Fully sintered dental zirconium oxide and preparation method thereof

Abstract

The present invention discloses a fully sintered dental zirconia and a preparation method thereof, primarily relating to the technical field of dental prostheses. 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 the composite zirconia, ethyl silicate is first hydrolyzed under alkaline conditions to produce a nano-silica sol. Hydroxyapatite is then coated on the surface of the zirconia using the nano-silica sol. Finally, the nano-silica sol is transformed from a sol to a gel through heat treatment and dehydrated to form a dense coating. The hydroxyl groups in the sol condense to form a more stable nano-silica network structure, ultimately producing a fully sintered dental zirconia with higher density, fracture toughness, and bonding strength.

Description

Technical Field

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

[0002] Zirconia materials have important applications in dental restorations and dentures. Its high strength, toughness, and excellent biocompatibility enable the precise fabrication of crowns, bridges, and other restorations, effectively restoring tooth form and function, and providing patients with aesthetically pleasing and durable dental restoration solutions. Zirconia has three crystal forms: monoclinic, tetragonal, and cubic. These forms undergo temperature transitions. For example, at room temperature, it exhibits a monoclinic structure, which transforms to a tetragonal structure at approximately 1100°C, and then to a cubic structure at approximately 1200°C. This phase transition behavior results in a significant "transition strengthening" effect in the mechanical properties of zirconia, thereby improving its crack resistance and toughness. Semi-sintered zirconia, typically in a pre-sintered state, exhibits low density and moderate hardness, making it easy to machine into complex tooth shapes. However, its strength and toughness are limited, requiring subsequent full sintering to further enhance its performance. Fully sintered zirconia, on the other hand, undergoes high-temperature sintering, resulting in high density and hardness, and possesses excellent flexural strength and wear resistance.

[0003] The existing methods for improving the performance of fully sintered zirconia mainly include optimizing the raw material formula and microstructure control. For example, by adding rare earth oxides and other stable crystal forms and inhibiting abnormal grain growth, uniform and fine tetragonal zirconia grains are formed to enhance the phase transformation toughening effect; or by improving the sintering process parameters and using microwave-assisted sintering and other technologies to increase density and reduce internal defects; surface modification treatments such as laser cladding and ion implantation can also be performed to form a compressive stress layer on the surface of the material or introduce a nano-coating to further enhance fatigue fracture resistance; zirconium oxide is combined with reinforcements such as carbon fiber and graphene to prepare composite materials to achieve synergistic optimization of mechanical properties and biocompatibility. It is worth noting that when processing zirconium oxide, it is also necessary to pay attention to the color and appearance matching natural teeth.

[0004] CN118515480A discloses a method for preparing dental zirconia ceramics by low-temperature sintering. This method involves mixing nano-silica powder with zirconia, shaking, dry-pressing, and heat-treating the mixture, followed by a heat treatment at 1400°C. This method achieves low-temperature sintering, shortening production time, reducing costs and energy consumption, and preserving the crystal structure. However, the patent does not address the technical benefits of improving the fracture toughness of zirconia.

[0005] CN117800717A discloses a zirconia-based composite powder, a zirconia pre-calcined body and its preparation method, a zirconia sintered body and its preparation method and application. This patent prepares a high-strength, high-density zirconia sintered body from a composite powder of yttrium oxide, aluminum oxide and zirconia, but this technology has high requirements for the control of raw materials and is relatively costly. 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 used in dental restorations.

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

[0008] A method for preparing fully sintered dental zirconia comprises the following steps, in parts by weight:

[0009] 15-25 parts of composite zirconia, 0.005-0.15 parts of zinc stearate, and 0.4-0.8 parts of polyvinyl alcohol are mixed, 140-180 parts of ball milling media are added, and ball milling is carried out for 2-4 hours. The ball milling media is removed to obtain a composite powder, and the composite powder is added to a mold and dry-pressed into a green body under pressure. The temperature is raised to 200-300° C. and maintained for 1-3 hours to remove the polyvinyl alcohol. The temperature is raised to 1200-1400° C. and maintained for 1-3 hours, and the mixture is cooled to room temperature to obtain the fully sintered dental zirconia.

