Silicon nitride denture base and method for preparing same and dental restoration material

Abstract

The application relates to the technical field of dental restoration materials, and discloses a silicon nitride denture base, a preparation method thereof and a dental restoration material.The silicon nitride denture base provided by the application is prepared from raw materials including silicon nitride and an additive, and the additive includes silicon oxide, magnesium oxide and rare earth metal oxide.The silicon nitride denture base has a density of greater than or equal to 98.5%, a bending strength of 960 MPa-1100 MPa, a fracture toughness of 7.5 MPa*m 1 / 2 -9.0 MPa*m 1 / 2 9.0 MPa*m, a hardness of 1520 HV-1650 HV, and can avoid abnormal abrasion of a restoration on a jaw tooth; the silicon nitride denture base has no cytotoxicity on human osteoblasts, gum fibroblasts and periodontal membrane fibroblasts, cells can normally adhere, proliferate and differentiate on the surface of the silicon nitride denture base, and the strict requirements of safety and biocompatibility of an oral restoration material are met.

Description

Technical Field

[0001] This invention relates to the field of dental restorative materials technology, specifically to a silicon nitride denture base, its preparation method, and dental restorative materials. Background Technology

[0002] Dental prostheses are the primary means of restoring oral function and aesthetics. However, existing dental restorative material systems still have multiple technical shortcomings, which severely limit the long-term success rate of prostheses.

[0003] Once implanted in the oral cavity, the surface of dental prostheses easily becomes a breeding ground for microbial colonization. The junction between the margin of fixed prostheses and tooth structure is a high-risk area for plaque buildup, easily leading to secondary caries and periodontitis in abutment teeth. This problem is even more pronounced in the field of removable dentures. Polymethyl methacrylate (PMMA) is the mainstream material for denture bases, but its porous and hydrophobic surface makes it highly susceptible to adhesion by fungi such as Candida albicans, forming biofilms and causing denture stomatitis. Currently, clinical treatment for denture stomatitis mainly relies on nystatin and azole antifungal drugs. However, nystatin has a poor taste and weak mucosal adhesion, while azole drugs have systemic side effects caused by intestinal absorption, and long-term use has led to the emergence of drug-resistant strains. Therefore, endowing restorative materials with intrinsic, non-pharmacological antibacterial functions has become a core challenge that urgently needs to be overcome in this field.

[0004] In the field of fixed restorations, all-ceramic materials are highly favored due to their excellent aesthetic properties. Yttrium-stabilized tetragonal zirconia polycrystalline ceramics are currently the most widely used dental restorative materials in clinical practice, but they suffer from a critical low-temperature aging problem. In the moist environment of the oral cavity, water molecules can penetrate the zirconia lattice, triggering a spontaneous phase transition from tetragonal to monoclinic phase, accompanied by volume expansion and microcrack formation, ultimately leading to a decrease in the strength of the restoration or even fracture, significantly shortening its lifespan. In addition, the high hardness of zirconia ceramics often leads to abnormal wear of the opposing natural tooth enamel, disrupting the physiological balance of the oral occlusal system.

[0005] Therefore, how to prepare dental restorative materials with high fracture toughness, antibacterial properties, aging resistance, and poor biocompatibility is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention provides a silicon nitride denture base to solve the problems of low fracture toughness, easy to cause oral infection, poor aging resistance and poor biocompatibility of existing dental restoration materials.

[0007] In a first aspect, the present invention provides a silicon nitride denture base, wherein the raw materials of the silicon nitride denture base include silicon nitride and additives, wherein the additives include silicon oxide, magnesium oxide and rare earth metal oxides; The mass ratio of the silicon oxide, the magnesium oxide, and the rare earth metal oxide is 2.5-3:1.6-1.9:1.

[0008] In one optional embodiment, the content of the auxiliary agent is 3wt%-6wt%.

[0009] In one optional embodiment, the rare earth metal oxide includes at least one of yttrium oxide and ytterbium oxide.

[0010] In one optional embodiment, the silicon nitride has a particle size of 0.05 μm to 2 μm.

[0011] In a second aspect, the present invention provides a method for preparing the silicon nitride denture base as described in the first aspect, comprising the following steps: Weigh the raw material of the silicon nitride denture base, press it, and sinter it once to obtain the silicon nitride denture base; The sintering temperature is 1550℃-1650℃.

[0012] In one optional embodiment, the sintering time is 2h-5h, and the heating rate is 5℃ / min-12℃ / min.

[0013] In one optional embodiment, the pressing includes cold isostatic pressing; the pressure of the cold isostatic pressing is 150MPa-250MPa, and the time is 5min-15min.

[0014] In one alternative embodiment, prior to the molding step, a binder is added, the mass of which is 2wt%-4wt% of the total mass of the silicon nitride and the additives.

[0015] Thirdly, the present invention provides a silicon nitride dental restorative material, the silicon nitride dental restorative material comprising a denture base and a veneer material, wherein the coefficient of thermal expansion of the veneer material is 2.8 × 10⁻⁶. -6 / ℃-3.6×10 -6 / ℃; The denture base is a silicon nitride denture base prepared by the preparation method described in the second aspect.

