摘要目的:探究3种不同定义的下颌平面MP(G)(颏顶点Gn与下颌角点Go连线)、MP(T)(下颌下缘最低部的切线)、MP(Me)(过颏下点Me与下颌角下缘切线)对下颌平面角测量的影响。方法:本研究为回顾性研究，收集我院正畸科初诊患者400例，测量分析头侧位片并进行高、低角筛选，分析影响下颌平面角测量的相关因素。结果:①在MP-SN组和MP-FH组中，MP(T)所成下颌平面角与MP(G)、MP(Me)所成下颌平面角差异有统计学意义[MP(G)-SN：37.00°±6.25°，MP(T)-SN：39.44°±7.08°，MP(Me)-SN：37.04°±7.12°；MP(G)-SN vs MP(T)-SN： P<0.001，MP(T)-SN vs MP(Me)-SN： P<0.001；MP(G)-FH：28.21°±5.58°，MP(T)-FH：30.65°±6.35°，MP(Me)-FH：28.25°±6.40°，MP(G)-FH vs MP(T)-FH： P<0.001，MP(T)-FH vs MP(Me)-FH： P<0.001]，而MP(G)与MP(Me)所成下颌平面角差异无统计学意义[MP(G)-SN vs MP(Me)-SN： P＝0.653；MP(G)-FH vs MP(Me)-FH： P＝0.620]；②MP(G)、MP(T)、MP(Me)平面在MP-SN、MP-FH两组组内及组间筛出高角、低角病例数不一致；③高角组中，MP(G)-FH与颏部形态无明显相关性(颏厚度/颏高度： r＝－0.090， P＝0.381；颏角： r＝－0.135， P＝0.189)；低角组中，MP(Me)-FH与颏部形态无明显相关性(颏厚度： r＝－0.258， P＝0.194；颏角： r＝－0.229， P＝0.109；颏前点高度/颏高度： r＝－0.318， P＝0.100)。 结论:医师在诊断分析中应注意MP(T)、MP(G)、MP(Me)所构成的下颌平面角存在差异，同组中MP(T)所构成的下颌平面角最大，MP(G)与MP(Me)所构成下颌平面角差异无统计学意义；建议可将MP(G)-FH、MP(Me)-FH分别作为筛选高角、低角病例时测量下颌平面的参考指标。

abstractsObjective:To investigate how the three mandibular plane definitions, which are MP(G), a line connecting the points Gonion to Gnathion, MP(T), a line tangent to the inferior border of the mandible, and MP(Me), a line tangent to the posterior lower border of the mandible and Mention) can affect the measurements of mandibular plane angle.Methods:Four hundred new cases in our hospital were collected and measured. The high and low angles cases were screened, and the factors affecting measurement of mandibular plane were analyzed.Results:① Significant differences were detected between MP (T) plane and MP (G) plane, or MP (Me) plane in both MP-SN group and MP-FH group[MP(G)-SN: 37.00°±6.25°, MP(T)-SN: 39.44°±7.08°, MP(Me)-SN: 37.04°±7.12°, MP(G)-SN vs MP(T)-SN: P<0.001, MP(T)-SN vs MP(Me)-SN: P<0.001; MP(G)-FH: 28.21°± 5.58°, MP(T)-FH: 30.65°± 6.35°, MP(Me)-FH: 28.25°±6.40°, MP(G)-FH vs MP(T)-FH: P<0.001, MP(T)-FH vs MP(Me)-FH: P<0.001; no statistical difference was found between MP(G)-SN and MP(Me)-SN, P=0.653, and MP(G)-FH and MP(Me)-FH: P=0.620]; ② The numbers of high angle and low angle cases screened by MP (G), MP (T) and MP (Me) were inconsistent both in MP-SN and MP-FH groups and between two groups; ③ In high angle group, only MP (G)-FH had no correlation with mental morphology (Ratio of chin thickness to Chin height: r=-0.090, P=0.381; Chin angle: r=-0.135, P=0.189); In low angle group, MP(Me)-FH had no correlation with the mental morphology (Chin thickness: r=-0.258, P=0.194; Chin angle: r=-0.229, P=0.109; Ratio of the height of Pogonion height to Chin height: r=-0.318, P=0.100). Conclusions:Orthodontists should pay attention to the difference of mandibular plane angle formed by MP (T), MP (G) and MP (Me) in diagnosis and analysis. The mandibular plane angle by MP (T) is larger than MP (G) and MP (Me) formed, which have no statistical difference. It is suggested that MP (G)-FH could be used as screen reference for the high angle case, and MP(Me)-FH as the reference for the low angle case.