Preparation process of 3d printing composite ceramic prosthetic denture

Abstract

The application relates to the technical field of ceramic denture additive manufacturing, and particularly discloses a 3D printing composite ceramic prosthetic denture preparation process. The process comprises the following steps: S1, drying and calcining to obtain a core-shell structure zirconia powder; the core-shell structure zirconia powder is mixed with montmorillonite nanosheets and conductive metal oxide submicron balls to obtain an electroactive ceramic composite powder; S2, preparing a photocuring printing slurry; S3, forming the photocuring printing slurry through photocuring 3D printing, performing heat debinding treatment to remove organic resin, and obtaining a porous green body; S4, preparing a densified colored denture blank; S5, cleaning the densified colored denture blank to obtain a 3D printing composite ceramic prosthetic denture. The composite ceramic prosthetic denture can be used for customized manufacturing of oral personalized prostheses, and has the advantages of simultaneously realizing blank densification and full-layer depth gradient coloring under low-temperature conditions.

Description

Technical Field

[0001] This application relates to the field of additive manufacturing technology for ceramic dentures, and more specifically, to a process for preparing 3D-printed composite ceramic restorative dentures. Background Technology

[0002] In the field of dental restoration, light-curing 3D printing technology has become a core process for personalized ceramic denture customization due to its high-precision molding and adaptability to complex structures. By curing photosensitive resin-based ceramic slurry layer by layer, it can accurately reproduce the shape of natural teeth, shorten the production cycle and improve the marginal fit of restorations compared to traditional lost-wax casting. At the same time, molten salt staining technology, as a mature means of ceramic modification, introduces color-producing ions in a high-temperature salt bath to achieve uniform adhesion of color on the surface of restorations, meeting the clinical needs for aesthetic restorations and promoting the development of denture manufacturing towards high efficiency and precision.

[0003] However, the densification of zirconia ceramic dentures relies on high-temperature solid-state sintering above 1400℃, which easily leads to volume shrinkage of more than 15%, resulting in a decrease in the fit between the restoration and the prepared body. In addition, high temperature will exacerbate abnormal grain growth and weaken the mechanical properties of the material. At the same time, existing coloring techniques mostly adopt surface penetration or external dyeing processes, and the coloring ions can only passively diffuse through the concentration gradient, making it difficult to penetrate into the deep layers of the green body, forming non-uniform coloring with a darker surface and a shallower interior. After long-term use, the white layer is prone to appear due to wear. Therefore, it is impossible to get rid of the shrinkage defects caused by high-temperature sintering, and it is also impossible to achieve full-layer depth gradient coloring under low-temperature conditions. Summary of the Invention

[0004] To address the shrinkage defects and uneven coloring issues that arise from the high-temperature solid-state sintering of zirconia ceramic dentures during long-term use, this application provides a 3D printing process for fabricating composite ceramic restorative dentures.

[0005] This application provides a 3D printing composite ceramic restorative denture fabrication process, which adopts the following technical solution: A 3D-printed composite ceramic dental prosthesis fabrication process includes the following steps: S1. A lithium silicate glass precursor is coated onto the surface of zirconia particles by a sol-gel method, and then dried and calcined to obtain core-shell structured zirconia powder. The core-shell structured zirconia powder is mixed with montmorillonite nanosheets and conductive metal oxide submicron spheres to obtain electroactive ceramic composite powder. S2. Prepare thermally responsive microcapsules, then mix the electroactive ceramic composite powder, the thermally responsive microcapsules and the photosensitive resin premix evenly and degas to obtain a photocurable printing paste; S3. The photocurable printing paste is formed by photocurable 3D printing to obtain a green blank; the green blank is subjected to thermal degreasing treatment to remove organic resin to obtain a porous preform; S4. Heat and melt nitrates and nitrites, and dissolve metal cation salts in them to obtain a functional molten salt bath; immerse the porous blank in the functional molten salt bath, first heat it to a first temperature range and keep it at that temperature, then heat it to a second temperature range and keep it at that temperature, and then cool it down and take it out to obtain a densified colored denture blank. S5. Clean the densified colored denture blank to obtain a 3D printed composite ceramic restorative denture.

[0006] By adopting the above technical solution, since a lithium silicate-based low-melting-point glass phase layer is pre-coated on the surface of zirconia particles, and redox-active montmorillonite nanosheets and conductive metal oxide submicron spheres are introduced into the interior of the green body in subsequent processes, the glass phase layer melts to form a liquid phase at a temperature far below the solid-phase sintering temperature of zirconia during the subsequent low-temperature molten salt bath treatment stage. This liquid phase drives the densification of the green body through a dissolution-precipitation mass transfer mechanism, reducing macroscopic volume shrinkage. At the same time, the ferrous ions loaded between the montmorillonite nanosheets and the conductive metal oxide submicron spheres form a micro galvanic cell structure in the molten salt ion conductor environment. The resulting micro-area electric field actively pulls the metal cations in the molten salt to migrate directionally along the grain boundaries, changing the coloring process from passive diffusion to controlled migration of the main body. This provides a driving force for full-layer depth gradient coloring, ultimately obtaining a ceramic denture with precise dimensions and body coloring capability.

[0007] Preferably, in step S1, the lithium silicate-based glass precursor is prepared by hydrolysis and polycondensation of tetraethyl orthosilicate, lithium carbonate, and alumina precursor under acidic conditions; the drying temperature is 60–120°C and the time is 2–8 hours; the calcination temperature is 500–700°C and the time is 1–3 hours, and the calcination atmosphere is air; in the core-shell structured zirconium oxide powder, the thickness of the glass phase shell is 5–20 nm.

[0008] By adopting the above technical solution, the glass precursor formed by the hydrolysis and condensation of tetraethyl orthosilicate, lithium carbonate, and alumina precursors through the sol-gel method combined with drying and calcination processes within a specific temperature range uniformly and densely coats the surface of each zirconia particle, forming a nanoscale continuous glass phase layer with controlled thickness. This glass phase layer plays a dual role in isolating and bonding the zirconia particles: it avoids excessive particle agglomeration during the greening stage, and during the molten salt bath treatment stage, it acts as an in-situ generated liquid-mediated phase, providing a uniform capillary driving force for the rearrangement and mass transfer of zirconia particles, thereby ensuring the uniformity of the densification process.

