A triple graded zirconia material for crown fabrication

Abstract

The present application relates to the technical field of dental material, and discloses a triple gradient zirconia material for crown production, which is a three-layer structure zirconia ceramic with strength gradient and color gradient characteristics, comprising a cervical margin layer, an intermediate layer and a cutting end layer, the bending strength of the cervical margin layer is 1200MPa, the bending strength of the intermediate layer is 1100MPa, and the bending strength of the cutting end layer is 670MPa, and the cervical margin layer, the intermediate layer and the cutting end layer are continuously transitioned, the overall color gradient range of the material covers A1 to D4 color numbers and contains three bleaching color transitions; through the design of the three-layer zirconia structure with strength gradient and color gradient, the crown restoration can simultaneously simulate the mechanical properties and aesthetic characteristics of natural teeth, ensure the mechanical strength requirement of the restoration in the area with larger stress, and realize the natural color transition in the aesthetic sensitive area.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dental materials, in particular to a triple gradient zirconia material for crown manufacturing. BACKGROUND

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

[0003] In the existing field of dental zirconia materials, the commercially available products generally use single strength design. When applied to crown manufacturing, it cannot adapt to the gradient distribution of the mechanical properties of natural teeth. Using high-strength zirconia in the incisal edge area may cause abnormal wear of the natural teeth. At the same time, single strength material cannot balance the high strength requirement of the bridge connection area and the physiological stress matching characteristics of the occlusal surface, which limits the bionic effect and long-term stability of the restoration. In addition, although pre-dyed zirconia can achieve basic color transition, it lacks a gradient mechanism that coordinates with the mechanical properties. When the restoration is subjected to functional load and aesthetic requirements at the same time, the non-coordination of strength and color change may cause local stress concentration and aesthetic distortion of the restoration, ultimately affecting the comprehensive clinical effect of crown restoration.

[0004] Therefore, the present application proposes a triple gradient zirconia material for crown manufacturing to solve the above problems. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a triple gradient zirconia material for crown manufacturing, which solves the problem that the material cannot balance the high strength requirement of the bridge connection area and the physiological stress matching characteristics of the occlusal surface, which limits the bionic effect and long-term stability of the restoration. The local stress concentration and aesthetic distortion of the restoration ultimately affect the comprehensive clinical effect of crown restoration.

[0006] To achieve the above purpose, the present application provides the following technical solution: a triple gradient zirconia material for crown manufacturing, the material is a three-layer structure zirconia ceramic with strength and color gradient characteristics, including a neck margin layer, an intermediate layer and an incisal edge layer.

[0007] The bending strength of the neck margin layer is 1200MPa, the bending strength of the intermediate layer is 1100MPa, and the bending strength of the incisal edge layer is 670MPa.

[0008] The neck edge layer, the intermediate layer and the incisal layer are continuously transitioned;

[0009] The whole color gradient range of the material covers A1 to D4 color numbers, and contains three bleached color transitions;

[0010] The interface bonding strength between the neck edge layer and the intermediate layer is 22-28 MPa, and the interface bonding strength between the intermediate layer and the incisal layer is 18-24 MPa;

[0011] The interlayer transition area meets the following microstructure characteristics:

[0012] The grain size gradient change rate is ≤0.15 μm / 10 μm;

[0013] The porosity increases from the neck edge layer to the incisal layer, and the gradient difference is 1.2±0.3 vol% / 100 μm;

[0014] The yttrium oxide stabilizer concentration is continuously gradient distributed, and the concentration change slope is ≤0.8 wt% / μm;

[0015] The microstructure characteristics in the process control steps in the material preparation process:

[0016] Grain size gradient control: through the segmented sintering process to realize the gradient growth of the grain, in the second sintering stage 1450-1550℃, the slow heating rate 5-8℃ / min and the accurate holding time control are adopted, the grain gradually grows from the neck edge layer to the incisal layer, the neck edge layer inhibits the excessive growth of the grain due to the higher yttrium oxide stabilizer concentration, the incisal layer naturally increases the grain size due to the lower stabilizer content, through the online monitoring of the scanning electron microscope, the grain size change rate is ≤0.15 μm / 10 μm;

[0017] Porosity gradient regulation: through the differential design of the sintering aid content of each layer, 0.5-1.5 parts of the neck edge layer→2-3 parts of the incisal layer, the porosity gradient is realized, the magnesium oxide sintering aid promotes liquid phase sintering at high temperature, the higher content of the sintering aid in the incisal layer leads to more closed pores remaining, the third sintering stage adopts the annealing after the controlled cooling to 800-1000℃, the pore distribution is homogenized, and the porosity increases from the neck edge layer to the incisal layer by 1.2±0.3 vol% / 100 μm of the gradient;

[0018] Yttria concentration gradient formation: during the tape casting stage, by controlling the shear rate 150-250 s⁻¹ and the casting speed 0.5-1.0 m / min→1.5-2.0 m / min, the yttria in each layer of powder diffuses at the interface, and the gradient temperature is controlled at 40℃→55℃→60℃ and the humidity is controlled at 60%RH→10%RH during the drying process, so as to stabilize the concentration distribution and form a continuous gradient with a concentration change slope of ≤0.8wt% / μm.

