WO2025200466A1 - Method for manufacturing lithium disilicate glass ceramic with gradient properties by using photocuring additive manufacturing - Google Patents

Abstract

A method for manufacturing a lithium disilicate glass ceramic with gradient properties by using photocuring additive manufacturing, the method comprising: performing wet mixing on a basic glass powder with a solvent, ball milling same until uniformity, drying same, then performing thermal treatment to reach a molten state, then quenching same to form original particles, and then granulating same to obtain lithium disilicate ceramic particles; respectively preparing n groups of pastes with gradually-changing colors and translucencies from n groups of the lithium disilicate ceramic particles, said paste preparation comprising: adding 3Y-TZP powder, a coloring agent and lithium disilicate ceramic particles to a resin mixture, mixing same, rolling same and performing vacuum defoaming to obtain a paste; adding the n groups of pastes in sequence into an additive manufacturing device to undergo photocuring forming, so as to obtain a green body; after the green body is cleaned and dried, degreasing the green body, and sintering same; and finally under a vacuum high-temperature condition, subjecting the sintered sample to an ion exchange reaction with a molten nitrate in a flowing state, so as to obtain a product.

Description

Method for light-curing additive manufacturing of gradient-graded lithium disilicate glass-ceramics Technical Field

The present invention relates to the technical field of lithium disilicate glass ceramic preparation, and in particular to a method for light-curing additive manufacturing of gradient-graded lithium disilicate glass ceramic.

Background Art

Lithium disilicate glass-ceramics have been used clinically for many years as dental restoration materials. Dental restorations include crowns, abutments, inlays, onlays, veneers, facets, bridges, and braces. Traditional lithium disilicate glass-ceramics preparation methods typically use a single ratio of raw materials to create a blank, which is then molded. The resulting product has consistent light transmittance and color. However, natural teeth vary in light transmittance and color, resulting in poor biomimetic results from traditional preparation methods.

To address this issue, some improved solutions for preparing lithium disilicate glass-ceramics using sintering methods have emerged. However, these solutions also have some disadvantages, including:

(1) Multicolor lithium silicate glass ceramics are prepared by introducing lithium silicate glass ceramic powders or suspensions of different colors. Although there is a gradient effect in color, its translucency does not change, and the optical effect is poor;

(2) The closer to the root of a natural tooth, the higher its flexural strength, that is, the flexural strength decreases from the root to the top, and the closer to the top the translucency is, the higher the translucency is. By controlling the different contents of colorants and the different particle sizes of the powder, a gradual change in light transmittance can be achieved. Although this method can achieve a gradual change in translucency, it will cause the flexural strength to increase from the root to the top, which is inconsistent with the actual mechanical properties. In addition, during preparation, the glass powders with gradient colors and translucency are molded in sequence and formed into blocks by dry pressing, resulting in insufficient bonding strength between layers. In addition, the thickness of each layer is fixed, which cannot achieve a high simulation effect of color and translucency, and cannot meet personalized color and translucency requirements.

In addition, when the particles of lithium disilicate glass-ceramics are too large, spherical grains are easily generated during the sintering process, reducing the generation of rod-shaped grains. In this way, a microstructure of interlocking grains cannot be formed, thereby reducing the flexural strength and limiting its application range.

(3) There are multiple sintering treatments during the preparation process. After multiple sintering, the crystallinity _{of Li2Si2O5} increases, the needle-shaped lithium _disilicate crystals become larger, and fuse into columnar crystals. The granular type also becomes larger spherical crystals. At the same time, the glass phase transforms into the crystal phase, which will affect the color and light transmittance of the restoration and reduce the fracture toughness.

Summary of the Invention

In response to the shortcomings of the existing technology, the present invention provides a method for photocuring additive manufacturing of gradient-graded lithium disilicate glass-ceramics, with the aim of making the flexural strength, translucency and color change characteristics of lithium disilicate glass-ceramics consistent with those of natural teeth, thereby enhancing the effect of bionic simulation.

