Sustained-release glass, method for manufacturing sustained-release glass, and dental composition

Abstract

Sustained-release glass according to the present invention comprises: sustained-release glass powder; and a sustained-release glass layer that covers the glass powder.

Description

Sustained-release glass, method for producing sustained-release glass, and dental composition

[0001] The present invention relates to sustained-release glass, a method for producing sustained-release glass, and a dental composition.

[0002] Sustained-release glasses that sustainably release functional ions have been conventionally known.

[0003] For example, Patent Document 1 discloses a technique of using inorganic glass particles that release phosphorus ions and calcium ions into water as a granular soil conditioner. Patent Document 2 discloses a technique of using antibacterial glass that elutes silver ions, which is known to have an antibacterial effect, in a resin molded article. Patent Document 3 discloses a technique of using bioglass in an injectable composite material for bone repair. Patent Document 4 discloses a technique of using bioglass in a medical implant. Patent Document 5 discloses a technique of using ion sustained-release glass in a deodorant composition.

[0004] Japanese Patent Application Laid-Open No. 2000-41482, Japanese Patent No. 6604499, Japanese Patent No. 6622416, Japanese Translation of PCT International Application No. 2020-535881, International Publication No. WO 2019 / 189851

[0005] Conventional sustained-release glasses have difficulty changing the type of ions to be sustained-released as time passes.

[0006] An object of the present invention is to provide a sustained-release glass in which the type of ions to be sustained-released changes as time passes.

[0007] The sustained-release glass according to one aspect of the present invention comprises a glass powder having sustained-release properties, and a glass layer having sustained-release properties that coats the glass powder.

[0008] According to one aspect of the present invention, there can be provided a sustained-release glass in which the type of ions to be sustained-released changes as time passes.

[0009] This is a schematic diagram showing the structure of sustained-release glass. This is a schematic diagram showing an example of the cross-sectional structure of sustained-release glass. This is a schematic diagram showing another example of the cross-sectional structure of sustained-release glass. This is a diagram showing the process of the manufacturing method of sustained-release glass. This is a photograph showing an SEM image of the cross-sectional structure of sustained-release glass. This is a photograph showing an elemental distribution image of the cross-sectional structure of sustained-release glass. This is a photograph showing an SEM image of the cross-sectional structure of a comparative example glass. This is a photograph showing an elemental distribution image of the cross-sectional structure of a comparative example glass. This is a graph showing the results of the ion elution test of sustained-release glass.

[0010] The embodiments of this disclosure will be described below with reference to the drawings. In each drawing, common parts may be denoted by the same or corresponding reference numerals as in the drawings, and their descriptions may be omitted.

[0011] <Sustained-Release Glass> Figure 1 is a schematic diagram showing the structure of sustained-release glass according to this embodiment. Figure 2 is a schematic diagram showing an example of the cross-sectional structure of sustained-release glass according to this embodiment, and Figure 3 is a schematic diagram showing another example of the cross-sectional structure of sustained-release glass according to this embodiment. The sustained-release glass 10 of this disclosure has glass powder 1 and a glass layer 2, as shown in Figure 1.

[0012] In this specification, sustained release means the property of a component dissolving and being gradually released in an ionic state. Glass is not limited to amorphous glass, but also includes crystalline glass, or a mixture of amorphous and crystalline glass. Furthermore, glass also includes glass ceramics, which are composed partly of glass.

[0013] <Glass Powder> Glass powder 1 has sustained release properties. Glass powder 1 is an aggregate of glass particles. The glass particles constituting the glass powder may be spherical or otherwise irregular in shape. The glass particles may be primary particles that have not aggregated, or secondary particles formed by the aggregation of primary particles, but primary particles are preferred.

[0014] The particle size of the glass particles constituting the glass powder is preferably 1 μm to 10 mm in median diameter, more preferably 3 μm to 1 mm, and even more preferably 5 μm to 100 μm. Here, the median diameter refers to the particle size (D50) at which the cumulative distribution based on volume, measured by laser diffraction and scattering, reaches 50%. By having a particle size of 1 μm to 10 mm in glass powder, the handling properties of the glass powder can be improved.

[0015] Glass powder 1 has sustained-release properties. Preferably, the glass constituting glass powder 1 is phosphate glass. Phosphate glass is readily soluble in water and can sustainably release ions in the presence of water.

