Single unit of prosthesis which lands on the tooth to give its own contour is called a crown, whereas, union of two or more crowns is called as a fixed partial denture(bridge).
one of the best ways to treat missing teeth is through fixed partial dentures. In this modality of treatment we take the support of adjacent teeth to replace the missing teeth. Number of adjacent teeth to be involved for support depends on number of missing teeth. The adjacent teeth have to be strong enough to give support to the bridge, otherwise more number of teeth have to be involved for more support.
Coming to the material aspect of crowns and bridges, the traditional way of replacing the missing teeth is through wrought metal crowns. It is succeded by metal ceramic crowns, in this variety the core component is made by metal over which a layer of ceramic is coated. Thereby it resembles a tooth. The major advantage is it looks in tooth colour and disadvantage is ceramic layer chips of after using it for couple of years, leaving the metal exposed. As it has metal underneath as coping,it has less translucency.
Full Ceramic/zirconia crowns; these are completely made up of ceramic, different kinds of ceramic crowns are available, which depend on the quality of the crown. ceramic crowns mimic the tooth inside to out in its appearance. there are many kinds of shades of tooth color, to give the full ceramic crown a beautiful natural look. the shade of white is selected though a shade guide. They are the most acceptable crowns among patients who seek for quality because of its strength, appearance and longevity. They have a life span of 8-15 years or even more depending upon their quality.