Triple gradient zirconia material for manufacturing dental crown

Abstract

The invention relates to the technical field of dental materials, and discloses a triple gradual change zirconia material for dental crown manufacturing, the material is three-layer structure zirconia ceramic with strength gradual change and color gradual change characteristics, the material comprises a neck edge layer, a middle layer and an incisal end layer, the bending strength of the neck edge layer is 1200 MPa, the bending strength of the middle layer is 1100 MPa, the bending strength of the incisal end layer is 1200 MPa, and the bending strength of the incisal end layer is 1100 MPa. The bending strength of the cutting end layer is 670 MPa, the neck edge layer, the middle layer and the cutting end layer are of a continuous transition structure, the overall color gradient range of the material covers the color numbers from A1 to D4, and three kinds of bleaching white transition are included. By designing the three-layer zirconium oxide structure with the strength gradient and the color gradient, the dental crown prosthesis can simulate the mechanical property and aesthetic characteristics of natural teeth at the same time, the mechanical strength requirement of the prosthesis in a large-stress area is guaranteed, and natural color transition in an aesthetic sensitive area is achieved.

Description

Technical Field

[0001] This invention relates to the field of dental materials technology, specifically to a triple-gradient zirconia material for dental crown fabrication. Background Technology

[0002] Zirconia ceramics are a new type of ceramic material with many excellent properties such as wear resistance, corrosion resistance, high strength, high toughness, and good thermal stability. Due to its excellent mechanical properties and biocompatibility, zirconia ceramics have become an important material in the field of dental restoration. Currently, zirconia on the market is divided into three categories: the first category is monochrome zirconia white zirconia, the second category has pre-stained zirconia, and the third category has pre-stained gradient zirconia.

[0003] In the field of existing dental zirconia materials, commercially available products generally adopt a single strength design, which makes it impossible to adapt to the mechanical property gradient distribution of natural teeth when applied to crown fabrication. Using high-strength zirconia in the incisal region may cause abnormal wear of the opposing natural teeth. At the same time, single-strength materials cannot meet the high strength requirements of the bridge connection area and the physiological stress matching characteristics of the occlusal surface, thus limiting the biomimetic effect and long-term stability of the restoration. In addition, although pre-stained zirconia can achieve a basic color transition, it lacks a gradient mechanism that coordinates with mechanical properties. When the restoration is subjected to both functional load and aesthetic requirements, the lack of coordination between strength and color changes may lead to local stress concentration and aesthetic distortion, ultimately affecting the overall clinical effect of the crown restoration.

[0004] Therefore, a triple-gradient zirconia material for dental crown fabrication is proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a triple-gradient zirconia material for dental crown fabrication. This solves the problems mentioned in the background art, such as the difficulty in balancing the high strength requirements of the bridge connection area with the physiological stress matching characteristics of the occlusal surface, which limits the biomimetic effect and long-term stability of the restoration; local stress concentration and aesthetic distortion in the restoration, ultimately affecting the overall clinical effect of the crown restoration.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a triple gradient zirconia material for dental crown fabrication, wherein the material is a three-layer zirconia ceramic with gradient strength and gradient color characteristics, including a cervical margin layer, an intermediate layer and an incisal edge layer; The bending strength of the neck edge layer is 1200 MPa, the bending strength of the intermediate layer is 1100 MPa, and the bending strength of the cut end layer is 670 MPa. The neck edge layer, the intermediate layer and the cut end layer have a continuous transition structure; The material's overall color gradient range covers color numbers A1 to D4, and includes three bleached white transitions; The interfacial bonding strength between the neck edge layer and the intermediate layer is 22-28 MPa, and the interfacial bonding strength between the intermediate layer and the cut edge layer is 18-24 MPa. The interlayer transition region satisfies the following microstructural characteristics: Grain size gradient change rate ≤ 0.15μm / 10μm; Porosity increases from the neck edge layer to the shear edge layer, with a gradient difference of 1.2 ± 0.3 vol% / 100 μm; The concentration of yttrium oxide stabilizer exhibits a continuous gradient distribution, with a concentration change slope ≤ 0.8 wt% / μm; Microstructure characteristics in the process control steps of material preparation: Grain size gradient control: Grain gradient growth is achieved through a segmented sintering process. In the second stage of sintering, the temperature is held at 1450-1550℃ for 2-4 hours. A slow heating rate of 5-8℃ / min and precise holding time control are used. The grains gradually grow from the neck edge layer to the cut end layer. Due to the higher concentration of yttrium oxide stabilizer in the neck edge layer, excessive grain growth is inhibited. Due to the lower stabilizer content in the cut end layer, the grain size naturally increases. The grain size change rate is ≤0.15μm / 10μm as monitored online by scanning electron microscopy. Porosity gradient control: By differentiating the content of sintering aids in each layer, 0.5-1.5 parts in the neck edge layer → 2-3 parts in the cut end layer, a porosity gradient is achieved. Magnesium oxide sintering aids promote liquid phase sintering at high temperatures. The higher content of sintering aids in the cut end layer results in more closed pores being retained. In the third stage of sintering, annealing is carried out after controlling the temperature to 800-1000℃ to homogenize the pore distribution and achieve a porosity gradient of 1.2±0.3 vol% / 100μm from the neck edge layer to the cut end layer. Yttrium oxide concentration gradient formation: During the casting stage, when the three layers of slurry are extruded simultaneously through a three-channel co-extrusion device, the shear rate is controlled at 150-250 s⁻¹ and the casting speed is initially 0.5-1.0 m / min → steady state 1.5-2.0 m / min. Limited interdiffusion of yttrium oxide in each layer of powder occurs at the interface. During the drying process, the temperature gradient is increased from 40℃ to 55℃ to 60℃ and the humidity is controlled from 60%RH to 10%RH to stabilize the concentration distribution and form a continuous gradient with a concentration change slope ≤0.8wt% / μm.

