12-year-old girl permanent teeth have not been replaced is generally a normal physiological phenomenon, but it can not be ruled out that the permanent teeth are missing, dental tumor, developmental delay and so on. 1. Physiological phenomenon: permanent teeth are the teeth that erupt after the loss of milk teeth. Generally, permanent teeth begin to erupt around the age of 6 and last until the age of 12~14, when they can replace all the milk teeth. Since the growth and development of each child is different, it may be normal for a 12-year-old girl to have her permanent teeth not yet replaced. 2. Missing permanent teeth: If the patient’s permanent teeth are congenitally missing, it may lead to root resorption obstacle of the milk teeth, so that the milk teeth remain in the mouth, thus the permanent teeth are not replaced. 3. Dentinoma: 12-year-old girl in the replacement period of delay in the eruption of new teeth, permanent teeth have not been replaced, may be a dentinoma blocking the normal eruption of new permanent teeth. Dentinoma is a tumor formed by epithelial and mesenchymal tissues in the tooth-forming organs. When the size of dentinoma increases, it can lead to difficulty in eruption of permanent teeth, accompanied by pain, loose or shifted teeth and other symptoms. 4. Developmental delay: lack of calcium and trace elements in the body can cause children’s growth and development to slow down and other abnormal phenomena. The 12-year-old girl has not finished replacing her permanent teeth, and after excluding physiological factors, she should consult a doctor in time to find out the cause of the disease.