[0009] Preferably, in step S1, the method for preparing the montmorillonite nanosheets is as follows: montmorillonite is immersed in hydrochloric acid solution for acid activation treatment, washed, and then immersed in ferrous sulfate or ferrous chloride solution, followed by centrifugation, washing, and drying; the conductive metal oxide submicron spheres are tin oxide submicron spheres or indium tin oxide submicron spheres with an average particle size of 100–300 nm; the mass ratio of the core-shell structure zirconium oxide powder, montmorillonite nanosheets, and conductive metal oxide submicron spheres is 100:0.5–3:0.5–3; the mixing is performed by ball milling, with anhydrous ethanol as the milling medium, a milling speed of 200–400 rpm, and a time of 4–12 hours.

[0010] By adopting the above technical solution, the layered structure of montmorillonite is fully opened due to acid activation and ferrous ion exchange treatment. The interlayer is loaded with divalent iron ions with reducing activity, which become the anode active sites of the micro galvanic cell. These functionalized montmorillonite nanosheets are mixed with tin oxide or indium tin oxide conductive microspheres and core-shell zirconium oxide powder in a certain proportion. Through the dispersion and grinding action of anhydrous ethanol in the ball milling medium, the three are uniformly distributed and closely contacted at the particle scale. This uniformly distributed micro-electroactive network is the structural basis for the subsequent in-situ construction of a micro electrochemical driving system in a molten salt bath, ensuring that directional ion traction force is generated throughout the blank, and avoiding the coloring ions from remaining only on the surface.

[0011] Preferably, in step S2, the thermally responsive microcapsule consists of a core, an inner shell, and an outer shell, arranged from the inside out; the core contains a metal ion compound, the inner shell is made of a metal-organic framework material, and the outer shell is made of borosilicate glass.

[0012] By adopting the above technical solution, the thermally responsive microcapsules employ a three-tiered structure design of core-inner shell-outer shell, with different materials and thermal response behaviors for the three functional layers. The release of coloring ions is precisely coordinated with the heating program of the molten salt bath. The borosilicate glass of the outer shell softens and integrates into the liquid phase network of the matrix in the early stage of the molten salt bath, pre-constructing ion release channels. The metal-organic framework material of the inner shell undergoes pyrolysis and disintegration at a specific intermediate temperature stage, triggering the concentrated release of colorants from the core. This asynchronous cascade release mechanism allows coloring ions to enter the interior of the preform in batches and stages, superimposing with the ongoing densification process and electrochemical migration process to form complex three-dimensional color layers that cannot be achieved by traditional single-penetration.

[0013] Preferably, the method for preparing the thermally responsive microcapsules is as follows: a solution containing a metal ion compound is spray-dried to form micron-sized particles to obtain a core; the core is dispersed in a solution containing a metal-organic framework precursor, and after separation and drying, a core-shell intermediate is obtained; the core-shell intermediate is dispersed in a sol containing a borosilicate glass precursor, spray-dried, and calcined at low temperature to form an outer shell layer to obtain thermally responsive microcapsules.

[0014] By adopting the above technical solution, the particle size of the core is controlled by spray drying parameters due to the step-by-step encapsulation and layer-by-layer assembly process. The inner shell of the metal-organic framework forms a tight encapsulation interface with the core through in-situ growth, while the outer shell of borosilicate glass forms a complete sealed layer through sol-gel encapsulation and low-temperature calcination. This preparation path ensures the bonding force and thickness uniformity between the shell layers, so that the structural integrity of the microcapsules is maintained during the printing slurry preparation and degreasing process. The microcapsules will disintegrate step by step only under the preset thermal triggering conditions, avoiding premature leakage or uncontrolled diffusion of the colorant.

[0015] Preferably, the metal ion compound contained in the core is at least one of erbium nitrate, cerium nitrate, or ferric nitrate; the metal-organic framework material inner shell is ZIF-8 or ZIF-67 with a pyrolysis temperature of 800–900°C; and the borosilicate glass outer shell has a softening point of 700–800°C.

[0016] By adopting the above technical solution, the core uses metal salts such as erbium nitrate, cerium nitrate, and ferric nitrate. Erbium ions impart a pink hue to the restoration, cerium ions simulate a mauve effect, and ferric ions produce a warm brown base. By selecting a combination of single or multiple color-producing ions, a color system close to that of natural teeth can be achieved. The inner shell uses metal-organic framework materials such as ZIF-8 or ZIF-67, which have a defined pyrolysis temperature. Their pyrolysis behavior occurs within a set second temperature range, ensuring that the large-scale release of colorants coincides with the middle and late stages of the densification process. The softening point of the outer shell borosilicate glass is lower than that of the inner shell pyrolysis temperature, ensuring that the outer shell melts first and fuses with the matrix glass network in the early stage of molten salt bath heating, reserving a connected release path for the core colorant.

[0017] Preferably, in step S2, the photosensitive resin premix comprises acrylate monomers, acrylate oligomers, a photoinitiator, and a dispersant; the mass ratio of the electroactive ceramic composite powder to the photosensitive resin premix is ​​1:1 to 4:1; the amount of the thermally responsive microcapsules added is 1 to 10% of the mass of the electroactive ceramic composite powder; the mixing speed is 800 to 2000 rpm, and the time is 10 to 60 min; the degassing is performed using vacuum degassing with a vacuum degree of -0.08 to -0.1 MPa for 10 to 30 min.

[0018] By adopting the above technical solution, the photosensitive resin premix uses acrylate monomers and oligomers as the main organic binders, and is rapidly cured and shaped under ultraviolet exposure with the help of photoinitiators, ensuring printing accuracy. The ratio of electroactive ceramic composite powder to photosensitive resin premix and the amount of thermally responsive microcapsules are balanced and designed so that the slurry has good fluidity and printability while ensuring that the green blank has sufficient solid content to reduce volume changes in the subsequent densification stage. Vacuum degassing treatment effectively removes air bubbles introduced during the mixing process, prevents the formation of pore defects in the printed layer, and ensures the uniform dispersion of microcapsules in the slurry, so that they can respond uniformly to temperature changes in subsequent stages.

[0019] Preferably, in step S3, the photopolymerization 3D printing uses digital light processing, the printing layer thickness is 25-100 μm, and the single-layer exposure time is 1-10 seconds; the thermal degreasing treatment is heated to 400-600℃ at a heating rate of 0.5-2℃ / min, held for 1-3 hours, and then heated to 700-900℃ at a heating rate of 1-3℃ / min, held for 0.5-2 hours, and the degreasing atmosphere is air or nitrogen.

