When the caries destroys the enamel and dentin, and the lesion reaches the pulp and causes pulpitis, the pulp blood vessel expands, fills with blood, and exudes more, and the diseased tooth has paroxysmal pain, which spreads to the opposite jaw teeth, head and face, behind the ear, etc. The doctor diagnoses it as “acute attack of chronic pulpitis”, and decides to remove the pulp tissue to eliminate the pain before further treatment. Before treatment, the pulp is usually deactivated with some kind of drug, which is called “nerve killing”. The posterior teeth are multi-rooted, with multiple root canals, rich in nerves, some roots are thin and curved, the treatment process is complex and long, and the effect is worse if the patient feels pain and does not cooperate. Using deactivating agents (arsenic, paraformaldehyde, toadstool preparations, etc.) on the toxic effect of the tissue, in a certain period of time (generally 2 days, 4 days, 7 days, etc.) so that the nerve cells of the pulp destroy, the pulp loses vitality, and then the treatment makes the patient painless, and the doctor also feels more convenient. The pulp is located in the center of the tooth and has the ability to nourish the tooth, form the dentin, feel the tooth, and provide some restorative defense. The “nerve killing” can relieve the patient from the pain of the tooth in a short period of time and create good conditions for pulpal filling. However, once the pulp is “killed”, the tooth has no nutrient supply and becomes a “dead tooth”, which is very fragile. If you bite into hard or fried objects, the tooth will easily split. Therefore, it is better to “not kill the nerve” as a last resort.