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牙是生长在口腔中颌骨上比骨组织还要硬的高度钙化的组织,牙齿是人体最硬的器官。刚刚出生的婴儿虽然口腔内没有牙齿,但在他们的颌骨内已经有了牙胚。到一定时间,这些牙齿就从牙龈表面钻出来,植立在口腔内。牙齿从颌骨内长出来的过程,在医学上叫做牙齿的“萌出”,也就是俗话说的长牙。首次萌出的为“乳牙”,人类共20个,一般在6—9个月时开始出牙,3岁出齐。有人说乳牙没有牙根,这只说对了一半。当乳牙刚长出来的时候原本是有牙根的,不然怎么能
Tooth is a highly calcified tissue that grows harder on the jaw than in bone in the mouth. Teeth are the hardest organ in the body. Newborn babies, although no teeth in their mouth, have tooth germs in their jaws. To a certain time, these teeth from the gums drilled out, built in the mouth. The process of teeth growing out of the jaw bone is medically called the “eruption” of teeth, which is the old saying goes. The first eruption of “deciduous teeth”, a total of 20 human beings, usually in 6-9 months to start teething, 3 years old together. Some people say that there is no tooth root deciduous teeth, which only say halfway. When the baby teeth just grow out of the original root, or how can