The second special pain of root canal treatment may be caused by apical infection, local injury, and irritation of sealant. 1. There is an infection in the pulp itself, and during the second root canal treatment, the infected material in the root canal is pushed to the root tip, resulting in localized infection and increased pressure, which can lead to pain. 2. It is possible that during the root canal treatment, the narrowed portion of the root canal is exceeded, damaging the local blood vessels, resulting in increased pressure after bleeding, and thus the pain that occurs. 3. It may also be due to the second root canal treatment, the doctor for root canal sealing, drug stimulation caused by pain. It is recommended that the patient who has a particularly painful second root canal treatment should consult the doctor in time and follow the doctor’s instructions to avoid delaying the condition.