What are dental crowns?

A dental crown is a dental prosthetic device to replace and/or protect the upper visible part of the tooth. Crowns have been fabricated to protect teeth for centuries. In the past, most crowns were made out of metal, gold being the primary choice. At present, dentists can still use gold and sometimes do, however, many patients do not wish to have a non-esthetic metallic crown visible anywhere in their mouth. Fortunately, the advances in ceramic materials have given dentists the ability to fabricate crowns utilizing both metals and porcelain materials. Porcelain crowns of the past were made of porcelain that was quite brittle. These were referred to as porcelain jacket crowns and were done on a limited basis. At the same time gold/resin crowns were made for repairing front teeth. The porcelain jackets would sometimes fail with apparently no provocation. They would just shatter in the same manner as dropping a ceramic coffee mug. The gold/resin crowns were sturdy but the resin was a soft plastic and picked up stain and wore down over a period of time. Many of those crowns have yellow gold that eventually shows through. Both of those types of crowns were replaced by porcelain-fused-to-metal(PFM) crowns which, as the name suggests, is a thin shell of metal with porcelain baked over the outer layer. The PFM crowns usually look quite nice for a long time because the edges are placed under the gum line so that they are not visible. However, if the gums recede, the edges of these crowns show and tend to appear grey in color. This is what is responsible for the grey line around crowns on front teeth.

Recently, all-porcelain crowns have returned to use because the materials have improved in strength. One technique for creating nice looking crowns for front teeth is the use of a CAD/CAM(computer-aided design/computer-aided manufacturing) system that mills the crown from a vacuum-fired solid block of porcelain. The two systems that do this are named CEREC and E4D. By milling the crown in the dental office, the dentist providing the service has more ability to customize the crown for the patient and many of these crowns are custom characterized in-office to more closely match the appearance of the natural teeth around them. Lastly, there exists a technology to make crowns with a tooth-colored zirconia base and to subsequently bake porcelain onto it. From a cosmetic standpoint, the CAD/CAM or the zirconia based crowns provide the best appearance with the strongest materials. Even if recession occurs, the all-ceramic crowns look much more like a normal tooth because a grey line does not exist.