Toothache is generally caused by gradual infection, mostly caused by tooth decay, tooth decay will further develop to pulpitis, the nerve itself has gradually necrosis, but at this time the nerve still has symptoms and will cause severe toothache, further develop to periapical inflammation, at this time the inflammation has developed to the root tip, relatively speaking the nerve in the pulp has basically necrosis. In clinical work, if you want to kill the nerve there are two methods: First, direct anesthetic to open the pulp and extract the pulp, after the injection of anesthetic to open the pulp, apply the pulp extraction needle to directly extract the pulp, which is considered to directly kill the nerve. Second, to inactivate the nerve with an inactivating agent. After opening the pulp, a chronic arsenic-based drug is placed on the pulp, which slowly necroses the pulp.