Crowns are a cap placed on an existing tooth and cemented into place.
Just like fillings, crowns are most often used to restore teeth that have been damaged from cavities. Crowns are necessary when the existing tooth has decayed to the point that it cannot support a traditional filling.
Crowns are also used to protect a weak tooth and hold together a cracked or broken tooth. A tooth that has become severely worn can be fixed with a crown and crowns are almost always indicated after a root canal procedure.
Cosmetic modification to cover misshapen teeth or unsightly stains may be done with crowns or veneers depending upon your particular needs and preferences.