[0010] The ball milling medium is a zirconia ceramic ball.

[0011] The heating rate to 200-300° C. is 1-4° C. / min.

[0012] The heating rate to 1200-1400° C. is 4-6° C. / min.

[0013] The green body density of the green body is 2.0-3.0 g / cm 3 .

[0014] The pressure condition is 100-140 MPa.

[0015] The dry pressing time is 30-60 seconds.

[0016] The preparation method of the composite zirconium oxide is as follows, in parts by weight:

[0017] M1. Add 0.5-1.5 parts of hydroxyapatite to 8-12 parts of ethanol and disperse under ultrasonication at room temperature for 1-2 hours to obtain a hydroxyapatite dispersion;

[0018] M2. Add 1-4 parts of ethyl silicate to 15-25 parts of ethanol, add 0.5-1.5 parts of aqueous ammonia dropwise, and stir at room temperature for 1-2 hours to obtain nano-silica sol;

[0019] 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;

[0020] M4. Add 15-25 parts of zirconium oxide to hydroxyapatite-nanosilica sol and stir for 1-2 hours, age for 5-10 hours, heat to 90-110°C at 4-6°C / min and keep for 0.5-1.5 hours to remove the solvent, heat to 350-450°C at 4-6°C / min and keep for 1-3 hours to dehydrate the nanosilica sol into a dense coating layer, and cool to room temperature to obtain composite zirconium oxide.

[0021] Preferably, the preparation method of the composite zirconium oxide is as follows, in parts by weight:

[0022] M1. Add 0.8-1.2 parts of hydroxyapatite to 8-12 parts of ethanol and disperse under ultrasonication at room temperature for 1-2 hours to obtain a hydroxyapatite dispersion;

[0023] M2. Add 1.8-2.2 parts of ethyl silicate to 15-25 parts of ethanol, add 0.5-1.5 parts of aqueous ammonia dropwise, and stir at room temperature for 1-2 hours to obtain nano-silica sol;

[0024] 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;

[0025] M4. Add 18-22 parts of zirconium oxide to hydroxyapatite-nanosilica sol and stir for 1-2 hours, age for 5-10 hours, heat to 90-110°C at 4-6°C / min and keep for 0.5-1.5 hours to remove the solvent, heat to 350-450°C at 4-6°C / min and keep for 1-3 hours to dehydrate the nanosilica sol into a dense coating layer, and cool to room temperature to obtain composite zirconium oxide.

[0026] The ammonia water is 25-35wt% ammonia water.

[0027] The fully sintered dental zirconia of the present invention is prepared from zinc stearate, polyvinyl alcohol and composite zirconia, wherein the zinc stearate plays a role of lubrication and demoulding, forms a lubricating film between the raw material particles and the mold surface, effectively reduces the friction between the particles and the friction between the particles and the mold wall, thereby facilitating the molding and demoulding of the green body, and also has the function of a dispersant, which can improve the fluidity of the particles and enhance the mixing uniformity; the polyvinyl alcohol plays a role of bonding, so that the raw material particles are tightly combined to form a green body during dry pressing, maintains the shape of the green body and improves the compactness, which not only improves the mechanical strength of the green body but also provides a basis for densification in the subsequent sintering process; in the preparation of the composite zirconia, ethyl silicate is firstly hydrolyzed under alkaline conditions to obtain a nano-silica sol, and then hydroxyapatite is wrapped on the surface of the zirconia by the nano-silica sol, and finally the nano-silica sol is transformed from a sol to a gel by heat treatment and dehydrated to form a dense coating layer, and the hydroxyl groups in the sol are condensed 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 denser, because its coating layer fills the gaps between zirconia particles, and finally a fully sintered dental zirconia with higher density, fracture toughness and bonding strength is prepared.