[0016] Examples of ions released from phosphate glass include those of the elements P, Li, Na, K, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr, Ta, Cu, Ag, Zn, B, Al, Ga, Si, Sn, and F. These elements may be present in the phosphate glass one or more of them. Among these, ions such as P, Na, Ca, Sr, Li, Al, Zn, Cu, Ag, B, Ga, and F are preferred.

[0017] The elements contained in the glass powder are preferably Ca, P, Zn, and F in that their sustained-release ions have a demineralization inhibitory effect on tooth structure, and preferably Ca and Sr in that they promote bone formation. Furthermore, Cu, Ag, Zn, B, Ga, and F are preferred in that their sustained-release ions have an antibacterial effect, Li is preferred in that their sustained-release ions have an anti-inflammatory effect, and P and Ca are preferred in that they have a remineralization effect on tooth structure.

[0018] The elemental content in the glass powder is not particularly limited and can be arbitrarily adjusted depending on the type of element.

[0019] For example, if the glass powder contains phosphorus (P), the P content is preferably 30% to 85% by mass in terms of oxides in the glass powder, more preferably 40% to 80% by mass, and even more preferably 50% to 75% by mass.

[0020] When the P content in the glass powder is within this range, the water solubility of the sustained-release glass can be increased, and the ionic sustained release of each component in the sustained-release glass can be increased. In addition, the phosphate ions (PO) released from the sustained-release glass ４ ３- This allows for the imparting of effects to the sustained-release glass, such as remineralization of tooth structure and prevention of caries, when used in dental compositions.

[0021] Furthermore, if the glass powder contains sodium (Na), the Na content is preferably 1% to 15% by mass in terms of oxides, more preferably 2% to 13% by mass, and even more preferably 3% to 10% by mass. When the Na content in the glass powder is within this range, it is possible to prevent a decrease in the chemical durability and water resistance of the sustained-release glass. Additionally, the viscosity of the sustained-release glass melt is reduced, improving the operability during the production of sustained-release glass.

[0022] Furthermore, if the glass powder contains strontium (Sr), the Sr content is preferably 5% by mass or more and 50% by mass or less in terms of oxide in the glass powder, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 15% by mass or more and 30% by mass or less.

[0023] When the Sr content in the glass powder is within this range, the sustained release of strontium ions in the sustained-release glass can be enhanced, improving the demineralization inhibitory effect on tooth structure when the sustained-release glass is used in dental compositions. Furthermore, the sustained release of strontium ions can promote bone formation. In addition, the viscosity of the sustained-release glass melt is reduced, improving the operability when the sustained-release glass is used in dental compositions.

[0024] Furthermore, when the glass powder contains aluminum (Al), the Al content is 0% by mass or more and 30% by mass or less in terms of oxide in the glass powder, preferably 0.1% by mass or more and 5% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less. When the Al content in the glass powder is within this range, it becomes easier to adjust the viscosity of the sustained-release glass melt and it is possible to prevent a decrease in the chemical durability of the sustained-release glass.

[0025] <Glass Layer> As shown in Figure 1, the glass layer 2 coats the glass powder 1. This allows the sustained-release glass 10 to have a two-layer structure consisting of glass powder 1 and glass layer 2. In this two-layer structure, the glass powder 1 can constitute the core layer or inner layer, and the glass layer 2 can constitute the coating layer or outer layer.

[0026] Furthermore, a sustained-release glass in which glass powder is coated with a glass layer may have an n-layer structure (where n is an integer of 3 or more) further coated with a glass layer.

[0027] The form of the glass powder 1 that coats the glass layer 2 is not particularly limited. For example, as shown in Figure 2, the glass powder 1 may consist of a single particle, or as shown in Figure 3, the glass powder 1 may consist of multiple particles.

[0028] The glass layer 2 has sustained release properties. The glass constituting the glass layer 2 is preferably silicate glass. Silicate glass is easy to prepare as a glass precursor sol, making it easy to form a glass layer that coats the glass powder 1.

[0029] Examples of ions released from silicate glass include those of the elements Li, Na, K, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr, Ta, Cu, Ag, Zn, B, Al, Ga, Si, Sn, P, and F. These elements may be present one or more times. Among these, ions of Si, P, Na, Ca, Sr, Li, Al, Zn, Cu, Ag, B, Ga, and F are preferred.

