Humans erupt the 1st mandibular milk incisor from the age of 6 months until the age of 3 years, when 20 milk teeth are erupted, and all these 20 milk teeth will be replaced, usually between the ages of 6-13 years. Throughout the replacement period, the 20 milk teeth will be replaced by 28-32 permanent teeth, in which the first 5 teeth counting from the center, all of which are previous milk teeth, definitely need to be replaced. The most important thing to pay attention to is the 6-year-old teeth, which are the permanent molars, also called the first molar, that erupt at the age of 6 years old, at the very end of the milk teeth, and once erupted, they will never be replaced again, so it can be said that it is a tooth that doesn’t need to be replaced, and it can be easily neglected by parents. Of course, in addition to the 6-year-old teeth, including the 2nd molar and wisdom teeth, all of these eruptions also do not replace any teeth, but start erupting at the very back of the tooth row.