The replacement of teeth may be caused by missing permanent teeth, injury, abnormal position and direction as well as thickening of the gums, which need to be treated after the cause is clarified by the doctor. 1. Some children may be missing permanent tooth germs due to genetic factors. After the loss of milk teeth, no permanent teeth will erupt, so they can only go to the hospital for filling treatment. 2. Inflammation at the root tip of the baby tooth may involve the permanent tooth germ located below the root tip of the baby tooth, resulting in damage to the permanent tooth germ and preventing it from erupting, or the area around the permanent tooth germ may become congested and edematous due to inflammation, resulting in an abnormal direction of eruption and prolonged eruption time of the permanent tooth germ. 3. When milk teeth are lost too early, the gums at the location of the lost teeth will be thickened locally, which will prevent the permanent teeth from erupting, and at the same time, the neighboring teeth will be tilted to the gap, and the gap will be too small, which will cause the permanent teeth to have no space for eruption, and then obstruction will occur. After the normal loss of milk teeth, permanent teeth will erupt in about 3~6 months, the specific time is affected by many factors, and a small number of children will not be able to grow permanent teeth for about 1 year. Therefore, after the loss of milk teeth, children can be observed for a period of time, and if permanent teeth do not erupt after 3~6 months, they should go to the hospital for consultation.