[0030] The elements contained in the glass layer 2 are preferably P, Ca, Zn, and F in that their sustained-release ions have a demineralization inhibitory effect on tooth structure, and preferably Ca and Sr in that they promote bone formation. Furthermore, Cu, Ag, Zn, B, Ga, and F are preferred in that their sustained-release ions have an antibacterial effect, and Li is preferred in that its sustained-release ions have an anti-inflammatory effect.

[0031] The elemental content in the glass layer is not particularly limited and can be arbitrarily adjusted depending on the type of element.

[0032] For example, when the glass layer contains silicon (Si), the Si content is preferably 10% to 80% by mass in terms of oxide in the glass layer, more preferably 20% to 70% by mass, and even more preferably 30% to 60% by mass. When the Si content in the glass layer is within this range, it is possible to prevent a decrease in the chemical durability and devitrification of the sustained-release glass.

[0033] Furthermore, if the glass layer contains phosphorus (P), the P content is preferably 20% to 75% by mass in terms of oxides in the glass layer, more preferably 30% to 70% by mass, and even more preferably 35% to 65% by mass.

[0034] When the P content in the glass layer is within this range, the water solubility of the sustained-release glass can be increased, and the ionic sustained release of each component in the sustained-release glass can be increased. In addition, phosphate ions (PO) released from the sustained-release glass ４ ３- This allows for the imparting of effects to the sustained-release glass, such as remineralization of tooth structure and prevention of caries, when used in dental compositions.

[0035] Furthermore, if the glass layer contains calcium (Ca), the Ca content is preferably 1% by mass or more and 55% by mass or less in terms of oxide in the glass layer, more preferably 5% by mass or more and 40% by mass or less, and even more preferably 10% by mass or more and 35% by mass or less.

[0036] When the Ca content in the glass layer is within this range, the water solubility of the sustained-release glass can be increased, and the ionic sustained-release properties of each component in the sustained-release glass can be enhanced. Furthermore, the sustained-release properties of calcium ions in the sustained-release glass can be increased, thereby improving the demineralization inhibitory effect on tooth structure when the sustained-release glass is used in dental compositions.

[0037] Furthermore, when the glass layer contains zinc (Zn), the Zn content is preferably 0% to 40% by mass in terms of oxide in the glass layer, more preferably 3% to 35% by mass, and even more preferably 5% to 30% by mass. When the Zn content in the glass layer is within this range, the sustained release of zinc ions in the sustained-release glass can be enhanced, and antibacterial properties can be imparted to the sustained-release glass. In addition, devitrification of the glass can be prevented.

[0038] Furthermore, when the glass layer contains silver (Ag), the Ag content is preferably 0 to 40% by mass in terms of oxide in the glass layer, more preferably 0.1% to 35% by mass, and even more preferably 1% to 30% by mass. When the Ag content in the glass layer is within this range, antibacterial properties can be imparted to the sustained-release glass. In addition, Ag can be introduced into the sustained-release glass while maintaining its shape.

[0039] The sustained-release glass of this disclosure is preferably in powder form. In the sustained-release glass of this disclosure, since the glass coating on the glass layer is in powder form, the sustained-release glass in which the glass powder is coated with the glass layer can also be in powder form. Being in powder form makes it easy to incorporate the sustained-release glass into compositions containing the sustained-release glass.

[0040] As described above, the sustained-release glass of this disclosure has glass powder and a glass layer coating the glass powder. Initially, the outer glass layer dissolves in water and ions are released slowly, suppressing the release of ions from the inner glass powder. Subsequently, the inner glass powder dissolves in water and ions are released slowly. Therefore, the sustained-release glass of this disclosure allows the type of ions released to change over time.

[0041] For example, sustained-release glass in which the inner glass powder contains Sr and the outer glass layer contains Zn or Ag can be used for dental applications. In this case, in the oral cavity where the sustained-release glass is applied, an antibacterial effect is initially obtained by the sustained release of Zn ions or Ag ions from the outer glass layer, and after a lapse of time, Sr ions are sustainedly released from the inner glass powder to obtain an osteogenesis-promoting effect. Therefore, the sustained-release glass of the present disclosure can change the effect imparted over time depending on the purpose.