[0020] By adopting the above technical solutions, the complex anatomical morphology and occlusal surface features of the restoration can be accurately reproduced by using digital light processing technology to form layers by thin-layer exposure. The thermal degreasing adopts a segmented heating system. In the low-temperature section, the organic resin is slowly decomposed and discharged in a slow manner to avoid cracking or deformation of the preform caused by concentrated gas release. In the medium-temperature section, the temperature continues to rise to near the softening point of the glass phase, so that the organic residue is completely removed while the glass phase layer has not yet undergone significant flow. This preserves the original spatial distribution configuration of microcapsules and electroactive particles inside the porous preform after degreasing, providing a complete structural template for subsequent molten salt bath treatment.

[0021] Preferably, in step S4, the mass ratio of nitrate to nitrite is 1:0.5-2; the metal cation salt is one or more of erbium nitrate, cerium nitrate, or ferric nitrate, and its addition amount is 0.5-5% of the total mass of the nitrate and nitrite; the heating and melting temperature is 400-600°C, and the functional molten salt bath is preheated for 0.5-2 hours before immersing the porous blank; The first temperature range is 750–850℃, the heating rate is 3–8℃ / min, and the holding time is 10–60min; the second temperature range is 850–950℃, the heating rate is 1–5℃ / min, and the holding time is 20–90min; the cooling is achieved by cooling to 400–500℃ at a cooling rate of 1–5℃ / min and then allowing the furnace to cool naturally to room temperature.

[0022] By adopting the above technical solution, the mixed system of nitrate and nitrite is selected as the basic molten salt medium, whose melting point and viscosity meet the requirements of low-temperature liquid phase treatment, and at the same time has good dissolving ability for metal cations. Before immersing the green body, the molten salt bath is preheated to completely remove moisture and dissolved gases from the salt bath and prevent bubble disturbance during the treatment process. The first temperature range corresponds to the initiation stage of glass phase melting and softening and liquid phase densification. The temperature rises rapidly in this stage to quickly establish a liquid phase environment, and at the same time, the micro-electrochemical reaction is activated, and the coloring ions begin to migrate along the grain boundaries. The second temperature range corresponds to the pyrolysis temperature of the inner shell of the microcapsule. The temperature rises more slowly to ensure that the colorant is released smoothly from the core and fully interacts with the established liquid phase permeation network to achieve deep color anchoring. The subsequent controlled slow cooling causes the liquid phase glass components to migrate to the outer surface of the green body under the drive of surface tension and solidify, forming a continuous surface self-glazing sealing layer. This sealing layer does not require subsequent glazing steps, simplifying the process.

[0023] Preferably, in step S5, the cleaning is performed using deionized water ultrasonic cleaning with an ultrasonic frequency of 40-80 kHz and a time of 5-20 min, followed by drying at 80-120°C.

[0024] By adopting the above technical solution, the densified colored denture blank is treated with deionized water and ultrasonic cleaning. The ultrasonic cavitation effect effectively peels off and dissolves the solidified salt residues attached to the surface of the restoration and in the open pores. The deionized water does not introduce impurity ions, thus avoiding the impact of salt residues on the surface color and biocompatibility of the restoration. The low-temperature drying step after cleaning smoothly removes the water that seeps in during the cleaning process, while not causing thermal disturbance to the already formed color gradient and self-enamel sealing layer, ultimately obtaining a finished restoration with a clean surface and stable color.

[0025] In summary, this application has the following beneficial effects: 1. Because this application employs a low-melting-point lithium silicate glass phase layer pre-coated on the surface of zirconia particles and constructs an electroactive network inside the green body consisting of montmorillonite nanosheets loaded with divalent iron ions and conductive metal oxide submicron spheres, the liquid phase formed by the melting of the glass phase layer during the low-temperature molten salt bath treatment stage drives the densification of the green body through a dissolution-precipitation mass transfer mechanism, avoiding the volume shrinkage associated with traditional high-temperature solid-state sintering. At the same time, the electroactive network spontaneously forms a micro galvanic cell in the molten salt ion conductor environment, and the generated micro-area electric field directionally pulls the metal cations in the molten salt, causing the coloring ions to change from passive diffusion to active migration, thereby simultaneously achieving the effects of green body densification and full-layer depth gradient coloring under low-temperature conditions.

[0026] 2. In this application, thermally responsive microcapsules are preferably used. The outer shell is made of low-melting-point borosilicate glass, the inner shell is made of metal-organic framework material, and the core is a metal ion compound. Since the thermal response temperature of each functional layer progresses sequentially, the microcapsules are activated in stages during the heating process in the molten salt bath: the outer shell melts and fuses with the matrix glass network first and reserves a release channel. When the inner shell reaches the preset pyrolysis temperature, it disintegrates and triggers the concentrated release of the core colorant, so that the coloring ions enter the interior of the preform in batches and couple with densification and electrochemistry, thereby achieving the effect of biomimetic layering and enhanced color fastness inside the restoration.

[0027] 3. The method of this application involves immersing the degreased porous green body in a molten salt bath containing a mixture of nitrates and nitrites with metal cations for heating treatment. In the first temperature range, glass phase melting and liquid phase densification are achieved. At the same time, the micro-electrochemical reaction inside the green body is activated to drive the directional migration of color-emitting ions. In the second temperature range, the inner shell of the microcapsule is pyrolyzed and a high concentration of colorant is released for secondary penetration coloring. Subsequently, the temperature is slowly lowered to allow the liquid phase glass components to migrate to the outer surface of the green body and solidify, forming a surface self-glazing sealing layer integrated with the green body. Therefore, densification, gradient coloring and surface sealing are integrated into a single molten salt bath treatment, which simplifies the process.

[0028] 4. In this application, montmorillonite, after acid activation and ferrous ion exchange treatment, is preferably used as the anodic active micro-region, and tin oxide or indium tin oxide submicron spheres are used as the cathode active micro-region. These are mixed with core-shell structured zirconium oxide powder through ball milling to achieve uniform distribution and close contact. Because this electroactive network spontaneously forms a micro galvanic cell array distributed throughout the entire blank in the liquid phase environment of molten salt bath treatment, the coloring ions are subjected to directional electric field attraction in each region of the blank. This avoids the problem of insufficient coloring depth and uneven distribution caused by the slow penetration of coloring ions into the interior of the blank during soaking coloring. Thus, the restoration can achieve a uniform and continuous color transition from the surface to the deep layer. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the fabrication process of a 3D-printed composite ceramic prosthesis proposed in this application; Figure 2 This is a schematic diagram showing the densification degree and volume shrinkage rate test results of the embodiments and comparative examples proposed in this application; Figure 3 This is a schematic diagram showing the color depth detection results of the embodiments and comparative examples proposed in this application; Figure 4 This is a schematic diagram showing the color uniformity and surface sealing effect test results of the embodiments and comparative examples proposed in this application. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] Technical concept: The densification of zirconia ceramic dentures relies on high-temperature solid-state sintering above 1400℃, which easily leads to volume shrinkage of more than 15%, resulting in a decrease in the fit between the restoration and the prepared body. In addition, high temperature will exacerbate abnormal grain growth and weaken the mechanical properties of the material. At the same time, existing coloring techniques mostly adopt surface penetration or external dyeing processes, and the coloring ions can only passively diffuse through the concentration gradient, making it difficult to penetrate into the deep layers of the green body, forming non-uniform coloring with a darker surface and a shallower interior. After long-term use, the white layer is prone to appear due to wear. Therefore, it is impossible to get rid of the shrinkage defects caused by high-temperature sintering, and it is also impossible to achieve full-layer depth gradient coloring under low-temperature conditions.

