If a tooth is damaged but not lost, a crown can be used to restore its shape, appearance and function. You may need a crown if you have a root canal , a large filling or a broken tooth. A crown is a hollow artificial tooth used to cover a damaged or decayed tooth. The crown restores the tooth and protects it from further damage. Crowns can also be used to cover a discoloured or misshapen tooth. A tooth that has been fixed with a crown looks and works very much like a regular tooth.