Generally speaking, the transparency of zirconia has an inverse relationship with its strength. The better the transmittance, the lower the strength.
1. Alumina has a certain toughening effect in zirconia, but the higher the alumina content, the greater the impact on transparency. The high content of alumina has good mechanical properties, but the transparency is greatly reduced.
2. The content of stabilizer yttrium oxide has a great relationship with transparency and strength.
3. The particle size and agglomeration size of zirconia powder also have a certain relationship with transparency and strength.
In addition, the technician's operation process also has a certain influence on the strength and transparency of zirconia, and this content will be discussed in the future.
How is the transparency of zirconia tested?
It is explained by the indicator of the remaining transmittance after a certain amount of light passes through a certain thickness of zirconia.
To make a simple analogy, the light of a flashlight is shining on a stainless steel plate with a certain thickness. On the other end of the stainless steel plate, if you cannot see the flashlight light, the transmittance of the steel plate is 0%; Replace the stainless steel with a glass plate of corresponding thickness. You can definitely see the flashlight on the other end of the glass plate. If the glass is transparent enough, the intensity of the light you see through the glass plate is almost the same as that after you remove the glass plate. The same, then the transmittance of that glass plate is close to 100%.
Initially, the transmittance of zirconia was more than 20%. With the continuous efforts of zirconia raw material manufacturers, it has a transmittance of 35%, 44%, 47%, and 50%, and also has a certain strength of dental zirconia raw materials. Appeared one after another.
Generally speaking, the zirconia block on the market now has a light transmittance of about 30%-35% (1mm thick sample, 740nm wavelength) with ordinary light transmittance, and the three-point bending strength is 1200-1400MPa;
For high light transmittance products, the light transmittance is about 40-45%, and the three-point bending strength is 1000-1200MPa; for ultra-high light transmittance products, the light transmittance is about 48-50%, and the three-point bending strength is 600. -1000MPa. There is also metal-colored zirconia that needs to be shielded for planting restoration. This zirconia needs to be extremely opaque, with a light transmittance of about 20% or less, and a strength of about 1000Mpa.
Aesthetically, we need zirconia with high transparency, close to the color of natural teeth, and sometimes extremely opaque zirconia for aesthetic purposes. The market demand is colorful, and raw material manufacturers and zirconia block manufacturers are also making unremitting efforts.
In order to make the zirconium oxide restoration more beautiful and closer to the gradient hair color of the patient's natural teeth, most zirconium block manufacturers have also introduced multi-colored zirconium oxide blocks (or called gradient colors) to simulate the anatomy and histological structure of natural teeth. Even the zirconium oxide block with fluorescence has appeared.
The natural teeth implanted in the alveolar bone are histologically classified as hard tissues including enamel, dentin and cementum. Soft tissue is the pulp (nerves, blood vessels, connective tissue) that fills the pulp cavity. For restorations, cementum does not need to be considered. What needs to be considered is the comprehensive color effect of tooth enamel, dentin and dental pulp, the most important of which is the color effect of tooth enamel and dentin. As we all know, almost all tooth enamel is composed of hydroxyapatite and has high transparency; while dentin contains a lot of organic matter, and there are differences in structure, the transparency is much worse than that of tooth enamel. In terms of structure, the distribution of enamel and dentin on the incisal end, one third of the incisional end, the body, and one third of the tooth neck is different, which shows that the hair color of each longitudinal layer of the tooth is different. To be more detailed, the front teeth and the back teeth are not the same. Each tooth position in the front teeth is different, and each tooth position in the molars is also different. Going further, the hair color of the same person's teeth is different when he is young, middle-aged, and old. This is an irresistible law, and it is also the amorous feelings that the world has given us.
The multi-colored zirconia block simulates the gradual color development of natural teeth. The multi-colored zirconia block can correspond to most applications, save dyeing operations, and can fully meet the aesthetic requirements of posterior teeth restoration and part of the front