[0007] Preferably, the thickness ratio of the neck edge layer, the intermediate layer, and the cut-end layer is 1.2-1.5:1:0.8-1.2, wherein the thickness of the neck edge layer is 0.4-0.6 mm, the thickness of the intermediate layer is 0.3-0.5 mm, and the thickness of the cut-end layer is 0.3-0.5 mm. Preferably, the neck edge layer is made from the following raw materials in parts by weight: The mixture contains 92-96 parts of yttrium-stabilized zirconia powder, 2-4 parts of alumina, 0.5-1.5 parts of coloring oxide, and 0.5-1.5 parts of sintering aid. The intermediate layer is made of the following raw materials in parts by weight: 90-94 parts of yttrium-stabilized zirconium oxide powder, 3-5 parts of alumina, 1-2 parts of coloring oxide, and 1-2 parts of sintering aid; The cut-end layer is made of the following raw materials in parts by weight: 88-92 parts of yttrium-stabilized zirconium oxide powder, 4-6 parts of alumina, 2-3 parts of coloring oxide, and 2-3 parts of sintering aid; Preferably, the coloring oxide includes at least one of iron oxide, cerium oxide, and praseodymium oxide, and the sintering aid includes at least one of magnesium oxide, calcium oxide, and silicon dioxide.

[0008] Preferably, the color gradient of the material is achieved by the following method: 0.5-1.5 wt% of dark-colored oxide is added to the neck edge layer, 0.3-1.0 wt% of intermediate-colored oxide is added to the middle layer, and 0.1-0.5 wt% of light-colored oxide is added to the cut edge layer, with the content of colored oxides in each layer varying in a gradient.

[0009] Preferably, the microstructure of the material is as follows: The grain size of the neck edge layer is 0.3-0.5 μm, the grain size of the middle layer is 0.4-0.6 μm, and the grain size of the cut end layer is 0.5-0.8 μm, and the grain size shows a continuous and gradual distribution between the layers.

[0010] Preferably, the preparation method of the material includes the following steps: Step 1: Raw material pretreatment, the required zirconium oxide powder for each layer is ball-milled, mixed and dried respectively; Step 2: Slurry preparation, mixing the powders of each layer with binder, plasticizer and solvent to prepare casting slurry; Step 3: Casting and forming, using a multi-layer co-extrusion casting process to prepare a three-layer composite green strip; Step 4: Green body processing, the green body is stamped into a crown blank and glue removal is performed; Step 5: Sintering and shaping, using a segmented sintering process to produce the final product.

[0011] Preferably, step three, casting, specifically includes: A three-channel co-extrusion casting device was used, with the viscosity of the neck layer slurry controlled at 3500±200cP, the viscosity of the middle layer slurry controlled at 2800±150cP, and the viscosity of the cut-end layer slurry controlled at 2200±100cP. The casting gap is set to 0.5-0.8mm, and the shear rate during the simultaneous extrusion of the three layers of slurry is controlled at 150-250s⁻¹; The casting speed is adjusted in two stages: initially 0.5-1.0 m / min for 30-60 seconds to allow the slurry to spread, then increased to 1.5-2.0 m / min for steady-state operation; The drying process uses a gradient temperature increase: 40℃ preheating zone, 60%RH for 2-3 minutes → 55℃ main drying zone, 30%RH for 5-8 minutes → 60℃ setting zone, 10%RH for 1-2 minutes. The width of the interlayer transition zone is controlled to be 80-120μm, and the transition slope angle θ satisfies 15°≤θ≤25°.

[0012] Preferably, the sintering process in step five is as follows: The first stage involves raising the temperature to 600-800℃ at a rate of 3-5℃ / min and holding it for 1-2 hours. The second stage involves raising the temperature to 1450-1550℃ at a rate of 5-8℃ / min and holding it for 2-4 hours. The third stage involves annealing after cooling to 800-1000℃ at a rate of 2-4℃ / min.

[0013] Beneficial effects Compared with the prior art, the present invention provides a triple-gradient zirconia material for dental crown fabrication, which has the following beneficial effects: 1. In this invention, by designing a three-layer zirconia structure with strength and color gradients, the dental crown restoration can simultaneously simulate the mechanical properties and aesthetic characteristics of natural teeth. This ensures the mechanical strength requirements of the restoration in areas with high stress while achieving a natural color transition in aesthetically sensitive areas, thereby improving the biomimetic performance and clinical applicability of the restoration.

[0014] 2. In this invention, by optimizing the multilayer casting process, a continuous and gradual transition between the three layers of materials is achieved, ensuring a tight bond between the interlayer interfaces and a smooth transition of performance, avoiding the stress concentration problem caused by abrupt interface changes in traditional multilayer materials, and improving the reliability and service life of the materials.

