中文摘要：

目的 利用CBCT对以S、N、Ba、Cg、PNS 5点构成的10种临床常用的正中矢状参考平面进行比较,评价其准确性,为建立CBCT三维头影测量面部对称性分析系统提供参考。方法 选择53例12～20岁面部基本对称的正畸患者,拍摄头颅CBCT片,以10种常用的正中矢状参考平面为基准,分别计算出每位患者的面部不对称指数。结果 10个平面间有显著性差异（P〈0.05）,标志点到以S、N、Ba确定的正中矢状参考平面的面部不对称指数（11.07±4.15）最小。结论 基于CBCT三维头影测量,以S、N、Ba点确定的正中矢状面的准确性最高。

英文摘要：

Objective To adopt Cone-beam CT to conduct the comparison among10 midsagittal reference planes which are made by the 5 points S, N, Ba, Cg, PNS, mostly used in the clinical orthodontics, to valuate their accuracy and provide references for the establishment of the CBCT three-dimensional eephalometry facial symmetry analysis system in the future. Methods 53 cases of 12～20- year-old patients with facial symmetry were selected, skull CBCT images were taken, and the facial asymmetry index of each patient was calculated on the basis of 10 kinds of commonly used midsagittal reference planes. Results There was a significant difference among the 10 planes（P〈0.05）, and the facial asymmetry index was the smallest of the midsagittal plane determined by S, N and Ba （11.07±4.15）. Conclusion Based on the resuhs of the CBCT three-dimensional cephalometry, the accuracy of the midsagittal reference plane determined by the S, N, Ba is the highest one.