Causes: periodontal disease, micro-odontia, too low or/and too long of lingual frenum, extraction of supernumerary tooth, labial movement because of bad bite habit and periodontal disease.

• 病因:牙周病、过小牙、唇系带过低、过长、多生牙拔除、不良咬合习惯和牙周病导致的牙齿唇向漂移。