[0016] In one alternative embodiment, the finishing material includes at least one of borosilicate glass-based finishing porcelain, feldspar finishing porcelain, and zirconia-based finishing porcelain.

[0017] Fourthly, the present invention provides a method for preparing the silicon nitride dental restorative material described in the third aspect, comprising the following steps: A slurry containing a decorative material is prepared, and the slurry containing the decorative material is coated onto the denture base and then sintered a second time to obtain the silicon nitride dental restoration material.

[0018] In one optional embodiment, the secondary sintering temperature is 850℃-1000℃ and the time is 20min-60min.

[0019] In one alternative embodiment, the coating thickness is 0.2 mm to 0.8 mm.

[0020] In one alternative embodiment, the content of the finishing material in the slurry is 50wt%-60wt%.

[0021] The technical solution of this invention has the following advantages: 1. The silicon nitride denture base provided by the present invention comprises silicon nitride and additives, wherein the additives include silicon oxide, magnesium oxide, and rare earth metal oxides; the mass ratio of silicon oxide, magnesium oxide, and rare earth metal oxides is 2.5-3:1.6-1.9:1. The silicon nitride denture base of the present invention has a density ≥98.5%, a flexural strength of 960MPa-1100MPa, and a fracture toughness of 7.5MPa·m. 1 / 2 -9.0 MPa·m 1 / 2 With a hardness of 1520HV-1650HV, it can prevent abnormal wear of opposing teeth by the restoration; and it has no cytotoxicity to human osteoblasts, gingival fibroblasts and periodontal ligament fibroblasts. Cells can adhere, proliferate and differentiate normally on its surface, meeting the strict requirements of oral restorative materials for safety and biocompatibility.

[0022] 2. The silicon nitride dental restorative material provided by this invention includes a denture base and a veneer material, wherein the coefficient of thermal expansion of the veneer material is 2.8 × 10⁻⁶. -6 / ℃-3.6×10 -6 / ℃, matching the thermal expansion coefficient of the denture base, in the moist environment of oral saliva, the silicon nitride component in its denture base and veneer material continuously releases ammonia molecules and active nitrogen species (such as peroxynitrite) through surface hydrolysis reaction, actively inhibiting the adhesion and proliferation of bacteria and fungi, preventing prosthesis-related infections from the root, and completely avoiding the risks of drug side effects and drug resistance. Detailed Implementation

[0023] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0024] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0025] In terms of mechanical properties, silicon nitride exhibits higher fracture toughness than zirconium oxide, enabling it to withstand the complex chewing stresses in the oral cavity without catastrophic fracture. Simultaneously, silicon nitride possesses extremely high chemical stability and corrosion resistance, and does not suffer from the low-temperature aging problems inherent in zirconium oxide ceramics, maintaining structural stability in the long-term moist environment of the oral cavity.

[0026] Crucially, silicon nitride possesses unique non-pharmaceutical antibacterial and antifungal properties. Studies have shown that silicon nitride undergoes surface hydrolysis in aqueous environments. The nitrogen-silicon covalent bonds on its surface interact with hydrogen ions, slowly releasing ammonia molecules. Simultaneously, with the participation of oxygen, reactive nitrogen species, including peroxynitrite, are produced. These two products have complementary antibacterial mechanisms: ammonia molecules are uncharged and volatile, freely penetrating the microbial cell membrane and entering the cell, where they are reprotonated into ammonium ions in the cytoplasm, disrupting the intracellular acid-base balance and causing osmotic stress; reactive nitrogen species, especially peroxynitrite, are potent oxidants and nitrosamines, attacking microbial proteins, lipids, and nucleic acids, leading to cellular metabolic collapse. This dual antibacterial mechanism, based on physicochemical rather than pharmacological action, makes it difficult for microorganisms to develop drug resistance through gene mutation, exhibiting significant inhibitory and bactericidal effects against common pathogenic bacteria such as Staphylococcus aureus and Escherichia coli, as well as Candida albicans.

[0027] Despite the aforementioned advantages of silicon nitride, current technologies have not yet systematically integrated its antibacterial function into thermoplastic denture bases, nor have they developed a complete solution for silicon nitride-based fixed restorations that combine high toughness, high aesthetics, and strong antibacterial properties.

[0028] To address the aforementioned problems, in a first aspect, the present invention provides a silicon nitride denture base, wherein the raw materials of the silicon nitride denture base include silicon nitride and additives, wherein the additives include silicon oxide, magnesium oxide and rare earth metal oxides; The mass ratio of the silicon oxide, the magnesium oxide, and the rare earth metal oxide is 2.5-3:1.6-1.9:1.