The technical solution adopted in the present invention is as follows:

A method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics, comprising:

S1. Prepare basic glass powder, which includes the following components in mass fractions: 59% to 70% SiO ₂ , 14% to 20% Li ₂ O, 3% to 5% K ₂ O, 1-5% P ₂ O ₅ , 1-3% ZnO and other components, wherein the other components include Al ₂ O ₃ , Na ₂ O, Tb ₄ O ₇ , La ₂ O ₃ , MgO and CaO;

S2, wet-mixing the basic glass powder with solvent, ball-milling it to uniformity, drying it, and then heat-treating it into a molten state, and then quenching it into a into primary particles, wherein the D50 particle size of the primary particles is 0.8 microns;

Granulating the original particles to obtain lithium disilicate ceramic particles, which include coarse powder and fine powder;

S3, mixing the photosensitive resin premix, dispersant, and photoinitiator to obtain a resin mixture;

S4, preparing n groups of lithium disilicate ceramic particles into pastes to obtain n groups of pastes, comprising: adding 3Y-TZP powder, a colorant, and the coarse powder to a resin mixture, mixing uniformly, then adding the fine powder and mixing uniformly, then rolling, and then adding nano-fumed silica to obtain a paste, and vacuum degassing the paste; the particle size of the 3Y-TZP powder is 20-80 nanometers;

The color and translucency of the n groups of pastes change gradually, and the color and translucency change is achieved by simulating the translucency change by using the gradient change of the 3Y-TZP content in the n groups of pastes and simulating the color change by using the gradient change of the colorant content, wherein n is greater than 4;

S5, placing the n groups of pastes in the order of color and translucency gradient into the additive manufacturing device for light-curing forming to obtain a green body, including: using the first group of pastes to cure to form a first layer, using the second group of pastes to cure to form a second layer, and so on, until the nth group of pastes is cured to form an nth layer, and the thickness of each layer is performed according to a preset value;

S6, washing the green body with a flowing liquid, and then drying;

S7, degreasing and sintering the cleaned and dried green body, comprising: controlling the oxygen content to 5%-8%, degreasing at 400°C-600°C, obtaining a degreased sample after a predetermined time, placing the degreased sample in a 21%-24% lithium polysilicate solution for vacuum impregnation, heating to 500°C in air after a predetermined time, evacuating the solution with a vacuum degree controlled below 10 mbar, further heating to 630°C, holding the temperature for 2 hours, then heating to 750°C-900°C for sintering, and cooling to room temperature after a predetermined time to obtain a sintered sample;

S8. Place the sintered sample in a flowing nitrate under the action of a stirring device in a high-pressure vacuum furnace, and heat it to 300-600°C under vacuum conditions, so that the sintered sample is immersed in the molten nitrate to undergo an ion exchange reaction with it. The reaction time is 0.5-2 hours to finally obtain the product; the nitrate is a mixture of sodium nitrate and rubidium nitrate in a mass ratio of 1:1.

Further technical solutions are:

When n=6, the mass content of 3Y-TZP in the first to sixth groups of pastes are 15-13%, 13-10%, 10-8%, 8-6%, 6-4%, and 4-2%, respectively, and the mass content of colorant is 0.12%, 0.1%, 0.08%, 0.07%, 0.06%, and 0.04%, respectively.

The solid contents of the n groups of pastes are consistent.

In said S2, the temperature of the heat treatment is 1400-1600°C;

The quenching is performed using flowing deionized water, the temperature of the deionized water is 20-25° C., and the flow rate is 1.5-2.5 m/s.

After granulation, the coarse powder has a D50 particle size of 20 microns, and the fine powder has a D50 particle size of 5 microns.

In the above-mentioned S7, the degreasing time is 1 to 2 hours, and the sintering time is 2 hours.

The colorant is one or more of CeO ₂ , Fe ₂ O ₃ , and Pr ₆ O ₁₁ .