[0019] Preferably, the thickness ratio of the neck rim layer, the intermediate layer and the incisal layer is 1.2-1.5:1:0.8-1.2, wherein the thickness of the neck rim layer is 0.4-0.6 mm, the thickness of the intermediate layer is 0.3-0.5 mm, and the thickness of the incisal layer is 0.3-0.5 mm.

[0020] Preferably, the neck rim layer is made of the following raw materials by weight:

[0021] Yttria stabilized zirconia powder 92-96 parts, aluminum oxide 2-4 parts, coloring oxide 0.5-1.5 parts, sintering aid 0.5-1.5 parts;

[0022] The intermediate layer is made of the following raw materials by weight: yttria stabilized zirconia powder 90-94 parts, aluminum oxide 3-5 parts, coloring oxide 1-2 parts, sintering aid 1-2 parts;

[0023] The incisal layer is made of the following raw materials by weight: yttria stabilized zirconia powder 88-92 parts, aluminum oxide 4-6 parts, coloring oxide 2-3 parts, sintering aid 2-3 parts;

[0024] 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.

[0025] Preferably, the color gradient of the material is achieved by the following method:

[0026] 0.5-1.5wt% of dark coloring oxide is added to the neck rim layer, 0.3-1.0wt% of intermediate coloring oxide is added to the intermediate layer, and 0.1-0.5wt% of light coloring oxide is added to the incisal layer, and the coloring oxide content in each layer changes in a gradient.

[0027] Preferably, the microstructure of the material is as follows:

[0028] The grain size of the neck rim layer is 0.3-0.5μm, the grain size of the intermediate layer is 0.4-0.6μm, and the grain size of the incisal layer is 0.5-0.8μm, and the grain size is continuously and gradually distributed between the layers.

[0029] Preferably, the method for preparing the material comprises the following steps:

[0030] Step one: raw material pretreatment, the required zirconia powder of each layer is respectively ball-mixed and dried;

[0031] Step two: slurry preparation, the powder of each layer is mixed with a binder, a plasticizer and a solvent to prepare a casting slurry;

[0032] Step three: casting forming, a three-layer composite green tape is prepared by using a multi-layer co-extrusion casting process;

[0033] Step four: green tape processing, the green tape is punched into a crown embryo and is subjected to degreasing treatment;

[0034] Step five: sintering forming, the final product is prepared by using a segmented sintering process.

[0035] Preferably, the step three of casting forming specifically comprises:

[0036] A three-channel co-extrusion casting device is used, the viscosity of the neck edge layer slurry is controlled at 3500±200 cP, the viscosity of the middle layer slurry is controlled at 2800±150 cP, and the viscosity of the incision end layer slurry is controlled at 2200±100 cP;

[0037] The casting gap is set to 0.5-0.8 mm, and the shear rate when the three layers of slurry are synchronously extruded is controlled at 150-250 s⁻¹;

[0038] The casting speed is adjusted in two stages: the initial stage is 0.5-1.0 m / min for 30-60 seconds to spread the slurry, and then it is increased to 1.5-2.0 m / min for steady operation;

[0039] The drying process adopts gradient heating: 40°C preheating zone, humidity 60%RH for 2-3 min→55°C main drying zone, humidity 30%RH for 5-8 min→60°C shaping zone, humidity 10%RH for 1-2 min;

[0040] The width of the interlayer transition zone is controlled at 80-120 μm, and the transition slope angle θ satisfies 15°≤θ≤25°.

[0041] Preferably, the sintering process in step five is:

[0042] The first stage is to increase the temperature to 600-800°C at a rate of 3-5°C / min and keep it for 1-2 h;

[0043] The second stage is to increase the temperature to 1450-1550°C at a rate of 5-8°C / min and keep it for 2-4 h;

[0044] The third stage is annealing treatment after decreasing to 800-1000℃ at 2-4℃ / min.

