Both crowns and most bridges are fixed prosthetic devices. Unlike removable devices such as dentures, which you can take out and clean daily, crowns and bridges are cemented onto existing teeth or implants, and can only be removed by a dentist.
Zirconia is a very hard ceramic that is used as a strong base material in some full ceramic restorations. The zirconia substructure (core) is usually designed on a digital representation of the patients mouth, which is captured with a 3d digital scan of the patient, impression, or model. The core is then milled from a block of zirconia in a soft pre-sintered state.
The zirconia core structure can be layered with aesthetic feldspathic porcelain to create the final color and shape of the tooth. Because bond strength of layered porcelain fused to zirconia is not strong, “monolithic” zirconia crowns are often made entirely of the zirconia ceramic with no aesthetic porcelain layered on top. Zirconia is the hardest known ceramic in industry and the strongest material used in dentistry. Monolithic zirconia crowns tend to be opaque in appearance with a high value and they lack translucency. For aesthetic reasons, many dentists will not use monolithic crowns on anterior (front) teeth.
To a large extent, materials selection in dentistry determine the strength and aesthetic properties of a crown. Some monolithic zirconia materials produce the strongest crowns in dentistry, but these crowns are not usually considered to be aesthetic enough for teeth in the front of the mouth. When porcelain is fused to the zirconia core, these crowns are more aesthetic than the monolithic zirconia crowns but they are not strong.
