把你的舌头放在牙齿后面，微笑，这样可以放松你的脸部。
Put your tongue behind your teeth and smile, which will relax your face.
非常明显，前面的牙齿先改变，后面的牙齿再改变。
这些早期翼龙嘴里都长满了牙齿，通常来说，小的牙齿长在后面，大的牙齿长在前面。
These early pterosaurs all had a mouth full of teeth, usually small at the back and larger at the front.
牙膏和饮水中的氟化物能够保护牙齿的表面，但在后面的磨牙需要特别的保护。
Fluoride in toothpaste and in drinking water protects the smooth surfaces of teeth but back teeth need extra protection.
也就是说把舌头放在口腔上方的牙齿的后面，靠近齿龈的地方。
William: Open your mouth slightly. Step two; put your tongue behind your teeth near the top of your mouth.
这幅图片清晰显示为什么牙齿是容易替换唯一的直接的在后面的牙齿。
This photo clearly shows how the teeth are easily replaced by the ones directly behind.
这幅图片清晰显示为什么牙齿是容易替换唯一的直接的在后面的牙齿。
This photo clearly shows how the teeth are easily replaced by the ones directly behind.
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