[0032] This application discloses a 3D-printed composite ceramic prosthesis fabrication process. The process includes the following steps: S1, drying and calcining to obtain core-shell structured zirconia powder; mixing the core-shell structured zirconia powder with montmorillonite nanosheets and conductive metal oxide submicron spheres to obtain electroactive ceramic composite powder; S2, preparing a photocurable printing paste; S3, molding the photocurable printing paste using photocurable 3D printing, followed by thermal degreasing to remove organic resin, resulting in a porous preform; S4, preparing a densified and colored prosthesis preform; S5, cleaning the densified and colored prosthesis preform to obtain a 3D-printed composite ceramic prosthesis.

[0033] This application employs a low-melting-point lithium silicate glass phase layer pre-coated on the surface of zirconia particles and constructs an electroactive network inside the green body consisting of montmorillonite nanosheets loaded with divalent iron ions and conductive metal oxide submicron spheres. Therefore, during the low-temperature molten salt bath treatment stage, the liquid phase formed by the melting of the glass phase layer drives the densification of the green body through a dissolution-precipitation mass transfer mechanism, avoiding the volume shrinkage associated with traditional high-temperature solid-state sintering. At the same time, the electroactive network spontaneously forms a micro galvanic cell in the molten salt ion conductor environment, and the generated micro-area electric field directionally pulls the metal cations in the molten salt, causing the coloring ions to change from passive diffusion to active migration, thereby simultaneously achieving the effects of green body densification and full-layer depth gradient coloring under low-temperature conditions.

[0034] Example 1: This example provides a 3D printing composite ceramic restorative denture fabrication process, which includes the following steps: S1. A lithium silicate glass precursor is coated onto the surface of zirconia particles by a sol-gel method, and then dried and calcined to obtain core-shell structured zirconia powder. The core-shell structured zirconia powder is mixed with montmorillonite nanosheets and conductive metal oxide submicron spheres to obtain electroactive ceramic composite powder. The lithium silicate glass precursor was prepared by hydrolysis and polycondensation of tetraethyl orthosilicate, lithium carbonate, and alumina precursor under acidic conditions; the drying temperature was 60℃ for 2 hours; the calcination temperature was 500℃ for 1 hour, and the calcination atmosphere was air; the thickness of the glass phase shell in the core-shell structure zirconia powder was 5 nm.

[0035] The preparation method of montmorillonite nanosheets is as follows: montmorillonite is immersed in hydrochloric acid solution for acid activation treatment, washed, and then immersed in ferrous sulfate or ferrous chloride solution. After centrifugation, washing, and drying, the montmorillonite nanosheets are obtained. The conductive metal oxide submicron spheres are tin oxide submicron spheres with an average particle size of 100 nm. The mass ratio of core-shell structure zirconium oxide powder, montmorillonite nanosheets, and conductive metal oxide submicron spheres is 100:0.5:0.5. The mixing is carried out by ball milling, with anhydrous ethanol as the ball milling medium, a ball milling speed of 200 rpm, and a time of 4 hours.

[0036] S2. Prepare thermally responsive microcapsules, then mix the electroactive ceramic composite powder, thermally responsive microcapsules and photosensitive resin premix evenly and degas to obtain photocurable printing paste; The thermally responsive microcapsule consists of a core, an inner shell, and an outer shell, arranged from the inside out. The core contains a metal ion compound, the inner shell is made of a metal-organic framework material, and the outer shell is made of borosilicate glass.

[0037] The method for preparing thermally responsive microcapsules is as follows: a solution containing a metal ion compound is spray-dried to form micron-sized particles to obtain a core; the core is dispersed in a solution containing a metal-organic framework precursor, and after separation and drying, a core-shell intermediate is obtained; the core-shell intermediate is dispersed in a sol containing a borosilicate glass precursor, spray-dried, and calcined at low temperature to form an outer shell layer, thereby obtaining thermally responsive microcapsules.

[0038] The core contains erbium nitrate as a metal ion compound; the inner shell is made of ZIF-8 metal-organic framework material with a pyrolysis temperature of 800℃; and the outer shell is made of borosilicate glass with a softening point of 700℃.

[0039] The photosensitive resin premix contains acrylate monomers, acrylate oligomers, photoinitiators, and dispersants; the mass ratio of electroactive ceramic composite powder to photosensitive resin premix is ​​1:1; the amount of thermally responsive microcapsules added is 1% of the mass of the electroactive ceramic composite powder; the mixing speed is 800 rpm and the time is 10 min; degassing is performed using vacuum degassing at a vacuum degree of -0.08 MPa for 10 min.

[0040] S3. The photocurable printing paste is formed by photocurable 3D printing to obtain a green body; the green body is subjected to thermal degreasing treatment to remove organic resin to obtain a porous preform; Among them, the photopolymerization 3D printing adopts digital light processing, the printing layer thickness is 25μm, and the single layer exposure time is 1 second; the thermal degreasing treatment is heated to 400℃ at a heating rate of 0.5℃ / min and held for 1 hour, then heated to 700℃ at a heating rate of 1℃ / min and held for 0.5 hours, with air as the degreasing atmosphere.

