The fact that the tooth still hurts after the first root canal treatment may be due to the fact that the effect of pulp inactivator has not yet taken full effect, normal reaction after the operation, incomplete removal of the nerve, or other affected teeth, etc. It is recommended to go to the hospital in time for examination and treatment. 1. When you have the first root canal treatment, you may put in the nerve killing medicine, which usually relieves the severe pain caused by pulpitis, but there will still be slight pain for two or three days, because the pulp inactivator is slow-acting, and it usually takes about a week to completely stop the pain. 2. If root canal preparation is performed in the first root canal treatment and the nerve is removed, the tooth still hurts probably due to the normal postoperative swelling and pain reaction after root expansion. 3. If the nerve is not completely removed, there may be a residual nerve that causes pain. 4. There may also be adjacent teeth or teeth in the opposite jaw with caries or pulpitis causing pain.