[0028] Beneficial effects of the present invention:

[0029] 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 the composite zirconia, ethyl silicate is first hydrolyzed under alkaline conditions to obtain nano-silica sol, and then hydroxyapatite is wrapped on the surface of the zirconia by the nano-silica sol. Finally, the nano-silica sol is transformed from a sol to a gel through heat treatment and dehydrated to form a dense coating layer. The hydroxyl groups in the sol are condensed 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. DETAILED DESCRIPTION

[0030] The parameters of the specific chemical substances used in the examples are derived from the following sources:

[0031] Zirconium oxide: The zirconium dioxide content is 94.7wt%, the crystal phase is 3Y tetragonal phase, the manufacturer is Hangzhou Hengge Nano Technology Co., Ltd., and the model is HN-R200KR.

[0032] Zirconia ceramic ball: 5mm, manufacturer is Zibo Rongsheng Ceramic Technology Co., Ltd., item number is RS955.

[0033] Hydroxyapatite: 12nm, manufactured by Chongqing Tingyi Biotechnology Co., Ltd.

[0034] Polyvinyl alcohol: The manufacturer is Xi'an Tianzheng Pharmaceutical Excipients Co., Ltd., the model is PVA24-88, the viscosity is 37-51mpas, and the average degree of polymerization is 2200-2500.

[0035] Example 1

[0036] A method for preparing fully sintered dental zirconia comprises the following steps:

[0037] 20g of composite zirconium oxide, 0.01g of zinc stearate, and 0.6g of polyvinyl alcohol were mixed, and 160g of zirconium oxide ceramic balls were added and ball-milled for 3 hours. The ball-milling medium was removed to obtain a composite powder. The composite powder was added to a mold and dry-pressed under a pressure of 120MPa for 45 seconds to form a green body with a green body density of 2.5g / cm 3 ; heating to 250°C at 2°C / min and holding for 2 hours to remove polyvinyl alcohol, heating to 1350°C at 5°C / min and holding for 2 hours, and naturally cooling to room temperature to obtain the fully sintered dental zirconia.

[0038] The preparation method of the composite zirconium oxide is as follows:

[0039] M1, add 0.8 g of hydroxyapatite to 10 g of ethanol, and disperse by ultrasonication at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion;

[0040] M2. Add 1.5 g of ethyl silicate to 20 g of ethanol, add 1 g of 30 wt% ammonia water dropwise, and stir at room temperature for 1.5 hours to obtain a nano-silica sol;

[0041] M3, mixing 10 g of hydroxyapatite dispersion and 20 g of nano-silica sol, stirring at 60° C. for 1.5 hours to obtain hydroxyapatite-nano-silica sol;

[0042] M4. Add 15 g of zirconium oxide to hydroxyapatite-nanosilica sol and stir for 1.5 hours. Age for 7 hours, heat to 100°C at 5°C / min and keep for 1 hour to remove the solvent, heat to 400°C at 5°C / min and keep for 2 hours to dehydrate the nanosilica sol into a dense coating layer, and cool to room temperature to obtain composite zirconium oxide.

[0043] Example 2

[0044] A method for preparing fully sintered dental zirconia comprises the following steps:

[0045] 20g of composite zirconium oxide, 0.01g of zinc stearate, and 0.6g of polyvinyl alcohol were mixed, and 160g of zirconium oxide ceramic balls were added and ball-milled for 3 hours. The ball-milling medium was removed to obtain a composite powder. The composite powder was added to a mold and dry-pressed under a pressure of 120MPa for 45 seconds to form a green body with a green body density of 2.5g / cm 3; heating to 250°C at 2°C / min and holding for 2 hours to remove polyvinyl alcohol, heating to 1350°C at 5°C / min and holding for 2 hours, and naturally cooling to room temperature to obtain the fully sintered dental zirconia.

