of the polymerizable monomer.
• the dental curable composition gives a cured product having a contrast ratio C of 0.20 to 0.50, which is defined as the ratio Yb / Yw , the ratio of Yb , which is the Y value measured against a black background, to Yw , which is the Y value measured against a white background, using a color difference meter for a 1 mm-thick cured product sample, and which is an index of transparency of the cured product of the dental curable composition.
• a contrast ratio C of 0.20 to 0.50 which is defined as the ratio Yb / Yw , the ratio of Yb , which is the Y value measured against a black background, to Yw , which is the Y value measured against a white background, using a color difference meter for a 1 mm-thick cured product sample, and which is an index of transparency of the cured product of the dental curable composition.
• the amount of the polymerization initiator is 0.01 to 0.5 parts by mass per 100 parts by mass of the polymerizable monomer. Furthermore, it is preferable that the full width at half maximum is 40° or less.
• the structural color dental hardenable composition of the present invention which is a dental hardenable composition known for use as a structural color CR, is blended with a specified amount of a specific X-ray opaque filler, and when used as a CR, it can impart high X-ray opacity to the hardened product without compromising the excellent characteristics of the structural color CR.
• the inventors conducted extensive research to solve the problem that it is difficult to obtain a cured product that is excellent in both X-ray opacity and transparency when using conventional curable compositions that use rare earth metal fluorides as the main component of the X-ray opaque filler.
• a curable composition containing a powder of crystalline rare earth metal fluoride particles such as crystalline ytterbium fluoride can improve X-ray opacity without reducing the transparency of the cured body.
• further investigations were conducted and it was found that such a phenomenon occurs when (i) the crystallinity of the crystalline rare earth metal fluoride particles is reduced by mechanochemical treatment, and (ii) the full width at half maximum (FWHM) of the maximum intensity peak of the crystalline rare earth metal fluoride measured in X-ray diffraction measurement, which corresponds to the crystallite size as an index of crystallinity, becomes a certain value or more (the degree of crystallinity is reduced to a certain level or more) as a result of such treatment.
• a novel X-ray opaque filler consisting of rare earth metal fluoride particles having such a specific crystallinity has already been proposed (PCT/JP2022/031237).
• the inventors further investigated the above-mentioned radiopaque filler and found that a relatively large amount was required to obtain sufficient radiopaqueness, and that when it was added to a structural color system CR, it tended to make it difficult for the desired structural color to appear (see Comparative Examples 3 and 4 below).
• the dental hardenable composition of the present invention is characterized by the incorporation of a specific X-ray opaque filler. Therefore, we will first explain the specific X-ray opaque filler and its manufacturing method, and then provide a detailed explanation of the dental hardenable composition of the present invention.
• the expression “x ⁇ y” using the numerical values x and y means “greater than or equal to x and less than or equal to y.” In such expressions, when a unit is assigned only to the numerical value y, the unit is also applied to the numerical value x.
• the term “(meth)acrylic” means both “acrylic” and “methacrylic.”
• the term “(meth)acrylate” means both “acrylate” and “methacrylate”
• the term “(meth)acryloyl” means both “acryloyl” and “methacryloyl.”
• the specific X-ray opaque filler is composed of organic-inorganic composite particles in which a plurality of crystalline rare earth metal fluoride particles having a full width at half maximum of 0.3° or more are dispersed in a resin matrix when the crystallinity of each crystalline rare earth metal fluoride particle constituting a powder made of crystalline rare earth metal fluoride particles is expressed by the full width at half maximum (unit: °) of the maximum peak derived from the crystalline rare earth metal fluoride in an X-ray diffraction pattern obtained by performing X-ray diffraction measurement on the powder.
• the specific X-ray opaque filler is usually composed only of the organic-inorganic composite particles (hereinafter also referred to as the "particle body"), but may contain external additive particles such as silica or titanium oxide (fine particles).
• the organic-inorganic composite particles (particle body) may have their surfaces subjected to physical surface treatment such as plasma treatment, or mechanical surface treatment such as long-term friction stirring, or may have been treated with a known coating agent such as silicone oil.
• the crystalline rare earth metal fluoride particles in the organic-inorganic composite particles (particle body) may be surface-treated with a known surface treatment agent such as a silane coupling agent or a titanate coupling agent.
• the full width at half maximum of the diffraction peak in X-ray diffraction measurements there is a correlation between the full width at half maximum of the diffraction peak in X-ray diffraction measurements and the crystallite size, known as the Scherrer equation, and it is known that the crystallite size is inversely proportional to the full width at half maximum.
• the full width at half maximum (FWHM) is also affected by the distortion of the crystal lattice, and as the full width at half maximum (FWHM) increases and the crystal lattice distortion increases, the full width at half maximum tends to widen.
• the crystallinity decreases when the crystallite distortion is large, the crystallite diameter becomes small, and the fine crystallites are oriented in various directions, so the full width at half maximum can be said to be an index of the crystallinity (more specifically, the perfection of the crystal) of rare earth metal fluorides.
• full width at half maximum means the full width at half maximum (unit: °) of the maximum peak attributable to the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained when X-ray diffraction measurement is performed on the powder to determine the crystallinity of each crystalline rare earth metal fluoride particle constituting the powder.
• Crystalline rare earth metal fluoride particles having a full width at half maximum of 0.3° or more do not significantly reduce the transparency of the dental hardenable composition hardened body even when they are directly mixed into a dental hardenable composition without being compounded with an organic resin to form organic-inorganic composite particles (see PCT/JP2022/031237 and Comparative Examples 3 and 4 described later).
• the reason for this effect is presumed to be as follows. First, the decrease in transparency in a system in which inorganic fine particles are dispersed in a resin matrix is largely due to the diffuse reflection of light at the interface between the two.
• the surface vicinity of the crystalline rare earth metal fluoride particles gradually becomes amorphous from the surface toward the inside due to the mechanochemical treatment.
• a layer hereinafter also referred to as a "refractive index gradient layer" in which the refractive index gradually decreases with a certain gradient from the inside toward the surface is formed in the surface vicinity of the crystalline rare earth metal fluoride particles.
• the formed refractive index gradient layer includes a portion having a refractive index that matches the refractive index of the resin matrix.
• the same effect can be obtained so long as the absolute value of the difference between the refractive index at 25°C of the hardened product of the polymerizable monomer (n (MX)) to sodium d line (n (F-MX)) and the refractive index at 25°C of the resin material constituting the resin matrix of the organic-inorganic composite particles constituting the specific X-ray opaque filler (n ( F-MX) ) is 0 to 0.1, preferably 0 to 0.05.
• the polymerizable monomer in the dental curable composition becomes a resin that constitutes the matrix of the hardened body of the dental curable composition, and when the refractive index: n (F-MX) value of the polymerizable monomer is close to the refractive index: n (F-MX) value of the resin material that constitutes the resin matrix of the organic-inorganic composite particles, diffuse reflection of light is less likely to occur on the surface of the organic-inorganic composite particles (in other words, the resin matrix of the organic-inorganic composite particles and the resin matrix of the hardened body of the dental curable composition become integrated), and the above-mentioned characteristics of the crystalline rare earth metal fluoride particles having a full width at half maximum of 0.3° or more are exhibited.
• the full width at half maximum of the crystalline rare earth metal fluoride particles As described above, by setting the full width at half maximum of the crystalline rare earth metal fluoride particles to 0.3° or more, when a curable composition containing the radiopaque filler of the present invention is cured, a cured body having excellent radiopaqueness and transparency can be easily obtained. In other words, even if the amount of the radiopaque filler of the present embodiment blended into the curable composition is increased in order to increase the radiopaqueness of the cured body, the transparency of the cured body can be prevented from decreasing.
• the full width at half maximum may be 0.3° or more, preferably 0.4° or more, and more preferably 0.5° or more.
• the upper limit of the full width at half maximum is not particularly limited, but in practical terms, it is preferably 40° or less, and more preferably 1° or less.
• the full width at half maximum can be determined by performing X-ray diffraction measurement on a powder sample to be subjected to X-ray diffraction measurement. Specifically, an X-ray diffraction pattern (chart) is obtained in which the horizontal axis indicates 2 ⁇ (°) and the vertical axis indicates diffraction intensity by performing X-ray diffraction measurement on the powder sample in the range of 2 ⁇ from 20° to 120° using an X-ray diffraction device. It is preferable to use a powder sample from which coarse particles have been removed, for example, by using a sieve with an opening of 100 ⁇ m, according to a conventional method.
• the peaks originating from the rare earth metal fluoride particles in the X-ray diffraction pattern are identified, and the full width at half maximum of the peak having the greatest intensity among the multiple peaks confirmed is obtained.
• the peak width is obtained as the absolute value (unit “deg [°]”) of the difference between the value of 2 ⁇ at one intersection point and the value of 2 ⁇ at the other intersection point at two intersection points where a convex peak line intersects with a straight line that is parallel to the horizontal axis of the X-ray diffraction pattern (chart) and at the position of 50% intensity.
• the full width at half maximum of the crystalline rare earth metal fluoride particles in the organic-inorganic composite particles (particle body) constituting the specific X-ray opaque filler can be confirmed based on the X-ray diffraction pattern obtained by performing powder X-ray diffraction measurement on a powder sample consisting of the particle body.
