Root canal refers to the hollow structure in the center of the root of a tooth, which contains the nerve of the tooth and the blood vessels that nourish the nerve, etc. 1. The tooth is divided into crown, neck and root. The crown is the part that can be seen in the mouth and the root is the part that is inside the alveolar bone. The part of the tooth that is hollow in the center of the tooth contains the pulp, and the upper part of the hollow is wide and is called the pulp cavity, while the lower part has a tube-like structure called the root canal. From the root canal, the dental nerve and the blood vessels that nourish the nerve can be derived. 2. Humans generally have 1 to 4 root canals per tooth, with more root canals in the posterior portion of the tooth. A tooth does not necessarily have 1 root, and each root does not necessarily have only one root canal within it; each root canal holds the root pulp. If a patient experiences discomfort in the tooth, he or she needs to actively seek medical attention, and in the case of diseases such as pulpitis and apical periodontitis, root canal treatment is mostly required.