If a child’s new teeth erupt and the milk teeth do not fall out, it is recommended to consult a doctor in time for extraction, regardless of whether the milk teeth are loose or not. Children’s tooth replacement begins at about six years old, first of all, the six-year-old teeth that is, the first molar, is erupting in a new position, at this time there is no case of milk teeth falling out; then from the front teeth to the back of the milk teeth to fall off and replace, the permanent teeth from the root of the milk teeth eruption, to thirteen years of age or so, the teeth are basically all replacement is completed. If the milk teeth do not fall out in time and the permanent teeth have already erupted (clinically known as retained milk teeth), the milk teeth must be extracted by a doctor in time; to avoid the normal eruption of the permanent teeth being blocked by the milk teeth, which may lead to symptoms such as “double rows of teeth”.