If there is no living pulp in the pulp cavity, the second change will not hurt; if there is still living pulp in the pulp cavity, there will still be pain when changing the medicine. The first visit will open the pulp chamber and seal a deactivator; the second visit will expand the root canal, remove all the pulp that has been killed and seal the medicine; the third visit will fill the root canal. If the nerve is taken out in the first visit, the second change of medication is to promote the anti-inflammation of the root tip, and there is no pain in this case.