Pulp necrosis is usually caused by pulpitis, but it can also be caused by trauma or the need for restoration, but the amount of preparation is too much. The pulp itself has poor restorative ability, so it is impossible to recover from pulp necrosis, and the pulp is more prone to bacterial infection than healthy pulp, so it is important to treat the pulp as soon as possible after necrosis. If left untreated, the inflammatory substances in the necrotic pulp will spread to the tissues outside the root and reach the root tip, causing what we call periapical inflammation. Symptoms of the patient after the emergence of periapical inflammation are, if there is chronic periapical inflammation patients will feel discomfort in biting, some patients even if they do not have discomfort in biting, after a period of time may find that the gums around the small pus, these are the manifestations of chronic periapical inflammation. If the chronic periapical inflammation to the acute attack patients will have spontaneous pain, and even can not bite things. Therefore, pulp necrosis cannot be cured, and it is recommended that patients do the treatment as soon as possible.