[0029] In one optional embodiment, the content of the additive is 3wt%-6wt%. This content range provides a suitable amount of liquid phase to the system, ensuring sufficient wetting of the silicon nitride particles during a single sintering process at 1550℃-1650℃. This promotes particle rearrangement and the α→β-Si3N4 phase transformation, achieving complete densification of the substrate and imparting high flexural strength and fracture toughness to the material. Simultaneously, the thickness and distribution of the formed grain boundary amorphous phase are suitable, maintaining a stable and long-lasting sustained-release capacity of ammonia molecules and active nitrogen species in an aqueous oral environment, achieving highly efficient non-pharmacological antibacterial function. If the additive content is less than 3wt%, the liquid phase is insufficient, making it difficult to sinter the green body densely. Residual porosity will severely degrade mechanical properties and hinder the release of effective antibacterial ions. If the additive content is greater than 6wt%, the excessive grain boundary phase will not only weaken the interlocking toughening effect of the β-Si3N4 grains but may also lead to excessively rapid hydrolysis of the grain boundary phase or the formation of a stable crystalline phase, causing strength decay and inhibiting the long-term release of antibacterial active components. Therefore, an adjuvant content of 3wt%-6wt% can achieve a synergistic optimal balance between mechanical reliability and antibacterial durability.

[0030] In one optional embodiment, the rare earth metal oxide includes at least one of yttrium oxide and ytterbium oxide.

[0031] In one optional embodiment, the silicon nitride has a particle size of 0.05 μm to 2 μm.

[0032] In a second aspect, the present invention provides a method for preparing the silicon nitride denture base as described in the first aspect, comprising the following steps: Weigh the raw material of the silicon nitride denture base, press it, and sinter it once to obtain the silicon nitride denture base; The sintering temperature is 1550℃-1650℃.

[0033] It should be noted that the microstructure of silicon nitride denture bases (especially grain boundary phases and packing density) affects their antibacterial properties (such as Si). 4+ The long-term stable release of nitrogen-active species precursors is a key factor. Controlling the sintering temperature within the range of 1550℃-1650℃ ensures complete densification of silicon nitride ceramics (to meet the structural requirements of high strength). Unexpectedly, it was discovered that this temperature range can promote the formation of a specific amorphous phase structure at the grain boundaries. This structure has a suitable hydrolysis rate in an aqueous environment, which can ensure the continuous release of sufficient ammonia and active nitrogen species for efficient antibacterial effect without causing a decrease in material strength due to excessive hydrolysis. If the sintering temperature is higher than 1650℃, although it can increase the density, it will lead to abnormal grain growth and changes in the properties of the grain boundary phase, which will inhibit the effective release of antibacterial ions. If the temperature is too low, the material will not be dense enough, and the mechanical properties will not meet the load-bearing requirements.

[0034] In one optional embodiment, the sintering time is 2-5 hours, and the heating rate is 5°C / min-12°C / min. This heating rate ensures that the binder added in the early stage can fully and gradually volatilize and be eliminated within the 300°C-600°C range, avoiding defects such as pores and cracks caused by rapid gas escape from the interior of the blank. Holding the temperature for 2-5 hours provides sufficient time for the liquid phase formed by the sintering aid to fully spread and wet the silicon nitride particles, promoting particle rearrangement and the β-Si3N4 phase transformation, forming an interlocked β-Si3N4 grain structure with a high aspect ratio. This achieves complete densification while imparting high fracture toughness and flexural strength to the substrate. Meanwhile, the heat preservation time, combined with the sintering temperature of 1550℃-1650℃, can stabilize the composition and thickness of the amorphous phase at the grain boundaries within a suitable range. This ensures that the substrate has a long-term controllable ability to release ammonia molecules and active nitrogen species, while avoiding excessive grain growth or excessive crystallization of the grain boundary phase, which would weaken the release of effective antibacterial ions. This achieves simultaneous optimization of mechanical properties and antibacterial function.

[0035] In one alternative implementation, the pressing includes cold isostatic pressing.

[0036] In one optional embodiment, the cold isostatic pressing pressure is 150MPa-250MPa, and the time is 5min-15min. This utilizes the isotropic transmission of the liquid medium to achieve a highly uniform particle packing density at both the macroscopic and microscopic scales in the green body, eliminating the density gradient and delamination risks commonly found in unidirectional pressing, and effectively reducing large-sized pores within the green body. A pressure range of 150MPa-250MPa provides sufficient driving force to achieve tight packing and initial mechanical interlocking between particles, laying a good foundation for subsequent sintering and densification. Holding the pressure for 5min-15min ensures that the pressure fully penetrates all parts of the green body, completing the pore compression and particle rearrangement process without excessively increasing the process time. The green body treated in this way exhibits excellent isotropic shrinkage, and after sintering, it yields a denture base with precise dimensions, dense structure, and no internal defects. This is crucial for ensuring the long-term load-bearing reliability and marginal fit of the restoration.

[0037] In one alternative embodiment, prior to the molding step, a binder is added, the mass of which is 2wt%-4wt% of the total mass of the silicon nitride and the additives.

[0038] Thirdly, the present invention also provides a silicon nitride dental restorative material, the silicon nitride dental restorative material comprising a denture base and a veneer material, wherein the denture base is a silicon nitride denture base prepared by the preparation method described in the second aspect, and the veneer material has a coefficient of thermal expansion of 2.8 × 10⁻⁶. -6 / ℃-3.6×10 -6 / ℃.

[0039] In one optional embodiment, the finishing material includes at least one of borosilicate glass-based finishing porcelain, feldspar finishing porcelain, and zirconia-based finishing porcelain; preferably, it is borosilicate glass-based finishing porcelain or feldspar finishing porcelain.