[0045] Advantages

[0046] Compared with the prior art, the present application provides a triple gradient zirconia material for crown manufacturing, which has the following advantages:

[0047] 1. In the present application, by designing a three-layer zirconia structure with strength gradient and color gradient, the crown restoration can simulate the mechanical properties and aesthetic characteristics of natural teeth, ensuring the mechanical strength requirements in areas with high stress and achieving natural color transition in aesthetic sensitive areas, thereby improving the bionic performance and clinical applicability of the restoration.

[0048] 2. In the present application, by optimizing the multi-layer flow casting process, continuous gradient transition between the three layers is achieved, ensuring the close bonding of the interlayer interface and the smooth transition of the performance, avoiding the stress concentration problem caused by the interface mutation of traditional multi-layer materials, and improving the reliability and service life of the material.

[0049] 3. In the present application, by synergistically controlling the mechanical property gradient and aesthetic property gradient of the material, the restoration meets the strength requirements of the mastication function area and the aesthetic requirements of the aesthetic area, realizing the unity of function and aesthetics, and improving the comprehensive performance of the crown restoration. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0051] Embodiment 1: A triple gradient zirconia material for crown manufacturing, the material is a three-layer structure zirconia ceramic with strength gradient and color gradient characteristics, including a neck rim layer, an intermediate layer and a cutting end layer.

[0052] The bending strength of the neck rim layer is 1200MPa, the bending strength of the intermediate layer is 1100MPa, and the bending strength of the cutting end layer is 670MPa.

[0053] The neck rim layer, the intermediate layer and the cutting end layer are continuously transitioned;

[0054] The overall color gradient range of the material covers A1 to D4 color numbers, and includes three bleached color transitions.

[0055] The interfacial bonding strength between the neck margin layer and the intermediate layer is 22 MPa, and the interfacial bonding strength between the intermediate layer and the incisal layer is 18 MPa;

[0056] The interlayer transition region satisfies the following microstructure characteristics:

[0057] The grain size gradient change rate is ≤0.15 μm / 10 μm, wherein 10 μm refers to a distance in a direction perpendicular to the interlayer interface, and the grain size change rate does not exceed 0.15 μm per 10 microns of distance;

[0058] The porosity increases from the neck margin layer to the incisal layer, and the gradient difference is 1.2±0.3 vol% / 100 μm, 100 μm: a reference distance unit set for quantifying the porosity gradient change rate, that is, the change amount of the porosity volume fraction of the material is 1.2%±0.3% per 100 microns of distance continuously crossed in the direction perpendicular to the interlayer interface;

[0059] The yttrium oxide stabilizer concentration is continuously gradient distributed, and the concentration change slope is ≤0.8 wt% / μm;

[0060] The microstructure characteristics in the process control step in the material preparation process:

[0061] Grain size gradient control: the gradual growth of grains is realized by a segmented sintering process, a slow heating rate of 5 ℃ / min and an accurate holding time control are adopted in the second sintering stage at 1450 ℃ for 2 h, so that the grains gradually grow from the neck margin layer to the incisal layer, the neck margin layer inhibits excessive grain growth due to the higher yttrium oxide stabilizer concentration, and the incisal layer naturally increases in grain size due to the lower stabilizer content, the grain size change rate is ≤0.15 μm / 10 μm through online monitoring by a scanning electron microscope; the continuous gradual change of the grain size eliminates the stress mutation at the interlayer interface;

[0062] Porosity gradient regulation: the difference in the content of sintering aids in each layer is designed, 0.5 parts in the neck margin layer→2 parts in the incisal layer, to realize the porosity gradient, magnesium oxide sintering aid promotes liquid phase sintering at high temperature, and the higher content of sintering aid in the incisal layer leads to more closed pores remaining, annealing after controlled cooling to 800 ℃ in the third sintering stage makes the pore distribution uniform, and finally realizes the porosity gradient of 1.2±0.3 vol% / 100 μm from the neck margin layer to the incisal layer; the porosity gradient design not only ensures the high density of the neck margin area, but also makes the incisal area have similar micro-pores to natural teeth;

[0063] Yttria concentration gradient formation: during the stage of tape casting, by controlling the shear rate 150 s-1 and the casting speed 0.5 m / min initially→1.5 m / min stably, the limited interdiffusion of yttria in the interface of each layer of powder occurs when three layers of slurry are extruded synchronously by a three-channel co-extrusion device, and the concentration distribution is further stabilized by gradient temperature rising 40℃→55℃→60℃ and humidity control 60%RH→10%RH during the drying process, and finally a continuous gradient with a concentration change slope ≤0.8wt% / μm is formed; the continuous distribution of yttria concentration avoids the phase transition cracking caused by the sudden change of stabilizer, so that the cycle number in the fatigue life test exceeds 10 6 times.

