Fully sintered dental zirconium oxide and preparation method thereof

Abstract

The invention discloses fully sintered dental zirconia and a preparation method thereof, and mainly relates to the technical field of dental prostheses. Compared with the prior art, the fully-sintered dental zirconium oxide is prepared from zinc stearate, polyvinyl alcohol and composite zirconium oxide; in the preparation of the composite zirconium oxide, ethyl silicate is hydrolyzed under an alkaline condition to obtain nano silicon dioxide sol, hydroxyapatite is wrapped on the surface of zirconium oxide through the nano silicon dioxide sol, and finally, the nano silicon dioxide sol is converted from sol to gel through heat treatment and is dehydrated to form a compact coating layer. Hydroxyl in the sol is condensed to form a more stable nano silicon dioxide network structure, and finally the fully-sintered dental zirconium oxide with higher compactness, fracture toughness and bonding strength is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of dental prostheses, and particularly to a fully sintered dental zirconia and a preparation method thereof. Background Art

[0002] Zirconia materials have important applications in the fields of dental restoration and dentures. With high strength, high toughness, and good biocompatibility, they can accurately fabricate restorations such as dental crowns and bridges, effectively restoring the shape and function of teeth, and providing aesthetic and durable dental restoration solutions for patients. Zirconia has three crystal forms: monoclinic, tetragonal, and cubic. These forms transform at different temperatures. For example, it has a monoclinic crystal structure at room temperature, transforms to a tetragonal crystal structure when the temperature rises to about 1100 °C, and further transforms to a cubic crystal structure when the temperature rises to about 1200 °C. This phase transition characteristic enables zirconia to exhibit a significant "transformation strengthening" effect in mechanical properties, thereby improving its crack resistance and toughness. Semi-sintered zirconia is usually in a pre-sintered state with a low density and moderate hardness, making it easy to be machined into complex dental shapes by cutting. However, its strength and toughness are limited, and its performance needs to be further improved through subsequent full-sintering processes; while fully sintered zirconia is fully sintered at high temperature, with a high density and hardness, and has excellent flexural strength and wear resistance.

[0003] In the prior art, the methods for improving the performance of fully sintered zirconia mainly include optimizing the raw material formula and microstructure control. For example, adding rare earth oxides to stabilize the crystal form and inhibit abnormal grain growth, forming uniform and fine tetragonal zirconia grains to enhance the phase transformation toughening effect; or improving the sintering process parameters, using technologies such as microwave-assisted sintering to increase the density and reduce internal defects; surface modification treatments such as laser cladding and ion implantation can also be carried out to form a compressive stress layer or introduce a nano-coating on the material surface to further improve the anti-fatigue fracture ability; composite materials are prepared by compounding zirconia with reinforcing bodies such as carbon fibers and graphene to achieve the synergistic optimization of mechanical properties and biocompatibility. It should be noted that when treating zirconia, attention should also be paid to the color appearance being matched with natural teeth.

[0004] CN118515480A discloses a method for preparing dental zirconia ceramics by low-temperature sintering. This patent mixes nano-silica powder with zirconia, and after oscillation, dry pressing, heat treatment, and heat preservation treatment at 1400 °C, realizes the preparation of dental zirconia ceramics by low-temperature sintering. Its advantages are that it reduces the sintering temperature, can shorten the preparation time, reduce costs and energy consumption, and does not change the crystal structure; however, this patent does not involve the technical effect of improving the fracture toughness of zirconia.

[0005] CN117800717A discloses a zirconia-based composite powder, a zirconia pre-sintered body and its preparation method, a zirconia sintered body and its preparation method and application. This patent prepares a high-strength and high-density zirconia sintered body through a composite powder of yttrium oxide, alumina and zirconia. However, this technology has high requirements for raw material control and high costs. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to improve the fracture toughness and bonding strength of zirconia applied in dental restoration.

[0007] To achieve the above object, the present invention provides a fully sintered dental zirconia and its preparation method.

[0008] A preparation method of a fully sintered dental zirconia includes the following steps, by weight: Mix 15 - 25 parts of composite zirconia, 0.005 - 0.15 parts of zinc stearate, and 0.4 - 0.8 parts of polyvinyl alcohol, add 140 - 180 parts of ball-milling medium and ball-mill for 2 - 4 hours, take out the ball-milling medium to obtain a composite powder, add the composite powder to a mold and dry-press it into a green body under pressure conditions, raise the temperature to 200 - 300 °C and keep it for 1 - 3 hours to remove polyvinyl alcohol, raise the temperature to 1200 - 1400 °C and keep it for 1 - 3 hours, and cool to room temperature to obtain the fully sintered dental zirconia.

