The process of root canal therapy is to prevent the occurrence of periapical lesions or to promote the healing of periapical disease by thoroughly removing the infected pulp as well as the infected dentin and toxic decomposition products through root canal irrigation, disinfection and tight filling of the root canal to isolate bacteria from entering the root canal and reinfecting it. 1.Reducing the patient’s pain and preventing the spread of infection: teeth that already have pulpitis will continue to deteriorate, eventually to pulp necrosis and even periapical lesions, a process that is quite painful, and root canal treatment not only relieves the patient’s pain, but also allows the tooth to be preserved. 2, as far as possible to maintain the tooth to avoid extraction: the purpose of root canal treatment is to preserve the pulp or periapical tissues, so that the tooth that has been violated can still be in a good healthy state in its supporting tissues to avoid extraction or continued deterioration to the fate of collapse. 3. Eliminate the infection of the lesion and rebuild the health of the affected tooth: Root canal treatment can not only eliminate the germs and their decomposers and toxins in the root canal, but also treat the infection of the tissues around the root tip, promote the repair and healing of the tissues around the root, and eliminate the source of the infection of the oral lesion. Root canal treatment also needs to pay attention to the following points: 1, the number of root canal treatment: root canal treatment is not all at once to complete the treatment, the doctor often according to the patient’s clinical examination, step by step treatment, generally speaking, root canal treatment should be divided into 2-4 visits to complete. 2, the root canal treatment doctor, instrument selection: because the root canal treatment is more complicated, requiring doctors must be familiar with the anatomical knowledge of the tooth structure and skilled operation techniques, while the need for special supporting root canal treatment instruments and equipment and materials, therefore, root canal treatment is more time-consuming and relatively high cost. 3, the root canal treatment of non-adaptation: root canal treatment during or after the completion of the discomfort may occur for a short period of time, usually taking anti-inflammatory or painkillers can relieve, local swelling and pain should be informed to the attending doctor to deal with. 4.Protection after root canal treatment: It is best to perform inlay or crown restoration after tooth treatment to prevent tooth fracture and prolong the life of the tooth. 5, the treatment of chronic periapical infection: chronic periapical inflammation of the apical lesions in the treatment of patients in a state of rest, or just the trend of acute attacks, self-conscious symptoms are not obvious, only a slight percussion pain at the time of the visit. The doctor must use instruments to operate in the root canal, which provokes the inflammatory lesion in the resting state. If the patient has low resistance and does not take anti-inflammatory drugs in time after treatment, acute inflammation will occur and pain will be felt. If the patient has high resistance, takes anti-inflammatory drugs in time after treatment, and is not overly fatigued, then, in general, no pain is caused.