Factors Affecting Semi-permeability Of Zirconia

1. Diameter of the crystal grain

The size of the crystal grains affects the transmittance. When the diameter of the crystal grain is closer to the wavelength of visible light in the range of 380 to 780 nm, the maximum light absorption will occur, resulting in low light transmittance; when the crystal grain size is smaller than the incident light wavelength, the light transmittance is high. Small and uniform particles can achieve compact arrangement, thereby increasing the material density, reducing the number of pores and reducing the pore size, which has a decisive impact on the improvement of the material's semi-permeability.

2. Types of added stabilizers

The transmittance is not directly affected by the added phase, but the relative density and grain diameter of the zirconia ceramics are changed to adjust the translucency of the ceramics. The presence of additional phases may also change the optical uniformity of zirconia ceramics, that is, increase the composition of the ceramic microstructure.

3. Types of added colorants

Natural teeth have a certain color, so the sintered zirconia block also needs to show a color matching the natural teeth. The praseodymium ion makes the zirconium oxide yellow, and the iron ion makes the zirconium oxide brown.

4. Proportion of cubic zirconia

The zirconia products on the market can be roughly divided into traditional zirconia, semi-permeable zirconia, high-permeability zirconia and super-permeable zirconia based on the proportion of cubic zirconia. The higher the proportion of the cubic phase of zirconia, the more transparent the product. A higher proportion of cubic phase can be achieved by adding a higher proportion of yttrium oxide to stabilize the zirconia composition.

5. Stoma

Translucent ceramics should minimize pores during the sintering process. The general oxide ceramics obtained by the solid phase sintering method are usually not transparent even if the density is high. This is due to the rapid growth of crystal grains in the final stage of sintering, forming scattered closed pores. Vacuum sintering, microwave sintering, etc. should also be used to optimize heat treatment to reduce pores.

6. Sintering temperature

Higher sintering temperature can reduce the number of pores. With the increase of temperature, ceramics gradually become densified, the crystal grain diameter increases, and the light transmittance of ceramics increases. However, the sintering temperature still needs to be controlled within a reasonable range. In addition to the sintering temperature, it is also necessary to control the heating rate to ensure uniform heating of the entire material, control the growth rate and size of the crystal, and achieve the purpose of reducing pores. The final sintering temperature and holding time directly affect the sintering density and the light transmittance of the material.