[0009] The ball-milling medium is zirconia ceramic balls.

[0010] The heating rate for raising the temperature to 200 - 300 °C is to raise the temperature to 200 - 300 °C at a rate of 1 - 4 °C / min.

[0011] The heating rate for raising the temperature to 1200 - 1400 °C is to raise the temperature to 1200 - 1400 °C at a rate of 4 - 6 °C / min.

[0012] The green body density of the green body is 2.0 - 3.0 g / cm 3 .

[0013] The pressure condition is 100 - 140 MPa.

[0014] The dry-pressing time is 30 - 60 seconds.

[0015] The preparation method of the composite zirconia is as follows, by weight: M1. Add 0.5 - 1.5 parts of hydroxyapatite to 8 - 12 parts of ethanol, and ultrasonically disperse at room temperature for 1 - 2 hours to obtain a hydroxyapatite dispersion; M2. Add 1 - 4 parts of tetraethyl orthosilicate to 15 - 25 parts of ethanol, dropwise add 0.5 - 1.5 parts of ammonia water, and stir at room temperature for 1 - 2 hours to obtain a nano-silica sol; M3. Mix 8 - 12 parts of hydroxyapatite dispersion and 15 - 25 parts of nano - silica sol, and stir at 55 - 65 °C for 1 - 2 hours to obtain hydroxyapatite - nano - silica sol; M4. Add 15 - 25 parts of zirconia to the hydroxyapatite - nano - silica sol, stir for 1 - 2 hours, age for 5 - 10 hours, heat up to 90 - 110 °C at a rate of 4 - 6 °C / min and hold for 0.5 - 1.5 hours to remove the solvent, then heat up to 350 - 450 °C at a rate of 4 - 6 °C / min and hold for 1 - 3 hours to dehydrate the nano - silica sol into a dense coating layer, and cool to room temperature to obtain composite zirconia.

[0016] Preferably, the preparation method of the composite zirconia is as follows, by weight: M1. Add 0.8 - 1.2 parts of hydroxyapatite to 8 - 12 parts of ethanol, and ultrasonically disperse at room temperature for 1 - 2 hours to obtain hydroxyapatite dispersion; M2. Add 1.8 - 2.2 parts of tetraethyl orthosilicate to 15 - 25 parts of ethanol, dropwise add 0.5 - 1.5 parts of ammonia water, and stir at room temperature for 1 - 2 hours to obtain nano - silica sol; M3. Mix 8 - 12 parts of hydroxyapatite dispersion and 15 - 25 parts of nano - silica sol, and stir at 55 - 65 °C for 1 - 2 hours to obtain hydroxyapatite - nano - silica sol; M4. Add 18 - 22 parts of zirconia to the hydroxyapatite - nano - silica sol, stir for 1 - 2 hours, age for 5 - 10 hours, heat up to 90 - 110 °C at a rate of 4 - 6 °C / min and hold for 0.5 - 1.5 hours to remove the solvent, then heat up to 350 - 450 °C at a rate of 4 - 6 °C / min and hold for 1 - 3 hours to dehydrate the nano - silica sol into a dense coating layer, and cool to room temperature to obtain composite zirconia.

[0017] The ammonia water is 25 - 35wt% ammonia water.

[0018] The fully sintered dental zirconia of the present invention is prepared from zinc stearate, polyvinyl alcohol and composite zirconia. Zinc stearate plays a role in lubricating and demolding, forming a lubricating film between the raw material particles and the mold surface, effectively reducing the friction between particles and the friction between particles and the mold wall, thus facilitating the forming and demolding of the green body. It also has the function of a dispersant, which can improve the fluidity of particles and enhance the mixing uniformity. Polyvinyl alcohol plays a binding role, enabling the raw material particles to be tightly combined during dry pressing to form a green body, maintaining the shape of the green body and increasing the compactness. This not only improves the mechanical strength of the green body but also provides a basis for densification during the subsequent sintering process. In the preparation of composite zirconia, tetraethyl orthosilicate is first hydrolyzed under alkaline conditions to obtain nano-silica sol, then hydroxyapatite is coated on the surface of zirconia through the nano-silica sol, and finally, through heat treatment, the nano-silica sol transforms from sol to gel and dehydrates to form a dense coating layer, and the hydroxyl groups in the sol condense to form a more stable nano-silica network structure. Compared with adding zirconia alone, adding composite zirconia can make the final fully sintered dental zirconia have a higher density because its coating layer fills the voids between zirconia particles, and finally, a fully sintered dental zirconia with higher density, fracture toughness, and bonding strength is prepared.

