Objective To evaluate the clinical effect of preserving the lower first molar with complete vertical fracture.
目的评价保存治疗纵折下颌第一磨牙的临床疗效。
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。
Methods: The thickness of enamel and dentin at different positions of 23 upper first and 18 lower first molars were measured by electronic ruler.
方法：用电子测量尺测量23颗上颌第一磨牙和18颗下颌第一磨牙牙合面不同部位牙釉质、牙本质的厚度。
Methods: The thickness of enamel and dentin at different positions of 23 upper first and 18 lower first molars were measured by electronic ruler.
方法：用电子测量尺测量23颗上颌第一磨牙和18颗下颌第一磨牙牙合面不同部位牙釉质、牙本质的厚度。
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