Method: 29 lower first molar Spaces were observed and the height of alveolar crest before and after treatment were analyzed with paired-t tests.

方法：观察下颌第一磨牙陈旧性拔牙间隙29处。测量矫治前后该处牙槽嵴高度，将测量值进行配对t检验。

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Method: 29 lower first molar Spaces were observed and the height of alveolar crest before and after treatment were analyzed with paired-t tests.

方法：观察下颌第一磨牙陈旧性拔牙间隙29处。测量矫治前后该处牙槽嵴高度，将测量值进行配对t检验。

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