[0042] Further, sustained-release glass in which the inner glass powder contains P and the outer glass layer contains Ca can be used for dental applications. In this case, in the oral cavity where the sustained-release glass is applied, a demineralization-inhibiting effect is initially obtained by the sustained release of Ca ions from the outer glass layer, and after a lapse of time, P ions are sustainedly released from the inner glass powder to obtain a remineralization effect on tooth substance. Therefore, an equivalent effect can be maintained while changing the effect imparted over time depending on the purpose.

[0043] <Method for Producing Sustained-Release Glass> In the method for producing sustained-release glass of the present disclosure, a sustained-release glass powder is coated with a sustained-release glass layer. According to the method for producing sustained-release glass of the present disclosure, as shown in Figs. 1 to 3, sustained-release glass 10 in which glass powder 1 is coated with a glass layer 2 is obtained. As a method for coating sustained-release glass with glass, for example, a sol-gel method can be mentioned.

[0044] Fig. 4 is a diagram showing the steps of the method for producing sustained-release glass. The method for producing sustained-release glass of the present disclosure includes a sol preparation step S1, a glass powder mixing step S2, a gelation step S3, a drying step S4, and a calcination step S5.

[0045] In the sol preparation step S1, a sol is formed. The sol constitutes a precursor of the glass layer. In the sol preparation step S1, for example, when the glass constituting the glass layer is silicate glass, tetraethyl orthosilicate (TEOS) is dispersed in ethanol, and water and nitric acid are added thereto to generate an acidic sol. A precursor solution for the glass layer is prepared by adding a raw material salt of the element of the ions to be sustained-released to this acidic sol.

[0046] In the glass powder mixing step S2, glass powder is mixed into the precursor solution. In the glass powder mixing step S2, the precursor solution is the precursor solution prepared in the sol preparation step S1. In the glass powder mixing step S2 of the present disclosure, for example, when the glass constituting the glass powder is phosphate glass, a slurry is prepared by mixing phosphate glass powder into the precursor solution.

[0047] In the gelation step S3, the slurry is gelled to form a gel. In the gelation step S3 of the present disclosure, the slurry is the slurry prepared in the glass powder mixing step S2. In the gelation step S3 of the present disclosure, ammonia is added to the slurry to gel the slurry, thereby preparing a gel.

[0048] In the drying step S4, the gel is dried. In the drying step S4, the gel is the gel prepared in the gelation step S3. The drying temperature is not particularly limited, but is preferably 120°C or lower, more preferably 100°C or lower, and still more preferably 50°C or higher and 80°C or lower. When the drying temperature is 150°C or lower, drying can be performed while suppressing thermal decomposition of the gel.

[0049] Further, the drying time is not particularly limited, but is preferably 1 hour to 7 days, more preferably 6 hours to 5 days, and still more preferably 12 hours to 2 days. When the drying time falls within this range, productivity can be improved while suppressing poor drying.

[0050] In the calcination step S5, the dried gel is calcined. In the calcination step S5, the dried gel is the gel dried in the drying step S4. In the present specification, calcination refers to a heat treatment in which gel-like particles produced by a sol-gel method are fired to obtain mixed particles.

[0051] The calcination temperature is not particularly limited, but is preferably 200°C to 800°C, more preferably 250°C to 500°C, and even more preferably 300°C to 400°C. When the calcination temperature is within this range, glass crystallization is suppressed, and a two-layer structure of glass powder 1 and glass layer 2 can be formed.

[0052] In addition, in the method for manufacturing sustained-release glass, after the calcination step S5 is completed, the sol preparation step S1, glass powder mixing step S2, gelation step S3, drying step S4, and calcination step S5 may be repeated to form an n-layer structure (where n is an integer of 3 or more) of sustained-release glass. In this case, in the glass powder mixing step S2, the sustained-release glass obtained in the calcination step S5 may be mixed instead of the glass powder.

[0053] In the method for manufacturing sustained-release glass according to the present disclosure, as described above, by coating glass powder with a glass layer, the obtained sustained-release glass has a two-layer structure in which glass powder is coated with a glass layer. In such a two-layer sustained-release glass, initially the outer glass layer dissolves in water and ions are released slowly, suppressing the release of ions from the inner glass powder, and then the inner glass powder dissolves in water and ions are released slowly. Therefore, according to the method for manufacturing sustained-release glass according to the present disclosure, it is possible to obtain sustained-release glass that can change the type of ions released over time.

