一般有经验的父母都会知道孩子是要到半岁左右才开始出牙的。但有的婴儿生下来才几天或十多天便在下颌长出两颗门牙,有的甚至出生时就已经长出了门牙。这是为什么呢?其实这是生理上的一种失常现象,是因为婴儿的乳牙胚长得比较表浅,长在牙槽骨的表层而与牙龈粘膜比较靠近,在牙冠生长发育和钙化的同时,就开始萌出。这牙在医学上叫「乳前 Generally experienced parents will know that children are about to start toothing until about half a year old. However, some babies are born only a few days or ten days in the jaw will grow two incisors, and some have even born at birth incisors. This is why? In fact, this is a physiological disorder, because the baby’s tooth germ is relatively long, grow in the surface of the alveolar bone and gingival mucosa closer to the crown growth and calcification At the same time, it began to erupt. This tooth is medically called "milk before