Root canal therapy is a treatment for pulpal and apical lesions of teeth. Root canal therapy is a treatment method to prevent periapical lesions or to promote healing of periapical lesions by removing necrotic material from the root canal, disinfecting it appropriately, and filling it to remove the adverse stimulation of the root canal contents to the periapical tissues. I. Root canal treatment is used in which cases 1, pulpitis and pulp necrosis can not retain the living pulp; 2, periapical lesions; 3, residual crown and root teeth, the restoration department needs to carry out pile crown restoration; 4, the morphological position of the tooth is not ideal before the restoration treatment preparation. The basic steps of root canal treatment: pre-treatment preparation, pulp opening, root canal preparation, root canal flushing, root canal disinfection, root canal filling, post-filling treatment. Root canal treatment is not always completed at one time, doctors often step by step according to the patient’s clinical examination, generally speaking, root canal treatment in 2-4 visits to complete. In the process of root canal treatment, doctors often ask the affected tooth to take X-ray before, during and after the root canal treatment to help diagnose, understand the location of the pulp chamber and the number and shape of root canals, measure the length of the root canal and provide a basis for future follow-up and evaluation of the treatment effect. 2, uncover the pulp chamber, remove the decay and original filling, uncover the top of the pulp chamber, see the entire pulp floor anatomy, pulp wall and root canal wall continuous and smooth, no cervical steps, no excessive cutting of pulp wall and pulp floor for smooth follow-up treatment. 3, determine the working length of root canal Apply parallel projection X-ray method, root canal length measuring instrument to determine the length of root canal The best way is: technology + experience + root canal length measuring instrument + X-ray The purpose of root canal cleaning and shaping is to remove the infected dentin from the root canal wall, remove the infected dentin by cutting with root canal instruments and clean the root canal wall of bacteria to facilitate root canal filling. The purpose of root canal rinsing is to remove microorganisms, flush out debris, lubricate root canal instruments and dissolve organic debris. The purpose of root canal filling is to seal the entire root canal system, block the primary and lateral root canal outlets, and prevent leakage of microorganisms and fluids. Discomfort may occur briefly during or after completion of root canal treatment and is usually relieved by anti-inflammatory or analgesic medication. After root canal treatment, the tooth may become brittle due to lack of nutrient supply and it is best to restore the tooth with an inlay or crown to prevent fracture.