The big teeth are the molars. Under normal circumstances, the crowns of the mandibular molars are tilted to the lingual side, and under disease conditions, destruction of periodontal supporting tissues, change of cohesion and other factors may cause the molars to be tilted to the lingual side, as follows. 1. Under normal conditions: the crowns of maxillary molars are straight and the crowns of mandibular molars are tilted lingually. 2. Disease conditions: (1) Destruction of periodontal supportive tissues: periodontitis can make the alveolar bone resorption, the supportive tissues are reduced after the affected teeth are subjected to the joint force is out of balance, secondary joint trauma occurs, and the teeth will be shifted in the direction of the force. (2) Alteration of the synergistic force: Abnormalities in tooth morphology and cuspal slope, integrity of the dental column, and the balance between synergistic force and labial, buccolingual and lingual muscle forces can produce abnormal synergistic forces on the teeth in the sideward direction, which can displace the teeth. There may be other reasons why the molars are tilted to the lingual side, so it is recommended to go to the hospital in time to clarify the cause of the disease and then carry out targeted treatment.