What factors affect the hardness of dental zirconia

The hardness of dental zirconia is affected by many factors, which can be summarized as material composition, microstructure, processing technology and environmental conditions. Here's a breakdown of these factors:

First, material composition

Zirconia purity: The higher the purity of zirconia, the higher its hardness often. High purity zirconia provides better physical properties, including hardness.

Additives: In order to improve the processability and mechanical properties of zirconia, a certain amount of auxiliary materials, such as alumina, yttrium oxide and other stabilizers, are usually added. The types and proportions of these additives affect the hardness of zirconia. For example, alumina plays a certain toughening role in zirconia, but its high content will reduce transparency and may have a certain impact on hardness. The content of yttrium oxide is closely related to transparency and hardness.

Second, microstructure

Crystal phase composition: Zirconia has a variety of crystal phases, such as tetragonal phase, monoclinic phase and cubic equal. Different crystalline phases of zirconia have different hardness. Tetragonal phase zirconia usually has a higher hardness, while cubic phase zirconia, although good light transmission, has a relatively low hardness.

Grain size: The grain size of zirconia also affects its hardness. In general, the smaller the grain size, the higher the hardness of zirconia. This is because small grains can resist external pressures more effectively, thereby increasing the hardness of the material.

Third, processing technology

Sintering temperature: Sintering temperature is one of the key factors affecting the hardness of zirconia. The increase of sintering temperature can increase the density of zirconia and reduce the porosity, thus increasing the hardness. However, too high sintering temperature may also lead to zirconia grain growth, but reduce the hardness.

Polishing treatment: Polishing treatment can remove micro-cracks and defects on the surface of zirconia, thereby improving its surface hardness and finish. However, it should be noted that the polishing treatment has a limited effect on the overall hardness of zirconia.

Fourth, environmental conditions

Hydrothermal aging: Under the action of oral environment and repeated chewing, zirconia will undergo hydrothermal aging, resulting in the transformation of the tetragonal monoclinic phase. This transition process will be accompanied by volume expansion and crack intrusion, which will reduce the hardness and flexural strength of zirconia.

Corrosion environment: Although zirconia itself has good corrosion resistance, it may still be affected by corrosion in some specific environments (such as strong acid and alkali environments), resulting in a decrease in hardness.