Crowns are "cemented" onto an existing tooth and fully cover 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.
Crowns or onlays (partial crowns) are needed when there is insufficient tooth strength remaining to hold a filling. Unlike fillings which apply the restorative material directly into your mouth, a crown is fabricated away from your mouth. Your crown is created in a lab from your unique tooth impression which allows a dental laboratory technician to examine all aspects of your bite and jaw movements. Your crown is then sculpted just for you so that your bite and jaw movements function normally once the crown is placed.