[0064] The thickness ratio of the neck edge layer, the intermediate layer and the incisal layer is 1.2:1:0.8, wherein the thickness of the neck edge layer is 0.48 mm, the thickness of the intermediate layer is 0.40 mm, and the thickness of the incisal layer is 0.32 mm.

[0065] The neck edge layer is made of the following raw materials by weight:

[0066] Yttria stabilized zirconia powder 92 parts, aluminum oxide 2 parts, coloring oxide 0.5 parts, sintering aid 0.5 parts;

[0067] The intermediate layer is made of the following raw materials by weight: yttria stabilized zirconia powder 90 parts, aluminum oxide 3 parts, coloring oxide 1 part, sintering aid 1 part;

[0068] The incisal layer is made of the following raw materials by weight: yttria stabilized zirconia powder 88 parts, aluminum oxide 4 parts, coloring oxide 2 parts, sintering aid 2 parts;

[0069] 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.

[0070] The color gradient of the material is realized by the following method:

[0071] 0.5wt% of dark coloring oxide is added in the neck edge layer, 0.3wt% of intermediate color coloring oxide is added in the intermediate layer, and 0.1wt% of light coloring oxide is added in the incisal layer, and the coloring oxide content in each layer changes in a gradient.

[0072] The microstructure of the material is as follows:

[0073] The grain size of the neck edge layer is 0.3μm, the grain size of the intermediate layer is 0.4μm, and the grain size of the incisal layer is 0.5μm, and the grain size is continuously and gradually distributed between the layers.

[0074] The preparation method of the material includes the following steps:

[0075] Step one: raw material pretreatment, the required zirconia powder of each layer is mixed by ball milling and dried respectively;

[0076] Step two: slurry preparation, the powder of each layer is mixed with binder, plasticizer and solvent to prepare casting slurry;

[0077] The plasticizer can be dibutyl phthalate, and the solvent can be a commonly used substance in the field of mixed solvents of ethanol and butanone;

[0078] Step three: casting forming, a three-layer composite green tape is prepared by using a multi-layer co-extrusion casting process;

[0079] Step four: green body treatment, the green tape is punched into a crown embryo and subjected to degreasing treatment;

[0080] Step five: sintering forming, the final product is prepared by using a segmented sintering process.

[0081] The casting forming in step three specifically includes:

[0082] A three-channel co-extrusion casting device is used, the neck edge layer slurry viscosity is controlled at 3300 cP, the middle layer slurry viscosity is controlled at 2650 cP, and the cutting end layer slurry viscosity is controlled at 2100 cP;

[0083] The casting gap is set to 0.5 mm, and the shear rate of the three-layer slurry is controlled at 150 s⁻¹ when extruded synchronously;

[0084] The casting speed is adjusted in two stages: the initial stage is 0.5 m / min for 30 seconds to spread the slurry, and then increased to 1.5 m / min for steady operation;

[0085] The drying process adopts gradient heating: 40℃ preheating zone, humidity 60%RH for 2min→55℃ main drying zone, humidity 30%RH for 5min→60℃ shaping zone, humidity 10%RH for 1min;

[0086] The width of the interlayer transition zone is controlled to be 80μm, and the transition slope angle θ satisfies 15°≤θ≤25°, wherein the transition slope angle θ is the angle of the interface transition zone formed by the slurry of each layer at the intersection during the casting forming process.

[0087] The sintering process in step five is:

[0088] The first stage is to increase the temperature to 600℃ at a rate of 3℃ / min and keep it for 1h;

[0089] The second stage is to increase the temperature to 1450℃ at a rate of 5℃ / min and keep it for 2h;

[0090] The third stage is to decrease the temperature to 800℃ at a rate of 2℃ / min and then perform annealing treatment.

[0091] Embodiment 2: A triple gradient zirconia material for crown fabrication, the material is a three-layer structure zirconia ceramic with strength and color gradient characteristics, including a cervical margin layer, an intermediate layer and a cutting end layer;

[0092] The bending strength of the cervical margin layer is 1200 MPa, the bending strength of the intermediate layer is 1100 MPa, and the bending strength of the cutting end layer is 670 MPa;

[0093] The cervical margin layer, the intermediate layer and the cutting end layer are continuously transitioned between them;

[0094] The overall color gradient range of the material covers A1 to D4 color numbers, and contains three bleached color transitions;

[0095] The interfacial bonding strength between the cervical margin layer and the intermediate layer is 25 MPa, and the interfacial bonding strength between the intermediate layer and the cutting end layer is 21 MPa;

[0096] The interlayer transition area meets the following microstructure characteristics:

[0097] The grain size gradient change rate is ≤0.15 μm / 10 μm, wherein 10 μm refers to the distance in the direction perpendicular to the interlayer interface, and the grain size change rate is not more than 0.15 μm per 10 microns;