In S3, the photosensitive resin premix comprises a monofunctional photosensitive resin monomer, a bifunctional photosensitive resin monomer, and a multifunctional photosensitive resin monomer in a mass ratio of 1:1:1 to 1:2:3;

The monofunctional photosensitive resin monomer includes one or more of hydroxyethyl methacrylate, lauryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and lauric acid methacrylate;

The bifunctional photosensitive resin monomer includes one or more of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, and dipropylene glycol diacrylate;

The trifunctional photosensitive resin monomer includes propoxylated glycerol triacrylate or ethoxylated trimethylolpropane triacrylate. Alkene esters.

In S3, the mass of the photoinitiator accounts for 0.5% to 2% of the mass of the photosensitive resin premix;

The photoinitiator includes one or both of diphenyl 2,4,6-trimethylbenzoylphosphine oxide and 1-hydroxycyclohexyl phenyl ketone;

The mass ratio of diphenyl 2,4,6-trimethylbenzoylphosphine oxide and 1-hydroxycyclohexyl phenyl ketone is 1:1;

The dispersant includes gamma-methacryloxypropyltrimethoxysilane and gamma-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1.

A dental crown prepared according to the method of light-curing additive manufacturing gradient-graded lithium disilicate glass-ceramics, wherein the root flexural strength of the dental crown is 700 MPa, the top flexural strength is 350 MPa, and the linear transmittance of the top is greater than 50%; the flexural strength of the dental crown gradually increases, the transmittance gradually decreases, and the color gradually changes from the top to the root.

The beneficial effects of the present invention are as follows:

The method of the present invention utilizes the gradient change of 3Y-TZP content to simulate the change of translucency, and utilizes the gradient change of colorant content to simulate the color change to set multiple groups of lithium disilicate glass ceramic powders with gradient colors and translucency, thereby obtaining multiple groups of pastes, wherein the gradient change of 3Y-TZP content is simultaneously used to adjust the flexural strength; and utilizing the characteristics of light-curing additive manufacturing layered molding, different layers are cured and molded using corresponding pastes, and the 3Y-TZP content of the prepared crown decreases from the bottom (root) to the top, the flexural strength decreases, and the translucency increases, thereby achieving the effect of crown flexural strength, light transmittance and chromaticity gradient, and the optimal flexural strength of the obtained single crown from the root to the top is 350MPa to 700MPa gradient. The present invention can be used for the preparation of various dental restorations, is easy to operate, and improves mechanical properties and aesthetic effects.

The additive manufacturing technology used in this invention, due to the layer-by-layer stacking process, creates a naturally occurring microstructure between the inner surface layers of the crown. This microstructure significantly enhances the bonding strength of the lithium disilicate glass-ceramic. Furthermore, parameters such as layer thickness can be flexibly set; meaning each layer has a different fixed thickness and can be adjusted to meet specific needs, achieving a truly biomimetic effect and fully satisfying personalized color and translucency requirements. Furthermore, because each layer of paste has a consistent solids content, shrinkage is consistent during the forming process, eliminating internal stress between the gradient material layers.

The present invention first prepares the basic glass powder, and then adds 3Y-TZP and colorant when the paste is subsequently prepared. Compared with the traditional method of adding 3Y-TZP when preparing glass powder, the advantages include: adding 3Y-TZP when preparing glass powder. If the amount added is too much, it will increase the viscosity of the glass in the molten state, thereby preventing the formation of lithium disilicate and lithium metasilicate. Therefore, the amount of 3Y-TZP added is limited, and the present application adds 3Y-TZP in subsequent steps so that the amount of 3Y-TZP added is not limited. On the basis of the preparation of the basic powder, 3Y-TZP and colorant can be added as needed according to the number of layers and gradient design to meet personalized customization needs, with high flexibility, avoiding the preparation of glass powder with gradual changes in strength and translucency from the beginning, and the need to reconfigure when replacing and optimizing the design, resulting in waste of raw materials.

The present invention utilizes flowing deionized water quenching to improve the coordinated degreasing and sintering processes. On the one hand, the heat of the molten mixture is quickly removed by the flowing water, preventing particle accumulation caused by quenching, reducing the formation of large particles, and obtaining small-sized particles. This effectively reduces the particle size after quenching and improves particle uniformity. This not only shortens the subsequent ball milling time but also facilitates the formation of more rod-shaped crystals during subsequent sintering. On the other hand, by setting different temperature rise stages and regulating the corresponding degreasing and sintering atmospheres and parameters, cracks and carbon residues are avoided, and the formation of rod-shaped crystals is further promoted. The interlocking structure formed by the rod-shaped grains greatly improves the mechanical properties.

