Obana's 6-year-old cousin Qiqi also plays together. Her cousin always complains about toothache and sometimes picks her mouth with her hand. I won't know until I ask my aunt. In fact, I found her first permanent tooth in her mouth two days ago. Although the deciduous teeth have been active for many days, they still don't mean to "retire", so Kiki is very uncomfortable now. Xiaohua just noticed that each of us will go through a period of tooth replacement. Why is this? There is only one pair of human tissues and organs, which will not be replaced after birth. It's just that the teeth are different. There are two pairs in life, and a "handover" is needed. One pair is called deciduous teeth. They are small but not wear-resistant, 20 * * *. It's called deciduous teeth because it begins to grow when you are breastfeeding. The other pair is permanent teeth, which gradually replace deciduous teeth from the age of 6. Usually, permanent teeth are large and wear-resistant, with 28 upper and lower teeth and 32 left and right teeth.

Primary teeth and permanent teeth have different functions. In addition to chewing food, deciduous teeth can also stimulate the development of gums and guide the growth of permanent teeth, which are mainly used for chewing food. People's gum bones have a development process from small to large. In early childhood, the gum bone is not large. At this time, if you grow a pair of permanent teeth, you can't stand on the gum bone. After entering adulthood, the gingival bone grows up. If those deciduous teeth are still there at this time, then the gum bone will not be filled, and it is difficult to play a normal chewing role. Therefore, people should grow two pairs of teeth.