[0098] The porosity increases from the cervical margin layer to the cutting end layer, and the gradient difference is 1.2±0.3 vol% / 100 μm, 100 μm: a reference distance unit set for quantifying the porosity gradient change rate, that is, the change amount of the porosity volume fraction of the material is 1.2%±0.3% per 100 microns in the direction perpendicular to the interlayer interface;

[0099] The yttrium oxide stabilizer concentration is continuously gradient distributed, and the concentration change slope is ≤0.8 wt% / μm;

[0100] The microstructure characteristics in the process control step in the material preparation process:

[0101] Grain size gradient control: through the segmented sintering process, the grain size gradually grows from the cervical margin layer to the cutting end layer, the cervical margin layer inhibits the excessive growth of the grain size due to the higher yttrium oxide stabilizer concentration, the cutting end layer naturally increases the grain size due to the lower stabilizer content, the grain size change rate is ≤0.15 μm / 10 μm through online monitoring by a scanning electron microscope; The continuous gradient of the grain size eliminates the stress mutation at the interlayer interface;

[0102] Pore ratio gradient control: through the differentiated design of the sintering aid content of each layer, 1.0 parts of the neck edge layer → 2.5 parts of the incisal edge layer, the pore ratio gradient is realized, and the magnesium oxide sintering aid promotes liquid phase sintering at high temperature. The higher content of sintering aid in the incisal edge layer leads to more closed pores remaining. The third stage of sintering adopts annealing after controlled cooling to 900°C, which makes the pore distribution homogenized, and finally realizes the gradient of 1.2±0.3vol% / 100μm from the neck edge layer to the incisal edge layer. The pore ratio gradient design not only ensures the high density of the neck edge area, but also makes the incisal edge area have similar micro-pores to natural teeth.

[0103] Yttrium oxide concentration gradient formation: during the casting forming stage, by controlling the shear rate 200s⁻¹ and the casting speed initial 0.75m / min→ steady 1.75m / min when the three-layer slurry is extruded synchronously by the three-channel co-extrusion device, the yttrium oxide in each layer of powder diffuses limitedly at the interface. During the drying process, the gradient temperature is controlled at 40℃→55℃→60℃ and the humidity is controlled at 60%RH→10%RH, which further stabilizes the concentration distribution, and finally forms a continuous gradient with a concentration change slope ≤0.8wt% / μm. The continuous distribution of yttrium oxide concentration avoids the phase transition cracking caused by the sudden change of stabilizer, so that the cycle number in the fatigue life test exceeds 10 6 times.

[0104] The thickness ratio of the neck edge layer, the intermediate layer and the incisal edge layer is 1.5:1:1.0, wherein the thickness of the neck edge layer is 0.6mm, the thickness of the intermediate layer is 0.4mm, and the thickness of the incisal edge layer is 0.4mm.

[0105] The neck edge layer is made of the following raw materials by weight parts:

[0106] Yttrium oxide stabilized zirconia powder 94 parts, aluminum oxide 3 parts, coloring oxide 1.0 part, sintering aid 1.0 part;

[0107] The intermediate layer is made of the following raw materials by weight parts: yttrium oxide stabilized zirconia powder 92 parts, aluminum oxide 4 parts, coloring oxide 1.5 parts, sintering aid 1.5 parts;

[0108] The incisal edge layer is made of the following raw materials by weight parts: yttrium oxide stabilized zirconia powder 90 parts, aluminum oxide 5 parts, coloring oxide 2.5 parts, sintering aid 2.5 parts.

[0109] The coloring oxide includes at least one of iron oxide, cerium oxide, praseodymium oxide, and the sintering aid includes at least one of magnesium oxide, calcium oxide and silicon dioxide.

[0110] The color gradient of the material is realized by the following method:

[0111] 1.0wt% of dark color coloring oxides are added in the cervical margin layer, 0.6wt% of intermediate color coloring oxides are added in the intermediate layer, 0.3wt% of light color coloring oxides are added in the incisal layer, and the coloring oxide content in each layer is gradiently changed.

[0112] The microstructure of the material is shown as follows:

[0113] The grain size of the cervical margin layer is 0.4μm, the grain size of the intermediate layer is 0.5μm, the grain size of the incisal layer is 0.65μm, and the grain size is continuously and gradually distributed between layers.