[0015] 3. In this invention, by synergistically controlling the mechanical and aesthetic property gradients of the material, the restoration meets the strength requirements of the chewing functional area and the aesthetic requirements of the aesthetic area, achieving a unity of function and aesthetics and improving the overall performance of the crown restoration. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: A triple gradient zirconia material for dental crown fabrication, the material being a three-layer zirconia ceramic with gradient strength and color characteristics, including a cervical margin layer, an intermediate layer, and an incisal edge layer; The bending strength of the neck layer is 1200 MPa, the bending strength of the intermediate layer is 1100 MPa, and the bending strength of the shear end layer is 670 MPa. The neck edge layer, intermediate layer, and shear edge layer form a continuous transition structure; The overall color gradient of the material covers color numbers A1 to D4, and includes three bleached white transitions; The interfacial bonding strength between the neck layer and the intermediate layer is 22 MPa, and the interfacial bonding strength between the intermediate layer and the shear layer is 18 MPa. The interlayer transition region satisfies the following microstructural characteristics: The grain size gradient change rate is ≤0.15μm / 10μm, where 10μm refers to the distance in the direction perpendicular to the interlayer interface, and the grain size change rate does not exceed 0.15μm for every 10 micrometers of distance. Porosity increases from the neck layer to the shear end layer, with a gradient difference of 1.2 ± 0.3 vol% / 100 μm. 100 μm is a reference distance unit set to quantify the rate of change of porosity gradient, that is, in the direction perpendicular to the interlayer interface, the change in the measured volume fraction of porosity of the material is 1.2% ± 0.3% for every 100 micrometers of distance continuously crossed. The concentration of yttrium oxide stabilizer exhibits a continuous gradient distribution, with a concentration change slope ≤ 0.8 wt% / μm; Microstructure characteristics in the process control steps of material preparation: Grain size gradient control: Grain gradient growth is achieved through a segmented sintering process. In the second stage of sintering, a slow heating rate of 5℃ / min and precise holding time control are used to allow the grains to grow gradually from the neck edge layer to the tangent layer. Due to the higher concentration of yttrium oxide stabilizer in the neck edge layer, excessive grain growth is inhibited. Due to the lower stabilizer content in the tangent layer, the grain size naturally increases. Online monitoring using scanning electron microscopy shows that the grain size change rate is ≤0.15μm / 10μm. The continuous gradual change in grain size eliminates stress abrupt changes at the interlayer interfaces. Porosity gradient control: By differentiating the content of sintering aids in each layer (0.5 parts in the neck edge layer → 2 parts in the cutting edge layer), a porosity gradient is achieved. Magnesium oxide sintering aids promote liquid phase sintering at high temperatures. The higher content of sintering aids in the cutting edge layer results in more closed pores being retained. In the third stage of sintering, annealing is carried out after controlled cooling to 800℃ to homogenize the pore distribution. Ultimately, a porosity gradient of 1.2±0.3 vol% / 100μm is achieved from the neck edge layer to the cutting edge layer. The porosity gradient design ensures both the high density of the neck edge region and the micropores of the cutting edge region similar to those of natural teeth. Yttrium oxide concentration gradient formation: During the casting stage, when the three layers of slurry are simultaneously extruded through a three-channel co-extrusion device, the shear rate is controlled at 150 s⁻¹ and the casting speed is initially 0.5 m / min → steady state 1.5 m / min. This allows limited interdiffusion of yttrium oxide in each layer of powder at the interface. During the drying process, the temperature is gradually increased from 40℃ to 55℃ to 60℃, and the humidity is controlled from 60%RH to 10%RH to further stabilize the concentration distribution, ultimately forming a continuous gradient with a concentration change slope ≤ 0.8 wt% / μm. This continuous distribution of yttrium oxide concentration avoids phase transformation cracking caused by sudden changes in stabilizer, allowing the number of cycles in fatigue life testing to exceed 10. 6 Second-rate.

[0018] The thickness ratio of the neck edge layer, intermediate layer, and cut edge layer is 1.2:1:0.8, with the neck edge layer having a thickness of 0.48 mm, the intermediate layer having a thickness of 0.40 mm, and the cut edge layer having a thickness of 0.32 mm. The neck layer is made from the following parts by weight of raw materials: 92 parts of yttrium-stabilized zirconia powder, 2 parts of alumina, 0.5 parts of coloring oxide, and 0.5 parts of sintering aid; The intermediate layer is made of the following raw materials in parts by weight: 90 parts of yttrium-stabilized zirconia powder, 3 parts of alumina, 1 part of coloring oxide, and 1 part of sintering aid; The cut-end layer is made of the following raw materials in parts by weight: 88 parts of yttrium-stabilized zirconia powder, 4 parts of alumina, 2 parts of coloring oxide, and 2 parts of sintering aid; The coloring oxide includes at least one of iron oxide, cerium oxide, and praseodymium oxide, and the sintering aid includes at least one of magnesium oxide, calcium oxide, and silicon dioxide.

[0019] Color gradients in materials are achieved through the following methods: 0.5 wt% of a dark-colored oxide was added to the neck edge layer, 0.3 wt% of an intermediate-colored oxide was added to the middle layer, and 0.1 wt% of a light-colored oxide was added to the cut edge layer, with the content of the colored oxides in each layer changing in a gradient.

[0020] The microstructure of the material is characterized as follows: The grain size of the neck layer is 0.3 μm, the grain size of the middle layer is 0.4 μm, and the grain size of the cut end layer is 0.5 μm. The grain size is continuously and gradually distributed between the layers.

