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.
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.
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.
方法：收集临床上因正畸需要拔除的前磨牙28颗，将每个牙齿分为近中和远中两个邻面标本。
Methods:28 human premolars extracted for orthodontic reasons were collected for the experiment. Every premolar was split vertically into medial and distal haves.
结论：拔除下颌第二前磨牙后，第三磨牙萌出间隙明显增大，有助于下颌第三磨牙的正常萌出。
Conclusion: Mandibular second premolar after pulling, the third molar eruption clearance increased obviously, conduce to the jaw third molar normal eruption.
方法将因正畸需要拔除的60颗前磨牙制成试样块并用树脂包埋，一面暴露作为测试面，去除其釉质暴露浅层牙本质并用砂纸磨平。
Methods The 60 premolars were made into test pieces and embedded with resin. One side was exposed as a test surface, with its enamel removed and superficial dentin polished with sandpaper.
方法将因正畸需要拔除的60颗前磨牙制成试样块并用树脂包埋，一面暴露作为测试面，去除其釉质暴露浅层牙本质并用砂纸磨平。
Methods The 60 premolars were made into test pieces and embedded with resin. One side was exposed as a test surface, with its enamel removed and superficial dentin polished with sandpaper.
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