How To Improve Semi-permeability Of Zirconia Ceramics For Dental Use?
Dec 28, 2021
Zirconia ceramics, due to their high strength and toughness, are known as ceramic steels, which can not only meet the mechanical properties required by the restoration, but also meet the aesthetic requirements of restoration to a certain extent. It can be used clinically for zirconia veneer porcelain. The basal crown of the crown can also be directly used as a full zirconia crown for oral restoration.
At the same time, how to make this dental material with excellent mechanical properties have a perfect aesthetic effect is the goal pursued by some scholars and physicians. When the color and shape of the restoration are comparable to those of natural teeth, and at the same time, it has a more consistent translucency to make the restoration lifelike.
Method for improving translucency of zirconia ceramics
1. Using nano ceramic powder
In recent years, nano-sized zirconia powder has appeared, such as the zirconia powder introduced by Japan’s TOSOH company with diameters of 40nm and 90nm. Due to the small particle size of the powder and the small difference in particle size, the diffusion path of the powder particles is uniform, and the distance of pore diffusion during sintering is shortened, and the pores are easily eliminated to make the 3Y-TZP ceramic structure uniform. Because of the application of nano-sized zirconia powder, new research progress has been made to improve the translucency of 3Y-TZP ceramics. In addition, infiltration of other composite materials such as molten glass into the microporous scaffold constructed by zirconia can significantly improve the translucency.
2. Heating rate
The study found that under the irradiation of visible light with a wavelength of 380-720nm, the transmission rate of the ceramics of the 100℃/h heating rate is higher, which is 7.904%, and the total light transmission rate is also higher, which is 26.66%. With the increase of the heating rate, the total light transmittance of the specimen shows a decrease. The electron microscope results show that when the heating rate is 100℃/h, the particle size range is mostly 250-350nm, and the size is relatively uniform. The experiment also found that with the increase of the heating rate, the size of the crystal grains showed a state of polarization. The faster the temperature rises, the more likely it is that larger and smaller particles coexist.
3. Add oxide stabilizer
Partially stabilized tetragonal zirconia crystals (t-ZrO2) are currently widely used in the field of dental prosthetics. t-ZrO2 is stable at 1173°C-2370°C. If oxide stabilizers such as Y2O3 are added, the tetragonal crystals can be It exists stably at room temperature. The stable t-phase crystal has excellent mechanical properties.
4. Vacuum environment
When zirconia is sintered in a vacuum environment, bubbles are easily discharged from the molten porcelain body, which increases the density of zirconia, thereby increasing the translucency of zirconia.
5 Utilize hot isostatic pressing technology
Hot isostatic pressing (HIP) is a technology that continuously densifies ceramic powder during the sintering process. HIP is mainly used to eliminate remaining pores in the sintered body to improve material properties. Under the action of HIP, the grain boundary begins to diffuse and move, and then the pores passively and continuously diffuse along the grain boundary, and merge and disappear; the pores spheroidize into a spherical shape under the action of surface tension, and continue to decrease. Until it disappears. The macroscopic performance is that the density of the sintered sample continues to increase, almost reaching the theoretical density.
6. Microwave sintering
Microwave sintering is a kind of overall heating. The material converts the absorbed microwave energy into the kinetic energy and potential energy of the molecules inside the material, so that all the molecules of the material can move at the same time and be heated uniformly. During the whole heating process, the temperature gradient inside the material is not or small, so the stress inside the material can be reduced to a minimum, so that even if the heating rate is high, the material will be less likely to crack.
