Sixth-age teeth do not change teeth except for missing dental implants. The first permanent tooth (first permanent molar) erupts around the age of six, which is easy to overlook because it erupts early. After the first permanent molar erupts, it will not be replaced by another tooth, and will be there for life, except in the case of caries damage, tooth extraction, and tooth loss. Most of the milk teeth come out around the age of 3. Between the ages of 6 and 12, the milk teeth are gradually replaced by permanent teeth in the same position, in which the 1st and 2nd premolars replace the 1st and 2nd milk teeth, the 2nd permanent molar erupts around the age of 12, and the 3rd permanent molar erupts after the age of 18 (some people don’t have any lifelong eruption). When there are oral diseases or tooth defects, etc., the first permanent molar may be missing, in order to maintain normal chewing function, some people choose to implant a tooth in that position, which may be replaced at this time.