[0054] Furthermore, in the method for producing sustained-release glass according to this disclosure, the slurry obtained by mixing glass powder in the glass powder mixing step S2 with the precursor solution prepared in the sol preparation step S1 is gelled in the gelling step S3, dried in the drying step S4, and calcined in the calcination step S5. This ensures the reliable formation of sustained-release glass having a two-layer structure of glass powder and a glass layer.

[0055] <Dental Compositions> The dental composition according to this embodiment includes the sustained-release glass of this disclosure. The sustained-release glass included in the dental composition of this embodiment has glass powder and a glass layer coating the glass powder. In this specification, dental composition refers to a composition used in dental applications.

[0056] In the dental composition according to this embodiment, the inclusion of such sustained-release glass provides the same effects as the sustained-release glass of this embodiment. Specifically, by including sustained-release glass having glass powder and a glass layer coating the glass powder, initially the outer glass layer dissolves in water and ions are released slowly, suppressing the release of ions from the inner glass powder, and then the inner glass powder dissolves in water and ions are released slowly. Therefore, according to the dental composition of this disclosure, the type of ions released slowly can be changed over time.

[0057] For example, by using a dental composition containing sustained-release glass in which the inner glass powder contains Sr and the outer glass layer contains Zn or Ag in the oral cavity, an antibacterial effect is initially obtained by the sustained release of Zn or Ag ions from the outer glass layer, and as time passes, Sr ions are sustained release from the inner glass powder, resulting in a bone formation promoting effect. Therefore, the dental composition disclosed herein can change the effect it imparts over time depending on the purpose.

[0058] Furthermore, by using a dental composition containing sustained-release glass in the oral cavity, in which the inner glass powder contains phosphorus (P) and the outer glass layer contains calcium (Ca), initially, a demineralization inhibitory effect is obtained as Ca ions are slowly released from the outer glass layer. Over time, P ions are slowly released from the inner glass powder, resulting in a tooth remineralization effect. Therefore, it is possible to maintain equivalent effects while changing the effect imparted over time according to the purpose.

[0059] The uses of dental compositions are not particularly limited and include, for example, dental composite resins, dental glass ionomer cements, dental cements, dental adhesives, pit and fissure filling materials, pulp capping compositions, dental bandages, short-term elastic relining materials for denture bases, toothpastes, and tooth surface cleaning materials.

[0060] Furthermore, in the dental compositions of this disclosure, the sustained-release glass of this disclosure may be used in powder form. Examples of dental compositions in which the sustained-release glass is used in powder form include dental bone graft materials. When the sustained-release glass is used as a filling material in a dental composition, the filling of the sustained-release glass is easy.

[0061] The present invention will be further described below with reference to examples. Various tests and evaluations will be carried out according to the following methods.

[0062] <Preparation of Glass Powder> Glass powder (Glass 1-1 to 1-4) was prepared with the compositions shown in Table 1. First, the raw materials were weighed, mixed in a mortar for 10 minutes, placed in a platinum crucible, melted at 1100°C for 1 hour, and the melt was cooled by an iron press. This was then ground in a ball mill for 30 minutes (ethanol wet grinding, 40 mm alumina balls, 100 rpm), and further ground in a ball mill for 30 minutes (ethanol wet grinding, 5 mm alumina balls, 100 rpm). After that, the glass powder was recovered by centrifugation, and the remaining ethanol was dried under reduced pressure (gauge pressure: -0.1 MPa, 40°C) to obtain glass powder (Glass 1-1 to 1-4).

[0063]

[0064] <Composition of Glass Powder> The composition of the obtained glass powders (glass 1-1 to 1-4) was confirmed. The glass powders (formed with PVC rings) were analyzed using an X-ray fluorescence analyzer (Rigaku Corporation, ZSX Primus® IV) to determine their composition. The results are shown in Table 1.

[0065] <Particle Size of Glass Powder> The particle size (diameter) of the obtained glass powders (glass 1-1 to 1-4) was measured. The particle size of the glass powder is defined as the median diameter (D50) at which the cumulative distribution of the volume-based distribution, measured by laser diffraction and scattering, reaches 50%. The glass powders were dispersed in ethanol and measured using a laser diffraction and scattering particle size analyzer (Horiba, Ltd., Partica® LA-960V2). It was confirmed that the D50 of all glass powders was 10 ± 2 μm.