The present invention obtains lithium disilicate ceramic particles including coarse powder and fine powder by granulating original particles. In the subsequent paste making process, the coarse powder is first mixed and then the gaps between the coarse powders are filled by fine powder, thereby fully improving the density of the paste.

The method of the present invention has high manufacturing precision, does not require hot pressing, reduces dependence on hot pressing equipment, and avoids the precision caused by the lost wax method. No need for multiple heat treatments, which can reduce the fracture toughness of the product. The product can be obtained directly without polishing or glazing.

Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic flow chart of the method of the invention.

DETAILED DESCRIPTION

The specific embodiments of the present invention are described below with reference to the accompanying drawings.

Example 1

As shown in FIG1 , a method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics according to this embodiment includes:

S1. Prepare basic glass powder, which includes the following components in mass fractions: 59%-70% _SiO2 , 14%-20% _Li2O , 3%-5% _K2O , 1-5% _P2O5 , _1-3 % ZnO and other components, wherein _the other components include _Al2O3 , _Na2O , _Tb4O7 , _La2O3 , _MgO and CaO _.

S2. Wet-mixing the base glass powder with a solvent, ball-milling the powder to obtain uniform powder, drying the powder, heat-treating the powder into a molten state, and quenching the powder to form primary particles, wherein the primary particles have a D50 particle size of 0.8 μm; and granulating the primary particles to obtain lithium disilicate ceramic particles, which include coarse powder and fine powder.

Specifically, the basic glass powder is wet-mixed with anhydrous ethanol, ball-milled and uniformly mixed, and then dried. The mixture is then heat-treated at 1400-1600° C. to obtain a molten mixture. The molten mixture is dropped into deionized water in a stable flow state and quenched to form primary particles in the deionized water. The temperature of the deionized water is 20-25° C., and the flow rate is 1.5-2.5 m/s.

Specifically, the raw particles are ball-milled and sieved to produce a powder with a particle size of 0.3 to 0.5 μm, which is then granulated by spray drying. The coarse powder of the lithium disilicate ceramic particles obtained by granulation has a particle size of 20 μm in D50 and a fine powder of 5 μm in D50.

S3, mixing the photosensitive resin premix, dispersant, and photoinitiator to obtain a resin mixture;

Specifically, the photosensitive resin premix includes a monofunctional photosensitive resin monomer, a bifunctional photosensitive resin monomer, and a multifunctional photosensitive resin monomer in a mass ratio of 1:1:1 to 1:2:3;

The monofunctional photosensitive resin monomer includes one or more of hydroxyethyl methacrylate, lauryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and lauric acid methacrylate;

The bifunctional photosensitive resin monomer includes one or more of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, and dipropylene glycol diacrylate;

The trifunctional photosensitive resin monomer includes propoxylated glycerol triacrylate or ethoxylated trimethylolpropane triacrylate.

Specifically, the mass of the photoinitiator accounts for 0.5% to 2% of the mass of the photosensitive resin premix;

The photoinitiator includes one or both of diphenyl 2,4,6-trimethylbenzoylphosphine oxide and 1-hydroxycyclohexyl phenyl ketone;

The mass ratio of diphenyl 2,4,6-trimethylbenzoylphosphine oxide to 1-hydroxycyclohexyl phenyl ketone is 1:1.

Specifically, the dispersant includes γ-methacryloxypropyltrimethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1.