• the full width at half maximum of the crystalline rare earth metal fluoride particles in the particle body can also be confirmed based on the X-ray diffraction pattern obtained by performing powder X-ray diffraction measurement on a powder sample consisting of the secondary raw material powder (since the crystallinity of the secondary raw material powder does not change or does not substantially change in the mixing and grinding process when preparing the raw material composition).
• the full width at half maximum of the crystalline rare earth metal fluoride particles in the specific X-ray opaque filler contained in the dental hardenable composition of the present invention can also be confirmed based on the X-ray diffraction pattern obtained by performing powder X-ray diffraction measurement on a powder sample containing organic-inorganic composite particles separated from these hardenable compositions or a powder sample obtained from a hardened body of these hardenable compositions.
• the rare earth metal fluoride particles contained in the organic-inorganic composite particles (particle body) are not particularly limited in material, so long as the full width at half maximum is 0.3° or more, and known rare earth metal fluoride particles can be appropriately used.
• the rare earth metal fluoride particles are preferably made of, for example, lanthanum fluoride (LaF 3 ), cerium fluoride (CeF 3 ), or ytterbium fluoride (YbF 3 ). Among these, ytterbium fluoride (YbF 3 ) is more preferable.
• the material of the rare earth metal fluoride particles is preferably lanthanum fluoride ( LaF3 ), cerium fluoride ( CeF3 ), or ytterbium fluoride ( YbF3 ), and further, from the viewpoint of ensuring X-ray opacity, ytterbium fluoride ( YbF3 ) is particularly preferable.
• the resin material constituting the resin matrix of the organic-inorganic composite particles (particle body) is not particularly limited, and known resin materials can be appropriately selected, such as (meth)acrylic resins and polyaryletherketone resins.
• (meth)acrylic resin means ⁇ i> a polymer polymerized using only (meth)acrylate monomers as the polymerizable monomer used in the polymerization of the (meth)acrylic resin, or ⁇ ii> a polymer in which the proportion of (meth)acrylate monomers in the total polymerizable monomers is 50 mol % or more when two or more types of polymerizable monomers including a (meth)acrylate monomer are used.
• a suitable combination of materials constituting the organic-inorganic composite particles (particle body) includes a combination of at least one selected from the group consisting of lanthanum fluoride ( LaF3 ), cerium fluoride ( CeF3 ) and ytterbium fluoride ( YbF3 ) as the material of the rare earth metal fluoride particles (Group A1), and a (meth)acrylic resin as the resin material constituting the resin matrix (Group B).
• a particularly suitable combination includes a combination of at least one selected from the group consisting of ytterbium fluoride ( YbF3 ) as the material of the rare earth metal fluoride particles (Group A2), and a (meth)acrylic resin as the resin material constituting the resin matrix (Group B).
• the content of rare earth metal fluoride particles in the organic-inorganic composite particles (particle body) is not particularly limited, but is preferably 60% by mass or more, and more preferably 70% by mass or more, based on the total mass of the organic-inorganic composite particles.
• the upper limit of the content is preferably 90% by mass or less, and more preferably 80% by mass or less.
• the average particle size of the organic-inorganic composite particles (particle body) is not particularly limited, but from the viewpoint of achieving a good balance between X-ray contrast and mechanical strength, it is preferably 22 to 70 ⁇ m, and more preferably 24 to 55 ⁇ m. Furthermore, when emphasis is placed on ensuring mechanical strength rather than X-ray contrast, the average particle size is preferably 3 to 38 ⁇ m, and more preferably 8 to 25 ⁇ m. On the other hand, when emphasis is placed on ensuring X-ray contrast rather than mechanical strength, the average particle size is preferably 38 ⁇ m or more, and more preferably 70 ⁇ m or more. The lower limit is not particularly limited, but from the viewpoint of ensuring a certain level of mechanical strength, 110 ⁇ m or less is preferable.
• the manufacturing method of the specific radiopaque filler (also referred to as the present manufacturing method) is not particularly limited as long as it is a method of granulating organic-inorganic composite particles using rare earth metal fluoride particles having a full width at half maximum of 0.3° or more and a resin material or a resin material precursor (polymerizable monomer, etc.), and a known manufacturing method of organic-inorganic composite particles can be appropriately used.
• the full width at half maximum of rare earth metal fluorides that are generally used as X-ray opaque materials and commercially available rare earth metal fluoride powders that are available as raw material powders is usually less than 0.3° (specifically, about 0.17° to 0.27°). For this reason, it is preferable to adopt this manufacturing method because it is possible to efficiently manufacture a specific X-ray opaque filler using such rare earth metal fluoride powder.
• the steps of this manufacturing method are explained below.
• the hardening step and the pulverizing step are sometimes referred to as the granulation step.
• Secondary raw material powder preparation process In the secondary raw material powder preparation process, a primary raw material powder consisting of a powder mainly composed of crystalline rare earth metal fluoride particles having a full width at half maximum of less than 0.3° is mechanochemically treated to obtain a secondary raw material powder consisting of a powder mainly composed of rare earth metal fluoride particles having a full width at half maximum of 0.3° or more.
• mainly composed means that it may contain a small amount of a substance other than the crystalline rare earth metal fluoride particles, for example, a surface treatment agent or an additive that is physically attached or chemically bonded to the surface of the crystalline rare earth metal fluoride particles, and the full width at half maximum of the crystalline rare earth metal fluoride particles must be less than 0.3° or 0.3° or more.
• rare earth metal fluorides that are generally used as X-ray opaque materials, or commercially available rare earth metal fluoride powders that are available as raw material powders and have a full width at half maximum of less than 0.3° (specifically, approximately 0.17° to 0.27°). It is preferable to measure the full width at half maximum of the primary raw material powder by X-ray diffraction measurement as necessary.
• the crystalline rare earth metal fluoride particles used as the primary raw powder may be particles whose surfaces have been coated with nanosilica or the like, or particles whose surfaces have been treated with a silane coupling agent or the like.
• the particles contained in the raw powder may be pulverized, and the secondary particles (agglomerated particles) and primary particles may be broken down, resulting in a smaller particle size.
• the coarse agglomerated particles are broken down, no significant change is observed in the particle size of the primary particles or submicron-level agglomerated particles.
• a powder with an average particle size of 0.1 to 0.6 ⁇ m as measured by the laser diffraction/scattering method, which can also measure the agglomerated particle size, and more preferably a powder with an average particle size of 0.1 to 0.3 ⁇ m.
• the average primary particle size is a value measured using a scanning electron microscope. Specifically, the powder was observed under an electron microscope at a magnification of 100,000 times, and the average primary particle size of 100 primary particles in the obtained observation image was determined.
• Mechanochemical treatment means a treatment that applies mechanical energy to the raw powder, specifically, at least one treatment selected from the group consisting of mechanical grinding, pulverization, and dispersion. From the viewpoint of easily controlling the full width at half maximum, which is also the degree of perfection of the crystals of the mechanochemically treated rare earth metal fluoride particles, to a desired value reliably and efficiently, it is preferable to adopt a wet method as the mechanochemical treatment method, and in particular, a treatment method using a wet bead mill is preferable.
• a solvent such as water or alcohol, or a polymerizable monomer
• a medium that is liquid at room temperature (15°C to 25°C) is preferable.
• a slurry of the raw material powder to be treated with the mechanochemical treatment and a medium is brought into contact with media (beads) that have been stirred, vibrated, or otherwise moved. This causes the raw material powder to be crushed and disintegrated.
• the material of the beads used as the media can be glass, alumina, zircon, zirconia, steel, or resin, but alumina or zirconia is preferred because of their excellent wear resistance and relatively low contamination.
• the size of the beads used can be selected according to the particle size of the desired radiopaque filler, and there is no particular restriction, but it is usually preferable to use beads with a diameter of 0.01 mm to 0.5 mm. Beads with such a diameter are also suitable for obtaining an radiopaque filler with a particle size suitable for addition to a dental hardenable composition.
• wet bead mills come in a variety of types, including batch types, in which the slurry and beads are directly fed into the equipment for processing, circulation types, in which the slurry is circulated between a tank and the equipment, and pass types, in which the slurry is passed through the equipment a set number of times.
• batch types in which the slurry and beads are directly fed into the equipment for processing
• circulation types in which the slurry is circulated between a tank and the equipment
• pass types in which the slurry is passed through the equipment a set number of times.
• the concentration of the slurry used in the mechanochemical treatment is preferably 50 parts by mass or less of raw material powder per 100 parts by mass of medium. If the raw material powder in the slurry exceeds 50 parts by mass, the viscosity of the slurry will increase, and mechanochemical treatment may become difficult.
• the increase in the viscosity of the slurry can be suppressed by adding a dispersant to the slurry. Therefore, by adding a dispersant to the slurry, it is possible to mechanochemically treat a slurry with a higher concentration.
• the dispersant used can be any known surfactant without any particular restrictions, and examples of such dispersants include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and polymeric surfactants thereof. Specific examples include glycerin fatty acid esters and their alkylene glycol adducts, aliphatic monocarboxylates, alkylamine salts, and alkylbetaines.
• a cationic surfactant from the viewpoint of dispersibility during mixing.
