The pain after the first root canal treatment is mainly produced by the sealed nerve-killing drugs or root canal preparation, and its symptoms are mild and usually disappear in one or two days. 1. If the first time of root canal treatment is sealed inactivator (i.e. nerve-killing drugs), the role of inactivator is to make the nerve gradually lose biological activity, which will gradually reduce the pain of the tooth; so there will be a short period of mild pain in one to two days after sealing the drug, and then the pain will disappear after the nerve is completely inactivated. 2. If the root canal treatment has been carried out for the first time, i.e., root canal preparation (i.e., the nerve will be cleaned up mechanically), the tooth will have a certain stress reaction to the mechanical preparation, i.e., slight pain and swelling; generally, the symptoms can be relieved in two to three days. However, if the pain is obvious and persistent after the root canal treatment, it is recommended to consult a doctor in time for symptomatic treatment.