S4, taking 6 groups of lithium disilicate ceramic particles and preparing pastes respectively to obtain n groups of pastes, including: adding 3Y-TZP powder, colorant, and the coarse powder to the resin mixture, mixing them evenly, then adding the fine powder and mixing them evenly, and then Rolling is performed, and then nano-fumed silica is added to obtain a paste, and the paste is vacuum degassed; the particle size of the 3Y-TZP powder is 20-80 nanometers;

The color and translucency gradient of the 6 groups of pastes are achieved by simulating the translucency change by using the gradient change of the 3Y-TZP content in the 6 groups of pastes, and simulating the color change by using the gradient change of the colorant content. As a specific embodiment, the 3Y-TZP content in the first to sixth groups of pastes is 15-13%, 13-10%, 10-8%, 8-6%, 6-4%, and 4-2%, respectively, and the colorant content is 0.12%, 0.1%, 0.08%, 0.07%, 0.06%, and 0.04%, respectively.

Specifically, the colorant is one or more of CeO ₂ , Fe ₂ O ₃ , and Pr ₆ O ₁₁ .

Specifically, coarse powder is added to the resin mixture, dispersed by ball milling, and then fine powder is added, mixed evenly in a homogenizer, and then rolled by a roller press.

The six paste groups all had consistent solids content, meaning the proportion of lithium disilicate glass ceramic in each paste group was consistent. Specifically, in each paste group, the lithium disilicate ceramic particles, 3Y-TZP, and colorant accounted for 70% to 85% of the total paste mass. Nano-fumed silica accounted for 0.1% to 0.5% of the paste mass, with a particle size of 7 nanometers.

The solid content of each group of paste is consistent, which can ensure consistent sintering shrinkage and prevent cracks.

As those skilled in the art will appreciate, 3Y-TZP refers to a zirconium oxide (ZrO ₂ ) ceramic material stabilized by 3 mol% of a rare earth oxide (typically Y ₂ O ₃ ). Compared to traditional zirconium oxide materials, 3Y-TZP has greater stability and toughness, and can resist fracture under high stress environments.

S5, placing the six groups of pastes in the order of color and translucency gradient into the additive manufacturing equipment for light-curing forming to obtain a green body, including: using the first group of pastes to cure to form a first layer, using the second group of pastes to cure to form a second layer, and so on, until the sixth group of pastes is cured to form a sixth layer, and the thickness of each layer is executed according to a preset value;

Specifically, the first to sixth groups of pastes are arranged in order of decreasing 3Y-TZP content, and the first to sixth layers formed correspond to the bottom (root) to the top of the crown respectively, thereby ensuring that the flexural strength of the final product from the bottom (root) to the top gradually decreases and the semipermeability gradually increases.

S6, washing the green body with flowing liquid, and then drying with hot air;

Specifically, the flowing liquid is composed of resin monomer, polyethylene glycol 200, and isopropyl alcohol in a mass ratio of 1:1:1.

S7, degreasing and sintering the cleaned and dried green body, comprising: controlling the oxygen content to 5%-8%, degreasing at 400°C-600°C, obtaining a degreased sample after a predetermined time, placing the degreased sample in a 21%-24% lithium polysilicate solution for vacuum impregnation, heating to 500°C in air after a predetermined time, evacuating the solution with a vacuum degree controlled below 10 mbar, further heating to 630°C, holding the temperature for 2 hours, then heating to 750°C-900°C for sintering, and cooling to room temperature after a predetermined time to obtain a sintered sample;

Specifically, the degreasing time is 1 to 2 hours, and the sintering time is 2 hours.

S8. Place the sintered sample in a flowing nitrate under the action of a stirring device in a high-pressure vacuum furnace, and heat it to 300-600°C under vacuum conditions, so that the sintered sample is immersed in the molten nitrate to undergo an ion exchange reaction with it. The reaction time is 0.5-2 hours, and finally a crown product is obtained; the nitrate is a mixture of sodium nitrate and rubidium nitrate in a mass ratio of 1:1.

Specifically, the sintered sample is placed in an alumina crucible, and then the whole is placed in nitrate in a high-pressure vacuum furnace for heating to facilitate obtaining the product after the reaction.

Among them, the purpose of ion exchange is to use large-sized cations (sodium and rubidium ions) to replace small-sized ions (lithium ions) to form a plugging effect. Residual compressive stress will be generated on the surface without changing the microstructure, thereby improving mechanical properties and quality.