[0041] S4. Heat and melt nitrates and nitrites, and dissolve metal cation salts in them to obtain a functional molten salt bath; immerse the porous blank in the functional molten salt bath, first heat it to the first temperature range and keep it at that temperature, then heat it to the second temperature range and keep it at that temperature, and then cool it down and take it out to obtain a densified colored denture blank. The mass ratio of nitrate to nitrite is 1:0.5; the metal cation salt is erbium nitrate, and the amount added is 0.5% of the total mass of nitrate and nitrite; the heating and melting temperature is 400℃, and the functional molten salt bath is preheated for 0.5 hours before immersing the porous blank; the first temperature range is 750℃, the heating rate is 3℃ / min, and the holding time is 10min; the second temperature range is 850℃, the heating rate is 1℃ / min, and the holding time is 20min; the cooling is carried out at a cooling rate of 1℃ / min to 400℃ and then naturally cooled to room temperature with the furnace.

[0042] S5. Clean the densified and stained denture blank to obtain a 3D printed composite ceramic restorative denture.

[0043] The cleaning process involves ultrasonic cleaning with deionized water at a frequency of 40 kHz for 5 minutes, followed by drying at 80°C.

[0044] Example 2: This example provides a 3D printing composite ceramic restorative denture fabrication process, which includes the following steps: S1. A lithium silicate glass precursor is coated onto the surface of zirconia particles by a sol-gel method, and then dried and calcined to obtain core-shell structured zirconia powder. The core-shell structured zirconia powder is mixed with montmorillonite nanosheets and conductive metal oxide submicron spheres to obtain electroactive ceramic composite powder. The lithium silicate glass precursor was prepared by hydrolysis and polycondensation of tetraethyl orthosilicate, lithium carbonate, and alumina precursor under acidic conditions; the drying temperature was 90℃ for 5 hours; the calcination temperature was 600℃ for 2 hours, and the calcination atmosphere was air; the thickness of the glass phase shell in the core-shell structure zirconia powder was 12.5 nm.

[0045] The preparation method of montmorillonite nanosheets is as follows: montmorillonite is immersed in hydrochloric acid solution for acid activation treatment, washed, and then immersed in ferrous sulfate or ferrous chloride solution. After centrifugation, washing, and drying, the montmorillonite nanosheets are obtained. The conductive metal oxide submicron spheres are indium tin oxide submicron spheres with an average particle size of 200 nm. The mass ratio of core-shell structure zirconium oxide powder, montmorillonite nanosheets, and conductive metal oxide submicron spheres is 100:1.75:1.75. The mixing is carried out by ball milling, with anhydrous ethanol as the ball milling medium, a ball milling speed of 300 rpm, and a time of 8 hours.

[0046] S2. Prepare thermally responsive microcapsules, then mix the electroactive ceramic composite powder, thermally responsive microcapsules and photosensitive resin premix evenly and degas to obtain photocurable printing paste; The thermally responsive microcapsule consists of a core, an inner shell, and an outer shell, arranged from the inside out. The core contains a metal ion compound, the inner shell is made of a metal-organic framework material, and the outer shell is made of borosilicate glass.

[0047] The method for preparing thermally responsive microcapsules is as follows: a solution containing a metal ion compound is spray-dried to form micron-sized particles to obtain a core; the core is dispersed in a solution containing a metal-organic framework precursor, and after separation and drying, a core-shell intermediate is obtained; the core-shell intermediate is dispersed in a sol containing a borosilicate glass precursor, spray-dried, and calcined at low temperature to form an outer shell layer, thereby obtaining thermally responsive microcapsules.

[0048] The core contains cerium nitrate as a metal ion compound; the inner shell is made of ZIF-67 metal-organic framework material with a pyrolysis temperature of 850℃; and the outer shell is made of borosilicate glass with a softening point of 750℃.

[0049] The photosensitive resin premix contains acrylate monomers, acrylate oligomers, photoinitiators, and dispersants; the mass ratio of electroactive ceramic composite powder to photosensitive resin premix is ​​2.5:1; the amount of thermally responsive microcapsules added is 5.5% of the mass of the electroactive ceramic composite powder; the mixing speed is 1400 rpm and the time is 35 min; degassing is performed by vacuum degassing at a vacuum degree of -0.09 MPa for 20 min.

[0050] S3. The photocurable printing paste is formed by photocurable 3D printing to obtain a green body; the green body is subjected to thermal degreasing treatment to remove organic resin to obtain a porous preform; Among them, the photopolymerization 3D printing adopts digital light processing, the printing layer thickness is 62.5μm, and the single layer exposure time is 5.5 seconds; the thermal degreasing treatment is heated to 500℃ at a heating rate of 1.25℃ / min and held for 2 hours, and then heated to 800℃ at a heating rate of 2℃ / min and held for 1.25 hours. The degreasing atmosphere is nitrogen.

[0051] S4. Heat and melt nitrates and nitrites, and dissolve metal cation salts in them to obtain a functional molten salt bath; immerse the porous blank in the functional molten salt bath, first heat it to the first temperature range and keep it at that temperature, then heat it to the second temperature range and keep it at that temperature, and then cool it down and take it out to obtain a densified colored denture blank. The mass ratio of nitrate to nitrite is 1:1.25; the metal cation salt is cerium nitrate, and the amount added is 2.75% of the total mass of nitrate and nitrite; the heating and melting temperature is 500℃, and the functional molten salt bath is preheated for 1.25 hours before immersing the porous green blank; the first temperature range is 800℃, the heating rate is 5.5℃ / min, and the holding time is 35min; the second temperature range is 900℃, the heating rate is 3℃ / min, and the holding time is 55min; the cooling is carried out at a cooling rate of 3℃ / min to 450℃ and then naturally cooled to room temperature with the furnace.

[0052] S5. Clean the densified and stained denture blank to obtain a 3D printed composite ceramic restorative denture.

[0053] The cleaning process involved ultrasonic cleaning with deionized water at a frequency of 60 kHz for 12.5 minutes, followed by drying at 100°C.

[0054] Example 3: This example provides a 3D printing composite ceramic restorative denture fabrication process, which includes the following steps: S1. A lithium silicate glass precursor is coated onto the surface of zirconia particles by a sol-gel method, and then dried and calcined to obtain core-shell structured zirconia powder. The core-shell structured zirconia powder is mixed with montmorillonite nanosheets and conductive metal oxide submicron spheres to obtain electroactive ceramic composite powder. The lithium silicate glass precursor was prepared by hydrolysis and polycondensation of tetraethyl orthosilicate, lithium carbonate, and alumina precursor under acidic conditions; the drying temperature was 120℃ for 8 hours; the calcination temperature was 700℃ for 3 hours, and the calcination atmosphere was air; the thickness of the glass phase shell in the core-shell structure zirconia powder was 20 nm.

