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目的:研究下切牙长轴(long axis of the lower incisors, IA)与颏轴(long axis of the mandibular symphysis, MA)在天然状态下的一致性情况，为正畸治疗中下切牙的健康定位提供参考。方法:从头颅侧位片数据库中等量选取安氏Ⅰ、Ⅱ、Ⅲ类治疗前患者共300例，定义四种颏轴，分别测量四种颏轴与下切牙长轴所成角度(angle between MA and IA，MIA)以及下中切牙角(incisor-mandibular plane angle, IMPA)，按照不同水平向和垂直向骨面型分组进行方差分析。结果:用于定义颏轴的标志点中，颊舌侧下齿槽缘点的中点Id-c和下颌联合中心点D，不同研究者定点的变异系数最小，可重复性最好。由Id-c和D构成的颏轴与下中切牙长轴所成角度MIA在安氏Ⅰ、Ⅱ、Ⅲ类的平均值分别为(9.45±4.06)°、(10.56±3.57)°、(4.35±3.71)°；在Ⅲ类高、均、低角分别为(2.89±0.87)°、(3.66±0.43)°、(5.84±0.71)°。既体现了下切牙牙轴在不同矢状向和垂直向骨面型的代偿倾向，又基本与颏轴保持一致，二者所成角度80%位于(2.18～13.87)°区间。结论:天然状态下，下切牙长轴与颏轴方向基本一致，颏轴与下中切牙长轴所成角度MIA与下中切牙角IMPA相比，受不同水平向和垂直向骨面型变异的影响更小，更能代表符合生理要求的下切牙倾斜度。正畸治疗可以考虑以此为进行下切牙的合理定位，从而确保咬合力的健康传递。“,”Objective:To investigate the consistency between the long axis of the lower incisors (IA) and the long axis of the mandibular symphysis (MA) and provide the reference for healthy location of the lower incisors in orthodontic treatment.Methods:Pre-treatment cephalograms of 300 patients were randomly selected from the data base and were equally distributed among Angle's Class Ⅰ, Ⅱ and Ⅲ malocclusions. MA was defined using four different methods. The angle between MA and the long axis of the lower incisors (MIA)were measured respectively. The incisor-mandibular plane angle (IMPA) was also measured. ANOVA analysis was performed to compare the difference among various sagittal and vertical skeletal patterns.Results:Among all the landmarks used to define MA, the mid-point of the buccal and lingual infradentales (Id-c) and the center of the mandibular symphysis (D) were found to have the lowest coefficient of variation and highest repeatability. Therefore, the MA constructed with Id-c and D was used to represent the long axis of the mandibular symphysis. The mean value of MIA was (9.45±4.06)°、(10.56±3.57)°、(4.35±3.71)° in Angle's Class Ⅰ, Ⅱ and Ⅲ respectively; (2.89±0.87)°、(3.66±0.43)°、(5.84±0.71)° in high, average and low mandibular plane angle Class Ⅲ respectively. This result indicated the compensation tendency of the lower incisor as well as the general consistency between the long axis of the lower incisor and the mandibular symphysis. 80% MIA ranges from 2.18°~13.87°.Conclusions:The long axis of lower incisors was generally consistent with the long axis of the mandibular symphysis in natural dentition. Compared with IMPA, MIA was less affected by various sagittal and vertical skeletal patterns. This association between teeth and bone could be referred for the reasonable position of the lower incisors in orthodontic treatment to ensure the healthy conduction of the occlusal force.