[0021] The preparation method of the material includes the following steps: Step 1: Raw material pretreatment, the required zirconium oxide powder for each layer is ball-milled, mixed and dried respectively; Step 2: Slurry preparation, mixing the powders of each layer with binder, plasticizer and solvent to prepare casting slurry; The plasticizer can be dibutyl phthalate, and the solvent can be a mixture of ethanol and methyl ethyl ketone, which are commonly used substances in the field. Step 3: Casting and forming, using a multi-layer co-extrusion casting process to prepare a three-layer composite green strip; Step 4: Green body processing, the green body is stamped into a crown blank and glue removal is performed; Step 5: Sintering and shaping, using a segmented sintering process to produce the final product.

[0022] Step three, casting, specifically includes: A three-channel co-extrusion casting device was used, with the viscosity of the neck layer slurry controlled at 3300 cP, the viscosity of the middle layer slurry controlled at 2650 cP, and the viscosity of the cut-end layer slurry controlled at 2100 cP. The casting gap is set to 0.5mm, and the shear rate during the simultaneous extrusion of the three layers of slurry is controlled at 150s⁻¹; The casting speed is adjusted in two stages: initially 0.5 m / min for 30 seconds to allow the slurry to spread, then increased to 1.5 m / min for steady-state operation; The drying process uses a gradient temperature increase: 40℃ preheating zone, 60%RH for 2 min → 55℃ main drying zone, 30%RH for 5 min → 60℃ setting zone, 10%RH for 1 min; The width of the interlayer transition zone is controlled to be 80μm, and the transition slope angle θ satisfies 15°≤θ≤25°, where the transition slope angle θ is the angle of the interface transition zone formed at the junction of each layer of slurry during the casting process.

[0023] The sintering process in step five is as follows: The first stage involves heating the temperature to 600℃ at a rate of 3℃ / min and holding it for 1 hour. The second stage involves heating the temperature to 1450℃ at a rate of 5℃ / min and holding it for 2 hours. The third stage involves annealing after cooling to 800℃ at a rate of 2℃ / min.

[0024] Example 2: A triple gradient zirconia material for dental crown fabrication, the material being a three-layer zirconia ceramic with gradient strength and color characteristics, including a cervical margin layer, an intermediate layer, and an incisal edge layer; The bending strength of the neck layer is 1200 MPa, the bending strength of the intermediate layer is 1100 MPa, and the bending strength of the shear end layer is 670 MPa. The neck edge layer, intermediate layer, and shear edge layer form a continuous transition structure; The overall color gradient of the material covers color numbers A1 to D4, and includes three bleached white transitions; The interfacial bonding strength between the neck layer and the intermediate layer is 25 MPa, and the interfacial bonding strength between the intermediate layer and the shear layer is 21 MPa. The interlayer transition region satisfies the following microstructural characteristics: The grain size gradient change rate is ≤0.15μm / 10μm, where 10μm refers to the distance in the direction perpendicular to the interlayer interface, and the grain size change rate does not exceed 0.15μm for every 10 micrometers of distance. Porosity increases from the neck layer to the shear end layer, with a gradient difference of 1.2 ± 0.3 vol% / 100 μm. 100 μm is a reference distance unit set to quantify the rate of change of porosity gradient, that is, in the direction perpendicular to the interlayer interface, the change in the measured volume fraction of porosity of the material is 1.2% ± 0.3% for every 100 micrometers of distance continuously crossed. The concentration of yttrium oxide stabilizer exhibits a continuous gradient distribution, with a concentration change slope ≤ 0.8 wt% / μm; Microstructure characteristics in the process control steps of material preparation: Grain size gradient control: Gradient grain growth is achieved through a segmented sintering process. In the second stage of sintering, a slow heating rate of 6.5℃ / min and precise holding time control are used to allow the grains to grow gradually from the neck edge layer to the tangent layer. Due to the higher concentration of yttrium oxide stabilizer in the neck edge layer, excessive grain growth is inhibited. Due to the lower stabilizer content in the tangent layer, the grain size naturally increases. Online monitoring using scanning electron microscopy shows that the grain size change rate is ≤0.15μm / 10μm. The continuous gradual change in grain size eliminates stress abrupt changes at the interlayer interfaces. Porosity gradient control: By differentiating the content of sintering aids in each layer (1.0 part in the neck edge layer → 2.5 parts in the cutting edge layer), a porosity gradient is achieved. Magnesium oxide sintering aids promote liquid phase sintering at high temperatures. The higher content of sintering aids in the cutting edge layer results in the retention of more closed pores. In the third stage of sintering, annealing is carried out after controlled cooling to 900℃ to homogenize the pore distribution. Finally, a porosity gradient of 1.2±0.3 vol% / 100μm is achieved from the neck edge layer to the cutting edge layer. The porosity gradient design ensures both the high density of the neck edge region and the micropores of the cutting edge region similar to those of natural teeth. Yttrium oxide concentration gradient formation: During the casting stage, when three layers of slurry are simultaneously extruded using a three-channel co-extrusion device, the shear rate is controlled at 200 s⁻¹ and the initial casting speed is 0.75 m / min → steady-state 1.75 m / min. This allows limited interdiffusion of yttrium oxide in each layer of powder at the interface. During the drying process, the temperature is gradually increased from 40℃ to 55℃ to 60℃, and the humidity is controlled from 60%RH to 10%RH to further stabilize the concentration distribution, ultimately forming a continuous gradient with a concentration change slope ≤ 0.8 wt% / μm. This continuous distribution of yttrium oxide concentration avoids phase transformation cracking caused by sudden changes in stabilizer, allowing the number of cycles in fatigue life testing to exceed 10. 6 Second-rate.

