Whether the dental nerve is necrotic or the time of necrosis is related to the nature of toothache, personal constitution, age and other factors, there is no more definite time. Factors affecting the necrosis of dental nerve: 1. Nature of pain: If the tooth has pain from hot and cold stimulation without obvious symptoms such as nocturnal pain, spontaneous pain, radiating pain, the dental nerve may not be invaded, it may just be cavity and needs filling treatment. 2. Physique and age: If the toothache is caused by inflammation of dental nerve in childhood, generally speaking, the necrosis of dental nerve may take several months; if occurs in adults and the resistance is higher, necrosis may take six months to one year or even longer. Due to the degree of inflammation and individual differences, the time of nerve necrosis is different for each person, and there is no more definite time. If symptoms such as tooth pain and discomfort occur, patients are advised to seek medical examination as soon as possible. The earlier the treatment, the better the prognosis of the tooth will generally be, otherwise the tooth may end up not being retained and need to be extracted.