[0114] The preparation method of the material comprises the following steps:

[0115] Step one: raw material pretreatment, the zirconia powder required by each layer is respectively ball-mixed and dried;

[0116] Step two: slurry preparation, the powder of each layer is mixed with a binder, a plasticizer and a solvent to prepare a casting slurry;

[0117] The plasticizer can be dibutyl phthalate, and the solvent can be a commonly used substance in the field of mixed solvents of ethanol and butanone;

[0118] Step three: casting forming, a three-layer composite green strip is prepared by using a multi-layer co-extrusion casting process;

[0119] Step four: green body treatment, the green strip is punched into a crown embryo and is subjected to degreasing treatment;

[0120] Step five: sintering forming, the final product is prepared by using a segmented sintering process.

[0121] The casting forming in step three specifically comprises:

[0122] A three-channel co-extrusion casting device is used, the viscosity of the cervical margin layer slurry is controlled at 3500cP, the viscosity of the intermediate layer slurry is controlled at 2800cP, and the viscosity of the incisal layer slurry is controlled at 2200cP;

[0123] The casting gap is set to 0.6mm, and the shear rate when the three-layer slurry is synchronously extruded is controlled at 200s⁻¹;

[0124] The casting speed is adjusted in two stages: the initial stage is 0.75m / min for 45 seconds to spread the slurry, and then it is increased to 1.75m / min for steady operation;

[0125] The drying process adopts gradient heating: 40℃ preheating zone, humidity 60%RH for 2.5min→55℃ main drying zone, humidity 30%RH for 6.5min→60℃ setting zone, humidity 10%RH for 1.5min;

[0126] The interlayer transition zone width is controlled to be 100 μm, and the transition slope angle θ satisfies 15°≤θ≤25°, wherein the transition slope angle θ is the angle of the interface transition zone formed by the intersection of the slurry of each layer during the casting process.

[0127] The sintering process in step five is as follows:

[0128] The first stage is to increase the temperature to 700℃ at a rate of 4℃ / min and keep it for 1.5h;

[0129] The second stage is to increase the temperature to 1500℃ at a rate of 6℃ / min and keep it for 3h;

[0130] The third stage is to decrease the temperature to 900℃ at a rate of 3℃ / min and then perform annealing treatment.

[0131] Example 3: A triple gradient zirconia material for crown manufacturing, the material is a three-layer structure zirconia ceramic with strength gradient and color gradient characteristics, including a neck margin layer, an intermediate layer, and a cutting end layer;

[0132] The bending strength of the neck margin layer is 1200MPa, the bending strength of the intermediate layer is 1100MPa, and the bending strength of the cutting end layer is 670MPa;

[0133] The neck margin layer, the intermediate layer, and the cutting end layer are continuously transitioned;

[0134] The overall color gradient range of the material covers A1 to D4 color numbers, and contains three bleached color transitions;

[0135] The interfacial bonding strength between the neck margin layer and the intermediate layer is 28MPa, and the interfacial bonding strength between the intermediate layer and the cutting end layer is 24MPa;

[0136] The interlayer transition region satisfies the following microstructure characteristics:

[0137] The grain size gradient change rate is ≤0.15 μm / 10 μm, wherein 10 μm refers to the distance in the direction perpendicular to the interlayer interface, and the grain size change rate does not exceed 0.15 μm for every 10 microns of distance;

[0138] The porosity increases from the neck margin layer to the cutting end layer, with a gradient difference of 1.2±0.3 vol% / 100 μm, 100 μm: a reference distance unit set for quantifying the porosity gradient change rate, i.e. the change in the volume fraction of the material's porosity measured for every 100 microns of distance continuously crossed in the direction perpendicular to the interlayer interface is 1.2%±0.3%;

[0139] The yttrium oxide stabilizer concentration is continuously gradient distributed, with a concentration change slope ≤0.8 wt% / μm;

[0140] Microstructure features in process control steps during material preparation:

[0141] Grain size gradient control: Gradient growth of grains is achieved by a segmented sintering process. In the second sintering stage at 1550°C for 4h, a slow heating rate of 8°C / min and precise holding time control are used to make the grains gradually grow from the neck layer to the incisal layer. The neck layer has a higher yttria stabilizer concentration, which inhibits excessive grain growth. The incisal layer has a lower stabilizer content, and the grain size naturally increases. Through online monitoring by a scanning electron microscope, the grain size change rate is ≤0.15 μm / 10 μm. The continuous and gradual change in grain size eliminates the stress discontinuity at the interface between the layers.

[0142] Pore rate gradient control: By differentiating the content of sintering aids in each layer, 1.5 parts in the neck layer and 3 parts in the incisal layer, a pore rate gradient is achieved. Magnesium oxide sintering aids promote liquid phase sintering at high temperatures, and the higher content of sintering aids in the incisal layer results in more closed pores being retained. In the third sintering stage, annealing is performed after controlled cooling to 1000°C, which makes the pore distribution uniform. Finally, a gradient of 1.2±0.3 vol% / 100 μm is achieved from the neck layer to the incisal layer. The pore rate gradient design not only ensures the high density of the neck area but also makes the incisal area have similar micro-porosity to natural teeth.