[0055] The preparation method of montmorillonite nanosheets is as follows: montmorillonite is immersed in hydrochloric acid solution for acid activation treatment, washed, and then immersed in ferrous sulfate or ferrous chloride solution. After centrifugation, washing, and drying, the montmorillonite nanosheets are obtained. The conductive metal oxide submicron spheres are tin oxide submicron spheres with an average particle size of 300 nm. The mass ratio of core-shell structure zirconium oxide powder, montmorillonite nanosheets, and conductive metal oxide submicron spheres is 100:3:3. The mixing is carried out by ball milling, with anhydrous ethanol as the ball milling medium, a ball milling speed of 400 rpm, and a time of 12 hours.

[0056] S2. Prepare thermally responsive microcapsules, then mix the electroactive ceramic composite powder, thermally responsive microcapsules and photosensitive resin premix evenly and degas to obtain photocurable printing paste; The thermally responsive microcapsule consists of a core, an inner shell, and an outer shell, arranged from the inside out. The core contains a metal ion compound, the inner shell is made of a metal-organic framework material, and the outer shell is made of borosilicate glass.

[0057] The method for preparing thermally responsive microcapsules is as follows: a solution containing a metal ion compound is spray-dried to form micron-sized particles to obtain a core; the core is dispersed in a solution containing a metal-organic framework precursor, and after separation and drying, a core-shell intermediate is obtained; the core-shell intermediate is dispersed in a sol containing a borosilicate glass precursor, spray-dried, and calcined at low temperature to form an outer shell layer, thereby obtaining thermally responsive microcapsules.

[0058] The core contains ferric nitrate as a metal ion compound; the inner shell is made of ZIF-8 metal-organic framework material with a pyrolysis temperature of 900℃; and the outer shell is made of borosilicate glass with a softening point of 800℃.

[0059] The photosensitive resin premix contains acrylate monomers, acrylate oligomers, photoinitiators, and dispersants; the mass ratio of electroactive ceramic composite powder to photosensitive resin premix is ​​4:1; the amount of thermally responsive microcapsules added is 10% of the mass of the electroactive ceramic composite powder; the mixing speed is 2000 rpm and the time is 60 min; degassing is performed by vacuum degassing at a vacuum degree of -0.1 MPa for 30 min.

[0060] S3. The photocurable printing paste is formed by photocurable 3D printing to obtain a green body; the green body is subjected to thermal degreasing treatment to remove organic resin to obtain a porous preform; Among them, the photopolymerization 3D printing adopts digital light processing, the printing layer thickness is 100μm, and the single layer exposure time is 10 seconds; the thermal degreasing treatment is heated to 600℃ at a heating rate of 2℃ / min and held for 3 hours, then heated to 900℃ at a heating rate of 3℃ / min and held for 2 hours, and the degreasing atmosphere is nitrogen.

[0061] S4. Heat and melt nitrates and nitrites, and dissolve metal cation salts in them to obtain a functional molten salt bath; immerse the porous blank in the functional molten salt bath, first heat it to the first temperature range and keep it at that temperature, then heat it to the second temperature range and keep it at that temperature, and then cool it down and take it out to obtain a densified colored denture blank. The mass ratio of nitrate to nitrite is 1:2; the metal cation salt is ferric nitrate, and the amount added is 5% of the total mass of nitrate and nitrite; the heating and melting temperature is 600℃, and the functional molten salt bath is preheated for 2 hours before immersing the porous green blank; the first temperature range is 850℃, the heating rate is 8℃ / min, and the holding time is 60min; the second temperature range is 950℃, the heating rate is 5℃ / min, and the holding time is 90min; the cooling is carried out at a cooling rate of 5℃ / min to 500℃ and then naturally cooled to room temperature with the furnace.

[0062] S5. Clean the densified and stained denture blank to obtain a 3D printed composite ceramic restorative denture.

[0063] The cleaning process involves ultrasonic cleaning with deionized water at a frequency of 80 kHz for 20 minutes, followed by drying at 120°C.

[0064] Comparative Example 1: This comparative example refers to the content of Example 1, except that in step S1, the zirconium oxide particles were not coated with lithium silicate glass precursors using the sol-gel method. Instead, uncoated zirconium oxide particles were directly mixed with montmorillonite nanosheets and conductive metal oxide submicron spheres. The rest of the content is the same as in Example 1.

[0065] Comparative Example 2: This comparative example refers to the content of Example 1, except that the montmorillonite nanosheets in step S1 were not subjected to ion exchange treatment with ferrous sulfate or ferrous chloride solution, that is, the montmorillonite was only acid activated and the interlayer was not loaded with divalent iron ions. The rest of the content is the same as that of Example 1.

[0066] Comparative Example 3: This comparative example refers to the content of Example 1, except that conductive metal oxide submicron spheres were not added in step S1. That is, the electroactive ceramic composite powder is composed only of core-shell structure zirconium oxide powder and montmorillonite nanosheets. The rest of the content is the same as that of Example 1.

[0067] Comparative Example 4: This comparative example refers to the content of Example 1, except that thermally responsive microcapsules were not prepared and added in step S2. That is, the photocurable printing paste is composed only of electroactive ceramic composite powder and photosensitive resin premix. The rest of the contents are the same as in Example 1.

[0068] Comparative Example 5: This comparative example refers to the content of Example 1, except that the functional molten salt bath in step S4 does not dissolve the metal cation salt, that is, the molten salt bath is composed only of a mixture of nitrate and nitrite and does not contain any added color-producing ions. The rest of the content is the same as that of Example 1.

[0069] Comparative Example 6: This comparative example refers to the content of Example 1, except that in step S4, after the porous blank is immersed in the functional molten salt bath, it is only heated to the first temperature range for heat preservation, and is not heated to the second temperature range. That is, it is kept at the first temperature range and then cooled down. The rest of the content is the same as Example 1.

[0070] Performance testing Sample preparation: 3D printed composite ceramic prosthetic samples were prepared according to the complete process steps described in the examples and comparative examples. The samples were cleaned and dried in step S5 without any additional surface treatment and were used for subsequent performance testing.

[0071] Densification degree test: The actual density of the samples prepared in the examples and comparative examples was determined by Archimedes' water displacement method. At the same time, the relative density was calculated based on the theoretical density of zirconia ceramic materials with the same composition. Before the test, the samples were ultrasonically cleaned in anhydrous ethanol and dried thoroughly. Five samples were taken from each group and the average value was taken. The density test standard refers to GB / T 25995-2010 "Test method for density and apparent porosity of fine ceramics".

