A dental crown, or cap, is a type of restoration that covers the visible portions of your tooth. The main purpose of a crown is to keep the tooth in your mouth when it has been damaged beyond what a filling can repair. Crowns restore the shape, appearance and function of the tooth, and protect it from sustaining further damage. Crowns are typically recommended when a tooth is fractured or cracked, severely decayed, has a large dental filling, or has had a root canal treatment.