Nerve necrosis is common in patients with chronic pulpitis, due to caries, trauma or hidden cracks in the teeth, making the pulp chronic infection, the pulp gradually lose vitality, while inflammation is a slow and long process, the symptoms of inflammation are usually not very obvious, the patient will not experience very severe pain, some patients do not have any sensory symptoms, the nerve has gradually necrosis. After the necrosis of the nerve, the main performance is that the teeth do not have any response to hot and cold stimuli, and the teeth gradually become black and brittle. In some cases, chronic inflammation of the periapical area develops, resulting in inflammatory polyps and pus-draining sinus tracts in the mucosa of the apical area of the tooth, and swelling and pain in the apical area of the tooth after biting and eating hard substances. A dead pulp tooth with necrotic nerve also requires root canal treatment to remove the infected necrotic nerve.