Objective To investigate the root and canal morphology of extracted maxillary second premolars.

目的观察上颌第二前磨牙的牙根及根管形态。

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Mandibular second premolars are the most frequently missing teeth while maxillary lateral incisors are second-most.

下颌第二前磨牙是最常见的缺失的牙齿，而上颌侧切是第二大。

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Results: After treatment, in maxilla the arch width and alveolar bone width between canines were in creased(P<0.01), those were decreased between second premolars(P<0.01 ).

结果：上颌矫治后尖牙间牙弓宽度和基骨宽度明显增加（P< 0 .0 1） ，前磨牙间牙弓宽度和基骨宽度明显减小（P< 0 .0 1）。

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