Hot pressing sintering molding method of zirconium oxide for dental all-ceramic

Abstract

The invention relates to the technical field of biomedicine, in particular to a dental all-ceramic zirconia hot pressing sintering forming method. According to the specific technical scheme, the preparation method comprises the following steps: uniformly mixing zirconia raw materials, putting the mixture into a closed container, heating to 200-500 DEG C at a speed of 3-5 DEG C / min, introducing inert gas into the container, pressurizing to 100-200 MPa at a speed of 5-10 MPa / min in an inert gas atmosphere, keeping the temperature and the pressure, cooling the container to room temperature, and releasing the pressure to obtain the dental all-ceramic zirconia. The sintered dental all-ceramic zirconium oxide is formed under the inert atmosphere and the sealing condition at the same pressure and the same temperature in all directions, the shrinkage of the product tends to be consistent, the internal structure is denser, and the finished product is high in mechanical property isotropy, small in shrinkage deformation and large in density.

Description

Technical Field

[0001] The present invention relates to the field of biomedical technology, and in particular to a method for hot-pressing and sintering zirconium oxide for dental all-ceramics. Background Art

[0002] Among the known oral restoration material systems, zirconium oxide (ZrO2) ceramics have high biocompatibility and are significantly superior to other materials in terms of mechanical properties such as strength and toughness. They have become the focus of current attention and research on oral materials. The preparation technology of traditional zirconium oxide ceramic blocks mainly includes the mixing of zirconium oxide powders, dry pressing-cold isostatic pressing-pre-sintering molding and final sintering of the finished product. Among them, dry pressing is the initial molding of the powder, cold isostatic pressing can further improve the density of the sample, the uniformity of the powder and reduce the sintering resistance, and pre-sintering is a key link in the preparation process of zirconium oxide ceramic blocks. Its main purpose is to remove the organic matter and impurities in the product at a certain temperature and holding time. Through sintering, the grains grow, the grain boundaries shrink, the porosity decreases, the volume shrinks and the density increases, and finally a dense and hard zirconium oxide ceramic block is formed. However, the current dry pressing-cold isostatic pressing-pre-sintering molding method has the following defects:

[0003] (1) The time of dry pressing-cold isostatic pressing-pre-firing is too long, the equipment consumes a lot of energy and has high maintenance costs. When using a push-plate tunnel kiln for pre-firing zirconia ceramic blocks, the heating and cooling rates of the equipment are slow, and the average time from the product entering the kiln to coming out is 80 to 100 hours.

[0004] (2) Since the environment inside the tunnel kiln is in contact with the external atmospheric environment, convection heat transfer causes uneven temperature distribution in various areas of the kiln, which may lead to excessively high porosity of the porcelain blocks, insufficient density, and inconsistent shrinkage in all directions, resulting in surface concave-convex deformation. Measurements show that the concave-convex deformation values on both sides of the pre-fired porcelain blocks are close to 0.2-0.3 mm. The size increase rate will be increased during the final firing, and there are risks of cracking and porcelain chipping in clinical restoration applications.

[0005] (3) Dry pressing and cold isostatic pressing are used. Due to the uneven pressure distribution in the radial and axial directions, the blank after molding often has defects such as delamination and cracks, which affects the size of the processed denture and ultimately makes it difficult to fit the teeth in place clinically.

[0006] (4) The organic binder in the zirconium oxide powder is completely eliminated during pre-firing, resulting in the brittleness of the product. Only the denture neck edge with a thickness of 0.2 to 0.5 mm can be processed, and ultra-thin veneers cannot be made. During clinical restoration, the neck edge is prone to porcelain stretching, and the customer's sense of fit is poor. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the present invention provides a hot pressing and sintering method for zirconia for dental all-ceramics.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] The invention discloses a hot-pressing sintering molding method for zirconia for dental all-ceramics. The method comprises the following steps: uniformly mixing zirconia raw materials, placing the mixture in a sealed container, heating the mixture to 200-500°C at a rate of 3-5°C / min, introducing an inert gas into the container, and pressurizing the mixture to 100-200 MPa at a rate of 5-10 MPa / min under the inert gas atmosphere. After heat and pressure maintenance, the container is cooled to room temperature and the pressure is released to obtain zirconia for dental all-ceramics.

[0010] Preferably, the inert gas is argon or ammonia.

[0011] Preferably, the heat preservation and pressure preservation time is 1 to 3 hours.

[0012] Preferably, the container is cooled to room temperature at 3-5°C / min in an inert gas environment.

[0013] Preferably, the inert gas in the container is gradually released at 5-10 MPa / min until the pressure returns to zero.

