结论：第二前磨牙拔除患者可发生第二磨牙近中移动，导致磨牙后间隙增加。

Conclusion This reflects that the second molars could move mesially during treatment in the second premolars extraction subjects, which can lead to the increase of the retromolar space.

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前言：目的：通过对磨牙拔除病例与前磨牙拔除病例的牙根吸收情况的对比，探讨关闭磨牙间隙是否加重牙根吸收。

Objective: To study if closing molar Spaces could cause severe root resorption through comparing the effects of molar and premolar extractions on root resorption.

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目的：比较正畸治疗中拔除第二磨牙与拔除第一前磨牙后第三磨牙牙胚位置的不同改变。

Objective:To compare the changes in third molar position in patients treated with second molar and first premolar extractions.

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