Crowns cover and support a tooth when there is not enough tooth structure left to physically support a filling.  A crown can be used to anchor a “bridge” in order to help fill in a gap where a tooth is missing.  It can be used to protect a weakened tooth from breaking, or to restore a tooth that is already broken.  A crown can also be used to cover a tooth which is discolored or badly shaped and give you a more beautiful smile.