[0014] Preferably, in terms of mass percentage, the zirconium oxide raw material comprises: 6.50-9.50 wt% Y2O3, 0.2-0.3 wt% Er2O3, 0.10-0.20 wt% Fe2O3, 0.01-0.03 wt% Mn2O3, and 90.5-92.5 wt% ZrO2.

[0015] The present invention has the following beneficial effects:

[0016] (1) Compared with the prior art, the hot pressing sintering of the present invention can be carried out simultaneously by combining dry pressing, cold isostatic pressing and pre-sintering, and the time is usually between 10 and 13 hours, which can greatly shorten the time, reduce equipment energy consumption and maintenance costs.

[0017] (2) Hot pressing sintering: Since the product is formed in an inert atmosphere and sealed conditions under isotropic pressure and temperature, the particles in the thermoplastic state are conducive to the contact diffusion and mass transfer process, thereby promoting more consistent shrinkage of the porcelain block and a more compact internal structure. The finished product has higher anisotropic mechanical properties, lower bending deformation (the bending deformation value of the porcelain block using the traditional dry pressing-cold isostatic pressing-pre-firing molding method is 0.2-0.3 mm, and the bending deformation value of hot pressing sintering is 0.1-0.2 mm), and greater density.

[0018] (3) The present invention adopts hot pressing and sintering molding technology, and the radial and axial shrinkage of the product are completely consistent. The processing size of the denture is completely accurate to the design value, and it can be completely matched and sutured with the braces when finally used in clinical end.

[0019] (4) The hot pressing sintering molding technology can retain part of the organic adhesive and can process ultra-thin veneers with a thickness as low as 0.1mm, meeting the clinical demand for ultra-thin veneers, while solving the sealing problem of the denture neck edge and ensuring seamless fitting between the restoration and the gums. DETAILED DESCRIPTION

[0020] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0021] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0022] The present invention discloses a method for hot-pressing and sintering zirconia for dental all-ceramic. The zirconia raw materials, calculated by mass percentage, include: 6.50-9.50 wt% Y2O3, 0.2-0.3 wt% Er2O3, 0.10-0.20 wt% Fe2O3, 0.01-0.03 wt% Mn2O3, and 90.5-92.5 wt% ZrO2. The vessel involved is a hot isostatic press, primarily composed of a high-pressure vessel, heater, compressor, vacuum pump, gas storage tank, cooler, control system, and safety system.

[0023] During the sintering and molding process of zirconia: after the zirconia raw materials are evenly mixed, they are placed in a sealed container and heated to 200-500°C at a rate of 3-5°C / min. Then, an inert gas (argon or ammonia) is pumped into the container. In an inert gas atmosphere, the pressure is increased to 100-200MPa at a rate of 5-10MPa / min. The temperature and pressure are maintained at the set temperature and pressure conditions (200-500°C, 100-200MPa) for 1-3 hours to uniformly heat and pressurize the porcelain block in all directions and improve densification. When the porcelain block is formed, the heating is stopped and the container is allowed to cool to room temperature at a rate of 3-5°C / min in an inert gas environment. The gas medium in the container is gradually released at a rate of 5-10MPa / min through the manual valve of the control system. Finally, after confirming that the pressure gauge shows zero, the container is opened and the product, i.e., zirconia for dental all-ceramics, is taken out.

[0024] Furthermore, the present invention places the mixed powder (zirconia raw material) into a corresponding cylindrical mold in a container, and obtains a cylindrical porcelain block of a required size by calculating the diameter and thickness shrinkage of the powder after hot pressing.

[0025] The present invention will be further described below with reference to specific embodiments.

[0026] Example 1

[0027] Calculated by mass percentage, the zirconium oxide raw material includes 8.0 wt % Y2O3, 0.25 wt % Er2O3, 0.15 wt % Fe2O3, 0.02 wt % Mn2O3, and 91.58 wt % ZrO2.

[0028] The hot-pressing sintering process involves heating the container to 200-500°C and applying pressure to 100-200 MPa in an inert gas atmosphere for 1-3 hours. Once the block is formed, heating is stopped, the block is cooled to room temperature, and the pressure in the container is released, resulting in the dental all-ceramic zirconia.

[0029] The effects of pressure and temperature on product performance were investigated by changing the hot pressing pressure and temperature parameters. When the hot pressing pressure was 140 MPa, the hot pressing temperature was 220°C, and the pressure was maintained for 2 hours, the density of the obtained ceramic block was 3.1 g / cm 3 The final fired density is 6.05g / cm 3 , three-point bending strength is 1200MPa, fracture toughness is 5.8MPa.m 1 / 2 .

[0030] When the hot pressing pressure is 160 MPa, the hot pressing temperature is 300 ° C, and the pressure is maintained for 2 hours, the density of the obtained ceramic block is 3.3 g / cm 3 The final fired density is 6.10g / cm 3 , three-point bending strength is 1240MPa, fracture toughness is 5.7MPa.m 1 / 2 .