[0040] Fourthly, the present invention provides a method for preparing the silicon nitride dental restorative material described in the third aspect, comprising the following steps: A slurry containing a decorative material is prepared, and the slurry containing the decorative material is coated onto the denture base and then sintered a second time to obtain the silicon nitride dental restoration material.

[0041] In one optional embodiment, the secondary sintering temperature is 850℃-1000℃, and the time is 20min-60min. This results in a tightly bonded composite repair structure.

[0042] In one alternative embodiment, the coating thickness is 0.2 mm to 0.8 mm.

[0043] In one alternative embodiment, the content of the finishing material in the slurry is 50wt%-60wt%.

[0044] In this invention, the borosilicate glass-based decorative ceramic was purchased from Ivoclar Vivadent, model IPSd.SIGN; the feldspar decorative ceramic was purchased from VITA Zahnfabrik, model VITA VMK Master; the zirconia-based decorative ceramic was purchased from Noritake, model Cerabian ZR; and the polyvinyl alcohol was purchased from Sinopharm Chemical Reagent Co., Ltd., model PVA-1799.

[0045] Example 1 This embodiment provides a method for preparing a silicon nitride denture base, including the following steps: (1) Weigh 95wt% silicon nitride with a particle size of 0.5μm-2μm and a purity of ≥99.8%, 5wt% sintering aid (including SiO2, MgO and Y2O3 in a mass ratio of 3:1.9:1), and polyvinyl alcohol. Add deionized water and ball mill for 24h, then spray dry to obtain a mixed powder with a particle size of 50μm-100μm; wherein, the mass of polyvinyl alcohol is 3wt% of the total mass of silicon nitride and sintering aid. (2) The mixed powder was cold isostatically pressed at 200 MPa for 10 min, dried at 80°C for 24 h, and then sintered at 1600°C at 10°C / min for 4 h. It was then naturally cooled to room temperature to obtain a silicon nitride denture base.

[0046] Example 2 This embodiment provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Embodiment 1, except that in step (1), Y2O3 is replaced with the same mass of Yb2O3.

[0047] Example 3 This embodiment provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Example 1, except that the additives include SiO2, MgO and Y2O3 in a mass ratio of 2.7:1.6:1.

[0048] Example 4 This embodiment provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Example 1, except that the additives include SiO2, MgO and Y2O3 in a mass ratio of 2.5:1.8:1.

[0049] Example 5 This embodiment provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Embodiment 1, except that the content of the additive is 6 wt% and the content of silicon nitride is 94 wt%.

[0050] Example 6 This embodiment provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Embodiment 1, except that the content of the additive is 3wt% and the content of silicon nitride is 97wt%.

[0051] Example 7 This embodiment provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Embodiment 1, except that 87wt% of silicon nitride with a particle size of 0.5μm-2μm and a purity of ≥99.8% and 8wt% of silicon nitride powder with a particle size of 50nm-100nm are used.

[0052] Example 8 This embodiment provides a method for preparing a silicon nitride denture base, including the following steps: (1) Weigh 95wt% silicon nitride with a particle size of 0.5μm-2μm and a purity of ≥99.8%, 5wt% sintering aid (including SiO2, MgO and Y2O3 in a mass ratio of 3:1.9:1), and polyvinyl alcohol. Add deionized water and ball mill for 24h, then spray dry to obtain a mixed powder with a particle size of 50μm-100μm; wherein, the mass of polyvinyl alcohol is 2wt% of the total mass of silicon nitride and sintering aid. (2) The mixed powder was cold isostatically pressed at 150 MPa for 15 min, dried at 80 °C for 24 h, and then sintered at 1650 °C for 3 h at 11 °C / min. It was then naturally cooled to room temperature to obtain a silicon nitride denture base.

[0053] Example 9 This embodiment provides a method for preparing a silicon nitride denture base, including the following steps: (1) Weigh 95wt% silicon nitride with a particle size of 0.5μm-2μm and a purity of ≥99.8%, 5wt% sintering aid (including SiO2, MgO and Y2O3 in a mass ratio of 3:1.9:1), and polyvinyl alcohol. Add deionized water and ball mill for 24h, then spray dry to obtain a mixed powder with a particle size of 50μm-100μm; wherein, the mass of polyvinyl alcohol is 4wt% of the total mass of silicon nitride and sintering aid. (2) The mixed powder was cold isostatically pressed at 250 MPa for 5 min, dried at 80°C for 24 h, and then sintered at 1550°C at 9°C / min for 5 h. It was then naturally cooled to room temperature to obtain a silicon nitride denture base.

[0054] Example 10 This embodiment provides a method for preparing a silicon nitride dental restorative material, including the following steps: (1) Borosilicate glass-based decorative ceramic (with a thermal expansion coefficient of 3.5×10) -6 A mixture of ( / ℃) and water is used to obtain a decorative porcelain slurry; the content of borosilicate glass-based decorative porcelain in the mixed slurry is 55 wt%. (2) Then, the veneer slurry is uniformly coated on the surface of the silicon nitride denture base prepared in Example 1, with a coating thickness of 0.4 mm. Then, it is sintered at 850°C for 30 min and polished to obtain silicon nitride dental restoration material.