[0019] Advantages of the present invention: Compared with the prior art, the fully sintered dental zirconia of the present invention is prepared from zinc stearate, polyvinyl alcohol and composite zirconia. In the preparation of composite zirconia, tetraethyl orthosilicate is first hydrolyzed under alkaline conditions to obtain nano-silica sol, then hydroxyapatite is coated on the surface of zirconia through the nano-silica sol, and finally, through heat treatment, the nano-silica sol transforms from sol to gel and dehydrates to form a dense coating layer, and the hydroxyl groups in the sol condense to form a more stable nano-silica network structure, and finally, a fully sintered dental zirconia with higher density, fracture toughness, and bonding strength is prepared. Specific embodiments

[0020] The parameters of the specific chemical substances used in the examples are as follows: Zirconia: The content of zirconium dioxide is 94.7 wt%, the crystal phase is 3Y tetragonal phase, the manufacturer is Hangzhou Hengge Nano Technology Co., Ltd., and the model is HN-R200KR.

[0021] Zirconia ceramic balls: 5 mm, the manufacturer is Zibo Rongsheng Ceramic Technology Co., Ltd., and the product number is RS955.

[0022] Hydroxyapatite: 12 nm, the manufacturer is Chongqing Tingyi Biotechnology Co., Ltd.

[0023] Polyvinyl alcohol: The manufacturer is Xi'an Tianzheng Pharmaceutical Excipients Co., Ltd., the model is PVA24-88, the viscosity is 37-51 mPas, and the average degree of polymerization is 2200-2500.

[0024] Example 1

[0025] A preparation method of fully sintered dental zirconia includes the following steps: Mix 20 g of composite zirconia, 0.01 g of zinc stearate, and 0.6 g of polyvinyl alcohol, add 160 g of zirconia ceramic balls and ball mill for 3 hours, take out the ball milling medium to obtain a composite powder; add the composite powder to a mold and dry press it into a green body at a pressure of 120 MPa for 45 seconds, and the density of the green body is 2.5 g / cm 3 ; Heat it to 250 °C at a rate of 2 °C / min and hold for 2 hours to remove polyvinyl alcohol, heat it to 1350 °C at a rate of 5 °C / min and hold for 2 hours, and naturally cool to room temperature to obtain the fully sintered dental zirconia.

[0026] The preparation method of the composite zirconia is as follows: M1. Add 0.8 g of hydroxyapatite to 10 g of ethanol, and ultrasonically disperse it at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion; M2. Add 1.5 g of tetraethyl orthosilicate to 20 g of ethanol, dropwise add 1 g of 30 wt% ammonia water, and stir at room temperature for 1.5 hours to obtain a nano-silica sol; M3. Mix 10 g of hydroxyapatite dispersion and 20 g of nano-silica sol, and stir at 60 °C for 1.5 hours to obtain a hydroxyapatite-nano-silica sol; M4. Add 15 g of zirconia to the hydroxyapatite-nano-silica sol and stir for 1.5 hours, age for 7 hours, heat it to 100 °C at a rate of 5 °C / min and hold for 1 hour to remove the solvent, heat it to 400 °C at a rate of 5 °C / min and hold for 2 hours to dehydrate the nano-silica sol into a dense coating layer, and cool to room temperature to obtain the composite zirconia.

[0027] Example 2

[0028] A preparation method of fully sintered dental zirconia includes the following steps: Mix 20 g of composite zirconia, 0.01 g of zinc stearate, and 0.6 g of polyvinyl alcohol, add 160 g of zirconia ceramic balls and ball mill for 3 hours, take out the ball milling medium to obtain a composite powder; add the composite powder to a mold and dry press it into a green body at a pressure of 120 MPa for 45 seconds, and the density of the green body is 2.5 g / cm 3 ; Heat it to 250 °C at a rate of 2 °C / min and hold for 2 hours to remove polyvinyl alcohol, heat it to 1350 °C at a rate of 5 °C / min and hold for 2 hours, and naturally cool to room temperature to obtain the fully sintered dental zirconia.

