One of the main things that determines whether or not root canal treatment is needed for secondary caries is the location of the secondary caries. If the secondary caries is only in the dentin layer or enamel layer and has not reached the pulp tissue, root canal treatment is not needed; if the secondary caries is very deep and has reached the pulp tissue or is close to the pulp tissue and there are already symptoms of irreversible pulpitis, root canal treatment is needed. Therefore, it is recommended to have an effective oral examination six months to one year after the filling of a bad tooth. If secondary caries is detected, the doctor will also perform routine filling treatment on the bad tooth to prevent spreading to the pulpal tissues and requiring root canal treatment. The management of secondary caries is the same as that of common caries, with early detection and treatment to prevent further progression of the lesion.