Babies usually start to erupt their baby teeth 4-10 months after birth. There are two sets of teeth in a person’s life, and the first set is called milk teeth, with 20 teeth, which start to erupt 4-10 months after birth, and those not erupted after 13 months are called delayed eruption of milk teeth. The order of eruption of milk teeth is generally lower jaw before upper jaw, from front to back, mostly before 3 years old, and the time and order of milk teeth eruption varies greatly among individuals, which is related to genetics, endocrine and food traits. The second set of teeth is called permanent teeth, there are 28-32 teeth in total, the first permanent molar, also known as the first permanent molar, also known as the sixth age teeth, starts to erupt at the age of 6. 6-12 years of age, the milk teeth are replaced one by one by the same permanent teeth, in which the first and second premolar teeth replace the first and second molar teeth, this period is a mixed dentition period. 12 years of age, the second permanent molar teeth erupt, about 18 years of age after the eruption of the third permanent molar teeth, also known as wisdom teeth, some people Some people do not have their third permanent molars erupted throughout their life.