[0029] The preparation method of the composite zirconia is as follows: M1. Add 1.4 g of hydroxyapatite to 10 g of ethanol, and ultrasonically disperse it at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion; M2. Add 2 g of tetraethyl orthosilicate to 20 g of ethanol, dropwise add 1 g of 30 wt% ammonia water, and stir at room temperature for 1.5 hours to obtain a nano-silica sol; M3. Mix 10 g of the hydroxyapatite dispersion and 20 g of the nano-silica sol, and stir at 60 °C for 1.5 hours to obtain a hydroxyapatite-nano-silica sol; M4. Add 20 g of zirconia to the hydroxyapatite-nano-silica sol, stir for 1.5 hours, age for 7 hours, heat up to 100 °C at a rate of 5 °C / min and hold for 1 hour to remove the solvent, then heat up to 400 °C at a rate of 5 °C / min and hold for 2 hours to dehydrate the nano-silica sol into a dense coating layer, and cool to room temperature to obtain the composite zirconia.

[0030] Example 3

[0031] A preparation method of fully sintered dental zirconia includes the following steps: Mix 20 g of the composite zirconia, 0.01 g of zinc stearate, and 0.6 g of polyvinyl alcohol, add 160 g of zirconia ceramic balls and ball-mill for 3 hours, take out the ball-milling medium to obtain a composite powder; add the composite powder to a mold and dry-press it into a green body at a pressure of 120 MPa for 45 seconds, and the density of the green body is 2.5 g / cm 3 ; Heat up to 250 °C at a rate of 2 °C / min and hold for 2 hours to remove the polyvinyl alcohol, then heat up to 1350 °C at a rate of 5 °C / min and hold for 2 hours, and naturally cool to room temperature to obtain the fully sintered dental zirconia.

[0032] The preparation method of the composite zirconia is as follows: M1. Add 1.2 g of hydroxyapatite to 10 g of ethanol, and ultrasonically disperse it at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion; M2. Add 2.5 g of tetraethyl orthosilicate to 20 g of ethanol, dropwise add 1 g of 30 wt% ammonia water, and stir at room temperature for 1.5 hours to obtain a nano-silica sol; M3. Mix 10 g of the hydroxyapatite dispersion and 20 g of the nano-silica sol, and stir at 60 °C for 1.5 hours to obtain a hydroxyapatite-nano-silica sol; M4. Add 20 g of zirconia to the hydroxyapatite-nano-silica sol, stir for 1.5 hours, age for 7 hours, heat up to 100 °C at a rate of 5 °C / min and hold for 1 hour to remove the solvent, then heat up to 400 °C at a rate of 5 °C / min and hold for 2 hours to dehydrate the nano-silica sol into a dense coating layer, and cool to room temperature to obtain the composite zirconia.

[0033] Example 4

[0034] A preparation method of fully sintered dental zirconia includes the following steps: Mix 20 g of composite zirconia, 0.01 g of zinc stearate, and 0.6 g of polyvinyl alcohol, add 160 g of zirconia ceramic balls and ball mill for 3 hours, then take out the ball milling medium to obtain a composite powder; add the composite powder into a mold and dry press it into a green body at a pressure of 120 MPa for 45 seconds, and the density of the green body is 2.5 g / cm 3 ; Heat it to 250 °C at a rate of 2 °C / min and hold for 2 hours to remove polyvinyl alcohol, then heat it to 1350 °C at a rate of 5 °C / min and hold for 2 hours, and naturally cool it to room temperature to obtain the fully sintered dental zirconia.

[0035] The preparation method of the composite zirconia is as follows: M1. Add 1 g of hydroxyapatite to 10 g of ethanol, and ultrasonically disperse it at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion; M2. Add 2 g of tetraethyl orthosilicate to 20 g of ethanol, dropwise add 1 g of 30 wt% ammonia water, and stir at room temperature for 1.5 hours to obtain a nano-silica sol; M3. Mix 10 g of hydroxyapatite dispersion and 20 g of nano-silica sol, and stir at 60 °C for 1.5 hours to obtain a hydroxyapatite-nano-silica sol; M4. Add 20 g of zirconia to the hydroxyapatite-nano-silica sol and stir for 1.5 hours, age for 7 hours, heat it to 100 °C at a rate of 5 °C / min and hold for 1 hour to remove the solvent, then heat it to 400 °C at a rate of 5 °C / min and hold for 2 hours to dehydrate the nano-silica sol into a dense coating layer, and cool it to room temperature to obtain the composite zirconia.

