Did you know that sharks never run out of teeth? When they lose a tooth another one just comes in to replace it.

你们知道鳖鱼牙齿永远不会掉光吗？它们每掉一颗牙，就会长一颗新牙来替补。

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As a result, you might lose the upper tooth.

结果，连这颗牙的牙齿也会脱落。

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But the lose of the activity of periodontal ligament cells and root replantation has influenced the successful rate of tooth replantation for a long time.

牙再植术的历史悠久，但是脱位牙根面部分牙周膜细胞活性丧失、牙根吸收，影响着牙再植术的成功率。

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