A crown is like a jacket or cap that fits over a prepared tooth. It has the same shape as the original tooth. If a tooth is badly broken down, a crown is often the only option. By fully enclosing the tooth it is strong, and where indicated it can have an excellent appearance, looking just like a real tooth. It can be made of a metal alloy, of porcelain, or a combination of both. To allow the crown to fit, the tooth must be prepared first. This involves trimming the tooth down a little. Crowns are fixed in place with cement.