[0036] Comparative Example 1

[0037] A preparation method of fully sintered dental zirconia includes the following steps: Mix 20 g of zirconia, 0.01 g of zinc stearate, and 0.6 g of polyvinyl alcohol, add 160 g of zirconia ceramic balls and ball mill for 3 hours, then take out the ball milling medium to obtain a composite powder; add the composite powder into a mold and dry press it into a green body at a pressure of 120 MPa for 45 seconds, and the density of the green body is 2.5 g / cm 3 ; Heat it to 250 °C at a rate of 2 °C / min and hold for 2 hours to remove polyvinyl alcohol, then heat it to 1350 °C at a rate of 5 °C / min and hold for 2 hours, and naturally cool it to room temperature to obtain the fully sintered dental zirconia.

[0038] Comparative Example 2

[0039] A preparation method of fully sintered dental zirconia includes the following steps: Mix 20 g of composite zirconia, 0.01 g of zinc stearate, and 0.6 g of polyvinyl alcohol, add 160 g of zirconia ceramic balls and ball mill for 3 hours, then remove the ball milling medium to obtain a composite powder; add the composite powder into a mold and dry press it into a green body under a pressure of 120 MPa for 45 seconds, and the density of the green body is 2.5 g / cm 3 ; Heat it to 250 °C at a rate of 2 °C / min and hold for 2 hours to remove polyvinyl alcohol, then heat it to 1350 °C at a rate of 5 °C / min and hold for 2 hours, and naturally cool it to room temperature to obtain the fully sintered dental zirconia.

[0040] The preparation method of the composite zirconia is as follows: M1. Add 2 g of tetraethyl orthosilicate to 20 g of ethanol, dropwise add 1 g of 30 wt% ammonia water, and stir at room temperature for 1.5 hours to obtain a nano-silica sol; stir at 60 °C for 1.5 hours to obtain a nano-silica sol; M2. Add 20 g of zirconia to the nano-silica sol and stir for 1.5 hours, age for 7 hours, heat it to 100 °C at a rate of 5 °C / min and hold for 1 hour to remove the solvent, then heat it to 400 °C at a rate of 5 °C / min and hold for 2 hours to dehydrate the nano-silica sol into a dense coating layer, and cool it to room temperature to obtain the composite zirconia.

[0041] Comparative Example 3

[0042] A preparation method of fully sintered dental zirconia includes the following steps: Mix 20 g of composite zirconia, 0.01 g of zinc stearate, and 0.6 g of polyvinyl alcohol, add 160 g of zirconia ceramic balls and ball mill for 3 hours, then remove the ball milling medium to obtain a composite powder; add the composite powder into a mold and dry press it into a green body under a pressure of 120 MPa for 45 seconds, and the density of the green body is 2.5 g / cm 3 ; Heat it to 250 °C at a rate of 2 °C / min and hold for 2 hours to remove polyvinyl alcohol, then heat it to 1350 °C at a rate of 5 °C / min and hold for 2 hours, and naturally cool it to room temperature to obtain the fully sintered dental zirconia.

[0043] The preparation method of the composite zirconia is as follows: M1. Add 1 g of hydroxyapatite to 10 g of ethanol and ultrasonically disperse it at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion; M2. Add 20 g of zirconia to the hydroxyapatite dispersion and stir for 1.5 hours, heat it to 100 °C at a rate of 5 °C / min and hold for 1 hour to remove the solvent, then heat it to 400 °C at a rate of 5 °C / min and hold for 2 hours, and cool it to room temperature to obtain the composite zirconia.

[0044] Test Example 1

[0045] The fully sintered dental zirconia obtained by the preparation methods of Examples 1-4 and Comparative Examples 1-3 was cut into pieces with the size of 6 mm × 6 mm × 10 mm, and polished successively with 400-mesh, 600-mesh, 800-mesh and 1000-mesh sandpapers for 60 s each, and then ultrasonically cleaned for 10 min to obtain the specimens of Examples 1-4 and Comparative Examples 1-3. The bond strength test was based on the fracture toughness test of the national standard GB 30367-2013 "Dentistry - Ceramic Materials". Five groups of specimens were prepared for each example, and the test data were averaged and summarized in Table 1 as follows.