• Mechanochemical treatment conditions vary depending on the operating method and bead diameter of the wet bead mill device used, the full width at half maximum of the raw material powder, and the concentration of the slurry. These conditions can be selected appropriately after conducting preliminary experiments using the device that will actually perform the mechanochemical treatment and checking the full width at half maximum of the raw material powder after mechanochemical treatment versus the mechanochemical treatment time. Furthermore, when mechanochemical treatment is performed, it is possible to obtain mechanochemically treated secondary raw material powder with the desired full width at half maximum by appropriately sampling the slurry during mechanochemical treatment as necessary and checking the full width at half maximum as appropriate.
• the secondary raw powder (mechanochemically treated rare earth metal fluoride particles) adjusted to a full width at half maximum of 0.3° or more by the mechanochemical treatment is usually subjected to post-treatment processes such as concentration, drying, and filtration as appropriate.
• post-treatment processes such as concentration, drying, and filtration as appropriate.
• a polymerizable monomer is used as a medium during the mechanochemical treatment, the post-treatment process can be omitted.
• the organic-inorganic composite particles can be granulated after adding other components such as a polymerization initiator to the mechanochemically treated slurry (composition containing raw powder and polymerizable monomer) as necessary.
• the raw powder that has been subjected to the mechanochemical treatment process and the post-treatment process may be subjected to a surface treatment to improve the affinity with the resin matrix raw material used in granulation of the organic-inorganic composite particles.
• a surface treatment agent used for the surface treatment compounds such as a silane coupling agent and a titanate coupling agent that are commonly used can be used.
• the full width at half maximum of the secondary raw material powder may be 0.3° or more, but from the viewpoint of more stably and reliably obtaining the X-ray impermeable filler of the present embodiment, it is preferably 0.35° or more, and more preferably 0.4° or more.
• the upper limit of the full width at half maximum of the secondary raw material powder is not particularly limited, and can be appropriately selected according to the target value of the full width at half maximum of the X-ray impermeable filler to be manufactured, but in practical terms, it is preferably 40° or less, and more preferably 1° or less.
• the granulation process for the organic-inorganic composite particles includes a curing process in which a raw material composition obtained by mixing a polymerizable monomer, which is the raw material for the resin matrix of the organic-inorganic composite particles, and a raw material containing the secondary raw material powder is cured to obtain a cured product, and a crushing process in which the cured product is crushed.
• polymerizable monomer that is the raw material of the resin matrix of the organic-inorganic composite particles
• known polymerizable monomers such as radical polymerizable monomers can be used, but it is particularly preferable to use (meth)acrylate monomers.
• various polymerization initiators such as chemical polymerization initiators, photopolymerization initiators, and thermal polymerization initiators, and other additives can also be used in the raw material composition for granulation as necessary.
• specific examples of the polymerizable monomers, polymerization initiators, and other additives are the same as those used in the curable composition of this embodiment described below.
• the resin matrix that constitutes the organic-inorganic composite particles (particle body) obtained by the first granulation method is composed of a material obtained by curing the remaining components (mainly polymerizable monomers) from the raw material composition for granulation, excluding the raw material powder.
• the refractive index: nX of the crystalline rare earth metal fluoride particles used as the first and second raw powders with respect to the sodium d line at 25°C is usually in the range of 1.50 to 1.65, and in the case of the crystalline ytterbium fluoride particles, it is 1.55.
• the refractive index: n (F-MX) of the resin material that is the main component of the resin matrix constituting the organic-inorganic composite particles (particle body) with respect to the sodium d line at 25°C is preferably 1.45 to 1.60.
• the "resin material that is the main component of the resin matrix” means a cured product of a polymerizable monomer (a cured product of a composition consisting of only a polymerizable monomer or a cured product of a composition consisting of a polymerizable monomer and a small amount of a polymerization initiator).
• nX and n (F-MX) can have values close to each other as described above, it becomes easier to improve the transparency of the curable composition using an X-ray opaque filler.
• the grinding process can be carried out using a known grinding method such as a ball mill.
• the organic-inorganic composite particles (particle bodies) obtained after grinding can be subjected to various surface treatments, coating treatments, external additive treatments, etc., as necessary.
• thermoplastic resin such as a polyaryl ether ketone resin
• a granulation method including at least a melt-kneading step of melt-kneading a granulation raw material composition containing at least a secondary raw material powder and a thermoplastic resin to obtain a molten kneaded product, and a crushing step of crushing the solidified product obtained by cooling and solidifying the molten kneaded product, can be used to manufacture the organic-inorganic composite particles and make them into a specific X-ray opaque filler.
• additives can be used in the granulation raw material composition as necessary.
• specific examples of other additives that can be used include those used in the dental curable composition of the present invention described below.
• a method for melt-kneading the granulation raw material composition a known melt-kneading method can be used, for example, the melt-kneading method disclosed in WO 2013/88921.
• the resin matrix that constitutes the organic-inorganic composite particles (particle body) obtained by the second granulation method is composed of the remaining components (mainly thermoplastic resin) excluding the raw material powder from the granulation raw material composition.
• Dental hardenable composition of the present invention (1) Overview of dental hardenable composition of the present invention
• the dental hardenable composition of the present invention is mainly characterized in that a predetermined amount of a specific X-ray opaque filler is blended into a dental hardenable composition used as a conventionally known structural color CR (existing structural color dental hardenable composition).
• the existing structural color dental hardenable composition means, as already explained as the prior art, a dental hardenable composition that contains a predetermined amount of each of a polymerizable monomer, an inorganic filler, and a polymerization initiator, and uses a filler containing spherical inorganic particles having a specific average particle size and particle size distribution, i.e., one or more "spherical particle groups of the same particle size" (G-PID), and makes the refractive index of the spherical inorganic particles higher than the refractive index of the resin part that becomes the matrix when hardened, specifically, when the amount of the polymerizable monomer contained in the dental hardenable composition is 100 parts by mass, the following conditions 1 to 3 are satisfied, thereby expressing a structural color that develops in a predetermined color tone that is independent of the angle of incidence of light due to light interference, scattering, etc.
• G-PID spherical particle groups of the same particle size
• the composition comprises an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within the range of 100 to 1000 nm, the individual inorganic spherical particles constituting the aggregate being substantially composed of the same substance, and containing one or more "groups of spherical particles of the same diameter" (G-PID) in total: 10 to 1500 parts by mass, in which 90% or more of the total number of particles in the number-based particle size distribution of the aggregate are present within a range of 5% around the predetermined average primary particle diameter; and a polymerization initiator.
• G-PID groups of spherical particles of the same diameter
• each "spherical particle group of the same diameter” is expressed as G-PID m (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more) in order of decreasing average primary particle diameter, when a is 2 or more, the materials constituting the individual particles of each G-PID m may be different from each other, and in that case, the average primary particle diameters of each G-PID m differ from each other by 25 nm or more.
• the dental hardenable composition of the present invention is characterized in that, in addition to the above-mentioned existing structural color dental hardenable composition, it also satisfies the following conditions 4 and 5.
• the radiopaque filler further contains 1 to 100 parts by mass, calculated as the total mass, of crystalline rare earth fluoride metal particles having a full width at half maximum of 0.3° or more.
• Condition 5 The absolute value of the difference between the refractive index at 25° C. of the cured product of the polymerizable monomer (n (MX)) to sodium d line (n (F-MX)) of the resin material constituting the resin matrix of the organic-inorganic composite particles constituting the X-ray opaque filler (n(F- MX) ) to sodium d line (n( F-MX) ) is 0 to 0.1.
• Such a feature of the dental hardenable composition of the present invention is due to the fact that the structural color expression state in the hardened product is almost equivalent to that of a hardened product of an existing structural color dental hardenable composition (also called a base existing structural color dental hardenable composition) that does not contain a specific X-ray opaque filler or a filler that adversely affects the expression of structural color.
• an existing structural color dental hardenable composition also called a base existing structural color dental hardenable composition
• Such a property can be confirmed by comparing the spectral reflectance ratio SR 1 /SR 2 of the hardened product of the dental hardenable composition of the present invention and the hardened product of the base existing structural color dental hardenable composition.
• SR 1 and SR 2 refer to the maximum spectral reflectance (SR 1 ) in the wavelength range of 600 nm or more and 750 nm or less (yellow to red range) and the maximum spectral reflectance (SR 2 ) in the wavelength range of 400 nm or more and 500 nm or less (blue range) in a spectral reflectance curve measured against a black background using a color difference meter for a 1 mm-thick cured body obtained by curing a dental curable composition, and the smaller the spectral reflectance ratio, the more blue the structural color (colored light) of the cured body is, and the larger the spectral reflectance ratio, the more reddish the structural color (colored light) of the cured body is.
• the average primary particle size of the G-PID to be blended is usually controlled so that the hardened composition will exhibit a desired structural color (giving a desired spectral reflectance ratio: SR 1 /SR 2 ratio).
• the spectral reflectance ratio is usually set to a range of 0.9 to 1.5.
• the dental hardenable composition of the present invention that satisfies the above conditions 4 and 5 is made by blending a specific X-ray opaque filler into a base existing structural color dental hardenable composition to give the hardened product high X-ray opacity, yet the spectral reflectance ratio is difficult to change, and it is possible to maintain a spectral reflectance ratio of, for example, 0.9 or more even without blending a toning agent such as a pigment.
• the dental curable composition of the present invention can provide a cured product having a contrast ratio C of, for example, 0.20 to 0.50, preferably 0.25 to 0.45.
