The most likely cause of pain in a child’s milk tooth is pulpitis or periapical infection in the milk tooth, and parents must take their child to the doctor for timely treatment. Both pulpitis and periapical infection in baby teeth can be treated with root canal therapy to remove the infection and solve the pain problem. The treatment begins with the removal of the infected pulp tissue, strict disinfection of the pulp chamber, and the filling of the root canal with a resorbable, specialized root canal filling material for milk teeth, after which the inflammation in the root and pulp chamber of the tooth is controlled. If the tooth develops pulpitis and periapical inflammation and the parents do not take the affected child for timely treatment, the inflammation in the periapical area of the baby tooth will spread to the alveolar bone, where the permanent tooth germ is gradually developing, and if the permanent tooth germ develops in an inflammatory environment for a long time, it will lead to abnormal development of the permanent tooth germ, resulting in the eruption of permanent teeth or abnormal formation of dental tissues.