How can a tooth still hurt when the dental nerve has been killed? A tooth is like a house. The four walls are hard and the middle is a cavity with blood vessels, nerves and other tissues inside the cavity, which are connected to the tissues around the tooth root through a small hole at the tip of the root. Therefore, when pulp disease is severe, it often affects the tissues around the roots. Even if the pulp is necrotic, the bacteria and toxins produced by the necrotic tissues will spread to the surrounding tissues through the roots, causing inflammation of the tissues around the roots. A portion of teeth that have undergone endodontic treatment may also cause inflammation of the roots or the tissues around the roots because the pulp has not been completely removed or the residual pulp is not treated thoroughly. It manifests as pain, afraid to bite the tooth together, facial swelling in severe cases, restricted opening and closing of the mouth, and even high fever and chills, etc. If not treated urgently, it can lead to the occurrence of sepsis, which is life-threatening. This is the reason why dead pulp teeth still hurt. Currently, a more thorough treatment for pulp is root canal therapy. With very canal treatment, the necrotic material in the root can be completely removed, properly disinfected, and the root can be tightly filled to completely eliminate the source of infection, and the root will no longer be inflamed. In the case of teeth that already have inflammation around the root, root canal treatment can also promote healing of the lesion so that the tooth can perform its normal chewing function. However, in outpatient treatment, it is common to see some patients who only treat the pulp in the crown during endodontic treatment, without any treatment of the necrotic nerve in the root of the tooth. This leaves a hidden danger that when the body’s resistance decreases at some point, the bacteria and toxins in the necrotic nerve remaining in the root can spread and cause severe pain in the tooth. However, root canal therapy is a complex and delicate treatment procedure that requires complete removal of the pulp after sterilization, filling and finally finishing the tooth, so the process takes several times to complete.