Crowns are a restorative procedure used to improve your tooth’s shape or to strengthen a tooth. Crowns are most often used for teeth that are broken, worn, or have portions destroyed by tooth decay. A crown is a “cap” cemented onto an existing tooth that usually covers the portion of your tooth above the gum line. In effect, the crown becomes your tooth’s new outer surface. Crowns can be made of porcelain, metal, or both. Porcelain crowns are most often preferred because they mimic the translucency of natural teeth and are very strong.