[0025] The thickness ratio of the neck edge layer, intermediate layer, and cut edge layer is 1.5:1:1.0, with the neck edge layer having a thickness of 0.6 mm, the intermediate layer having a thickness of 0.4 mm, and the cut edge layer having a thickness of 0.4 mm.

[0026] The neck layer is made from the following parts by weight of raw materials: 94 parts of yttrium oxide-stabilized zirconia powder, 3 parts of alumina, 1.0 part of coloring oxide, and 1.0 part of sintering aid; The intermediate layer is made of the following raw materials in parts by weight: 92 parts yttrium-stabilized zirconia powder, 4 parts alumina, 1.5 parts coloring oxide, and 1.5 parts sintering aid; The cut-end layer is made from the following raw materials in parts by weight: 90 parts yttrium-stabilized zirconia powder, 5 parts alumina, 2.5 parts coloring oxide, and 2.5 parts sintering aid.

[0027] The coloring oxide includes at least one of iron oxide, cerium oxide, and praseodymium oxide, and the sintering aid includes at least one of magnesium oxide, calcium oxide, and silicon dioxide.

[0028] Color gradients in materials are achieved through the following methods: 1.0 wt% of a dark-colored oxide was added to the neck edge layer, 0.6 wt% of an intermediate-colored oxide was added to the middle layer, and 0.3 wt% of a light-colored oxide was added to the cut edge layer, with the content of the colored oxide in each layer changing in a gradient.

[0029] The microstructure of the material is characterized as follows: The grain size of the neck layer is 0.4 μm, the grain size of the middle layer is 0.5 μm, and the grain size of the cut end layer is 0.65 μm. The grain size is continuously and gradually distributed between the layers.

[0030] The preparation method of the material includes the following steps: Step 1: Raw material pretreatment, the required zirconium oxide powder for each layer is ball-milled, mixed and dried respectively; Step 2: Slurry preparation, mixing the powders of each layer with binder, plasticizer and solvent to prepare casting slurry; The plasticizer can be dibutyl phthalate, and the solvent can be a mixture of ethanol and butanone, which are commonly used substances in the field. Step 3: Casting and forming, using a multi-layer co-extrusion casting process to prepare a three-layer composite green strip; Step 4: Green body processing, the green body is stamped into a crown blank and glue removal is performed; Step 5: Sintering and shaping, using a segmented sintering process to produce the final product.

[0031] Step three, casting, specifically includes: A three-channel co-extrusion casting device is used, with the viscosity of the neck layer slurry controlled at 3500 cP, the viscosity of the middle layer slurry controlled at 2800 cP, and the viscosity of the cut-end layer slurry controlled at 2200 cP. The casting gap is set to 0.6mm, and the shear rate during the simultaneous extrusion of the three layers of slurry is controlled at 200s⁻¹; The casting speed is adjusted in two stages: initially 0.75 m / min for 45 seconds to allow the slurry to spread, and then increased to 1.75 m / min for steady-state operation. The drying process employs a gradient temperature increase: 40℃ preheating zone, 60%RH for 2.5 min → 55℃ main drying zone, 30%RH for 6.5 min → 60℃ setting zone, 10%RH for 1.5 min. The width of the interlayer transition zone is controlled to be 100μm, and the transition slope angle θ satisfies 15°≤θ≤25°, where the transition slope angle θ is the angle of the interface transition zone formed at the junction of each layer of slurry during the casting process.

[0032] The sintering process in step five is as follows: The first stage involves heating at 4℃ / min to 700℃ and holding for 1.5 hours. The second stage involves heating at 6℃ / min to 1500℃ and holding for 3 hours. The third stage involves annealing after cooling to 900℃ at a rate of 3℃ / min.

[0033] Example 3: A triple gradient zirconia material for dental crown fabrication, the material being a three-layer zirconia ceramic with gradient strength and color characteristics, including a cervical margin layer, an intermediate layer, and an incisal edge layer; The bending strength of the neck layer is 1200 MPa, the bending strength of the intermediate layer is 1100 MPa, and the bending strength of the shear end layer is 670 MPa. The neck edge layer, intermediate layer, and shear edge layer form a continuous transition structure; The overall color gradient of the material covers color numbers A1 to D4, and includes three bleached white transitions; The interfacial bonding strength between the neck layer and the intermediate layer is 28 MPa, and the interfacial bonding strength between the intermediate layer and the shear layer is 24 MPa. The interlayer transition region satisfies the following microstructural characteristics: The grain size gradient change rate is ≤0.15μm / 10μm, where 10μm refers to the distance in the direction perpendicular to the interlayer interface, and the grain size change rate does not exceed 0.15μm for every 10 micrometers of distance. Porosity increases from the neck layer to the shear end layer, with a gradient difference of 1.2 ± 0.3 vol% / 100 μm. 100 μm is a reference distance unit set to quantify the rate of change of porosity gradient, that is, in the direction perpendicular to the interlayer interface, the change in the measured volume fraction of porosity of the material is 1.2% ± 0.3% for every 100 micrometers of distance continuously crossed. The concentration of yttrium oxide stabilizer exhibits a continuous gradient distribution, with a concentration change slope ≤ 0.8 wt% / μm; Microstructure characteristics in the process control steps of material preparation: Grain size gradient control: Grain gradient growth is achieved through a segmented sintering process. In the second stage of sintering, a slow heating rate of 8℃ / min and precise holding time control are used to allow the grains to grow gradually from the neck edge layer to the tangent layer. Due to the higher concentration of yttrium oxide stabilizer in the neck edge layer, excessive grain growth is inhibited. Due to the lower stabilizer content in the tangent layer, the grain size naturally increases. Online monitoring using scanning electron microscopy shows that the grain size change rate is ≤0.15μm / 10μm. The continuous gradual change in grain size eliminates stress abrupt changes at the interlayer interfaces. Porosity gradient control: By differentiating the content of sintering aids in each layer (1.5 parts in the neck edge layer → 3 parts in the cutting edge layer), a porosity gradient is achieved. Magnesium oxide sintering aids promote liquid phase sintering at high temperatures. The higher content of sintering aids in the cutting edge layer results in the retention of more closed pores. In the third stage of sintering, annealing is carried out after controlled cooling to 1000℃ to homogenize the pore distribution. Ultimately, a porosity gradient of 1.2±0.3 vol% / 100μm is achieved from the neck edge layer to the cutting edge layer. The porosity gradient design ensures both the high density of the neck edge region and the micropores of the cutting edge region similar to those of natural teeth. Yttrium oxide concentration gradient formation: During the casting stage, when the three layers of slurry are simultaneously extruded through a three-channel co-extrusion device, the shear rate is controlled at 250 s⁻¹ and the casting speed is initially 1.0 m / min → steady state 2.0 m / min. This allows limited interdiffusion of yttrium oxide in each layer of powder at the interface. During the drying process, the temperature is gradually increased from 40℃ to 55℃ to 60℃, and the humidity is controlled from 60%RH to 10%RH to further stabilize the concentration distribution, ultimately forming a continuous gradient with a concentration change slope ≤ 0.8 wt% / μm. This continuous distribution of yttrium oxide concentration avoids phase transformation cracking caused by sudden changes in stabilizer, allowing the number of cycles in fatigue life testing to exceed 10. 6 Second-rate.

