The current clinical dental nerve-killing drug usually needs to be put for two weeks. Because the current application is paraformaldehyde, the role of paraformaldehyde is to coagulate the protein in the pulp, making the pulp aseptic necrosis, its effect is more moderate, it is safer to use, its sealing time is about two weeks. After two weeks, a follow-up visit is required to remove the paraformaldehyde and then proceed to the next step of root canal treatment, including root canal preparation and root canal filling. If arsenic sealant is used to kill the nerve, it usually takes 5-7 days for permanent teeth and 2-4 days for milk teeth; if arsenious acid is applied to kill the nerve, it takes a shorter time, usually 1-2 days.