Patient: I had my (so-called) porcelain teeth placed in a private clinic 3 years ago, and my gums are turning black. My dentures are placed on the original missing teeth, please ask: this situation is the need to extract teeth or remove the porcelain teeth placed on? How long will it take to remove and replace the porcelain teeth? How much will it cost? Jiang Ting, Department of Prosthodontics, Peking University Stomatological Hospital: The old porcelain crown needs to be removed and restored, but before removing it, make sure that the root of the tooth is not so bad that it cannot be repaired after removing the crown. Other issues vary from place to place, please ask the hospital you visit.