[0034] The thickness ratio of the neck edge layer, intermediate layer, and cut edge layer is 1.4:1:1.0, with the neck edge layer having a thickness of 0.42 mm, the intermediate layer having a thickness of 0.30 mm, and the cut edge layer having a thickness of 0.30 mm.

[0035] The neck layer is made from the following parts by weight of raw materials: 96 parts of yttrium-stabilized zirconia powder, 4 parts of alumina, 1.5 parts of coloring oxide, and 1.5 parts of sintering aid; The intermediate layer is made of the following raw materials in parts by weight: 94 parts yttrium-stabilized zirconia powder, 5 parts alumina, 2 parts coloring oxide, and 2 parts sintering aid; The cut-end layer is made from the following raw materials in parts by weight: 92 parts of yttrium-stabilized zirconia powder, 4-6 parts of alumina, 3 parts of coloring oxide, and 3 parts of sintering aid.

[0036] The coloring oxide includes at least one of iron oxide, cerium oxide, and praseodymium oxide, and the sintering aid includes at least one of magnesium oxide, calcium oxide, and silicon dioxide.

[0037] Color gradients in materials are achieved through the following methods: 1.5 wt% of a dark-colored oxide was added to the neck edge layer, 1.0 wt% of an intermediate-colored oxide was added to the middle layer, and 0.5 wt% of a light-colored oxide was added to the cut edge layer, with the content of the colored oxides in each layer changing in a gradient.

[0038] The microstructure of the material is characterized as follows: The grain size of the neck edge layer is 0.5 μm, the grain size of the middle layer is 0.6 μm, and the grain size of the cut end layer is 0.8 μm. The grain size is continuously and gradually distributed between the layers.

[0039] The preparation method of the material includes the following steps: Step 1: Raw material pretreatment, the required zirconium oxide powder for each layer is ball-milled, mixed and dried respectively; Step 2: Slurry preparation, mixing the powders of each layer with binder, plasticizer and solvent to prepare casting slurry; The plasticizer can be dibutyl phthalate, and the solvent can be a mixture of ethanol and methyl ethyl ketone, which are commonly used substances in the field. Step 3: Casting and forming, using a multi-layer co-extrusion casting process to prepare a three-layer composite green strip; Step 4: Green body processing, the green body is stamped into a crown blank and glue removal is performed; Step 5: Sintering and shaping, using a segmented sintering process to produce the final product.

[0040] Step three, casting, specifically includes: A three-channel co-extrusion casting device was used, with the viscosity of the neck layer slurry controlled at 3700 cP, the viscosity of the middle layer slurry controlled at 2950 cP, and the viscosity of the cut-end layer slurry controlled at 2300 cP. The casting gap is set to 0.8mm, and the shear rate during the simultaneous extrusion of the three layers of slurry is controlled at 250s⁻¹; The casting speed is adjusted in two stages: initially 1.0 m / min for 60 seconds to allow the slurry to spread, then increased to 2.0 m / min for steady-state operation; The drying process uses a gradient temperature increase: 40℃ preheating zone, 60%RH for 3 min → 55℃ main drying zone, 30%RH for 8 min → 60℃ setting zone, 10%RH for 2 min. The width of the interlayer transition zone is controlled at 120μm, and the transition slope angle θ satisfies 15°≤θ≤25°, where the transition slope angle θ is the angle of the interface transition zone formed at the junction of each layer of slurry during the casting process.

[0041] The sintering process in step five is as follows: The first stage involves heating to 800℃ at a rate of 5℃ / min and holding for 2 hours. The second stage involves heating at 8℃ / min to 1550℃ and holding for 4 hours. The third stage involves annealing after cooling to 1000℃ at a rate of 4℃ / min.

