What is “Yttria”?
Yttria, otherwise known as Yttrium Oxide (Y2O3) is an additive used in all dental grade zirconia material. It is used to stabilize the zirconia during sintering. As your zirconia restoration is sintered, it experiences a crystalline phase change. As the zirconia undergoes this phase change, it is inherently unstable. Without the addition of yttria, the zirconia we use would not have the properties needed for dental crowns.
Interesting Details about “Yttria”
- Pure, unstabilized zirconia undergoes a phase transition from monoclinic (below 1170 °C) to tetragonal (between 1170 °C and 2370 °C) then to cubic (above 2370 °C). The use of a stabilization agent like yttria enables control of this crystalline growth. By changing the amount of yttria, we can control the strength and toughness of the final material.
- The use of yttria in dental zirconia essentially “locks-in” the desired microstructure during sintering, thus allowing the correct crystalline phases in the material to develop. The stabilized zirconia has a much wider processing window, which allows multiple sintering temperatures and a reduction of the material’s sensitivity to variations in sintering process.
- The concentration of yttria directly effects the strength and translucency characteristics of the zirconia material. Generally, the more yttria that is in the mix the more material will enter the cubic phase – resulting in more translucency and less flexural strength. This is why more translucent materials tend to be weaker.
- “Zirconia” is a slang term. In the dental lab industry, when someone says “zirconia” it’s shoptalk for “Yttria Stabilized Zirconia”, or “YSZ”.
Thanks for reading! We hope this break down of the term “Yttria” has been of value. Stay tuned next week for another post like this!
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