Zirconia dental crowns are made from zirconium dioxide, a white powdered ceramic material. Its ceramic properties and the fact that is milled from a single block make it a strong dental prosthetic. In fact, its strength allows for far thinner dental crowns than those made with metals.
It's a type of ceramic — or, in more specific terms, a zirconium oxide — that's stronger than porcelain and some metal alloys, and it gets fewer sharp edges from the normal "wear and tear" that happens over time. Zirconia crowns tend to cause less stress and damage on opposing pieces than their porcelain counterparts.