[0042] Comparative Example 1 differs from Example 1 in that: this comparative example uses a single formulation with a flexural strength of 1200 MPa, uncolored zirconia powder, without any layered structure design, and adopts conventional dry pressing and sintering to obtain homogeneous materials.

[0043] Comparative Example 2 differs from Example 1 in that it uses the same three-layer gradient powder with strengths of 1200 MPa, 1100 MPa, and 70 MPa as Example 1, but no coloring oxides are added to any of the layers. The same casting process is used. This comparative example is used to verify the effect of simple strength gradient on performance in the absence of color gradient synergy.

[0044] Comparative Example 3 differs from Example 1 in that: this comparative example uses zirconia powder with a flexural strength of 1100 MPa as the matrix, and adds different amounts of coloring oxides to the three layers to achieve a color gradient from the neck edge to the cut end. The same casting process as Example 1 is used. This comparative example is used to verify the effect of simple color gradient on performance in the absence of the synergistic effect of strength gradient.

[0045] Comparative Example 4 differs from Example 1 in that it uses a traditional two-step sintering process to directly heat the temperature to 1500℃ and hold it for 2 hours instead of segmented temperature-controlled sintering.

[0046] The performance of the triple-gradient zirconia materials prepared in Examples 1-3 and Comparative Examples 1-4 was tested. The test items and test methods are as follows: Bending strength test: The local strength of the neck area, middle area and shear end area was measured by the three-point bending method, with a span of 20 mm and a loading speed of 1 mm / min; Color gradient uniformity: The color difference values ​​at 5 sites from the neck to the cut edge of the restoration were measured using a spectrophotometer under a D65 light source, and the average color difference gradient was calculated. Interfacial bonding strength test: The interfacial bonding strength between the neck layer and the intermediate layer, and between the intermediate layer and the cut end layer was determined by tensile shear test; Fatigue life test: Simulate oral chewing cycle, load 50-300N, frequency 2Hz, and record the number of cycles in which the restoration cracks.

[0047] The experimental data comparing the microstructure characteristics of the triple-gradient zirconia materials prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below: The test data of the zirconia materials prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below: By comparing and analyzing the data in the table, it can be seen that the triple gradient zirconia material prepared using the processes in Examples 1-3 has significantly better performance than that in Comparative Examples 1-4. This indicates that by designing a three-layer zirconia structure with strength and color gradients, the present invention enables the dental crown restoration to simultaneously simulate the mechanical properties and aesthetic characteristics of natural teeth. This ensures the mechanical strength requirements of the restoration in areas with high stress while achieving a natural color transition in aesthetically sensitive areas, thus improving the biomimetic performance and clinical applicability of the restoration. By optimizing the multi-layer casting process, a continuous gradient transition between the three layers is achieved, ensuring a tight bond between the interlayer interfaces and a smooth transition of performance. This avoids the stress concentration problem caused by abrupt interface changes in traditional multi-layer materials, improving the reliability and service life of the material. By synergistically controlling the mechanical and aesthetic performance gradients of the material, the restoration meets the strength requirements of the masticatory functional area and the aesthetic requirements of the aesthetic area, achieving a unity of function and aesthetics and improving the overall performance of the dental crown restoration.

[0048] By comparing and analyzing the relevant data in the table, it can be seen that the triple-gradient zirconia material prepared by this invention simultaneously achieves physiological adaptation of mechanical properties, natural simulation of aesthetic transition, and improved service life. This indicates that the triple-gradient zirconia material for dental crown fabrication provided by this invention has a broader market prospect and is more suitable for widespread application.

[0049] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A triple-gradient zirconia material for dental crown fabrication, characterized in that: The material is a three-layer zirconia ceramic with gradient strength and color characteristics, including a neck layer, an intermediate layer and a cut-end layer; The bending strength of the neck edge layer is 1200 MPa, the bending strength of the intermediate layer is 1100 MPa, and the bending strength of the cut end layer is 670 MPa. The neck edge layer, the intermediate layer and the cut end layer have a continuous transition structure; The material's overall color gradient range covers color numbers A1 to D4, and includes three bleached white transitions; The interfacial bonding strength between the neck edge layer and the intermediate layer is 22-28 MPa, and the interfacial bonding strength between the intermediate layer and the cut end layer is 18-24 MPa. The interlayer transition region satisfies the following microstructural characteristics: Grain size gradient change rate ≤ 0.15μm / 10μm; Porosity increases from the neck edge layer to the shear edge layer, with a gradient difference of 1.2 ± 0.3 vol% / 100 μm; The concentration of yttrium oxide stabilizer exhibits a continuous gradient distribution, with a concentration change slope ≤ 0.8 wt% / μm; Microstructure characteristics in the process control steps of material preparation: Grain size gradient control: Grain gradient growth is achieved through a segmented sintering process. In the second stage of sintering, the temperature is held at 1450-1550℃ for 2-4 hours. A slow heating rate of 5-8℃ / min and precise holding time control are used. The grains gradually grow from the neck edge layer to the cut end layer. Due to the higher concentration of yttrium oxide stabilizer in the neck edge layer, excessive grain growth is inhibited. Due to the lower stabilizer content in the cut end layer, the grain size naturally increases. The grain size change rate is ≤0.15μm / 10μm as monitored online by scanning electron microscopy. Porosity gradient control: By differentiating the content of sintering aids in each layer, 0.5-1.5 parts in the neck edge layer → 2-3 parts in the cut end layer, a porosity gradient is achieved. Magnesium oxide sintering aids promote liquid phase sintering at high temperatures. The higher content of sintering aids in the cut end layer results in more closed pores being retained. In the third stage of sintering, annealing is carried out after controlling the temperature to 800-1000℃ to homogenize the pore distribution and achieve a porosity gradient of 1.2±0.3 vol% / 100μm from the neck edge layer to the cut end layer. Yttrium oxide concentration gradient formation: During the casting stage, when the three layers of slurry are extruded simultaneously through a three-channel co-extrusion device, the shear rate is controlled at 150-250 s⁻¹ and the casting speed is initially 0.5-1.0 m / min → steady state 1.5-2.0 m / min. Limited interdiffusion of yttrium oxide in each layer of powder occurs at the interface. During the drying process, the temperature gradient is increased from 40℃ to 55℃ to 60℃ and the humidity is controlled from 60%RH to 10%RH to stabilize the concentration distribution and form a continuous gradient with a concentration change slope ≤0.8wt% / μm.

