A crown is a hollow cap that fits over a tooth, giving it strength and/or improving its appearance. The supporting tooth has to be reduced in size to make room for the crown. Crowns may be made from a variety of materials. Crowns are indicated for teeth, which are too extensively decayed, damaged or discoloured for treatment by other means. A well made crown or bridge, in a situation where the overall dental outlook is favourable, should last for 10 or more years.