[0066] <Preparation of Glass Precursor Solution> Ethanol or isopropyl alcohol was added to a conical beaker to obtain the composition shown in Table 2. Tetraethyl orthosilicate (TEOS) and distilled water were added and stirred (300 rpm), and an aqueous nitric acid solution was added to prepare an acidic silica sol. Then, raw materials of various elements (elements of the ions to be released sustainedly) were added and dissolved to prepare the glass precursor solution.

[0067]

[0068] <Preparation of Glass Precursors> A gel was prepared by dropping ammonia water into the glass precursor solution, and dried on a hot plate at 60°C for one day to obtain a dry gel. The dry gel was heated to 300°C or 400°C at a heating rate of 5°C / min and held for 2 hours. After that, it was allowed to cool to room temperature to obtain powder samples. The composition of the obtained powder samples (glass 2-1 to 2-8) was confirmed. The powder samples (formed with PVC rings) were analyzed using an X-ray fluorescence analyzer (Rigaku Corporation, ZSX Primus® IV) to determine the composition of the powder samples. The results are shown in Table 2.

[0069] <Preparation of sustained-release glass> Glass powders (glass 1-1 to 1-4) prepared separately were added to the glass precursor solution described above and dispersed. Ammonia water was then immediately added dropwise to prepare a gel. The obtained gel was dried on a hot plate at 60°C for one day to obtain a dry gel. The dry gel was heated to 300°C or 400°C at a heating rate of 5°C / min and held for 2 hours. After that, it was allowed to cool to room temperature to obtain a powder sample. In addition, glass samples (Examples 1 to 3) were prepared as sustained-release glass in the combinations shown in Table 3, by blending various raw materials so that the charging ratio of glass powder (glass 1-1 to 1-4) and the solid component of the glass precursor solution (glass 2-1 to 2-8) was 1:2 (mass%).

[0070]

[0071] <Preparation of Comparative Samples> Glass powder samples with the same composition as shown in Table 2 were prepared by the sol-gel method. Ethanol or isopropyl alcohol was added to a conical beaker, and tetraethyl orthosilicate (TEOS) and distilled water were added and stirred (300 rpm). Nitric acid aqueous solution was then added to prepare an acidic silica sol. Raw materials of various elements were then added and dissolved to prepare a glass precursor solution. After that, ammonia water was added dropwise to prepare a gel. The obtained gel was dried on a hot plate at 60°C for one day to obtain a dry gel. The dry gel was heated to 300°C, 400°C, or 500°C at a heating rate of 5°C / min and held for 2 hours. After that, it was allowed to cool to room temperature to obtain a powder sample. As shown in Table 3, a powder sample with the composition of glass 2-2, prepared by calcining at 500°C, was designated as Comparative Example 1. Of the glass powders (glasses 1-1 to 1-4) prepared according to the above preparation method, glass 1-2 was designated as Comparative Example 2. Furthermore, Comparative Example 1 and Comparative Example 2 were weighed in a ratio of 1:2 (mass%) and mixed in an agate mortar to prepare a composite sample, which was designated as Comparative Example 3.

[0072] <Cross-sectional observation of the sample by SEM-EDS> The prepared glass sample (Example 1) was embedded in a two-part epoxy resin, and then its cross-section was cut by ion milling. Surface observation was then performed using a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). After mixing the two-part epoxy resin, the glass powder sample was mixed in and spread onto a silicon wafer. A cover glass was placed on top, vacuum degassing was performed, and then it was heat-cured at 180°C on a hot plate. The epoxy resin-embedded material thus obtained was processed with an ion beam using an ion milling device (Hitachi High-Technologies Corporation, IM4000). The processed portion of the test specimen after ion milling was observed using SEM-EDS (JEOL Ltd., JCM-7000 NeoScope®). For Example 1, the SEM image is shown in Figure 5 and the elemental distribution image is shown in Figure 6.

[0073] Furthermore, Comparative Example 3, a composite powder sample, was placed on a carbon tape and then observed using SEM-EDS. The SEM image for Comparative Example 3 is shown in Figure 7, and the elemental distribution image is shown in Figure 8.

[0074] Samples in which a bilayer structure was confirmed by SEM-EDS analysis were marked with "○" (contains bilayer structure), and samples in which a bilayer structure could not be confirmed were marked with "×" (does not contain bilayer structure).

