Lower incisors that is, mandibular incisors, 40 years old mandibular incisors are active generally periodontitis leads to alveolar bone resorption, which causes loose teeth, as follows. Alveolar bone resorption leads to a decrease in periodontal support tissues, which is the main cause of tooth loosening. A small amount of alveolar bone resorption does not cause tooth loosening, with the development of periodontitis, alveolar bone resorption reaches the root length of more than 1/2, the tooth loosening symptoms. When alveolar bone resorption occurs on all sides of the tooth, the ratio of the clinical crown to the length of the clinical root is out of proportion, and the looseness of the tooth gradually increases. If the tooth loosening is serious, or other symptoms appear, it is recommended to go to the hospital in time to receive early professional treatment.