Root canal therapy is a necessary treatment for endodontic and periapical diseases. In the early stage of dental caries, the bacterial infection is confined to the hard tissues of the tooth, the carious and decayed enamel and dentin are removed, and the nerve of the tooth is not infected, so the tooth can be directly filled and treated, and root canal treatment is not necessary. After the pulp tissue is infected, the nerve inside the tooth root is inflamed, and symptoms of periapical disease such as pain when eating or gum pustules appear, and the nerve needs to be removed for root canal sealing to control the inflammation, and ultimately a tight root canal filling is performed to eliminate re-infection. Therefore, root canal treatment is not necessary in the early stages of tooth decay, but is necessary after the nerve becomes infected with symptoms of pulpitis and periapical disease.