[0046] Table 1 Fracture Toughness Test

[0047] As can be seen from Examples 1-4, the differences in the amounts of hydroxyapatite, tetraethyl orthosilicate and zirconia used will affect the properties of the obtained composite zirconia. After hydrolysis, tetraethyl orthosilicate can generate nano-silica sol, and nano-silica can fill into the microstructure of the material, improving the density and uniformity of the material, thereby enhancing the fracture toughness of the material. However, too much may lead to too high a silica content in the material, making the material brittle and affecting the fracture toughness again; the dosage ratio of hydroxyapatite and zirconia will affect the overall preparation concentration of the composite zirconia, so different dosage combinations will change the internal microstructure of the composite zirconia, thus affecting the fracture toughness. Compared with Comparative Example 1, the zirconia was replaced with composite zirconia in the preparation of Examples 1-4, and the fracture toughness was gradually improved. In Comparative Example 2, the composite zirconia was obtained by using the nano-silica sol obtained by the hydrolysis of tetraethyl orthosilicate to coat zirconia and then continuing to combine. The dense coating layer formed by the dehydration of the gel can fill the gaps between zirconia particles. The nano-silica network structure consumes energy by buffering deformation, increasing the fracture toughness; in Comparative Example 3, hydroxyapatite was added to the composite zirconia to improve the fracture toughness by its own toughness and the interfacial combination with zirconia; in Example 4, the composite zirconia was obtained by using the nano-silica sol obtained by the hydrolysis of tetraethyl orthosilicate to coat both hydroxyapatite and nano-silica at the same time. Hydroxyapatite disperses stress through its own deformation and interfacial debonding, and the nano-silica network further buffers stress and fills pores. The two work together to significantly improve the energy dissipation ability and form a denser structure, ultimately reducing the risk of fracture damage and increasing the fracture toughness.

[0048] Test Example 2

[0049] The fully sintered dental zirconia obtained by the preparation methods of Example 4 and Comparative Examples 1-3 was cut into pieces with a size of 4 mm×4 mm×1 mm, and polished successively with 400-mesh, 600-mesh, 800-mesh and 1000-mesh sandpapers for 60 s each, and then ultrasonically cleaned for 10 min to obtain the denture materials of Example 4 and Comparative Examples 1-3. Five denture materials were prepared for each example. The enamel of the simulated extracted teeth (manufactured by Shanghai Yingnuo Industry Co., Ltd., model: KQBYYL) was removed with a dental burr to expose a bonding surface with a size of 4 mm×4 mm×1 mm, and polished successively with 400-mesh, 600-mesh and 800-mesh sandpapers for 60 s each. After cleaning, the treated simulated extracted teeth were obtained. The bonding surface of the treated simulated extracted teeth was bonded to the denture material with Variolink N resin cement to obtain the test specimens.

[0050] One denture material from Example 4 and Comparative Examples 1-3 was taken respectively and added to a 10 mL screw-cap bottle together with 5 mL of artificial saliva. After sealing, it was placed in a constant temperature incubator for 6 months, and the artificial saliva was replaced once every 7 days; after 6 months, the shear bond strength was tested. The specimen was fixed in a special fixture, the shear direction was parallel to the bonding surface of the specimen, the loading speed was set at 1.0 mm / min, the shear force when the bonding surface of the bonded specimen was damaged was recorded, and the average value of the bond strength was calculated and summarized as shown in Table 2. The bond strength (MPa) = shear force (N) when the bonding surface is damaged / bonding area (mm 2 )

