Zirconia: some practical aspects from the technologist's point of view.

During the past decade, zirconia-based ceramics have been successfully introduced into the clinic to fabricate small and large restorations. Today, we have a better understanding of the physical properties, characteristics, and practical behavior of zirconia, which has led to a more predictable fabrication of clinically acceptable, long-term restorations.1 Zirconia is normally milled from blocks or discs using various zirconia brands. The selection of the right zirconia is important, and is mainly based on the knowledge of the fabrication process. Even if the chemical composition of the different brands is similar, they can vary widely. Zirconia exists in three phases: monoclinic, tetragonal, and cubic. The tetragonal phase is the most interesting because, when a crack initiates on the surface, the stress concentration at the top of the crack causes the tetragonal crystals to transform into monoclinic crystals with associated volumetric expansion. In the end, this is what shields the crack tip from the applied stress and enhances the fracture toughness. A discussion of the various types of zirconia most often used in clinical dentistry follows. Zirconia: some practical aspects from the technologist’s point of view