[0143] Yttria concentration gradient formation: During the casting process, by synchronously extruding three layers of slurry through a three-channel co-extrusion device, the shear rate is controlled at 250 s⁻¹ and the casting speed is initially controlled at 1.0 m / min and then stabilized at 2.0 m / min. This causes the yttria in the powder of each layer to undergo limited interdiffusion at the interface. During the drying process, the temperature is gradually increased from 40°C to 55°C to 60°C, and the humidity is controlled from 60% RH to 10% RH, which further stabilizes the concentration distribution. Finally, a continuous gradient with a concentration change slope of ≤0.8 wt% / μm is formed. The continuous distribution of yttria concentration avoids phase transformation cracking caused by sudden changes in the stabilizer, and the number of cycles in the fatigue life test exceeds 10 6 times.

[0144] The thickness ratio of the neck layer, the intermediate layer, and the incisal layer is 1.4:1:1.0, wherein the thickness of the neck layer is 0.42 mm, the thickness of the intermediate layer is 0.30 mm, and the thickness of the incisal layer is 0.30 mm.

[0145] The neck layer is made from the following raw materials by weight parts:

[0146] 96 parts of yttria-stabilized zirconia powder, 4 parts of aluminum oxide, 1.5 parts of coloring oxide, and 1.5 parts of sintering aid;

[0147] The intermediate layer is made from the following raw materials by weight parts: 94 parts of yttria-stabilized zirconia powder, 5 parts of aluminum oxide, 2 parts of coloring oxide, and 2 parts of sintering aid;

[0148] The chamfer layer is made of the following raw materials by weight: yttria-stabilized zirconia powder 92 parts, alumina 4-6 parts, coloring oxide 3 parts, sintering aid 3 parts.

[0149] The coloring oxide includes at least one of iron oxide, cerium oxide, praseodymium oxide, and the sintering aid includes at least one of magnesium oxide, calcium oxide, and silicon dioxide.

[0150] The color gradient of the material is achieved by the following method:

[0151] 1.5wt% of dark coloring oxide is added to the neck margin layer, 1.0wt% of intermediate coloring oxide is added to the intermediate layer, and 0.5wt% of light coloring oxide is added to the chamfer layer, and the coloring oxide content in each layer changes in a gradient.

[0152] The microstructure of the material is as follows:

[0153] The grain size of the neck margin layer is 0.5μm, the grain size of the intermediate layer is 0.6μm, the grain size of the chamfer layer is 0.8μm, and the grain size is continuously and gradually distributed between the layers.

[0154] The method for preparing the material includes the following steps:

[0155] Step one: raw material pretreatment, the zirconia powder required for each layer is ball-mixed and dried respectively;

[0156] Step two: slurry preparation, the powder of each layer is mixed with a binder, a plasticizer, and a solvent to prepare a casting slurry;

[0157] The plasticizer can be dibutyl phthalate, and the solvent can be a commonly used substance in the field of mixed solvents of ethanol and butanone;

[0158] Step three: casting forming, a three-layer composite green tape is prepared by using a multi-layer co-extrusion casting process;

[0159] Step four: green tape processing, the green tape is punched into a crown embryo and subjected to degreasing treatment;

[0160] Step five: sintering forming, the final product is prepared by using a segmented sintering process.

[0161] The casting forming in step three specifically includes:

[0162] A three-channel co-extrusion casting device is used, the viscosity of the neck margin layer slurry is controlled at 3700cP, the viscosity of the intermediate layer slurry is controlled at 2950cP, and the viscosity of the chamfer layer slurry is controlled at 2300cP;

[0163] The casting gap is set to 0.8mm, and the shear rate when the three layers of slurry are synchronously extruded is controlled at 250s⁻¹;

[0164] The casting speed was adjusted in two stages: the initial stage was 1.0 m / min for 60 seconds to spread the slurry, and then increased to 2.0 m / min for steady operation.

[0165] The drying process adopted gradient temperature: 40℃ preheating zone, humidity 60%RH for 3min→55℃ main drying zone, humidity 30%RH for 8min→60℃ setting zone, humidity 10%RH for 2min.

[0166] The width of the interlayer transition zone was controlled to be 120μm, and the transition slope angle θ satisfied 15°≤θ≤25°, wherein the transition slope angle θ was the angle of the interface transition zone formed by the slurry of each layer at the intersection in the casting process.

