Abstract: Objective   Compare and analyze the differences between three-dimensional and two-dimensional measurements of craniomaxillofacial hard tissue by Steiner and Tweed analyses for young adults in Xi′an. Methods　Totally 120 adults（60 males and 60 females）between 18 to 40 years old in Xi′an were recruited to take CBCT and lateral cephalometric films. Twenty-four markers and 18 measurement items related to Steiner and Tweed analysis were selected and measured by Invivo Dental 5.2 software and WinCeph 8.0 software respectively. The results were processed by SPSS 19.0 statistical software. Results　（1）CBCT 3D cephalometric fixed points based on MPR method had high accuracy and stability，but B and U1crown-R points were not located well on X axis（ICC < 0.90）. （2）Compared with 2D measured values，3D measured line distance values were larger，while angle values were smaller. The 2D measured angle values were larger in both male and female SNA（the angle of anteroposterior position of the maxillary apical base to a line passing through the anterior cranial base），SNB（the angle of anteroposterior position of the mandibular apical base to a line passing through the anterior cranial base），ANB（the angle of anteroposterior position of the maxilla to the anteroposterior position of the mandible），U1-NA（the angle of maxillary incisor to the line between Nasion and the innermost point on the contour of the premaxilla），L1-NB（the angle of mandibular incisor to the line between Nasion and the innermost point on the contour of the mandibular symphysis），GoGn-SN（the angle of line between Gonion and Gnathion to the sella-nasion plane），FMA（the angle of mandibular plane to Frankfort horizontal plane），IMPA（the angle of mandibular incisor to mandibular plane）and male SND（the angle of midpoint of osteomandibular joint to the sella-nasion plane）. The 3D measured line values were larger in both male and female SL（the distance between sella and the intersecting point of perpendicular line of Pogonion to SN plane），SE-R and SE-L（the distance of both right and left sides between sella and the intersecting point of perpendicular line of Condylar vertex to SN plane）and female Pog-NB（the distance of Pogonion to the line between Nasion and the innermost point on the contour of the mandibular symphysis）. The difference of results was statistically significant （P < 0.05）. Conclusion　The accuracy of 3D fixed point is not good enough on X axis，but better on Y axis and Z axis. The 3D measurement result is not affected by the magnification and overlap error of the 2D image，and the accuracy is higher. The 2D cephalometric index is not fully suitable for 3D measurement of stereo image.

Key words: nomal occlusion；cone-beam CT, CBCT；3D measurement；cephalometrics

摘要： 目的    比较并分析西安地区正常牙合青年颅颌面硬组织Steiner和Tweed分析法三维及二维测量值差异。方法    招募120名18 ~ 40岁符合个别正常牙合标准的西安籍志愿者拍摄锥形束CT（CBCT）及头颅侧位片。选择Steiner和Tweed分析法相关24个标志点及18个测量项目，应用Invivo Dental 5.2和WinCeph 8.0 软件分别定点测量，应用SPSS 19.0软件对测量结果进行统计学分析。结果    （1）CBCT三维数据采用多平面重建法定点，精确性和稳定性均较高，但B（下齿槽座点）、U1crowN_R（右上中切牙切点）在X轴上定位欠佳（ICC < 0.90）；（2）同二维测量值相比，三维测量角度值偏小，线距值偏大。在角度指标中，男性及女性SNA（蝶鞍点和鼻根点连线与鼻根点和上齿槽座点连线的夹角）、SNB（蝶鞍点和鼻根点连线与鼻根点和下齿槽座点连线的夹角）、ANB（鼻根点和上齿槽座点连线与鼻根点和下齿槽座点连线的夹角）、U1-NA（上中切牙长轴与鼻根点和上齿槽座点连线的交角）、L1-NB（下中切牙长轴与鼻根点和下齿槽座点连线的交角）、GoGn-SN（下颌平面与前颅底平面的交角）、FMA（眶耳平面与下颌平面的夹角）、IMPA（下中切牙长轴延长线和下颌平面的夹角）及男性SND（蝶鞍点和鼻根点连线与鼻根点和骨性下颌联合中点连线的夹角）的二维测量值较大；在线距指标中，男性及女性SL（颏前点向前颅底平面作垂线的交点与蝶鞍点的距离）、SE-L和SE-R（左、右两侧髁突顶点向前颅底平面作垂线的交点与蝶鞍点的距离）及女性Pog-NB（颏前点到下齿槽座点和鼻根点连线的距离）的三维测量值较大，差异均有统计学意义（均P < 0.05）。结论    三维定点在X轴上个别标志点精确度欠佳，在Y轴及Z轴上精确度较好；三维测量结果不受二维影像放大率及重叠误差影响，准确度更高。二维头影测量指标并不完全适用于对立体图像的三维测定。

关键词: 正常牙合, 锥形束CT, 三维测量, 头影测量