• the contrast ratio C is defined as the ratio Yb/Yw between Yb, which is the Y value measured against a black background using a color difference meter for a 1 mm-thick cured product sample, and Yw , which is the Y value measured against a white background, and serves as an index of the transparency of the cured product of the dental curable composition .
• the smaller the contrast ratio the higher the transparency.
• the contrast ratio of the hardened body of the dental hardenable composition of the present invention is less than 0.20, the brightness (shade of color) of the hardened body at the filling site will be low, the transmitted light at the filling site will be strong, and the colored light from the hardened body will be weak. Therefore, when a deep cavity (e.g., a class IV cavity) is filled, it is considered that it is difficult to obtain the color matching effect of the present invention.
• a deep cavity e.g., a class IV cavity
• the contrast ratio C of the hardened body of the hardenable composition is in the range of 0.20 to 0.50, and more preferably in the range of 0.20 to 0.45.
• rare earth metal fluoride particles when rare earth metal fluoride particles are blended as is, the individual particles, which have weak X-ray opacity (small), are uniformly dispersed, causing the overall X-ray opacity to become blurred, whereas when they are blended as organic-inorganic composite particles, the "regions with locally high density of rare earth metal fluoride particles" (regions with locally high X-ray opacity) are uniformly dispersed (scattered) throughout, making them clearly distinguishable when viewed as an image.
• rare earth metal fluoride particles are compounded as they are, the particles will enter between the particles of the same particle diameter spherical particle group (G-PID) that forms an ideal periodic structure, disrupting the periodic structure.
• G-PID particle diameter spherical particle group
• the absolute number of particles is reduced compared to when rare earth metal fluoride particles are compounded as they are, and the frequency of disrupting the periodic structure of G-PID is reduced.
• the particle size increases due to the organic-inorganic composite, making it less likely to enter between the periodic structures of G-PID.
• the rare earth metal fluoride particles into organic-inorganic composite particles it becomes less likely to disrupt the periodic structure formed by G-PID, and it is believed that there is no adverse effect on the expression of the desired structural color.
• the components constituting the dental hardenable composition of the present invention and the amounts of the components, etc. are basically the same as those in the existing structural color dental hardenable compositions disclosed in Patent Documents 1 and 2, except that a specific X-ray opaque filler is blended in a predetermined amount. Therefore, the dental hardenable composition of the present invention will be described below after briefly explaining these components.
• (2-1) Polymerizable Monomers Polymerizable monomers used in the existing structural color dental hardenable compositions and dental hardenable compositions can be those that can be used in conventional dental hardenable compositions without any particular restrictions, but it is preferable to use (meth)acrylate monomers.
• (meth)acrylate monomers that can be suitably used include methyl (meth)acrylate, glycidyl (meth)acrylate, 2-cyanomethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, allyl (meth)acrylate, 2-hydroxyethyl mono(meth)acrylate, 2,2,3,3,-tetrafluoropropyl methacrylate (TFM), ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate (3G), nonaethylene glycol di(meth)acrylate, propylene ...
• polymerizable monomer examples include acrylate, dipropylene glycol di(meth)acrylate, 2,2-bis[4-(meth)acryloyloxyethoxyphenyl]propane, 2,2-bis[4-(meth)acryloyloxypolyethoxyphenyl]propane (D-2,6E), 2,2-bis ⁇ 4-[3-(meth)acryloyloxy-2-hydroxypropoxy]phenyl ⁇ propane, 1,4-butanediol di(meth)acrylate, 1,3-hexanediol di(meth)acrylate, 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane (UDMA), trimethylolpropane di(meth)acrylate, etc. Two or more of these polymerizable monomers can be used in appropriate combination.
• bifunctional to tetrafunctional polymerizable monomers are preferred due to their high polymerizability and the particularly high mechanical strength of the cured body, and from the viewpoint of the transparency of the cured body of the curable composition, it is more preferable to use any one of ethylene glycol di(meth)acrylate, 2,2-bis[4-(meth)acryloyloxyethoxyphenyl]propane, 2,2-bis ⁇ 4-[3-(meth)acryloyloxy-2-hydroxypropoxy]phenyl ⁇ propane, 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane (UDMA), or a combination of two or more of these polymerizable monomers.
• ethylene glycol di(meth)acrylate 2,2-bis[4-(meth)acryloyloxyethoxyphenyl]propane
• the type and amount of the polymerizable monomer so that the refractive index of the polymerizable monomer composition (mixture) at 25°C with respect to the sodium d line is in the range of 1.38 to 1.55. That is, when a silica-titanium group element oxide-based composite oxide, which has an easily adjustable refractive index, is used as the inorganic spherical particle, the refractive index at 25°C with respect to the sodium d line is in the range of about 1.45 to 1.58 depending on the silica content.
• the refractive index of the polymerizable monomer composition in the range of 1.38 to 1.55, the refractive index of the obtained hardened body can be adjusted to about 1.40 to 1.57, making it easy to satisfy the above condition.
• the refractive index of the polymerizable monomer or the hardened body of the polymerizable monomer can be determined at 25°C using an Abbe refractometer.
• the dental curable composition of the present invention from the viewpoint of not decreasing the transparency of the cured product of the dental curable composition,
• the blend ratios thereof are the same or similar.
• G-PID Group of spherical particles with the same particle size: G-PID
• the existing structural color dental hardenable composition and the same particle diameter spherical particle group used in the dental hardenable composition: G-PID are a predetermined average particle size in the range of 100 nm or more and 1000 nm or less (100 to 1000 nm).
• the aggregate is made of inorganic spherical particles having a primary particle diameter, and each inorganic spherical particle constituting the aggregate is made of substantially the same material and has a number-based particle size distribution of the aggregate that is smaller than the total particle diameter. It means the above aggregate, 90% or more of whose number exists within a range of 5% around the given average primary particle diameter.
• the average primary particle diameter of inorganic spherical particles here means the average value obtained by taking a photograph of the G-PID using a scanning electron microscope, selecting 100 or more particles observed within a unit field of view of the photograph, and determining the primary particle diameter (maximum diameter) of each.
• spherical means that it is sufficient for the particle to be approximately spherical, and does not necessarily have to be a perfect sphere.
• a photograph of the G-PID is taken using a scanning electron microscope, the maximum diameter of each particle (100 or more) within the unit field of view is measured, and the average uniformity obtained by dividing the particle diameter in the direction perpendicular to the maximum diameter by the maximum diameter should be 0.6 or more, more preferably 0.8 or more.
• each constituent particle of G-PID has a specific short-range order structure and is dispersed in a resin matrix, so that diffraction interference occurs in accordance with the Bragg condition, light of a specific wavelength is emphasized, and colored light of a color tone according to the average primary particle diameter is generated (structural color is expressed). That is, in order for structural color to be expressed, 90% (number) or more of the inorganic spherical particles that constitute G-PID must be present within a range of 5% around the average primary particle diameter.
• the ratio (%) of the "number of particles present within a range of 5% around the average primary particle diameter" to the “total number of particles that constitute G-PID" is defined as the "5% particle content”
• the 5% particle content must be 90% or more.
• the average primary particle diameter of the inorganic spherical particles that constitute G-PID must be within the range of 100 to 1000 nm. When spherical particles with an average primary particle size smaller than 100 nm are used, the phenomenon of visible light interference is unlikely to occur, and structural color is also unlikely to appear.
• the average primary particle diameter is 230-800 nm, a yellow to red structural color (colored light) is likely to be produced, and when the average primary particle diameter is less than 150-230 nm, a blue structural color (colored light) is likely to be produced. Because G-PID produces a yellow to red structural color (colored light) that is preferred as a dental filling and restorative material, the average primary particle diameter is preferably 230-800 nm, more preferably 240-500 nm, and particularly preferably 260-350 nm.
• the resulting colored light is yellowish, which is useful for repairing teeth that fall into the B-type (red-yellow) category in the shade guide (VITA Classical, manufactured by VITA), and is particularly useful for repairing cavities formed from the enamel to the dentin.
• the colored light obtained is reddish, which is useful for restoring teeth in the A-type (reddish brown) category in the shade guide (VITA Classical, manufactured by VITA), and is particularly useful for restoring cavities formed from enamel to dentin.
• the embodiment using only G-PID with an average primary particle size in the range of 260 to 350 nm is most preferable because it has good compatibility with a wide range of restored teeth of various colors.
• the embodiment using only G-PID with a particle size in the range of less than 150 to 230 nm is used, as described above, the colored light obtained is blued, and for cavities formed from enamel to dentin, the color compatibility with the tooth structure is likely to be poor, but it is useful for restoring enamel, and is particularly useful for restoring incisal edges.
• the existing structural color dental curable composition and the dental curable composition may contain one or more types of G-PID.
• the number of G-PIDs contained: a is preferably 1 to 5, more preferably 1 to 3, and most preferably 1 or 2.
• the average primary particle diameters of the G-PIDs must differ from each other by 25 nm or more.
• each G-PID is expressed as G-PID m (where m is 1 when a is 1, and is a natural number from 1 to a when a is 2 or more) in order of decreasing average primary particle diameter
• each G-PID can be dispersed in a form like an aggregate of a small number of inorganic spherical particles, not exceeding about 20, which is aggregated with a very loose binding force, and thus it is possible to disperse with a short-range order structure that can express a structural color for each G-PID, and as a result, it is possible to express a unique structural color (according to the average primary particle size) for each G-PID.