[0167] The sintering process in step five was as follows:

[0168] The first stage was to increase the temperature to 800℃ at a rate of 5℃ / min and keep it for 2h;

[0169] The second stage was to increase the temperature to 1550℃ at a rate of 8℃ / min and keep it for 4h;

[0170] The third stage was to decrease the temperature to 1000℃ at a rate of 4℃ / min and then perform annealing treatment.

[0171] Comparative Example 1, the difference between this comparative example and Example 1 was that this comparative example used a single formula of zirconia powder with a bending strength of 1200MPa, which was not colored, and did not design any layered structure, and used conventional dry pressing and sintering to obtain a homogeneous material.

[0172] Comparative Example 2, the difference between this comparative example and Example 1 was that this comparative example used the same three-layer gradient powder with strengths of 1200MPa, 1100MPa and 70MPa as in Example 1, but all layers did not add any coloring oxide, and the same casting process was used, and this comparative example was used to verify the effect of pure strength gradient on performance without the synergistic effect of color gradient.

[0173] Comparative Example 3, the difference between this comparative example and Example 1 was that this comparative example used zirconia powder with a bending strength of 1100MPa as the matrix, and added different amounts of coloring oxide in the three layers to achieve color gradient from the neck to the incisal edge, and used the same casting process as in Example 1, and this comparative example was used to verify the effect of pure color gradient on performance without the synergistic effect of strength gradient.

[0174] Comparative Example 4, the difference between this comparative example and Example 1 was that this comparative example used a traditional two-step sintering process to directly increase the temperature to 1500℃ and keep it for 2h instead of segmented temperature control sintering.

[0175] The triple gradient zirconia materials prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests, and the test items and test methods were as follows:

[0176] Bending strength test: The local strength of the neck edge area, the middle area and the incisal area was measured by the three-point bending method, with a span of 20 mm and a loading speed of 1 mm / min;

[0177] Color gradient uniformity: The color difference values of 5 sites from the neck to the incisal end of the restoration were measured using a spectrophotometer under D65 light source, and the average color difference gradient was calculated;

[0178] Interface bonding strength test: The interface bonding strength of the neck edge layer-middle layer and the middle layer-incisal layer was determined by tensile shear test;

[0179] Fatigue life test: The mastication cycle in the oral cavity was simulated, with a load of 50-300 N and a frequency of 2 Hz, and the cycle number at which the restoration appeared cracks was recorded.

[0180] The microstructure characteristics of the triple gradient zirconia materials prepared in Examples 1-3 and Comparative Examples 1-4 were compared and the test data were recorded in the following table:

[0181]

[0182] The test data of the zirconia materials prepared in Examples 1-3 and Comparative Examples 1-4 were recorded in the following table:

[0183]

[0184] By comparing and analyzing the data in the table, it can be seen that the triple gradient zirconia material prepared by the process in Examples 1-3 has significantly better performance than Comparative Examples 1-4, which shows that the three-layer zirconia structure with strength gradient and color gradient designed in the present application can simulate the mechanical properties and aesthetic characteristics of natural teeth for the crown restoration, ensuring the mechanical strength requirements in the high-stress area and achieving natural color transition in the aesthetic sensitive area, thereby improving the bionic performance and clinical applicability of the restoration; by optimizing the multi-layer flow casting process, the continuous gradient transition between the three layers is realized, ensuring the close combination of the layer interfaces and the smooth transition of the performance, avoiding the stress concentration problem caused by the interface mutation of traditional multi-layer materials, and improving the reliability and service life of the material; by synergistically controlling the mechanical property gradient and the aesthetic property gradient of the material, the restoration meets the strength requirements of the mastication function area and the aesthetic requirements of the aesthetic area, realizes the unity of function and aesthetics, and improves the comprehensive performance of the crown restoration.

[0185] By comparing and analyzing the related data in the table, it can be known that the triple gradient zirconia material prepared by the application realizes physiological adaptation of mechanical properties, natural simulation of aesthetic transition and service life improvement simultaneously. Therefore, the triple gradient zirconia material for crown manufacturing provided by the application has a broader market prospect and is more suitable for promotion.

[0186] It should be noted that, in this document, the terms such as first and second are used merely to distinguish one entity or action from another, and do not necessarily require or imply that these entities or actions exist in any actual relationship or order. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or equipment including the element.

[0187] Although the embodiments of the application have been shown and described, it will be understood by those of ordinary skill 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 application, and the scope of the application 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 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 is gradually 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. 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.

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 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.

4. 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.

5. 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.

6. 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.

7. The triple-gradient zirconia material for dental crown fabrication according to claim 6, 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°.

8. The triple-gradient zirconia material for dental crown fabrication according to claim 6, 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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