[0046] The preparation method of the composite zirconium oxide is as follows:

[0047] M1, add 1.4 g of hydroxyapatite to 10 g of ethanol, and disperse by ultrasonication at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion;

[0048] M2. Add 2 g of ethyl silicate to 20 g of ethanol, add 1 g of 30 wt% ammonia water dropwise, and stir at room temperature for 1.5 hours to obtain a nano-silica sol;

[0049] M3, mixing 10 g of hydroxyapatite dispersion and 20 g of nano-silica sol, stirring at 60° C. for 1.5 hours to obtain hydroxyapatite-nano-silica sol;

[0050] M4. Add 20 g of zirconium oxide to hydroxyapatite-nanosilica sol and stir for 1.5 hours. Age for 7 hours, heat to 100°C at 5°C / min and keep for 1 hour to remove the solvent, heat to 400°C at 5°C / min and keep for 2 hours to dehydrate the nanosilica sol into a dense coating layer, and cool to room temperature to obtain composite zirconium oxide.

[0051] Example 3

[0052] A method for preparing fully sintered dental zirconia comprises the following steps:

[0053] 20g of composite zirconium oxide, 0.01g of zinc stearate, and 0.6g of polyvinyl alcohol were mixed, and 160g of zirconium oxide ceramic balls were added and ball-milled for 3 hours. The ball-milling medium was removed to obtain a composite powder. The composite powder was added to a mold and dry-pressed under a pressure of 120MPa for 45 seconds to form a green body with a green body density of 2.5g / cm 3 ; heating to 250°C at 2°C / min and holding for 2 hours to remove polyvinyl alcohol, heating to 1350°C at 5°C / min and holding for 2 hours, and naturally cooling to room temperature to obtain the fully sintered dental zirconia.

[0054] The preparation method of the composite zirconium oxide is as follows:

[0055] M1. Add 1.2 g of hydroxyapatite to 10 g of ethanol and disperse under ultrasonication at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion;

[0056] M2. Add 2.5 g of ethyl silicate to 20 g of ethanol, add 1 g of 30 wt% ammonia water dropwise, and stir at room temperature for 1.5 hours to obtain a nano-silica sol;

[0057] M3, mixing 10 g of hydroxyapatite dispersion and 20 g of nano-silica sol, stirring at 60° C. for 1.5 hours to obtain hydroxyapatite-nano-silica sol;

[0058] M4. Add 20 g of zirconium oxide to hydroxyapatite-nanosilica sol and stir for 1.5 hours. Age for 7 hours, heat to 100°C at 5°C / min and keep for 1 hour to remove the solvent, heat to 400°C at 5°C / min and keep for 2 hours to dehydrate the nanosilica sol into a dense coating layer, and cool to room temperature to obtain composite zirconium oxide.

[0059] Example 4

[0060] A method for preparing fully sintered dental zirconia comprises the following steps:

[0061] 20g of composite zirconium oxide, 0.01g of zinc stearate, and 0.6g of polyvinyl alcohol were mixed, and 160g of zirconium oxide ceramic balls were added and ball-milled for 3 hours. The ball-milling medium was removed to obtain a composite powder. The composite powder was added to a mold and dry-pressed under a pressure of 120MPa for 45 seconds to form a green body with a green body density of 2.5g / cm 3 ; heating to 250°C at 2°C / min and holding for 2 hours to remove polyvinyl alcohol, heating to 1350°C at 5°C / min and holding for 2 hours, and naturally cooling to room temperature to obtain the fully sintered dental zirconia.

