Babies usually teethe around 6 months after birth, and around 2.5 years old the eruption of the milk teeth is completed. From 2.5 years old to around 6 years old is the period of the milk tooth row, where generally there are only milk teeth in the mouth. At the age of 6, the permanent teeth are replaced, and the last tooth that erupts from the milk teeth is the sixth tooth, which does not replace the milk teeth, but is a permanent tooth that serves the human body for life, and this tooth is recommended to be sulcus closed and well preserved. The order of replacement of milk teeth is generally from the middle to the two sides, about 6 years old began to replace the lower front teeth and upper front teeth, probably this process until about 11-12 years old to replace the finished, probably at the age of 12 years old is the normal human permanent tooth row, this tooth row will never move again.