[0075] In Example 1, it was confirmed that the inner glass layer was covered by the outer glass layer in the cross-section of the sample, indicating a two-layer structure. Specifically, as shown in Table 3, Figures 5 and 6, it was found that the inner glass layer containing Na and Sr was covered by the outer glass layer containing Si, Ca, and Zn.

[0076] On the other hand, in Comparative Example 3, which was a sample obtained by mixing glass 2-2 and glass 1-2, the respective powder samples were scattered, and a two-layer structure could not be obtained by simply mixing them. Specifically, as shown in Table 3, Figures 7 and 8, it was found that glass powder containing Si, Ca, and Zn and glass powder containing Na and Sr were scattered.

[0077] <Ion Elution Test> A 50 mg glass powder sample was immersed in 10 mL of ultrapure water and stored at 37°C while shaking using a rotator. The sample was then filtered through a syringe filter with a pore diameter of 0.22 μm to obtain the filtrate. The obtained filtrate was diluted with ultrapure water to prepare the test solution. The ions contained in the test solution were measured using ICP-OES (iCAP 7000 Duo, Thermo Fisher Scientific). The detection result was multiplied by the dilution factor to obtain the amount of eluted ions (unit: ppm). The test results are shown in Figure 9.

[0078] As shown in Figure 9, in Examples 1 to 3, the amount of Ca ion elution from the outer glass component decreased over time, while the amount of Si ion elution continued. Furthermore, the amount of Na ion elution from the inner glass component increased over time. Similarly, the amount of Sr ion elution from the inner glass component remained at the same level as the initial value, maintaining its ion elution ability even after 7 days of immersion.

[0079] On the other hand, in Comparative Examples 1 and 2, the amount of Si and Ca ions eluted decreased over time in Comparative Example 1, and the amount of Na and Sr ions eluted decreased over time in Comparative Example 2.

[0080] Based on the above, it can be said that sustained-release glass, in which sustained-release glass powder is coated with a sustained-release glass layer, can change the type of ions released over time.

[0081] The embodiments disclosed above include, for example, the following aspects.

[0082] <1> A sustained-release glass comprising a sustained-release glass powder and a sustained-release glass layer coating the glass powder.

[0083] <2> The glass layer comprises silicate glass, as described in <1> above.

[0084] <3> The sustained-release glass according to <1> or <2>, wherein the glass powder is a phosphate glass.

[0085] <4> The sustained-release glass is in the form of a powder, as described in any one of <1> to <3> above.

[0086] <5> A method for producing sustained-release glass, comprising coating a sustained-release glass powder with a sustained-release glass layer.

[0087] <6> A method for producing sustained-release glass according to <5>, comprising: a sol preparation step for preparing a sol constituting the precursor of the glass layer; a glass powder mixing step for preparing a slurry by mixing the glass powder with the sol; a gelation step for gelling the slurry to form a gel; a drying step for drying the gel; and a calcination step for calcining the dried gel.

[0088] <7> A dental composition comprising the sustained-release glass described in any one of <1> to <4> above.

[0089] Although embodiments of the present invention have been described above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the invention as described in the claims.

[0090] This application claims priority based on Japanese Patent Application No. 2025-056009, filed on 28 March 2025, and Japanese Patent Application No. 2025-282549, filed on 25 December 2025, the entire contents of which are incorporated herein by reference.

[0091] 10. Slow-release glass: 1. Glass powder, 2. Glass layer

Claims

1. A sustained-release glass comprising a sustained-release glass powder and a sustained-release glass layer coating the glass powder.

2. The sustained-release glass according to claim 1, wherein the glass layer comprises silicate glass.

3. The sustained-release glass according to claim 1, wherein the glass powder is a phosphate glass.

4. The sustained-release glass according to claim 1, wherein the sustained-release glass is in the form of a powder.

5. A method for producing sustained-release glass, comprising coating a sustained-release glass powder with a sustained-release glass layer.

6. A method for producing sustained-release glass according to claim 5, comprising: a sol preparation step of preparing a sol constituting a precursor of the glass layer; a glass powder mixing step of mixing the glass powder with the sol to prepare a slurry; a gelation step of gelling the slurry to form a gel; a drying step of drying the gel; and a calcination step of calcining the dried gel.

7. A dental composition comprising the sustained-release glass described in any one of claims 1 to 4.

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