[0072] Volume shrinkage rate detection: In the green body stage after photopolymerization 3D printing in step S3, the external dimensions of each sample in three dimensions—from tooth cusp to neck, mesiodistal, and buccal-lingual—are measured and recorded using digital vernier calipers. After all process steps are completed in each embodiment and comparative example, the final dimensions of the same sample in the corresponding dimensions are measured again, and the linear shrinkage rate and volume shrinkage rate in each dimension are calculated. The test standard for volume shrinkage rate refers to the evaluation method for dimensional accuracy in GB / T 39952-2021 "Technical Requirements for Dimensional Deviation of Additive Manufacturing Photopolymerization Ceramic 3D Printed Parts".

[0073] Staining depth testing: The samples prepared in the examples and comparative examples were cut along the long axis of the tooth using a low-speed diamond cutter to expose the cross section. After gradient polishing and ultrasonic cleaning of the cross section, the depth of penetration of staining ions from the surface of the restoration into the interior was observed and measured under a stereomicroscope at a fixed magnification. The thickness distribution of the staining layer in different areas of the cross section was recorded to evaluate the penetration degree of the color gradient. The testing standard for staining depth refers to the evaluation principles of color penetration in YY 0300-2009 "Dental Ceramic Materials".

[0074] Color uniformity test: The cross-sections of the samples prepared in the examples and comparative examples were placed under a spectrophotometer. Multiple color measurement points were selected in the surface, middle and deep regions of the sample cross-section to measure the colorimetric values. The standard deviation of the colorimetric values ​​in each region was calculated to evaluate the uniformity of color distribution from the surface to the deep layer. The test standard for color uniformity refers to GB / T 3979-2008 "Methods for measuring the color of objects".

[0075] Surface sealing effect test: The surface of the samples prepared in the examples and comparative examples was coated with methylene blue indicator solution, and after standing for a certain period of time, it was rinsed with running deionized water and dried. The presence of dye penetration traces on the sample surface was observed under a stereomicroscope. The amount of liquid adsorption on the surface was evaluated by measuring the change in sample mass before and after dyeing, so as to evaluate the integrity and sealing effect of the self-glaze sealing layer. The test standard for surface sealing effect refers to the evaluation principle of surface water absorption in GB / T3810.3-2016 "Test Methods for Ceramic Tiles Part 3: Determination of Water Absorption, Apparent Porosity, Apparent Relative Density and Bulk Density".

[0076] Table 1: Results of Densification Degree and Volume Shrinkage Rate Tests Table 2: Results of Shading Depth Detection Table 3: Test Results of Coloring Uniformity and Surface Sealing Effect Example Conclusion: As can be seen from Examples 1-3 and Comparative Example 1, and Table 1, when the lithium silicate-based glass precursor coating treatment on the surface of zirconia particles is omitted, the interior of the preform lacks a low-temperature liquid-mediated phase. The molten salt bath treatment stage cannot achieve particle rearrangement and densification through the dissolution-precipitation mass transfer mechanism, resulting in a decrease in relative density and an increase in volume shrinkage. The examples, through pre-coating with a glass phase layer, establish a uniform liquid phase environment under low-temperature conditions, drive the preform to be fully densified, and control volume change with the assistance of the liquid phase, thereby achieving a simultaneous improvement in densification degree and dimensional stability.

[0077] Combining Examples 1-3 and Comparative Example 2 with Tables 2 and 3, it can be seen that when montmorillonite nanosheets are not loaded with ferrous ions, although the layered structure of montmorillonite is retained inside the blank, it lacks the anodic active sites necessary to form a micro galvanic cell. The electrochemical driving effect in the molten salt bath cannot be activated, and the color-emitting ions can only passively diffuse by relying on the concentration gradient. Their penetration depth and distribution uniformity are significantly limited. In the examples, by treating montmorillonite with ferrous ions, a complete redox couple is formed inside the blank. In the molten salt liquid phase environment, the color-emitting ions are spontaneously driven to migrate directionally along the grain boundaries, thereby obtaining continuous color penetration and uniform color distribution from the surface to the deep layers.

[0078] Combining Examples 1-3 and Comparative Example 3 with Tables 2 and 3, it can be seen that when the electroactive ceramic composite powder lacks conductive metal oxide submicron spheres, the interior of the green body only contains montmorillonite nanosheets loaded with ferrous ions, which cannot form a closed micro galvanic cell circuit. The electrochemical traction effect is difficult to establish effectively, the driving force for the migration of coloring ions is insufficient, and both the coloring depth and uniformity decrease. The examples, by simultaneously introducing montmorillonite nanosheets and conductive metal oxide submicron spheres, constructed a fully distributed micro-electroactive network, which spontaneously formed a micro galvanic cell array throughout the green body in the molten salt ion conductor environment. This ensured that the coloring ions were fully directionally attracted in each region, achieving the effect of uniform coloring across the entire layer depth.

[0079] Combining Examples 1-3 and Comparative Example 4 with Table 2, it can be seen that when no thermally responsive microcapsules are added to the photocurable printing paste, the molten salt bath treatment in step S4 relies solely on the color-producing ions dissolved in the molten salt for one-time penetration. The colorant lacks a phased release mechanism, and the coloring depth is limited. The examples introduce microcapsules with a three-order thermally responsive structure, which allow the color-producing ions to be released in batches during the heating process of the molten salt bath. The initial penetration and the later concentrated release are superimposed, expanding the range of color-producing ions migrating to the depth of the preform and forming a three-dimensional color gradient that runs through the entire layer of the restoration.

[0080] As can be seen from Examples 1-3 and Comparative Example 5, and Tables 2 and 3, when the metal cation salt is not dissolved in the functional molten salt bath, although the green body completes densification and surface sealing during the molten salt bath treatment, it lacks a source of coloring ions, and the cross section of the restoration cannot achieve the body coloring effect. The examples, by pre-dissolving the metal cation salt in the molten salt bath, allow the coloring ions to be fully mixed with the molten salt medium. At the same time as the liquid phase densification, the coloring ions begin to penetrate into the interior of the green body, ensuring that the coloring process and the densification process are carried out simultaneously, and achieving full-layer coloring of the restoration.

