When the tooth bites something painful, the following situations are common: 1, when suffering from periodontal disease, the alveolar bone is obviously absorbed, the root of the tooth is exposed, causing the tooth to loosen, and the tooth pulls the surrounding periodontal ligament when biting something, causing pain; 2, when there is a hidden fissure or deep cavity in the crown, the embedded food residue generates wedge-shaped force, which is transmitted to the pulp causing pain; 3, when periapical inflammation occurs, the root tip produces a large amount of inflammatory under bacterial infection When periapical infection occurs, the root of the tooth is suspended in the alveolar sockets and does not dare to chew; 4.When the tooth is heavily worn and the dentin is exposed, biting will squeeze the pulp cavity and cause obvious pain; 5.When the x-ray shows that the tooth is longitudinally fractured, the root of the tooth is separated and cannot bear the chewing force.