Patients who suffer from pulpitis, periapical periodontitis, and joint lesions of the teeth usually need root canal treatment. 1. Pulpitis: When pulpitis occurs in a tooth, especially irreversible pulpitis, patients will experience significant pain at night, severe pain after hot and cold stimulation, and postural pain. When it cannot be solved by pulp capping or soothing analgesia, the pulp cannot be retained and needs to be extracted, at which time root canal treatment is required. 2. Periapical periodontitis: It is caused by bacterial infection inside the pulp cavity, which spreads to the surrounding tissues through the apical opening. Root canal treatment is needed to control the inflammation around the root tip. 3. Combined endodontic-periodontal lesions: For patients with combined endodontic-periodontal lesions, root canal treatment should be carried out on the affected teeth along with periodontal sequential treatment. Through root canal treatment, the lesion site can be improved accordingly, and combined with periodontal sequence treatment, combined endodontic and periodontal lesions can be controlled. When a patient develops a dental disease, it is recommended that he or she seek medical attention in a timely manner and be treated accordingly under the guidance of the doctor.