[0062] The preparation method of the composite zirconium oxide is as follows:

[0063] M1, add 1g of hydroxyapatite to 10g of ethanol and disperse by ultrasonic at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion;

[0064] M2. Add 2 g of ethyl silicate to 20 g of ethanol, add 1 g of 30 wt% ammonia water dropwise, and stir at room temperature for 1.5 hours to obtain a nano-silica sol;

[0065] M3, mixing 10 g of hydroxyapatite dispersion and 20 g of nano-silica sol, stirring at 60° C. for 1.5 hours to obtain hydroxyapatite-nano-silica sol;

[0066] M4. Add 20 g of zirconium oxide to hydroxyapatite-nanosilica sol and stir for 1.5 hours. Age for 7 hours, heat to 100°C at 5°C / min and keep for 1 hour to remove the solvent, heat to 400°C at 5°C / min and keep for 2 hours to dehydrate the nanosilica sol into a dense coating layer, and cool to room temperature to obtain composite zirconium oxide.

[0067] Comparative Example 1

[0068] A method for preparing fully sintered dental zirconia comprises the following steps:

[0069] 20g of zirconium oxide, 0.01g of zinc stearate, and 0.6g of polyvinyl alcohol were mixed, and 160g of zirconium oxide ceramic balls were added and ball-milled for 3 hours. The ball-milling medium was removed to obtain a composite powder. The composite powder was added to a mold and dry-pressed under a pressure of 120MPa for 45 seconds to form a green body with a green body density of 2.5g / cm 3 ; heating to 250°C at 2°C / min and holding for 2 hours to remove polyvinyl alcohol, heating to 1350°C at 5°C / min and holding for 2 hours, and naturally cooling to room temperature to obtain the fully sintered dental zirconia.

[0070] Comparative Example 2

[0071] A method for preparing fully sintered dental zirconia comprises the following steps:

[0072] 20g of composite zirconium oxide, 0.01g of zinc stearate, and 0.6g of polyvinyl alcohol were mixed, and 160g of zirconium oxide ceramic balls were added and ball-milled for 3 hours. The ball-milling medium was removed to obtain a composite powder. The composite powder was added to a mold and dry-pressed under a pressure of 120MPa for 45 seconds to form a green body with a green body density of 2.5g / cm 3 ; heating to 250°C at 2°C / min and holding for 2 hours to remove polyvinyl alcohol, heating to 1350°C at 5°C / min and holding for 2 hours, and naturally cooling to room temperature to obtain the fully sintered dental zirconia.

[0073] The preparation method of the composite zirconium oxide is as follows:

[0074] M1. Add 2 g of ethyl silicate to 20 g of ethanol, add 1 g of 30 wt% ammonia water dropwise, 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;

[0075] M2. Add 20 g of zirconium oxide to the nano-silica sol and stir for 1.5 hours. Age for 7 hours, heat to 100°C at 5°C / min and keep for 1 hour to remove the solvent, heat to 400°C at 5°C / min and keep for 2 hours to dehydrate the nano-silica sol into a dense coating layer, and cool to room temperature to obtain composite zirconium oxide.

[0076] Comparative Example 3

[0077] A method for preparing fully sintered dental zirconia comprises the following steps:

[0078] 20g of composite zirconium oxide, 0.01g of zinc stearate, and 0.6g of polyvinyl alcohol were mixed, and 160g of zirconium oxide ceramic balls were added and ball-milled for 3 hours. The ball-milling medium was removed to obtain a composite powder. The composite powder was added to a mold and dry-pressed under a pressure of 120MPa for 45 seconds to form a green body with a green body density of 2.5g / cm 3; heating to 250°C at 2°C / min and holding for 2 hours to remove polyvinyl alcohol, heating to 1350°C at 5°C / min and holding for 2 hours, and naturally cooling to room temperature to obtain the fully sintered dental zirconia.

[0079] The preparation method of the composite zirconium oxide is as follows:

[0080] M1, add 1g of hydroxyapatite to 10g of ethanol and disperse by ultrasonic at room temperature for 1.5 hours to obtain a hydroxyapatite dispersion;

[0081] M2. Add 20 g of zirconium oxide to the hydroxyapatite dispersion and stir for 1.5 hours. Heat to 100°C at 5°C / min and keep for 1 hour to remove the solvent. Heat to 400°C at 5°C / min and keep for 2 hours. Cool to room temperature to obtain composite zirconium oxide.