• the particle size distribution of the inorganic spherical particles as a whole becomes broad, and probably the inorganic spherical particles constituting each G-PID are dispersed by mutual substitution, and it becomes difficult to express a structural color, probably because a phenomenon similar to that occurs when an aggregate of a single inorganic spherical particle that does not satisfy the condition of the number-based particle size distribution is used occurs.
• the average primary particle size d m of each G-PID m differs from each other by 30 nm or more, particularly 40 nm or more.
• each G-PID has an extremely sharp particle size distribution and has the above-mentioned difference in average primary particle diameter, so the particle size distributions of each G-PID are unlikely to overlap, and even if they overlap partially, it is possible to confirm the particle size distribution of each G-PID. That is, the particle size distribution of the inorganic particles contained in the composite material according to this embodiment has the same number of independent peaks as the number of G-PIDs contained in the composite material in the range of 100 to 1000 nm, and even if each peak partially overlaps, the average primary particle diameter and number-based particle size distribution of each G-PID can be confirmed by performing waveform processing. In addition, the particle size distribution of the inorganic particles contained in the present invention can also be confirmed, for example, by image processing an electron microscope photograph of the internal surface of the composite material according to this embodiment.
• G-PID is formed by agglomerating inorganic spherical particles to form an aggregate particle size.
• the average aggregate particle size of G-PID is preferably within the range of 5 to 200 ⁇ m, and more preferably within the range of 10 to 100 ⁇ m.
• the average aggregate particle size of G-PID refers to the median diameter of volume statistics obtained based on the measurement results using a particle size distribution meter using the laser diffraction-scattering method.
• the inorganic spherical particles constituting G-PID are not particularly limited in material as long as they satisfy the above-mentioned conditions for constituting G-PID.
• materials that can be suitably used include amorphous silica, silica-titanium group element oxide composite oxide particles (silica-zirconia, silica-titania, etc.), quartz, alumina, barium glass, strontium glass, lanthanum glass, fluoroaluminosilicate glass, ytterbium fluoride, zirconia, titania, colloidal silica, etc.
• silica-titanium group element oxide composite oxide particles sica-zirconia, silica-titania, etc.
• quartz alumina
• barium glass strontium glass
• lanthanum glass fluoroaluminosilicate glass
• ytterbium fluoride zirconia
• titania colloidal silica, etc.
• the silica-titanium group element oxide composite oxide particles refer to a composite oxide of silica and an oxide of a titanium group element (group 4 element of the periodic table), and the refractive index for sodium d-line at 25°C can be changed in the range of about 1.45 to 1.58 depending on the content of silica.
• Specific examples of silica-titanium group element oxide composite oxide particles include silica-titania, silica-zirconia, and silica-titania-zirconia, but it is preferable to use silica-zirconia.
• the composite ratio in silica-zirconia is not particularly limited, but from the viewpoint of imparting sufficient X-ray opacity and setting the refractive index in the preferred range described below, it is preferable that the silica content is 70 to 95 mol% and the titanium group element oxide content is 5 to 30 mol%. It should be noted that these silica-titanium group element oxide composite oxide particles can also be composites of metal oxides other than silica and titanium group element oxides, as long as the amount is small. Specifically, alkali metal oxides such as sodium oxide and lithium oxide may be contained in an amount of up to 10 mol%.
• the method for producing such silica-titanium group element oxide composite oxide particles is not particularly limited, but in order to obtain spherical fillers, for example, the so-called sol-gel method is preferably used, in which a mixed solution containing a hydrolyzable organosilicon compound and a hydrolyzable organotitanium group metal compound is added to an alkaline solvent, and hydrolysis is carried out to precipitate a reaction product.
• These inorganic spherical particles made of silica-titanium group element oxide composite oxides are preferably surface-treated with a silane coupling agent such as ⁇ -methacryloyloxyalkyltrimethoxysilane or hexamethyldisilazane.
• n (MX) ⁇ n (G-PIDm) If the above relationship is not satisfied, even if a structural color is expressed, light of short wavelengths is likely to be scattered in the resin matrix in the hardened product of the dental hardenable composition, making it difficult to confirm the expressed structural color.
• the difference ⁇ n between n (G-PIDm) and n (MX) is set to 0. It is preferably 0.001 or more and 0.1 or less, more preferably 0.002 or more and 0.1 or less, and most preferably 0.005 or more and 0.05 or less.
• the refractive index (n (MX) ) of the cured product that becomes the resin matrix can be set in the range of 1.40 to 1.57.
• the refractive index (n (G-PIDm) ) of the silica-titanium group element oxide composite oxide can be changed in the range of about 1.45 to 1.58 by changing the silica content. Therefore, for example, by utilizing these relationships, ⁇ n can be easily set in the suitable range.
• an organic-inorganic composite filler that does not contain uniform-particle-size spherical particle groups other than the one type of uniform-particle-size spherical particle group (i.e., an organic-inorganic composite filler that contains only a single G-PID).
• the organic-inorganic composite filler means a powder consisting of a composite in which an inorganic filler is dispersed in an (organic) resin matrix, or a filler consisting of an aggregate in which primary particles of an inorganic filler are bound together by an (organic) resin.
• the organic-inorganic composite filler for example, when three types of G-PIDs having different average primary particle sizes, namely G-PID 1 , G-PID 2 , and G-PID 3 , are contained, all or a part of at least one of them is blended as an "organic-inorganic composite filler containing only a single G-PID".
• G-PID 1 is blended in the curable composition as an organic-inorganic composite filler containing only G-PID 1 (composite filler 1), only G-PID 1 is contained in the composite filler 1, and a short-range ordered structure that exhibits the structural color of G-PID 1 is realized, so that the structural color of G-PID 1 is reliably exhibited even in a composite material obtained by curing the curable composition.
• the refractive index at 25°C of the resin matrix of the organic-inorganic composite filler for the sodium d line: n' (F-MX) must be smaller than the refractive index at 25°C of the inorganic spherical particles for the sodium d line (n (G-PIDm) ).
• ⁇ n' which is the difference between n (G-PIDm) and n' (F-MX)
• ⁇ n' which is the difference between n (G-PIDm) and n' (F-MX)
• the refractive index at 25°C of the hardened body of the polymerizable monomer in the subsequent color dental hardenable composition of the present invention (specifically, the hardened body of a composition consisting of a polymerizable monomer and a small amount of polymerization initiator) with respect to the sodium d line: n (MX) and the refractive index n' (F-MX) mentioned above
• must be 0 to 0.1.
• the amount of inorganic spherical particles mixed into the organic-inorganic composite filler is preferably 30 to 95% by mass, and particularly preferably 40 to 90% by mass.
• the average particle size is not particularly limited, but from the viewpoint of improving the mechanical strength of the composite material and the operability of the curable composition, the median size determined based on the results of measurements using a particle size distribution meter using a laser diffraction-scattering method is preferably 2 to 100 ⁇ m, more preferably 5 to 50 ⁇ m, and even more preferably 5 to 30 ⁇ m.
• the total content of G-PID in the existing structural color dental curable composition and the structural color dental curable composition of the present invention is 10 to 1500 parts by mass relative to 100 parts by mass of the polymerizable monomer.
• the obtained composite material has a moderate transparency and a high effect of expressing the structural color, it is preferably 50 to 1500 parts by mass, more preferably 100 to 1500 parts by mass, even more preferably 100 to 450 parts by mass, and particularly preferably 150 to 400 parts by mass.
• the content of each G-PID may be appropriately set to an amount in which the total content is within the above range, taking into consideration the color tone of the structural color due to each G-PID and the color tone desired in the composite material.
• polymerization initiator used in the existing structural color dental hardenable composition and dental hardenable composition can be the same as the polymerization initiator in the dental hardenable composition of the present invention. Since the composition is often hardened in the oral cavity, it is preferable to use a chemical polymerization initiator and/or a photopolymerization initiator, and it is more preferable to use a photopolymerization initiator because there is no need for a mixing operation. These polymerization initiators may be used alone, but two or more types may be mixed and used.
• the amount of the polymerization initiator to be added may be selected according to the purpose, and is usually 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, even more preferably 0.2 to 1.5 parts by mass, and even more preferably 0.01 to 0.5 parts by mass, relative to 100 parts by mass of the polymerizable monomer.
• photopolymerization initiators examples include benzoin alkyl ethers, benzil ketals, benzophenones, ⁇ -diketones, thioxanthone compounds, and bisacylphosphine oxides.
• a reducing agent is often added to the photopolymerization initiator. Examples of reducing agents include aromatic amines, aliphatic amines, aldehydes, and sulfur-containing compounds. Furthermore, trihalomethyltriazine compounds, aryliodonium salts, and the like can also be added as necessary.
• thermal polymerization initiators include peroxides such as benzoyl peroxide, p-chlorobenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxydicarbonate, and diisopropylperoxydicarbonate; azo compounds such as azobisisobutyronitrile; boron compounds such as tributylborane, tributylborane partial oxide, sodium tetraphenylborate, sodium tetrakis(p-fluorophenyl)borate, and triethanolamine tetraphenylborate; barbituric acids such as 5-butylbarbituric acid and 1-benzyl-5-phenylbarbituric acid; and sulfinic acid salts such as sodium benzenesulfinate and sodium p-toluenesulfinate.