[0031] When the hot pressing pressure is 180 MPa, the hot pressing temperature is 350 ° C, and the pressure is maintained for 2 hours, the density of the obtained ceramic block is 3.5 g / cm 3 The final fired density is 6.15g / cm 3 , three-point bending strength is 1300MPa, fracture toughness is 5.6MPa.m 1 / 2 Under these conditions, a zirconia block of the required diameter and thickness is obtained in a custom mold. Using CAD / CAM technology, a 0.1mm thick green veneer can be milled out. After sintering, polishing, dyeing, and glazing, an ultra-thin zirconia veneer is obtained.

[0032] Comparative Example 1

[0033] Compared with the traditional dry pressing-cold isostatic pressing-pre-sintering molding method, the density of the sintered zirconia ceramic block is 2.8-3.0g / cm 3 , final fired density 6.0~6.05g / cm 3 , three-point bending strength 800~1200Mpa, fracture toughness>5.0MPa.m 1 / 2.

[0034] The specific steps are as follows: a fully automatic servo hydraulic press is used for dry pressing. First, the powder raw material (same as Example 1) is loaded into a special mold cavity, and the dry pressing pressure is set to 3.5-5 MPa. The hydraulic cylinder is started by an external power supply to control the upper punch to move downward and the lower punch to move upward to perform bidirectional pressure on the powder. The pressure is maintained for 10-15 seconds, and the porcelain block is demolded and taken out after forming; the porcelain block initially formed by dry pressing is sealed and packaged for vacuuming, placed in the high-pressure cylinder of the cold isostatic press, and the cylinder cover is installed. The pressure is gradually increased to 240-280 MPa, and the pressure is maintained at this pressure for 3 minutes, and finally the pressure is released to take out the product; the cold isostatic pressed porcelain block is removed from the vacuum bag and placed in a sagger. The porcelain block is run from room temperature to the high-temperature zone through a push-plate tunnel kiln track. The high-temperature zone is set to a temperature of 1150-1170°C and kept warm for 4 hours. Finally, it is pre-fired to room temperature in the cold zone of the furnace.

[0035] When the dry pressing pressure is 3.5MPa and the holding time is 15s; the cold isostatic pressing pressure is 240MPa and the holding time is 3min; the pre-firing temperature is 1160℃ and the holding time is 3h, the density of the obtained porcelain block is 2.8g / cm 3 The final fired density is 6.0g / cm 3 , three-point bending strength is 800MPa, fracture toughness is 5.1MPa.m 1 / 2 .

[0036] When the dry pressing pressure is 5 MPa and the holding time is 15 seconds, the cold isostatic pressing pressure is 280 MPa and the holding time is 3 minutes, and the pre-firing temperature is 1160℃ and the holding time is 4 hours, the density of the obtained ceramic block is 3.0 g / cm 3 The final fired density is 6.05g / cm 3 , three-point bending strength is 1200MPa, fracture toughness is 5.2MPa.m 1 / 2 At this time, the performance of the ceramic block reaches the best, but compared with Example 1, its performance is worse than the ceramic block produced by the hot pressing sintering technology disclosed in the present invention.

[0037] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A hot pressing sintering method for forming zirconia for dental all-ceramics, characterized by: After the zirconium oxide raw materials are evenly mixed, they are placed in a sealed container, heated to 200-500°C at a rate of 3-5°C / min, an inert gas is introduced into the container, and in an inert gas atmosphere, the pressure is increased to 100-200 MPa at a rate of 5-10 MPa / min. After heat and pressure maintenance, the container is cooled to room temperature and the pressure is released to obtain zirconium oxide for dental all-ceramics.

2. The method for hot pressing and sintering zirconia for dental all-ceramics according to claim 1, characterized in that: The inert gas is argon or ammonia.

3. The method for hot pressing and sintering zirconia for dental all-ceramics according to claim 1, characterized in that: The time for heat preservation and pressure maintenance is 1 to 3 hours.

4. The method for hot pressing and sintering zirconia for dental all-ceramics according to claim 1, characterized in that: The container was cooled to room temperature at 3-5°C / min in an inert gas environment.

5. The method for hot pressing and sintering zirconia for dental all-ceramics according to claim 4, characterized in that: Release the inert gas in the container gradually at 5-10 MPa / min until the pressure returns to zero.

6. A method for hot pressing and sintering zirconia for dental all-ceramics according to any one of claims 1 to 5, characterized in that: Calculated by mass percentage, the zirconium oxide raw material includes: 6.50-9.50wt% Y2O3, 0.2-0.3wt% Er2O3, 0.10-0.20wt% Fe2O3, 0.01-0.03wt% Mn2O3, and 90.5-92.5wt% ZrO2.