A crown is a cap (made from porcelain +/- metal) which covers the entire visible surface of the tooth. It acts to strengthen and reinforce weakened and broken teeth. Often they are placed on teeth where a large portion has broken away or on those which have undergone extensive procedures, including Root Canal Treatment.
Crowns can also be used to enhance the appearance of smile teeth in a way similar to porcelain veneers. They can alter the shape and colour of teeth, or some patients simply want it to match and blend in with their remaining teeth.
A thin layer of tooth structure is removed from the surface before an impression is taken. The tooth is then protected by a temporary crown, which is removed on the following appointment where your porcelain crown is inserted.