[0081] Combining Examples 1-3 and Comparative Example 6 with Table 2, it can be seen that when the molten salt bath treatment in step S4 only raises the temperature to the first temperature range and not to the second temperature range, the inner shell of the thermally responsive microcapsule has not yet reached the pyrolysis temperature, and the high concentration of colorant in the core has not been released. It only relies on the color-producing ions initially dissolved in the molten salt and a small amount of ions released by the melting of the microcapsule shell for penetration, resulting in a difference in coloring depth compared to the examples. The examples, by setting the heating and heat preservation in the second temperature range, enable the inner shell of the microcapsule to fully pyrolyze and release the colorant in a concentrated manner at the preset temperature, forming a relay effect with the liquid phase permeation network established in the first temperature range. The secondary penetration coloring is connected with the initial penetration, realizing the continuous migration and full anchoring of coloring ions to the deep layers of the billet.

[0082] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A 3D-printed composite ceramic restorative denture fabrication process, characterized in that, Includes the following steps: S1. A lithium silicate glass precursor is coated onto the surface of zirconia particles by a sol-gel method, and then dried and calcined to obtain core-shell structured zirconia powder. The core-shell structured zirconia powder is mixed with montmorillonite nanosheets and conductive metal oxide submicron spheres to obtain electroactive ceramic composite powder. S2. Prepare thermally responsive microcapsules, then mix the electroactive ceramic composite powder, the thermally responsive microcapsules and the photosensitive resin premix evenly and degas to obtain a photocurable printing paste; S3. The photocurable printing paste is formed by photocurable 3D printing to obtain a green blank; the green blank is subjected to thermal degreasing treatment to remove organic resin to obtain a porous preform; S4. Heat and melt nitrates and nitrites, and dissolve metal cation salts in them to obtain a functional molten salt bath; immerse the porous blank in the functional molten salt bath, first heat it to a first temperature range and keep it at that temperature, then heat it to a second temperature range and keep it at that temperature, and then cool it down and take it out to obtain a densified colored denture blank. S5. Clean the densified colored denture blank to obtain a 3D printed composite ceramic restorative denture.

2. The 3D printing composite ceramic restorative denture fabrication process according to claim 1, characterized in that, In step S1, the lithium silicate-based glass precursor is prepared by hydrolysis and polycondensation of tetraethyl orthosilicate, lithium carbonate, and alumina precursor under acidic conditions; the drying temperature is 60–120°C and the time is 2–8 hours; the calcination temperature is 500–700°C and the time is 1–3 hours, and the calcination atmosphere is air; in the core-shell structured zirconium oxide powder, the thickness of the glass phase shell is 5–20 nm.

3. The 3D printing composite ceramic restorative denture fabrication process according to claim 1, characterized in that, In step S1, the method for preparing the montmorillonite nanosheets is as follows: montmorillonite is immersed in hydrochloric acid solution for acid activation treatment, washed, and then immersed in ferrous sulfate or ferrous chloride solution, followed by centrifugation, washing, and drying; the conductive metal oxide submicron spheres are tin oxide submicron spheres or indium tin oxide submicron spheres with an average particle size of 100–300 nm; the mass ratio of the core-shell structure zirconium oxide powder, montmorillonite nanosheets, and conductive metal oxide submicron spheres is 100:0.5–3:0.5–3; the mixing is performed by ball milling, with anhydrous ethanol as the milling medium, a milling speed of 200–400 rpm, and a time of 4–12 hours.

4. The 3D printing composite ceramic restorative denture fabrication process according to claim 1, characterized in that, In step S2, the thermally responsive microcapsule consists of a core, an inner shell, and an outer shell, arranged from the inside out. The core contains a metal ion compound, the inner shell is made of a metal-organic framework material, and the outer shell is made of borosilicate glass.

5. The 3D printing composite ceramic restorative denture fabrication process according to claim 4, characterized in that, The method for preparing the thermally responsive microcapsules is as follows: a solution containing a metal ion compound is spray-dried to form micron-sized particles, thus obtaining the core. The core is dispersed in a solution containing a metal-organic framework precursor, and after separation and drying, a core-shell intermediate is obtained. The core-shell intermediate is dispersed in a sol containing a borosilicate glass precursor, spray-dried, and calcined at low temperature to form an outer shell layer, thus obtaining thermally responsive microcapsules.

6. The 3D printing composite ceramic restorative denture fabrication process according to claim 4, characterized in that, The core contains at least one of erbium nitrate, cerium nitrate, or ferric nitrate; the metal-organic framework material inner shell is ZIF-8 or ZIF-67 with a pyrolysis temperature of 800–900°C; and the borosilicate glass outer shell has a softening point of 700–800°C.

7. The 3D printing composite ceramic restorative denture fabrication process according to claim 1, characterized in that, In step S2, the photosensitive resin premix contains acrylate monomers, acrylate oligomers, photoinitiators, and dispersants; the mass ratio of the electroactive ceramic composite powder to the photosensitive resin premix is ​​1:1 to 4:1; the amount of thermally responsive microcapsules added is 1 to 10% of the mass of the electroactive ceramic composite powder; the mixing speed is 800 to 2000 rpm, and the time is 10 to 60 min; the degassing is performed using vacuum degassing with a vacuum degree of -0.08 to -0.1 MPa for 10 to 30 min.

8. The 3D printing composite ceramic restorative denture fabrication process according to claim 1, characterized in that, In step S3, the photopolymerization 3D printing uses digital light processing, the printing layer thickness is 25-100μm, and the single-layer exposure time is 1-10 seconds; the thermal degreasing treatment is heated to 400-600℃ at a heating rate of 0.5-2℃ / min and held for 1-3 hours, then heated to 700-900℃ at a heating rate of 1-3℃ / min and held for 0.5-2 hours, and the degreasing atmosphere is air or nitrogen.

9. The fabrication process for a 3D-printed composite ceramic restorative denture according to claim 1, characterized in that, In step S4, the mass ratio of nitrate to nitrite is 1:0.5-2; the metal cation salt is one or more of erbium nitrate, cerium nitrate, or ferric nitrate, and its addition amount is 0.5-5% of the total mass of the nitrate and nitrite; the heating and melting temperature is 400-600℃, and the functional molten salt bath is preheated for 0.5-2 hours before immersing the porous blank; The first temperature range is 750–850℃, the heating rate is 3–8℃ / min, and the holding time is 10–60min; the second temperature range is 850–950℃, the heating rate is 1–5℃ / min, and the holding time is 20–90min; the cooling is achieved by cooling to 400–500℃ at a cooling rate of 1–5℃ / min and then allowing the furnace to cool naturally to room temperature.

10. The 3D printing composite ceramic restorative denture fabrication process according to claim 1, characterized in that, In step S5, the cleaning is performed using deionized water ultrasonic cleaning with an ultrasonic frequency of 40-80 kHz and a time of 5-20 min. After cleaning, the water is dried at 80-120°C.

Images