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。
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。
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）。
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.
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。
Absence of more than two first premolars or absence of a first and a second premolar.
缺少超过两个第一前臼齿或者一个第一和一个第二前臼齿。
Absence of more than two first premolars or absence of a first and a second premolar.
缺少超过两个第一前臼齿或者一个第一和一个第二前臼齿。
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