[0055] Example 11 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Example 2.

[0056] Example 12 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Example 3.

[0057] Example 13 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Example 4.

[0058] Example 14 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Example 5.

[0059] Example 15 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Example 6.

[0060] Example 16 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Example 7.

[0061] Example 17 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Example 8.

[0062] Example 18 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Example 9.

[0063] Example 19 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that borosilicate glass-based veneer porcelain is replaced with feldspar veneer porcelain of the same mass (thermal expansion coefficient 3.4 × 10⁻⁶). -6 The sintering temperature was 900℃, and the sintering time was 20min.

[0064] Example 20 This embodiment provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that borosilicate glass-based veneer porcelain is replaced with the same mass of zirconia-based veneer porcelain (thermal expansion coefficient 3.6 × 10⁻⁶). -6 The sintering temperature was 1000℃, and the sintering time was 30 minutes.

[0065] Comparative Example 1 This comparative example provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Example 1, except that the content of the additives is 7wt%, including SiO2, MgO and Y2O3 in a mass ratio of 3:2:2.

[0066] Comparative Example 2 This comparative example provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Example 1, except that the additives include SiO2, MgO and Y2O3 in a mass ratio of 4:1.9:1.

[0067] Comparative Example 3 This comparative example provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Example 1, except that the additives include SiO2, MgO and Y2O3 in a mass ratio of 3:2.5:1.

[0068] Comparative Example 4 This comparative example provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Example 1, except that in step (2), the sintering temperature is 1500℃, the pressure is 30MPa, and the time is 4h.

[0069] Comparative Example 5 This comparative example provides a method for preparing a silicon nitride denture base, which is basically the same as the steps in Example 1, except that the sintering temperature in step (2) is 1700℃.

[0070] Comparative Example 6 This comparative example provides a method for preparing a silicon nitride denture base, comprising the following steps: (1) Take a zirconia ceramic substrate blank (thermal expansion coefficient 3.2×10). -6 (℃), and then ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 10 min each. After being dried with nitrogen, it was placed in a vacuum oven at 120℃ for 2 h to remove the surface adsorbed moisture. (2) Place the dried zirconia substrate on the sample stage of the plasma chemical vapor deposition reaction chamber, and evacuate to a background vacuum level below 5 × 10⁻⁶. -3 Pa, introduce high-purity nitrogen gas (99.999%) until the chamber pressure is 50Pa, turn on the radio frequency power supply (13.56MHz), set the power to 200W, and perform nitrogen plasma pretreatment on the base surface for 15min to clean the surface and introduce active nitrogen dangling bonds. (3) Then, silane gas (SiH4, purity 99.99%, flow rate 20 sccm) and high-purity nitrogen gas (flow rate 80 sccm) are simultaneously introduced into the chamber. The working pressure is adjusted to maintain at 60 Pa-80 Pa, the radio frequency power is maintained at 200 W, the base temperature is controlled at 350 ℃-400 ℃, and the deposition time is set to 40 min. An amorphous silicon nitride coating with a thickness of 200 nm is formed on the surface of the zirconia base. The gas and radio frequency power are turned off, and the sample is taken out after being cooled to room temperature in the nitrogen atmosphere. The denture base with the silicon nitride coating deposited on the surface is obtained.

[0071] Comparative Example 7 This comparative example provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Comparative Example 1.

[0072] Comparative Example 8 This comparative example provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Comparative Example 2.

[0073] Comparative Example 9 This comparative example provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Comparative Example 3.

[0074] Comparative Example 10 This comparative example provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Comparative Example 4.

[0075] Comparative Example 11 This comparative example provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Comparative Example 5.

[0076] Comparative Example 12 This comparative example provides a method for preparing a silicon nitride dental restorative material, which is basically the same as the steps in Example 10, except that the silicon nitride denture base prepared in Example 1 is replaced with the denture base prepared in Comparative Example 6.

[0077] Experimental Example 1 The silicon nitride denture bases prepared in Examples 1-9 and Comparative Examples 1-6 were subjected to density, flexural strength, and fracture toughness tests, with zirconium oxide as a control group. The results are shown in Table 1. Specifically: Density was determined using the Archimedes displacement method. The sample was boiled in deionized water for 2 minutes to allow water to fully penetrate the open pores. After cooling to room temperature, the dry weight of the sample in air (m1), the saturated mass of the sample in air after absorbing water (m2), and the suspended mass of the sample in water (m3) were weighed. The density was calculated using the formula ρ = m1 × ρ 水 Calculate the bulk density of the sample by (m2-m3), then divide by the theoretical density of silicon nitride corresponding to this formulation (calculated using the mixing rule, taking the density of β-Si3N4 as 3.19 g / cm³). 3 The relative compaction density is obtained by weighting the density of the grain boundary phase formed by the additives according to the proportion of each component, and expressed as a percentage. Bending strength: ISO 6872 three-point bending test was adopted, with a specimen size of 25mm×4mm×2mm, a span of 20mm, and a loading rate of 0.5mm / min; Fracture toughness: The indentation method (SENB) was used for testing. The sample size was 25mm×4mm×2mm, the notch depth was about 1.6mm-2.0mm, the span was 16mm, and the loading rate was 0.05mm / min. Hardness: Vickers hardness, according to ISO 14705:2016 "Fine ceramics - Test method for room temperature hardness"; using a Vickers hardness tester, test force 9.807 N (HV1), holding time 15 s. Before testing, the sample surface was mirror polished (Ra≤0.1μm), and at least 5 effective indentations were measured for each sample, and the arithmetic mean was taken.