• peroxides such as benzoyl peroxide,
• the polymerizable monomer used as the raw material (of the matrix resin) in the specific X-ray opaque filler blended in the structural color dental hardenable composition of the present invention has the same composition as or a similar composition to the polymerizable monomer in the structural color dental hardenable composition of the present invention.
• is preferably 0 to 0.07, more preferably 0 to 0.05, and particularly preferably 0 to 0.035.
• the amount of the specific X-ray opaque filler blended in the dental hardenable composition of the present invention is, in terms of the X-ray opacity, transparency and structural color expression of the cured product, 1 to 100 parts by mass, preferably 15 to 75 parts by mass, and more preferably 28 to 80 parts by mass, per 100 parts by mass of the polymerizable monomer, calculated as the total mass of the crystalline rare earth fluoride metal particles having a full width at half maximum of 0.3° or more contained in the X-ray opaque filler of the present invention. If the amount is less than 1 part by mass (lower limit), sufficient X-ray opacity cannot be obtained, and if the amount is more than 100 parts by mass (upper limit), transparency and structural color expression are significantly reduced.
• the dental curable composition of the present invention may contain ultrafine particles (G-SFP), which are particle aggregates made of inorganic particles having an average primary particle diameter of less than 100 nm, for the purpose of adjusting the viscosity of the composition or the transparency of the cured product.
• G-SFP ultrafine particles
• the average primary particle diameter of the G-SFP must be 25 nm or more smaller than the average primary particle diameter (d 1 ) of G-PID 1 , which has the smallest average primary particle diameter among the G-PIDs contained in the composition. If such conditions are not satisfied, the dispersion state of the inorganic spherical particles is adversely affected, making it difficult to express structural color.
• the shape of the inorganic particles constituting the G-SFP is not particularly limited, and may be amorphous or spherical.
• the lower limit of the average primary particle diameter is usually 2 nm.
• the average primary particle diameter of the G-SFP is preferably 3 to 75 nm, more preferably 5 to 50 nm, because it has little effect on the expression of structural color.
• the average primary particle diameter of G-SFP is preferably 30 nm or more smaller than the average primary particle diameter (d 1 ) of G-PID 1 , and more preferably 40 nm or more smaller.
• the material of the inorganic particles constituting G-SFP the same as that of the inorganic spherical particles can be used without any particular limitation.
• G-SFP may be appropriately determined taking into consideration the viscosity of the curable composition, the transparency of the cured body (or the contrast ratio serving as an index thereof), and the like, but is usually 0.1 to 50 parts by mass, and preferably 0.2 to 30 parts by mass, relative to 100 parts by mass of the polymerizable monomer.
• the dental hardenable composition of the present invention may contain rare earth metal fluoride particles other than the rare earth metal fluoride particles blended as the specific X-ray opaque filler, so long as the effect of the present invention is not significantly impaired.
• the amount of such rare earth metal fluoride particles blended is preferably 5 parts by mass or less, and more preferably 0 to 3 parts by mass, relative to 100 parts by mass of the polymerizable monomer.
• the amount of crystalline rare earth fluoride metal particles having a full width at half maximum of less than 0.3° is preferably 0 to 0.5 parts by mass or less.
• the content of the crystalline rare earth fluoride metal particles having a full width at half maximum of 0.3° or more contained in the specific X-ray opaque filler and the total amount of the non-composite particles blended is 0 to 100 parts by mass, and more preferably 0 to 50 parts by mass, relative to 100 parts by mass of the polymerizable monomer.
• the dental curable composition of the present invention may contain other additives, such as polymerization inhibitors and ultraviolet absorbers, to the extent that the effect of the composition is not impaired.
• the cured product of the structural color dental curable composition of the present invention exhibits structural color without using coloring substances such as pigments. Therefore, it is not necessary to add a pigment that may discolor over time to the curable composition of this embodiment.
• the addition of a pigment is not denied, and a pigment may be added to the extent that it does not interfere with colored light due to interference from the spherical filler.
• a pigment may be added in an amount of about 0.0005 to 0.5 parts by mass, preferably about 0.001 to 0.3 parts by mass, per 100 parts by mass of the polymerizable monomer.
• the dental curable composition of the present invention contains each of the above-mentioned components in a predetermined amount, and thus can give a cured product that exhibits a structural color of a predetermined color tone independent of the angle of incidence of light. From the viewpoint of ensuring the expression of the structural color, the dental curable composition of the present invention is preferably prepared as follows.
• the method includes a mixing step in which all of the components that are the raw materials for the dental hardenable composition of the present invention are weighed out in predetermined amounts and mixed together, and it is preferable that the mixture obtained in the mixing step is prepared by a method in which mixing conditions are adopted that have been confirmed to satisfy the following conditions (I) and (II) in the dispersion state of the inorganic particles in the hardened body obtained by hardening the mixture obtained in the mixing step.
• the x-axis is a dimensionless number (r/ r0 ) obtained by dividing the distance from the center of any inorganic spherical particle dispersed in the cured body by the average particle size r0 of all the inorganic spherical particles dispersed in the cured body
• the y-axis is the radial distribution function g(r)
• the nearest inter-particle distance r1 which is defined as the r corresponding to the peak top of the peak closest to the origin among the peaks appearing in the radial distribution function graph, is a value that is 1 to 2 times the average particle size r0 of all the inorganic spherical particles dispersed in the cured body of the mixture.
• the radial distribution function g(r) is a well-known function for calculating the probability of the presence of another particle at a point a distance r away from any given particle, and is defined by the following formula (1).
• ⁇ > represents the average particle density of the particles in the plane
• dn represents the distance between two circles having radii r and r+dr, each of which has a center on an arbitrary particle in the plane.
• da represents 2 ⁇ r ⁇ dr, which is the area of the region.
• the radial distribution function g(r) is generally represented by a radial distribution function graph with distance r on the x-axis (distance axis) and the value of g(r) at r (the calculation result of the above formula (1)) on the y-axis (vertical axis), or by a radial distribution function graph with a dimensionless number normalized by dividing r by the average particle diameter of the particles on the distance axis and the value of g(r) at r corresponding to the x-axis value (the calculation result of the above formula) on the y-axis (vertical axis).
• ⁇ >, dn, and da can be determined as follows. First, the mixture is hardened, and a plane (observation plane) on which the dispersion state of the inorganic spherical particles inside the hardened material can be observed is exposed on the surface by means of polishing the surface of the obtained hardened material.
• the observation plane is observed by a scanning electron microscope, and a microscopic image of a region containing at least 500 inorganic spherical particles in the plane is obtained.
• the obtained scanning electron microscope image is analyzed by image analysis software (e.g., "Simple Digitizer ver. 3.2" free software) to determine the coordinates of the inorganic spherical particles in the region.
• the average particle density ⁇ > (unit: particles/cm2) can be determined by selecting one coordinate of any inorganic spherical particle from the obtained coordinate data, drawing a circle with a radius of distance r centered on the selected inorganic spherical particle and including at least 200 inorganic spherical particles, and counting the number of inorganic spherical particles included within the circle.
• dr when the average particle diameter of the inorganic spherical particles is represented by r0 , dr is set so that its length is about r0 /100 to r0 /10, and one arbitrarily selected inorganic spherical particle is taken as the central particle, and dn can be determined by counting the number of inorganic spherical particles contained within the region between a circle whose radius is the distance r from the center and a circle of radius r+dr having the same center as the circle. Furthermore, da, which is the area of the region between the two circles, is determined as 2 ⁇ r ⁇ dr based on the length of dr that is actually set.
• the x-axis is a dimensionless number (r/r 0 ) obtained by dividing the distance r from the center of any inorganic spherical particle dispersed in the hardened body by the average particle diameter r 0 of all inorganic spherical particles dispersed in the composite material
• the y-axis is a radial distribution function g( r ) representing the probability that other inorganic spherical particles are present at a point distant by a distance r from the center of any inorganic spherical particle.
• the radial distribution function graph shows the relationship between r/r 0 and g(r) corresponding to r at that time.
• r 1 /r 0 is 1.0 to 2.0, preferably 1.0 to 1.5.
• the minimum value of the radial distribution function g(r) between the nearest interparticle distance r 1 and the next nearest interparticle distance r 2 is a value of 0.56 to 1.10, preferably a value of 0.56 to 1.00.
• the mixing step it is preferable to mix the inorganic spherical particles (G-PID) as an organic-inorganic composite filler having a particle diameter of 5 to 50 ⁇ m, preferably 5 to 30 ⁇ m, or as aggregated particles having a particle diameter of 5 to 200 ⁇ m, preferably 10 to 100 ⁇ m.
• G-PID inorganic spherical particles
• a defoaming method it is preferable to adopt a method of defoaming under reduced pressure because it is possible to remove air bubbles in a short time even from a composition with high viscosity.
• inorganic spherical particles are mixed while paying attention to such points, in principle, the above conditions will be satisfied if sufficient stirring is performed, but even if it is judged to be in a uniform state by visual inspection, the stirring may be insufficient from the viewpoint of satisfying the above conditions, and it is difficult to determine the end point. Therefore, it is preferable to carry out the mixing step after determining the end point by the above method (a) or (b) or while determining the end point.