[0082] Test Example 1

[0083] The fully sintered dental zirconia prepared by the methods of Examples 1-4 and Comparative Examples 1-3 were cut into 6 mm × 6 mm × 10 mm pieces. The samples were polished for 60 seconds using 400-, 600-, 800-, and 1000-grit sandpaper, respectively, and ultrasonically cleaned for 10 minutes to obtain the samples of Examples 1-4 and Comparative Examples 1-3. Bond strength testing was performed according to the fracture toughness test specified in the national standard GB 30367-2013, "Dental Ceramic Materials." Five sets of samples were prepared for each example, and the average test data are summarized in Table 1.

[0084] Table 1 Fracture toughness test

[0085]

[0086] Examples 1-4 show that the difference in the amount of hydroxyapatite, ethyl silicate, and zirconium oxide affects the performance of the resulting composite zirconia. After hydrolysis, ethyl silicate can generate nano-silica sol. Nano-silica can be filled 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 cause the silica content in the material to be too high, making the material brittle and affecting the fracture toughness. The ratio of hydroxyapatite and zirconium oxide will affect the overall composite zirconia preparation concentration. Therefore, different dosage combinations will change the internal microstructure of the composite zirconia, thereby affecting the fracture toughness. Compared with Comparative Example 1, Examples 1-4 replace zirconium oxide with composite zirconia during preparation, and the fracture toughness is gradually improved. The composite zirconia in comparative example 2 is obtained by hydrolyzing ethyl silicate to obtain a nano-silica sol, which is coated with zirconia and further combined. The dense coating layer formed by dehydration of the gel can fill the gaps between the zirconia particles. The nano-silica network structure consumes energy by buffering deformation, thereby improving the fracture toughness. The composite zirconia in comparative example 3 is compounded with hydroxyapatite, and its own toughness and interface bonding with zirconia are used to improve the fracture toughness. The composite zirconia in embodiment 4 is obtained by hydrolyzing ethyl silicate to obtain a nano-silica sol, and simultaneously coated with hydroxyapatite and nano-silica. The hydroxyapatite disperses stress by its own deformation and interface debonding, and the nano-silica network further buffers stress and fills pores. The two work together to significantly improve the energy dissipation capacity and form a denser structure, ultimately reducing the risk of fracture damage and improving fracture toughness.

[0087] Test Example 2

[0088] The fully sintered dental zirconia obtained by the preparation method of Example 4 and Comparative Examples 1-3 was cut into a size of 4mm×4mm×1mm, and polished with 400, 600, 800, and 1000 mesh sandpaper for 60 seconds in sequence, and ultrasonically cleaned for 10 minutes 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 ex vivo tooth (manufacturer: Shanghai Yingnuo Industrial Co., Ltd., model number: KQBYYL) was removed with a bur to expose a bonding surface of 4mm×4mm×1mm in size. The surface was polished with 400, 600, and 800 mesh sandpaper for 60 seconds in sequence, and cleaned to obtain the treated simulated ex vivo tooth. VariolinkN resin cement was used to bond the bonding surface of the treated simulated ex vivo tooth to the denture material to obtain a test sample.

[0089] One denture material from Example 4 and Comparative Examples 1-3 was added to a 10 mL screw-cap bottle together with 5 mL of artificial saliva. The bottles were sealed and placed in a constant temperature incubator for 6 months, with the artificial saliva replaced every 7 days. After 6 months, the bonding shear strength was tested. The specimens were fixed in a special fixture with the shear direction parallel to the bonding surface of the specimens. The loading speed was set to 1.0 mm / min. The shear force at the time of failure of the bonding surface of the bonding specimens was recorded. The bonding strength was calculated and the average value was summarized as shown in Table 2. Bonding strength (MPa) = shear force at failure of the bonding surface (N) / bonding area (mm 2 ).

