The root canals in mandibular first premolars failed to be treated;
目的 确定人上颌第一前磨牙的颊舌向根管弯曲程度和情况。
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。
Methods 20 subjects were chosen with 4 first premolars extraction based on diagnosis.
方法选择拔除4颗第一双尖牙的患者2 0例，采用方丝弓技术治疗。
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