There are two sets of teeth in a person’s life. Milk teeth, commonly known as milk teeth, are the first set of teeth in life, which start to appear 7-8 months after birth and come out one after another around 2.5 years old. The permanent teeth are the second set of teeth in life, if for some reason they are missing. There will be no tooth replacement for life. Around the age of six, the first permanent molar grows on the back side of the last molar, and from then until the age of 12, the milk teeth fall out and the permanent teeth replace them accordingly. There are 28-32 permanent teeth, and the permanent teeth start to emerge from the age of 6-7 years old until all 32 teeth are grown, which takes about ten years, that is, about 20 years old. The timing of tooth replacement varies slightly with the child’s health and nutritional status. If the baby teeth are still there after the tooth replacement period, it is a medical term for “retained baby teeth” and it is best to seek medical attention. Usually, the embryo (tooth germ) of the permanent tooth is in an abnormal position, or the tooth germ is missing. If the embryo of the permanent tooth is in an abnormal position, an orthodontist may be needed to help the permanent tooth erupt by dragging the abnormally positioned tooth to where it should be, known medically as “eruption assistance”. Another common situation is when the baby tooth is lost prematurely and the permanent tooth has not yet erupted, but an x-ray reveals a normal permanent tooth germ underneath the original baby tooth. If this situation is not treated in time, the teeth on both sides of the deciduous teeth will move to the middle, making the gap between the original deciduous teeth smaller, so that the eruption of permanent teeth lacks sufficient normal gap, and the permanent teeth will erupt in the wrong position, affecting the beauty and function of teeth. In this case, the orthodontist can help the child to make a “gap retainer” on the gap of the prematurely lost baby teeth to maintain the gap of the baby teeth to facilitate the eruption of the permanent teeth. It is also important to chew more hard foods during tooth replacement to help stimulate jawbone growth and align teeth. Therefore, tooth replacement is related to the health and beauty of your permanent teeth for life, so do not take it lightly and see your doctor promptly if you have any problems.