[0090] Table 2 Adhesion strength test

[0091]

[0092] Test Example 2 used the fully sintered dental zirconia prepared by the methods of Example 4 and Comparative Examples 1-3 as a filling material, and simulated the effect of the filling material's bonding strength in an oral saliva environment. Comparative Example 1, which did not composite the zirconia raw material, exhibited the lowest bonding strength. The nanosilica coating in Comparative Example 2 contained hydroxyl groups, which could form chemical bonds with the silane coupling agent in the resin cement, enhancing interfacial bonding. The dense structure also reduced interfacial voids, improving bonding strength. The hydroxyapatite coating in Comparative Example 3, containing calcium and phosphorus active sites, could form ionic bonds and mechanical intercalation with the resin cement. However, due to the lack of the chemical crosslinking effect of the nanosilica, the bonding improvement was limited. In Example 4, 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 bonding strength with the resin cement; the nano-silica coating served as a barrier layer to resist the erosion of the bonding interface by artificial saliva and prevent the destruction of the bonding performance; and zinc stearate and polyvinyl alcohol played a lubricating and bonding role in the preparation process, which helped to improve the molding quality of the green body, thereby indirectly improving the bonding strength of the final material.

[0093] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for preparing fully sintered dental zirconia, characterized in that: The method comprises the following steps, in parts by weight: 15-25 parts of composite zirconia, 0.005-0.15 parts of zinc stearate, and 0.4-0.8 parts of polyvinyl alcohol are mixed, 140-180 parts of ball milling medium are added, and the mixture is ball milled for 2-4 hours. The ball milling medium is removed to obtain a composite powder, the composite powder is added to a mold and dry-pressed into a green body under pressure, the mixture is heated to 200-300° C. and maintained for 1-3 hours to remove the polyvinyl alcohol, the mixture is heated to 1200-1400° C. and maintained for 1-3 hours, and the mixture is cooled to room temperature to obtain the fully sintered dental zirconia; The preparation method of the composite zirconium oxide is as follows, in parts by weight: M1. Add 0.5-1.5 parts of hydroxyapatite to 8-12 parts of ethanol and disperse under ultrasonication at room temperature for 1-2 hours to obtain a hydroxyapatite dispersion; M2. Add 1-4 parts of ethyl silicate to 15-25 parts of ethanol, add 0.5-1.5 parts of aqueous ammonia dropwise, 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 15-25 parts of zirconium oxide to hydroxyapatite-nanosilica sol and stir for 1-2 hours, age for 5-10 hours, heat to 90-110°C at 4-6°C / min and keep for 0.5-1.5 hours to remove the solvent, heat to 350-450°C at 4-6°C / min and keep for 1-3 hours to dehydrate the nanosilica sol into a dense coating layer, and cool to room temperature to obtain composite zirconium oxide.

2. The method for preparing fully sintered dental zirconia according to claim 1, wherein: The ball milling medium is zirconia ceramic balls.

3. The method for preparing fully sintered dental zirconia according to claim 1, wherein: The heating rate to 200-300° C. is 1-4° C. / min.

4. The method for preparing fully sintered dental zirconia according to claim 1, wherein: The heating rate to 1200-1400° C. is 4-6° C. / min.

5. The method for preparing fully sintered dental zirconia according to claim 1, wherein: The green body density of the green body is 2.0-3.0 g / cm 3 .

6. The method for preparing fully sintered dental zirconia according to claim 1, wherein: The pressure condition is 100-140 MPa.

7. The method for preparing fully sintered dental zirconia according to claim 1, wherein: The dry pressing time is 30-60 seconds.

8. The method for preparing fully sintered dental zirconia according to claim 1, wherein: The concentration of the ammonia water is 25-35 wt %.

9. A fully sintered dental zirconia, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 8.

Images