This video is a response to an email question I received about zirconia breaking during and after processing. "I've recently had zirconia crowns that have cracks or are broken, some during milling and some after sintering. Have you seen this and what do you think is the cause?"
Several things to consider:
What brand is being milled?
Dry or wet mill?
Is the zirconia considered a 3Y, 4Y, or 5Y strength?
More zirconia brands and aesthetic zirconia options are starting to enter the chairside market. One thing to keep in mind! Currently, the more translucent the zirconia, the weaker the strength. For instance, the Katana STMLmulti-layered zirconia needs more occlusal and axial reduction than high strength zirconia like the CEREC Sirona zirconia or the Ivoclar ZirCAD LT. If the Katana STML does not have enough thickness during the milling stage, I am hearing that it is sometimes breaking during and after sintering when the preparation is inadequate for material indications.
Another factor to address is making sure the milling unit is calibrated and DO NOT use the fast-milling mode. Carbide burs provide the best mill. Green zirconia is like chalk and needs to be handled accordingly. It is very easy to crack or chip before sintering regardless of the brand.