A six-year-old baby with two loose lower incisors and one growing inside is considered to have retained milk teeth, which is an abnormal phenomenon. Retained milk teeth are related to abnormal root resorption of milk teeth, as well as impaired eruption of inherited teeth and some congenital defects. In a few cases, it is also associated with systemic diseases such as rickets and dwarfism caused by calcium deficiency. Usually, the permanent teeth have erupted, but the milk teeth have not been lost, and the milk teeth may be loose or not loose. Treatment is mainly based on the extraction of milk teeth, while the inheritance of permanent teeth needs to be considered. The main purpose of extracting the milk teeth is to make room for the growth of the permanent teeth, so as not to affect the normal growth of the permanent teeth, so it is best to extract them. If the retained milk teeth are more complete, but the loosening is also more obvious, the amount of permanent teeth eruption is relatively small, you can observe for a period of time, if a long time the milk teeth do not fall out, you need to consult a doctor as soon as possible, so as not to affect the baby’s permanent teeth eruption.