The penultimate large tooth in the milk tooth row (clinically known as the first milk molar) will be replaced normally when associated diseases (e.g. rickets, congenital absence of permanent teeth, etc.) are ruled out. All milk teeth are replaced. The first molar begins to erupt at about two years of age, and there are four of them in total; and they are usually replaced at about ten years of age, when the first premolar erupts in place of the first molar. Therefore, under the exclusion of rickets, congenital absence of permanent tooth germs and other diseases, the first molar teeth will all fall out; and during the replacement period, it is necessary to appropriately increase the chewing of hard objects (such as apples, sugarcane, or nuts, etc.) in order to promote the normal replacement of the teeth, and to maintain oral hygiene in order to prevent the newly erupted teeth from caries or pain and other symptoms.