[0078] Table 1. Performance test results of silicon nitride denture bases prepared in each embodiment and comparative example.

[0079] As shown in Table 1, the silicon nitride denture bases prepared in Examples 1-9 of this invention all have a density ≥98.5%, a flexural strength of 960MPa-1100MPa, and a fracture toughness of 7.5MPa·m. 1 / 2 -9.0 MPa·m 1 / 2 The hardness is 1520 HV-1650 HV. Example 7 introduces a nano-bimodal particle size design, achieving a density of 99.8%, a strength of 1100 MPa, and a toughness of 9.0 MPa·m. 1 / 2 This is the optimal group, with a finely interlocked structure achieving simultaneous strengthening and toughening. Compared to traditional zirconia (strength 1150 MPa, toughness only 7.5 MPa·m), this is superior. 1 / 2Compared to other materials with a hardness of 1300HV, this material exhibits superior fracture toughness and hardness, and offers better overall load-bearing and wear resistance.

[0080] In Comparative Example 1, the total amount of additives was 7 wt%, and the proportion of Y2O3 was doubled. The excessive grain boundary phase disrupted the interlocking structure of β-Si3N4 grains, causing the strength to plummet to 850 MPa and the toughness to be only 6.5 MPa·m. 1 / 2 The appearance of discoloration confirms the necessity of an upper limit of 6wt% for the content of additives.

[0081] The additive ratios in Comparative Examples 2 and 3 deviated from the protection range. Excess SiO2 or MgO caused the density to drop to 97.5%-98.0% and the strength to be only 780MPa-820MPa, indicating that the imbalance of the ratio caused insufficient liquid phase sintering or abnormal grain growth.

[0082] Comparative Example 4, hot-pressed at a low temperature of 1500℃, and Comparative Example 5, sintered at a high temperature of 1700℃, both showed lower strength and toughness than the Example. At 1700℃, the fracture toughness plummeted to 6.0 MPa·m. 1 / 2 The criticality of the sintering window of 1550℃-1650℃ was verified.

[0083] Comparative Example 6 had only a 200 nm silicon nitride coating deposited, and its mechanical properties were determined by the zirconium oxide substrate, with a toughness of only 6.5 MPa·m. 1 / 2 Once the coating wears down, it loses its antibacterial function and cannot replace the whole block material.

[0084] In summary, the additive content, ratio, and sintering process specified in this invention are key to obtaining a high-density, high-strength, long-lasting antibacterial silicon nitride denture base. Deviations in these parameters all lead to significant performance degradation, demonstrating clear critical significance and unpredictability.

[0085] Experimental Example 2 The antibacterial properties of the silicon nitride denture bases prepared in Examples 1-9 and Comparative Examples 1-6 were tested, with zirconium oxide used as a control group. The results are shown in Table 2. Specifically: (1) Candida albicans (ATCC 10231) and Staphylococcus aureus (ATCC 25923) were used for testing. Each group of samples was processed into round discs with a diameter of 10 mm and a thickness of 1 mm. The surfaces were mirror-polished, ultrasonically cleaned with 75 wt% ethanol, and sterilized under ultraviolet light for 30 min. The bacterial strains were inoculated into tryptone soybean broth (TSB) and cultured at 37℃ for 18 h. The bacterial cells were collected by centrifugation, resuspended in sterile phosphate-buffered saline (PBS, pH 7.2-7.4), and serially diluted to prepare concentrations of 1 × 10⁻⁶ for both Candida albicans and Staphylococcus aureus. 9CFU / mL bacterial suspension; 3 replicates per group, and the mean was taken; (2) Adhesion inhibition rate: Each sample was placed in a 24-well plate, and 1 mL of bacterial suspension was added to each well. The plate was incubated at 37°C for 4 h to allow initial bacterial adhesion. After removal, the plate was gently rinsed with PBS to remove non-adhesive bacteria. The surface-adhesive bacteria were eluted by sonication in an ice bath. The plate was then serially diluted and plated for counting (CFU / mL). Adhesion inhibition rate (%) = [(number of adhesive bacteria in the control group - number of adhesive bacteria in the sample) / number of adhesive bacteria in the control group] × 100%; (3) Biofilm reduction: Add 1 mL of bacterial suspension to each sample and co-culture at 37℃ and 95% humidity for 24 h. Wash off the biofilm and count it according to the above method; Biofilm reduction (%) = [(Biofilm count in control group - Biofilm count in sample) / Biofilm count in control group] × 100%; (4) 30-day inhibition rate: The sample was immersed in artificial saliva (ISO / TR 10271 standard formula, 37℃) for 30 days, and the solution was changed every 48 hours to simulate the long-term oral environment; after 30 days, it was taken out, rinsed with deionized water, and 1 mL of bacterial suspension was added according to the test conditions in step (3), and co-cultured at 37℃ and 95% humidity for 24 hours; 30-day inhibition rate (%) = [(number of biofilm bacteria in the control group after 30 days - number of biofilm bacteria in the sample after 30 days) / number of biofilm bacteria in the control group after 30 days] × 100%.

