When the nerve of a tooth is damaged or infected by bacteria, it is susceptible to nerve necrosis, also known as pulpal necrosis, which is a common condition in dentistry. To determine whether it is dental nerve necrosis, the diagnosis can be made clearly through clinical symptoms and auxiliary examinations. 1, clinical manifestations 1, nerve necrosis can be manifested as loss of pulpal sensation, loose teeth, percussion pain, red and swollen gums or fistula, etc. 2. There may be deep caries cavity or other dental hard tissue disease in the crown, or there are filling body, deep periodontal pocket, etc. 3.The crown of the tooth is discolored, dull yellow or gray, and the surface loses its luster. Auxiliary examination 1.X-ray examination can show the widening of periodontal space and low density image in the apical area; when there is loss of pulpal sensation, accompanied by crown discoloration or abnormal X-ray examination, it can also be diagnosed as dental nerve necrosis. 2. No response to pulp vitality test. Tooth nerve necrosis will adversely affect the normal life of patients, such as pain, hot and cold soreness, etc. Daily attention should be paid to the prevention of tooth nerve necrosis: 1.Treatment as early as possible when there is tooth decay in the mouth, otherwise, delayed treatment will lead to further development of decay accumulated tooth nerve and root tip area, and finally lead to tooth nerve necrosis. 2.Avoid foreign body injury: some oral diseases are caused by long-term food embedment, trauma and other factors, attention should be paid to the trauma produced when treating oral diseases, or the instrument injury produced when cleaning and treating teeth. 3.Avoid trauma: wear a dental brace when exercising to avoid dental trauma. Seek medical consultation as soon as possible after the occurrence of dental trauma.