In this embodiment, nitrate is used for ion exchange because it is relatively stable, easy to remove, and will not form insoluble precipitated compounds with the exchanged ions.

In this embodiment, ion exchange is performed under vacuum conditions, which draws out gas molecules, thereby increasing the space and rate of ion exchange. This helps accelerate ion diffusion and penetration, increasing the migration rate of ions within the material, thereby shortening the ion exchange time and improving exchange efficiency. Furthermore, the nitrate is in a mobile state, further increasing the exchange rate.

Compared with the time required for ion exchange in a static molten state of nitrate, which is more than 8 hours, the ion exchange under high pressure vacuum conditions in this embodiment can be completed in only 0.5-2 hours.

The crown produced by the method of this embodiment has a root flexural strength of 700 MPa, a top flexural strength of 350 MPa, and a top linear transmittance of more than 50%. The flexural strength of the crown decreases gradually from the root to the top, the translucency increases gradually, and the color changes gradually.

Example 2

The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics in this embodiment is the same as that in Example 1 under the following conditions and parameters:

In step S4, four groups of lithium disilicate ceramic particles are prepared into pastes to obtain four groups of pastes. The contents of 3Y-TZP in the first to fourth groups of pastes are 15-13%, 13-10%, 10-8%, and 8-6%, respectively. The content of the colorant is set in a gradient according to actual needs.

The crown produced by this embodiment has a root flexural strength of 700 MPa, a top flexural strength of 420 MPa, and a top light transmittance of 25%. The flexural strength of the crown decreases gradually from the root to the top, the translucency increases gradually, and the color changes gradually.

Example 3

The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics in this embodiment is the same as that in Example 1 under the following conditions and parameters:

In step S4, three groups of lithium disilicate ceramic particles are prepared into pastes to obtain four groups of pastes. The contents of 3Y-TZP in the first to third groups of pastes are 15-13%, 13-10%, and 10-8%, respectively. The content of the colorant is set in a gradient according to actual needs.

The crown produced by this embodiment has a root strength of 700 MPa, a top flexural strength of 460 MPa, and a top light transmittance of 20%. From the root to the top, the flexural strength of the crown decreases, the translucency increases, and the color changes gradually.

In summary, six layers of bionic simulation have better effects, and this application prefers six layers.

Those skilled in the art will understand that the foregoing descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will be able to modify the technical solutions described in the foregoing embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims (10)