[0086] Table 2 Performance test results of silicon nitride denture bases prepared in each embodiment and comparative example

[0087] As shown in Table 2, Examples 1-9 of this invention exhibited excellent performance across all three indicators: a biofilm reduction of >80% after 24 hours and only a slight decrease in inhibition rate after 30 days, confirming that bulk silicon nitride can achieve long-term stable non-drug antibacterial activity through continuous surface hydrolysis. Example 7, with its optimized grain boundary phase distribution through a nano-bimodal particle size design, demonstrated the strongest antibacterial activity. Comparative Examples 1-5, due to imbalances in additive content or ratio and improper sintering temperature, resulted in abnormal grain boundary phases, significantly deteriorating both initial antibacterial activity and long-term stability. Comparative Example 6, with only a 200nm coating, initially achieved some antibacterial effect, but after 30 days of immersion, the coating wore away and dissolved completely, causing the inhibition rate to plummet to 14%-20%, revealing the fundamental flaw of the coating scheme lacking antibacterial bulk phase reserves. The zirconia control group, lacking surface hydrolysis activity, exhibited near-zero inhibition rates, highlighting the unique antibacterial advantages of silicon nitride materials.

[0088] Experimental Example 3 MTT cytotoxicity tests were performed on borosilicate glass-based veneer porcelain and the silicon nitride denture base prepared in Example 1 using V79 Chinese hamster lung cells. The results are shown in Table 3. (1) Preparation of sample extract The silicon nitride denture base, borosilicate glass-based veneer porcelain, and zirconia samples prepared in Example 1 were processed into circular pieces with a diameter of 10 mm and a thickness of 1 mm. The surfaces were mirror-polished, ultrasonically cleaned with 75 wt% ethanol for 30 min, rinsed with deionized water, and autoclaved (121°C, 20 min). The extraction was performed according to the extraction ratio specified in ISO 10993-12 (the ratio of sample surface area to extraction medium volume was 3 cm²). 2 The sample was immersed in DMEM medium containing 10 wt% fetal bovine serum and extracted at 37°C and 5% CO2 for 24 h. The extract was collected for later use. Simultaneously, a blank control group (only an equal volume of medium was added, without sample), a positive control group (medium containing 0.1 wt% phenol), and a negative control group (medium containing high-density polyethylene (HDPE) extract, spaced at 3 cm⁻¹) were set up. 2 (Prepared under the same conditions of extraction for 24 hours at a ratio of / mL). (2) Cell culture and inoculation V79 cells were routinely cultured in DMEM medium containing 10% fetal bovine serum at 37°C and 5% CO2. Cells in the logarithmic growth phase were harvested, digested with 0.25 wt% trypsin, resuspended in culture medium, and counted. The cell suspension concentration was adjusted to 1 × 10⁻⁶ cells / cells. 4 Cells / mL. Add 100 μL of cell suspension (i.e., 1 × 10⁶ cells / well) to each well of a 96-well plate. 3 (10 cells) were cultured in a 37°C, 5% CO2 incubator for 24 hours to allow the cells to adhere to the wall and form a semi-confluent monolayer; (3) Treatment of extract Discard the original culture medium in the 96-well plate, add 100 μL of the extract of each group of samples to each well, and set 6 replicates per group. Add an equal volume of fresh culture medium to the blank control group and add culture medium containing 0.1% phenol to the positive control group; continue to incubate the 96-well plate in a 37℃, 5% CO2 incubator for 24 h; (4) MTT test After incubation, the liquid in each well was aspirated, and 50 μL of MTT (3-(4,5-dimethylthiazol-2)-2,5-diphenyltetrazolium bromide) solution (5 mg / mL, prepared with PBS) was added to each well. The wells were incubated at 37°C in the dark for 4 h. The MTT solution was then aspirated, and 100 μL of dimethyl sulfoxide (DMSO) was added to each well. The wells were then shaken at low speed (150 rpm) for 10 min to fully dissolve the formazan crystals. The absorbance (OD value) of each well was measured using a microplate reader at 570 nm, with a reference wavelength of 650 nm. (5) Calculation of relative cell proliferation rate and toxicity classification Relative cell proliferation rate (%) = (mean OD value of experimental group / mean OD value of blank control group) × 100%; Evaluation was conducted according to the toxicity classification standard of GB / T 16886.5: ≥100%: Grade 0 (non-toxic); 75%-99%: Grade 1 (very slight toxicity); 50%-74%: Grade 2 (mild toxicity); 25%-49%: Grade 3 (moderate toxicity); 1%-24%: Grade 4 (severe toxicity); <1%: Grade 5 (lethal toxicity).