2. The triple-gradient zirconia material for dental crown fabrication according to claim 1, characterized in that: The thickness ratio of the neck edge layer, the intermediate layer, and the cut-end layer is 1.2-1.5:1:0.8-1.2, wherein the thickness of the neck edge layer is 0.4-0.6 mm, the thickness of the intermediate layer is 0.3-0.5 mm, and the thickness of the cut-end layer is 0.3-0.5 mm.

3. The triple-gradient zirconia material for dental crown fabrication according to claim 1, characterized in that: The neck edge layer is made from the following parts by weight of raw materials: The mixture contains 92-96 parts of yttrium-stabilized zirconia powder, 2-4 parts of alumina, 0.5-1.5 parts of coloring oxide, and 0.5-1.5 parts of sintering aid. The intermediate layer is made of the following raw materials in parts by weight: 90-94 parts of yttrium-stabilized zirconium oxide powder, 3-5 parts of alumina, 1-2 parts of coloring oxide, and 1-2 parts of sintering aid; The cut-end layer is made from the following raw materials in parts by weight: 88-92 parts of yttrium-stabilized zirconia powder, 4-6 parts of alumina, 2-3 parts of coloring oxide, and 2-3 parts of sintering aid.

4. The triple-gradient zirconia material for dental crown fabrication according to claim 3, characterized in that: The coloring oxide includes at least one of iron oxide, cerium oxide, and praseodymium oxide, and the sintering aid includes at least one of magnesium oxide, calcium oxide, and silicon dioxide.

5. The triple-gradient zirconia material for dental crown fabrication according to claim 1, characterized in that: The color gradient of the material is achieved through the following method: 0.5-1.5 wt% of dark-colored oxide is added to the neck edge layer, 0.3-1.0 wt% of intermediate-colored oxide is added to the middle layer, and 0.1-0.5 wt% of light-colored oxide is added to the cut edge layer, with the content of colored oxides in each layer varying in a gradient.

6. The triple-gradient zirconia material for dental crown fabrication according to claim 1, characterized in that: The microstructure of the material is characterized as follows: The grain size of the neck edge layer is 0.3-0.5 μm, the grain size of the middle layer is 0.4-0.6 μm, and the grain size of the cut end layer is 0.5-0.8 μm, and the grain size shows a continuous and gradual distribution between the layers.

7. The triple-gradient zirconia material for dental crown fabrication according to claim 1, characterized in that: The preparation method of the material includes the following steps: Step 1: Raw material pretreatment, the required zirconium oxide powder for each layer is ball-milled, mixed and dried respectively; Step 2: Slurry preparation, mixing the powders of each layer with binder, plasticizer and solvent to prepare casting slurry; Step 3: Casting and forming, using a multi-layer co-extrusion casting process to prepare a three-layer composite green strip; Step 4: Green body processing, the green body is stamped into a crown blank and glue removal is performed; Step 5: Sintering and shaping, using a segmented sintering process to produce the final product.

8. The triple-gradient zirconia material for dental crown fabrication according to claim 7, characterized in that: Step three, the casting process, specifically includes: A three-channel co-extrusion casting device was used, with the viscosity of the neck layer slurry controlled at 3500±200cP, the viscosity of the middle layer slurry controlled at 2800±150cP, and the viscosity of the cut-end layer slurry controlled at 2200±100cP. The casting gap is set to 0.5-0.8mm, and the shear rate during the simultaneous extrusion of the three layers of slurry is controlled at 150-250s⁻¹; The casting speed is adjusted in two stages: initially 0.5-1.0 m / min for 30-60 seconds to allow the slurry to spread, then increased to 1.5-2.0 m / min for steady-state operation; The drying process uses a gradient temperature increase: 40℃ preheating zone, 60%RH for 2-3 minutes → 55℃ main drying zone, 30%RH for 5-8 minutes → 60℃ setting zone, 10%RH for 1-2 minutes. The width of the interlayer transition zone is controlled to be 80-120μm, and the transition slope angle θ satisfies 15°≤θ≤25°.

9. A triple-gradient zirconia material for dental crown fabrication according to claim 7, characterized in that: The sintering process in step five is as follows: The first stage involves raising the temperature to 600-800℃ at a rate of 3-5℃ / min and holding it for 1-2 hours. The second stage involves raising the temperature to 1450-1550℃ at a rate of 5-8℃ / min and holding it for 2-4 hours. The third stage involves annealing after cooling to 800-1000℃ at a rate of 2-4℃ / min.

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