• a known polymerization means may be appropriately adopted according to the polymerization initiation mechanism of the polymerization initiator used. Specifically, light irradiation by a light source such as a carbon arc, a xenon lamp, a metal halide lamp, a tungsten lamp, a fluorescent lamp, sunlight, a helium cadmium laser, an argon laser, heating using a heating polymerization device, or a combination of these methods may be used without any restrictions.
• a light source such as a carbon arc, a xenon lamp, a metal halide lamp, a tungsten lamp, a fluorescent lamp, sunlight, a helium cadmium laser, an argon laser, heating using a heating polymerization device, or a combination of these methods may be used without any restrictions.
• the irradiation time varies depending on the wavelength and intensity of the light source, and the shape and material of the cured body, so it may be determined in advance by preliminary experiments.
• the curable composition of this embodiment is used for dental purposes, it is generally preferable to adjust the blending ratio of various components so that the irradiation time is in the range of about 5 to 60 seconds.
• Polymerizable monomer UDMA 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane 3G: triethylene glycol dimethacrylate D-2,6E: 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane TFM: 2,2,3,3-tetrafluoropropyl methacrylate.
• Polymerizable monomer composition (monomer composition) M1 A liquid composition prepared by stirring and mixing a mixture of UDMA (80 parts by mass), 3G (20 parts by mass), CQ (0.2 parts by mass) and DMBE (0.35 parts by mass) for 6 hours.
• FM1 A liquid composition prepared by stirring and mixing a mixture of UDMA (80 parts by weight), 3G (20 parts by weight), and AIBN (1 part by weight) for 6 hours.
• FM2 A liquid composition prepared by stirring and mixing a mixture of D-2, 6E (100 parts by mass) and AIBN (1 part by mass) for 6 hours.
• FM3 A liquid composition prepared by stirring and mixing a mixture of D-2, 6E (50 parts by mass), 3G (50 parts by mass), and AIBN (1 part by mass) for 6 hours.
• FM4 A liquid composition prepared by stirring and mixing a mixture of D-2, 6E (20 parts by mass), 3G (80 parts by mass), and AIBN (1 part by mass) for 6 hours.
• FM5 A liquid composition prepared by stirring and mixing a mixture of UDMA (70 parts by mass), TFM (30 parts by mass), and AIBN (1 part by mass) for 6 hours.
• FM6 A liquid composition prepared by stirring and mixing a mixture of UDMA (40 parts by mass), TFM (60 parts by mass), and AIBN (1 part by mass) for 6 hours.
• the refractive indices of the curable components M1 and FM1 to FM6 before and after curing, measured according to the method described below, are shown in Table 1.
• the content of the polymerization initiator per 100 parts by mass of the monomer is 0.2 parts by mass.
• Crystalline rare earth metal fluoride particles YbF3-40 ytterbium fluoride having the following characteristics (manufactured by Sukgyung Co., Ltd.) ⁇ Average primary particle diameter: 40nm ⁇ Average secondary particle diameter: 0.6 ⁇ m Refractive index: 1.55 These physical property values are values measured according to the methods described below.
• the surface was treated with an agent (methacrylic acid-3-(trimethoxysilyl)propyl-3-(methacryloyloxy)propyltrimethoxysilane (Tokyo Chemical Industry Co., Ltd.)).
• ⁇ Average primary particle diameter 260nm Refractive index: 1.515
• Uniformity 0.90 ⁇ 5% particle content: 92%
• the uniformity refers to the ratio (D2/D1) of the maximum diameter D1 of a spherical particle to the particle diameter D2 in a direction perpendicular to the maximum diameter D1.
• the average primary particle diameter and the refractive index are expressed by The values were measured according to the method described below.
• the monomer composition was filled into a through hole (diameter 7 mm, through hole length 0.5 mm) provided in a mold, and then both openings of the through hole were sealed while being pressed with a polyester film.
• the curable component M1 filled in the through hole was cured by irradiating it with light for 30 seconds using a halogen-type dental light irradiator (Demetron LC, manufactured by Cypron) with a light amount of 500 mW/cm 2.
• a halogen-type dental light irradiator (Demetron LC, manufactured by Cypron) with a light amount of 500 mW/cm 2.
• M2 instead of irradiating it with light, it was cured by heating it at 100 ° C.
• the average primary particle diameter of rare earth metal fluoride particles was determined using a scanning electron microscope according to the following procedure. First, a measurement sample was prepared by fixing rare earth metal fluoride particles on a sample stage with carbon paste and then subjecting them to a conductive treatment (platinum vapor deposition). Next, this measurement sample was observed at a magnification of 100,000 times using an electron microscope (JSM-7800F PRIME, manufactured by JEOL Ltd.), and the average particle diameter of 100 primary particles in the obtained observation image was determined as the average primary particle diameter.
• the average secondary particle size of rare earth metal fluoride particles was determined by particle size distribution measurement in the following procedure. First, a suspension was prepared by suspending 0.1 g of powder (rare earth metal fluoride particles) in 10 mL of ion-exchanged water. Next, while irradiating this suspension with ultrasonic waves, a particle size distribution measurement was performed using a particle size distribution meter (LS13-320, manufactured by BECKMAN COULTER) to obtain a volumetric particle size distribution. Then, the particle size (D50v value) that is 50% cumulative from the small diameter side of the volumetric particle size distribution was determined as the average secondary particle size of the rare earth metal fluoride particles.
• LS13-320 particle size distribution meter
• G-PID Average primary particle size of G-PID This was determined by particle size distribution measurement in the following procedure. First, a suspension was prepared by suspending 0.1 g of powder (G-PID) in 10 mL of ion-exchanged water. Next, while irradiating this suspension with ultrasonic waves, particle size distribution was measured using a particle size distribution meter (LS13-320, manufactured by BECKMAN COULTER) to obtain a number particle size distribution. Then, the particle size (D50p value) that is 50% cumulative from the small diameter side of the number particle size distribution was taken as the average primary particle size.
• LS13-320 particle size distribution meter
• Mechanochemical treatment of crystalline rare earth metal fluoride particles was carried out by the following procedure. First, 855 g of ion-exchanged water was mixed with 45 g of crystalline rare earth metal fluoride particles to prepare a slurry. Then, the slurry was dispersed at a rotation speed of 3,000 rpm using a circulation type wet bead mill SC50 (manufactured by Mitsui Mining Co., Ltd.) and 100 g of zirconia beads (diameter: 0.3 mm) as a medium. The dispersion treatment conditions at this time are shown in Table 2.
• the slurry after dispersion treatment was concentrated using a rotary evaporator at a bath temperature of 50°C to obtain a powder. This powder was dried under vacuum at 80°C for 15 hours to obtain mechanochemically treated rare earth metal fluoride particles.
• rare earth metal fluoride particles F-1 crystalline rare earth metal fluoride particles YbF3-40 themselves
• the average primary particle size was measured using the method described in 2.
• (2) and the full width at half maximum S was measured using the method described below. The results are also shown in Table 2.
• Measurement method of full width at half maximum S A measurement sample was prepared by removing coarse particles from the powder (rare earth metal fluoride particles) to be subjected to X-ray diffraction measurement using a sieve. Next, the measurement sample was filled into the sample stage of an X-ray diffraction device (Smartlab, manufactured by Rigaku Corporation) and X-ray diffraction measurement was performed to obtain an X-ray diffraction pattern (chart) with the horizontal axis representing 2 ⁇ (°) and the vertical axis representing diffraction intensity.
• X-ray diffraction pattern chart
• CuK ⁇ rays were used as the X-rays for the X-ray diffraction measurement.
• the full width at half maximum C of the X-ray opaque filler can be obtained in the same manner.
• the obtained cured product and zirconia balls (diameter: 25 mm) were placed in a zirconia pot and subjected to a rotary grinding treatment for 60 minutes to obtain a pulverized product of the cured product.
• the pulverized product was removed from the pulverized product using a stainless steel sieve with a mesh size of 45 ⁇ m to obtain a radiopaque filler CF-1.
• the average particle size and full width at half maximum C of the radiopaque filler CF-1 were measured. The results are shown in Table 3.
• the average particle size of the radiopaque filler was determined by particle size distribution measurement using the following procedure. That is, first, a suspension was prepared by suspending 0.1 g of powder (radiopaque filler) in 10 mL of ethanol. Next, while irradiating this suspension with ultrasound, particle size distribution measurement was performed using a particle size distribution analyzer (LS13-320, manufactured by BECKMAN COULTER) to obtain a volumetric particle size distribution. The particle size (D50v value) that is 50% cumulative from the small diameter side of the volumetric particle size distribution was determined as the average particle size of the radiopaque filler. The full width at half maximum C was measured in the same manner as the full width at half maximum S.
• Examples 1 to 27 and Comparative Examples 1 to 5 (1) Preparation of curable composition To the monomer composition M1 (20 parts by mass), an X-ray impermeable filler (16 parts by mass) and G-PID:PF-1 (64 parts by mass) were added, and then mixed in an agate mortar to obtain a mixture. The mixture was then degassed under vacuum to remove air bubbles, to obtain a paste-like curable composition. In addition, in preparing the curable composition, the type of X-ray impermeable filler was changed as shown in Table 4 to prepare the curable compositions of Examples 1 to 27 and Comparative Examples 1 to 5.