[0051] Table 2 Shear Bond Strength Test

[0052] Test Example 2 The fully sintered dental zirconia obtained by the preparation methods of Example 4 and Comparative Examples 1-3 was used as a dental filling material, and the influence of the bond strength of the dental filling material in the oral saliva environment was simulated. In Comparative Example 1, the zirconia raw material was not subjected to composite treatment, and the bond strength was the lowest; the nano-silica coating layer in Comparative Example 2 contained hydroxyl groups, which could form chemical bonds with the silane coupling agent in the resin cement, enhance the interfacial bonding, and at the same time the dense structure reduced the interfacial voids, resulting in an increase in the bond strength; the hydroxyapatite coating layer in Comparative Example 3 contained calcium and phosphorus active sites, which could form ionic bonds and mechanical interlocking with the resin cement, but lacked the chemical cross-linking effect of nano-silica, and the increase in bond strength was limited. In Example 4, the composite zirconia was prepared by introducing hydroxyapatite and nano-silica, which not only improved the density of the composite zirconia, but also enhanced its surface activity, thereby improving the bond strength with the resin cement; the nano-silica coating layer acted as a barrier layer to resist the erosion of artificial saliva on the bonding interface and prevent the destruction of the bonding performance; while zinc stearate and polyvinyl alcohol played a lubricating and bonding role in the preparation process, which helped to improve the forming quality of the green body, thereby indirectly improving the bond strength of the final material.

[0053] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field according to the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A preparation method of fully sintered dental zirconia, characterized in that, It includes the following steps, by weight: Mix 15 - 25 parts of composite zirconia, 0.005 - 0.15 parts of zinc stearate, and 0.4 - 0.8 parts of polyvinyl alcohol, add 140 - 180 parts of ball - milling medium and ball - mill for 2 - 4 hours. Take out the ball - milling medium to obtain the composite powder. Add the composite powder into a mold and dry - press it into a green body under pressure conditions. Heat it to 200 - 300 °C and keep it for 1 - 3 hours to remove polyvinyl alcohol. Then heat it to 1200 - 1400 °C and keep it for 1 - 3 hours, and cool it to room temperature to obtain the fully - sintered dental zirconia. The composite zirconia is obtained by mixing zirconia with a hydroxyapatite dispersion liquid and a nano - silica sol generated by the hydrolysis of tetraethyl orthosilicate, followed by aging and gradient heat treatment to form a dense coating layer.

2. The preparation method of the fully sintered dental zirconia according to claim 1, wherein, The ball - milling medium is zirconia ceramic balls.

3. The preparation method of the fully sintered dental zirconia according to claim 1, characterized in that The heating rate for heating to 200 - 300 °C is to heat to 200 - 300 °C at a rate of 1 - 4 °C / min.

4. The preparation method of the fully sintered dental zirconia according to claim 1, characterized in that The heating rate for heating to 1200 - 1400 °C is to heat to 1200 - 1400 °C at a rate of 4 - 6 °C / min.

5. The preparation method of the fully sintered dental zirconia according to claim 1, characterized in that, The green density of the green body is 2.0 - 3.0 g / cm 3 .

6. The preparation method of the fully sintered dental zirconia according to claim 1, wherein The pressure condition is 100 - 140 MPa.

7. The preparation method of the fully sintered dental zirconia according to claim 1, characterized in that, The dry - pressing time is 30 - 60 seconds.

8. The preparation method of the fully sintered dental zirconia according to claim 1, characterized in that, The preparation method of the composite zirconia is as follows, by weight: M1: Add 0.5 - 1.5 parts of hydroxyapatite to 8 - 12 parts of ethanol, and ultrasonically disperse it at room temperature for 1 - 2 hours to obtain a hydroxyapatite dispersion liquid. M2: Add 1 - 4 parts of tetraethyl orthosilicate to 15 - 25 parts of ethanol, dropwise add 0.5 - 1.5 parts of ammonia water, and stir at room temperature for 1 - 2 hours to obtain a nano - silica sol. M3: Mix 8 - 12 parts of the hydroxyapatite dispersion liquid and 15 - 25 parts of the nano - silica sol, and stir at 55 - 65 °C for 1 - 2 hours to obtain a hydroxyapatite - nano - silica sol. M4: Add 15 - 25 parts of zirconia to the hydroxyapatite - nano - silica sol and stir for 1 - 2 hours, age for 5 - 10 hours, heat to 90 - 110 °C at a rate of 4 - 6 °C / min and keep it for 0.5 - 1.5 hours to remove the solvent, then heat to 350 - 450 °C at a rate of 4 - 6 °C / min and keep it for 1 - 3 hours to dehydrate the nano - silica sol into a dense coating layer, and cool it to room temperature to obtain the composite zirconia.

9. The preparation method of the fully sintered dental zirconia according to claim 8, characterized in that, The concentration of the ammonia water is 25 - 35 wt%.

10. A fully sintered dental zirconia, characterized in that, Prepared by the preparation method described in any one of claims 1 - 9.

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