When a child reaches the period of tooth replacement, a large tooth will quietly grow in the space behind the milk teeth, which is the first permanent molar that erupts the earliest. Because the first permanent molar erupts around the age of six, it is called the six-year-old tooth. The function of the six-year-old teeth is the crown of all the teeth, which has the largest crown, the widest jaw surface, complex shape, strong crushing force, and almost all the food chewing is inseparable from it. Sixth age teeth have the most roots, solid foundation, growth in the chewing muscle, temporal muscle and wing inside and outside the role of the center of the muscle, and thus chewing the heavy load more by it to bear. Its powerful chewing function can strongly stimulate the healthy development of the upper and lower jaws. As soon as the six-age teeth erupt before the other permanent teeth, it lays the foundation for the establishment of the permanent dentition. Due to its constant position, especially the maxillary first permanent molar plays a very important role in stabilizing the normal arrangement of the teeth in the whole mouth and the relationship between the upper and lower teeth. Four six-year-old teeth up and down occlusion, the arch can be locked in a fixed occlusal position, the doctor often use it as a sign to test and judge the jaw position is correct or not. If you look at the entire mouth as a hall, the six-age teeth are like four pillars in the hall, which hold up the space of the hall, so that the child’s face from the bottom of the nose to the chin to show the length of the face should be, which grows into the shape of the adult face. However, the six-age teeth are the most vulnerable to caries, if caries and extraction, not only to the child chewing food difficulties, but also will cause the neighboring teeth tipping shift, resulting in a full mouth teeth bite disorder, the worst can also affect the normal development of children’s jaw and face.