• the X-ray contrast of the cured product of the curable composition was measured by the following procedure. First, the curable composition was filled into a through hole (diameter 15 mm, through hole length 1.0 mm) provided in a polytetrafluoroethylene mold, and then both end openings of the through hole were sealed while being pressed with a polypropylene film. Next, light was irradiated in a state in which a dental light irradiator (TOKUSO POWER LIGHT, manufactured by Tokuyama Corporation) was placed so as to be in close contact with the surface of the polypropylene film sealing the opening of the through hole.
• a dental light irradiator TOKUSO POWER LIGHT, manufactured by Tokuyama Corporation
• the positions of light irradiation were 5 positions (1 position at the center of the through hole and 4 positions on the inner side of the outer edge of the through hole) on one opening side of the through hole, and 5 positions (1 position at the center of the through hole and 4 positions on the inner side of the outer edge of the through hole) on the other opening side. Then, light irradiation was performed for 20 seconds at each light irradiation position to obtain a cured product. The thickness of the obtained cured product was confirmed using a micrometer. The cured product having a thickness of 1.0 mm ⁇ 0.1 mm was used as a test piece for measuring X-ray contrast properties.
• an X-ray film (ultra-sensitive dental X-ray film, Kodak) was placed on a 2.0 mm thick lead sheet, and then a test piece and an aluminum step wedge with five different thicknesses (thickness: 1.0 ⁇ 0.01 mm, 2.0 ⁇ 0.01 mm, 3.0 ⁇ 0.01 mm, 4.0 ⁇ 0.01 mm, 5.0 ⁇ 0.01 mm) were placed on the X-ray film.
• the test piece and the step wedge were irradiated with X-rays from a height of 40 cm from the surface of the X-ray film using an X-ray irradiator (PANPAS-E, YOSHIDA).
• the irradiation conditions were tube voltage: 60 kVp, irradiation time: 0.3 seconds.
• the X-ray film was then developed and printed on photographic paper.
• the optical density of the test piece image and the step wedge image on the photographic paper were then measured.
• a calibration curve was created based on the five thicknesses of the step wedge and the optical densities corresponding to these five thicknesses, and the thickness of the step wedge (i.e., the aluminum material) at which the optical density of the test piece coincided with the optical density of the step wedge was determined based on this calibration curve.
• the calculated aluminum material thickness was converted to Al%, and used as an evaluation index for X-ray contrast, assuming that the optical density of an aluminum material with a thickness of 1 mm is the standard (100 Al%).
• test pieces of Examples 1, 13, and 19 and Comparative Examples 1 and 4, as well as the aluminum material (thicknesses 1, 2, 3, and 4 mm), were observed using a tabletop X-ray transmission inspection device ( ⁇ B1300, manufactured by Matsusada Precision Co., Ltd.).
• the X-ray irradiation conditions were tube voltage: 55 kV, tube current: 0.30 mA.
• the observed images were imported into dedicated image capture software ( ⁇ RayVision, manufactured by Matsusada Precision Co., Ltd.), and the X-ray contrast images were saved as digital images.
• the X-ray contrast images (digital images) obtained by this method are shown in Figure 1.
• the transparency of the cured product of the curable composition was measured by the following procedure. First, the curable composition was filled into a hole (diameter 0.7 cm, through hole length 0.1 cm) provided in a polyacetal mold, and both ends of the through hole were sealed while being pressed with a polypropylene film. Next, a dental light irradiator (TOKUSO POWER LIGHT, manufactured by Tokuyama Corporation) was placed at a position 0.5 cm away from the opening surface of the hole, and light irradiation was performed for 20 seconds to obtain a cured product. The thickness of the obtained cured product was confirmed using a micrometer.
• TOKUSO POWER LIGHT manufactured by Tokuyama Corporation
• the cured product having a thickness of 1.0 mm ⁇ 0.1 mm was used as the cured product to be used for the evaluation of transparency.
• the Y value (a value related to brightness among the tristimulus values of the XYZ color system specified in JIS Z8701) of this cured product was measured using a color difference meter (SE7700, manufactured by Nippon Denshoku Co., Ltd.) under a black background and a white background.
• the contrast ratio C calculated by the following formula was used as an index of transparency for evaluation. Note that the closer the contrast ratio C value is to 1, the more opaque the material is, and the closer the contrast ratio C value is to 0, the more transparent the material is.
• Formula C Yb / Yw
• Yb means the Y value when the cured product is measured against a black background
• Yw means the Y value when the cured product is measured against a white background.
• the spectral reflectance ratio of the cured product of the curable composition was determined by the following procedure. First, the spectral reflectance of the cured product used for the evaluation of transparency was measured in the wavelength range of 380 nm to 780 nm against a black background using a color difference meter (SE7700, manufactured by Nippon Denshoku Co., Ltd.). Then, the spectral reflectance ratio R was calculated based on the following formula.
• SR1 means the maximum reflectance in the yellow to red wavelength region (600 nm to 750 nm)
• SR2 means the maximum reflectance in the blue wavelength region (400 nm to 500 nm).
• the bending strength of the cured body was measured by the following procedure. First, a through hole (length 25 mm, width 2 mm, through hole length 2 mm) provided in a stainless steel mold was filled with a curable composition, and both ends of the through hole were sealed while being pressed with a polypropylene film. Next, light was irradiated in a state in which a dental light irradiator (TOKUSO POWER LIGHT, manufactured by Tokuyama Corporation) was placed so as to be in close contact with the surface of the polypropylene film sealing the opening of the through hole.
• a dental light irradiator TOKUSO POWER LIGHT, manufactured by Tokuyama Corporation
• the positions of light irradiation were three positions on one opening side of the through hole (one position in the center of the through hole and two positions inside the outer edges at both ends of the through hole in the length direction) and three positions on the other opening side (one position in the center of the through hole and two positions inside the outer edges at both ends of the through hole in the length direction). Then, light irradiation was performed for 20 seconds at each light irradiation position to obtain a cured body. The obtained cured product was adjusted with #1500 waterproof abrasive paper to have dimensions of 25 mm ⁇ 2 mm in length, 2 mm ⁇ 0.1 mm in width, and 2 mm ⁇ 0.1 mm in thickness.
• the adjusted dimensions and shape of the cured product were used as a test piece for measuring bending strength.
• the test piece was attached to a precision universal testing machine (Autograph AG5000D, manufactured by Shimadzu Corporation) and the three-point bending strength was measured under the conditions of a branch distance of 20 mm and a crosshead speed of 1 mm/min, to obtain a load-deflection curve.
• the bending strength was then calculated based on the following formula.
• ⁇ B bending strength (Pa)
• P load at the time of fracture of the test piece (N)
• S distance between supports (m)
• W width of test piece (m)
• B thickness of test piece (m).
• this measurement sample was observed at a magnification of 10,000 times using an electron microscope (JSM-7800F PRIME, manufactured by JEOL Ltd.), and the coordinates in the observation image were obtained for 1,000 inorganic spherical particles in the obtained observation image using image analysis software (Simple Digiizer ver. 3.2, free software).
• One coordinate of an inorganic spherical particle was arbitrarily selected from the obtained coordinate data, and a circle was drawn with a radius of distance t, which includes at least 200 inorganic spherical particles, centered on the selected inorganic spherical particle, and the number of spherical particles included in the circle was determined, and the average particle density ⁇ > (unit: particles/cm 2 ) was calculated.
• dr is a value of about r 0 /100 to r 0 /10 (r 0 indicates the average primary particle diameter of the inorganic spherical particles), and the number dn of particles included in the region between the circle at the distance r from the central inorganic spherical particle and the circle at the distance r + dr, and the area da of the region were calculated.
• the radial distribution function g(r) was calculated.
• a graph showing the relationship between the radial distribution function and r/ r0 (r indicates an arbitrary distance from the center of the circle, and r0 indicates the average primary particle diameter of the inorganic spherical particles) was created, and based on the obtained graph, it was evaluated whether the following conditions (I) and (II) were satisfied ( ⁇ ) or not ( ⁇ ).
• the nearest inter-particle distance: r1 which is defined as the r corresponding to the peak top of the peak that is closest to the origin among the peaks appearing in a radial distribution function graph, is a value that is 1 to 2 times the average particle size: r0 .
• the minimum value of the radial distribution function g(r) between the next nearest interparticle distance r2 which is defined as the r corresponding to the peak top of the second nearest peak from the origin among the peaks appearing in a radial distribution function graph, and the nearest interparticle distance r1 , is a value of 0.56 or more and 1.10 or less.
• Comparative Example 1 is an example of a dental hardenable composition based on an existing structural color, which is formulated to have a spectral reflectance of 1.16 so as to show excellent color compatibility (expressing a structural color in the yellow to red range) when used as a CR for restoring cavities formed in dentin or from enamel to dentin, but does not show sufficient X-ray contrast because it does not contain a radiopaque filler.
• the lower the content of crystalline rare earth metal fluoride particles in the organic-inorganic composite particles constituting the X-ray opaque filler to be blended the lower the X-ray contrast property and the more transparent the cured body tends to be, whereas the higher the content, the higher the X-ray contrast property and the more opaque the cured body tends to be.
• the content of crystalline rare earth metal fluoride particles in the organic-inorganic composite particles constituting the X-ray opaque filler does not affect the evaluation of the spectral reflectance ratio or radial distribution function.

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