The baby’s big teeth (clinically known as molar teeth) will all be replaced, and the replacement time is around 9 to 10 years old. Molar teeth are located at the end of the baby’s milk teeth, there are 8 of them in total, including the first molar and the second molar; among them, the first molar will start to be replaced around 9 years old, and the permanent teeth that will erupt from replacing the first molar is the first premolar; the second molar will start to be replaced by the permanent second premolar around 10 years old. During the replacement period of baby’s milk molar, it is necessary to increase the chewing of hard objects to promote its normal replacement; if the milk molar is not lost in time and the new tooth erupts (clinically known as retained milk teeth), it is necessary to seek medical treatment for extraction; usually, it is necessary to do a good job of oral care in order to prevent the newly erupted permanent teeth from developing caries or tartar and other symptoms.