A method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics, characterized by comprising: S1. Prepare basic glass powder, which includes the following components in mass fractions: 59% to 70% SiO ₂ , 14% to 20% Li ₂ O, 3% to 5% K ₂ O, 1-5% P ₂ O ₅ , 1-3% ZnO and other components, wherein the other components include Al ₂ O ₃ , Na ₂ O, Tb ₄ O ₇ , La ₂ O ₃ , MgO and CaO; S2, wet-mixing the basic glass powder with a solvent, ball-milling the powder to form a uniform mixture, drying the powder, heat-treating the powder into a molten state, and quenching the powder to form primary particles, wherein the D50 particle size of the primary particles is 0.8 μm; Granulating the original particles to obtain lithium disilicate ceramic particles, which include coarse powder and fine powder; S3, mixing the photosensitive resin premix, dispersant, and photoinitiator to obtain a resin mixture; S4, preparing n groups of lithium disilicate ceramic particles into pastes to obtain n groups of pastes, comprising: adding 3Y-TZP powder, a colorant, and the coarse powder to a resin mixture, mixing uniformly, then adding the fine powder and mixing uniformly, then rolling, and then adding nano-fumed silica to obtain a paste, and vacuum degassing the paste; the particle size of the 3Y-TZP powder is 20-80 nanometers; The color and translucency of the n groups of pastes change gradually, and the color and translucency change is achieved by simulating the translucency change by using the gradient change of the 3Y-TZP content in the n groups of pastes and simulating the color change by using the gradient change of the colorant content, wherein n is greater than 4; S5, placing the n groups of pastes in the order of color and translucency gradient into the additive manufacturing device for light-curing forming to obtain a green body, including: using the first group of pastes to cure to form a first layer, using the second group of pastes to cure to form a second layer, and so on, until the nth group of pastes is cured to form an nth layer, and the thickness of each layer is performed according to a preset value; S6, washing the green body with a flowing liquid, and then drying; S7, degreasing and sintering the cleaned and dried green body, comprising: controlling the oxygen content to 5%-8%, degreasing at 400°C-600°C, obtaining a degreased sample after a predetermined time, placing the degreased sample in a 21%-24% lithium polysilicate solution for vacuum impregnation, heating to 500°C in air after a predetermined time, evacuating the solution with a vacuum degree controlled below 10 mbar, further heating to 630°C, holding the temperature for 2 hours, then heating to 750°C-900°C for sintering, and cooling to room temperature after a predetermined time to obtain a sintered sample; S8. Place the sintered sample in a high-pressure vacuum furnace in a flowing nitrate under the action of a stirring device, and heat it to 300-600°C under vacuum conditions, so that the sintered sample is immersed in the molten nitrate to undergo an ion exchange reaction with it. The reaction time is 0.5-2 hours, and the product is finally obtained; the nitrate is a mixture of sodium nitrate and rubidium nitrate in a mass ratio of 1:1. The method for photocuring additive manufacturing gradient-graded lithium disilicate glass-ceramics according to claim 1, in n groups of pastes, when n=6, the mass content of 3Y-TZP in the first to sixth groups of pastes is 15-13%, 13-10%, 10-8%, 8-6%, 6-4%, and 4-2%, respectively, and the mass content of the colorant is 0.12%, 0.1%, 0.08%, 0.07%, 0.06%, and 0.04%, respectively. The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics according to claim 1, characterized in that the solid content of the n groups of pastes is consistent. The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics according to claim 1, characterized in that in S2, the temperature of the heat treatment is 1400-1600°C; The quenching is performed using flowing deionized water, the temperature of the deionized water is 20-25° C., and the flow rate is 1.5-2.5 m/s. The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics according to claim 1 is characterized in that After granulation, the coarse powder has a D50 particle size of 20 μm, and the fine powder has a D50 particle size of 5 μm. The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics according to claim 1, characterized in that in S7, the degreasing time is 1 to 2 hours and the sintering time is 2 hours. The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics according to claim 1, characterized in that the colorant is one or more of CeO ₂ , Fe ₂ O ₃ , and Pr ₆ O ₁₁ . The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics according to claim 1, characterized in that in S3, the photosensitive resin premix comprises a monofunctional photosensitive resin monomer, a bifunctional photosensitive resin monomer, and a trifunctional photosensitive resin monomer in a mass ratio of 1:1:1 to 1:2:3; The monofunctional photosensitive resin monomer includes one or more of hydroxyethyl methacrylate, lauryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and lauric acid methacrylate; The bifunctional photosensitive resin monomer includes one or more of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, and dipropylene glycol diacrylate; The trifunctional photosensitive resin monomer includes propoxylated glycerol triacrylate or ethoxylated trimethylolpropane triacrylate. The method for photocuring additive manufacturing of gradient-graded lithium disilicate glass ceramics according to claim 1, characterized in that in S3, the mass of the photoinitiator accounts for 0.5% to 2% of the mass of the photosensitive resin premix; The photoinitiator includes one or both of diphenyl 2,4,6-trimethylbenzoylphosphine oxide and 1-hydroxycyclohexyl phenyl ketone; The mass ratio of diphenyl 2,4,6-trimethylbenzoylphosphine oxide and 1-hydroxycyclohexyl phenyl ketone is 1:1; The dispersant includes gamma-methacryloxypropyltrimethoxysilane and gamma-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1. A dental crown prepared according to the method for light-curing additive manufacturing of gradient-graded lithium disilicate glass-ceramics according to any one of claims 1 to 9, characterized in that the root flexural strength of the dental crown is 700 MPa, the top flexural strength is 350 MPa, and the linear transmittance of the top is greater than 50%; the flexural strength of the dental crown gradually increases, the transmittance gradually decreases, and the color changes gradually from the top to the root.