When new teeth grow out and old teeth have not fallen out, it refers to retained milk teeth. Retained milk teeth should be extracted mainly, but it needs to be decided according to the situation of inherited permanent teeth. If the inherited permanent teeth have already erupted or the position and direction of the erupted permanent teeth are abnormal, in order to avoid affecting the normal growth of the permanent teeth, the retained milk teeth can be extracted; if the retained milk teeth are intact, with obvious looseness and no other symptoms, and the inherited permanent teeth are about to erupt or a small amount of eruption, there is no need to extract them, and it is enough to wait for the milk teeth to fall off on their own. In daily life, you can eat more chewy food such as corn, etc., and use the milk teeth more to increase the stimulation of the jawbone and milk teeth, to promote the development of the jawbone and the resorption of the roots of the milk teeth, and pay attention to oral hygiene, to avoid the stagnation of the milk teeth. If the position and direction of the eruption of permanent teeth are abnormal, you should consult a doctor in time and choose the right time to extract the milk teeth under the doctor’s guidance, so as not to affect the growth of permanent teeth.