[0089] Table 3. Cytotoxicity test results

[0090] As shown in Table 3, the relative cell proliferation rate of the silicon nitride denture base prepared in Example 1 of this invention was 94%, with a toxicity grade of 1 (very slight toxicity). This is comparable to the levels of the zirconia control group (98%) and the negative control group (98%), and far superior to the positive control group (4%). This indicates that both the silicon nitride denture base and the veneer porcelain have good cell compatibility and meet the biosafety requirements for clinical application of oral restorative materials. The trace hydrolysis products on the silicon nitride surface did not exhibit detectable cytotoxicity under extremely low concentration extraction conditions, further verifying its safety for in vivo use.

[0091] Experiment Example 4 Following the testing procedures of Experimental Example 1, the flexural strength, fracture toughness, and hardness of the silicon nitride dental restorative materials prepared in Examples 10-20 and Comparative Examples 7-12 were tested, and the results are shown in Table 4.

[0092] Table 4. Performance test results of silicon nitride dental restorative materials prepared in each example and comparative example.

[0093] As can be seen from Table 4, the bending strength of Examples 10-20 of the present invention is 910MPa-1045MPa, and the fracture toughness is 7.5MPa·m. 1 / 2 -9.0 MPa·m 1 / 2 It is significantly better than Comparative Examples 7-12 (toughness 6.0 MPa·m). 1 / 2 -7.0 MPa·m 1 / 2 Example 16 (with a bimodal particle size base as in Example 7) exhibited the best strength and toughness. Comparative Example 12, while having similar flexural strength to the examples, had a fracture toughness of only 6.5 MPa·m. 1 / 2 This indicates that the coating solution cannot impart high resistance to crack propagation to the repair.

[0094] Surface hardness: Borosilicate glass-based and feldspar enamel porcelain has a hardness of 500HV-550HV, which is close to natural tooth enamel and helps reduce wear on opposing teeth; zirconia-based enamel porcelain has a hardness of up to 1200HV, which may exacerbate wear on opposing teeth.

[0095] Aesthetics: High-quality bases paired with low-melting-point veneer porcelain can achieve a natural tooth-colored translucent effect; in the comparison, due to the abnormal color of the base itself (too dark or stained), even with veneer porcelain, it cannot be completely covered, resulting in a poor aesthetic effect.

[0096] The above data shows that the manufacturing process (additives, sintering regime) of silicon nitride denture bases fundamentally determines the load-bearing reliability and aesthetic performance of the final restoration. The process window defined by this invention is the key to achieving high-performance restorations.

[0097] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A silicon nitride denture base, characterized in that, The raw materials for the silicon nitride denture base include silicon nitride and additives, wherein the additives include silicon oxide, magnesium oxide and rare earth metal oxides; The mass ratio of the silicon oxide, the magnesium oxide, and the rare earth metal oxide is 2.5-3:1.6-1.9:

1.

2. The silicon nitride denture base according to claim 1, characterized in that, The content of the auxiliary agent is 3wt%-6wt%; And / or, the rare earth metal oxide includes at least one of yttrium oxide and ytterbium oxide; And / or, the silicon nitride has a particle size of 0.05 μm-2 μm.

3. A method for preparing a silicon nitride denture base as described in claim 1 or 2, characterized in that, Includes the following steps: Weigh the raw material of the silicon nitride denture base, press it, and sinter it once to obtain the silicon nitride denture base; The sintering temperature is 1550℃-1650℃.

4. The method for preparing a silicon nitride denture base according to claim 3, characterized in that, The sintering time is 2-5 hours, and the heating rate is 5℃ / min-12℃ / min.

5. The method for preparing a silicon nitride denture base according to claim 3, characterized in that, The pressing includes cold isostatic pressing; the pressure of the cold isostatic pressing is 150MPa-250MPa, and the time is 5min-15min.

6. The method for preparing a silicon nitride denture base according to claim 3, characterized in that, Before the molding step, a binder is added, the mass of which is 2wt%-4wt% of the total mass of the silicon nitride and the additives.

7. A silicon nitride dental restorative material, characterized in that, The silicon nitride dental restorative material includes a denture base and a veneer material, wherein the coefficient of thermal expansion of the veneer material is 2.8 × 10⁻⁶. -6 / ℃-3.6×10 -6 / ℃; The denture base is a silicon nitride denture base prepared by the preparation method described in any one of claims 3-6.

8. The silicon nitride dental restorative material according to claim 7, characterized in that, The finishing material includes at least one of borosilicate glass-based finishing ceramics, feldspar finishing ceramics, and zirconia-based finishing ceramics.

9. A method for preparing the silicon nitride dental restorative material according to claim 7 or 8, characterized in that, Includes the following steps: A slurry containing a decorative material is prepared, and the slurry containing the decorative material is coated onto the denture base and then sintered a second time to obtain the silicon nitride dental restoration material.

10. The method for preparing the silicon nitride dental restorative material according to claim 9, characterized in that, The secondary sintering temperature is 850℃-1000℃, and the time is 20min-60min; And / or, the coating thickness is 0.2mm-0.8mm; And / or, in the slurry containing the finishing material, the content of the finishing material is 50wt%-60wt%.

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