Root canal treatment for the second time is not painful. The first root canal treatment has been performed to open the pulp and drain or make the pulp lose its vitality, and only a small amount of vital pulp remains in the root canal, which causes pain that is not obvious. The second root canal treatment mainly involves using a root canal file or enlargement needle to completely remove the superficial dentin from the infected root canal wall and gradually expand the root canal to form a conical canal lumen, using 3% hydrogen peroxide solution or 5.25% sodium hypochlorite solution to alternately rinse and effectively remove the residual material and debris, using a paper tip to absorb the liquid from the canal lumen, placing calcium hydroxide or camphor phenol, etc. for root canal disinfection, and the whole process There will be no severe pain.