三维颅面水平参考平面的确定方法

目的:比较在三维影像选取双侧耳点和双侧眶下点构建的不同水平面之间差异,分析不同水平面对双侧耳点和双侧眶下点位置的影响,为颅面部三维头影测量水平参考平面的确定提供依据。方法:选取32名正畸治疗前面部基本对称患者(颏下点离正中矢状面≤2 mm), 获取DICOM格式的大视野锥形束CT数据并导入到Dolphin软件,将鼻根点、蝶鞍点和枢椎齿突最高点构建正中矢状面,测量双侧耳点和双侧眶下点中随机三点构建的4种水平参考平面。分别定义为,平面1:水平面由右侧耳点和双侧眶下点构成;平面2:水平面由左侧耳点和双侧眶下点构成;平面3:水平面由双侧耳点与右侧眶下点构成;平面4:水平面由双侧耳点与左侧眶点构成。记录4个平面在三维空间当中的俯仰角、侧偏角和横滚角。间隔两周,一位研究者进行两次测量。计算组间相关系数(interclass correlation coefficient,ICC)比较两次测量结果的一致性,检验测量者自身的可靠性,进行单因素重复测量方差分析检验组内4个平面之间的差异,按年龄分为13~17岁组和≥18岁组。以枢椎齿突最高点为原点计算双侧耳点和双侧眶下点位置,应用圆周长公式分析头部转动对双侧耳点和双侧眶下点的影响。结果:单因素重复测量方差分析结果显示,不同三点构建的4种平面之间俯仰角、侧偏角和横滚角差异均无统计学意义(P=0.196、0.314、0.341)。头位转动对双侧耳点和双侧眶下点的影响分析结果为:1°俯仰角变化产生耳点约0.5 mm、眶下点约1.6 mm的变化;1°侧偏角变化产生耳点约1.1 mm、眶下点约1.5 mm的变化;1°横滚角变化产生耳点约1.2 mm、眶下点约0.7 mm的变化。结论:对于面部基本对称个体,应用三维头颅影像对双侧耳点和双侧眶下点中随机选取三个点构建的4种水平面之间差异无统计学意义;以双侧眶下点和右侧耳点构建的水平面可能最适合临床使用;头部不同方向的转动使双侧耳点和双侧眶下点产生不同位置的变化。

Using three-dimensional craniofacial images to construct horizontal reference plane

Objective: To compare four different three-dimensional horizontal planes and detect anatomical landmarks so as to provide theoretical reference for horizontal reference plane constructed by three-dimensional cephalometry. Methods: The subjects of this study were 32 facial symmetry patients (menton from mid-sagittal plane ≤2 mm). Cone-bead computed tomography (CBCT) was obtained before orthodontic treatment, and the data were imported into Dolphin imaging soft in DICOM format. The sagittal plane was passing through the Nasion, Sella and Dent. Four horizontal reference planes were constructed by three points of bilateral porion and bilateral orbitale. Plane 1: horizontal reference plane constructed by right porion and bilateral orbitale. Plane 2: horizontal reference plane constructed by left porion and bilateral orbitale. Plane 3: horizontal reference plane constructed by bilateral porion and right orbitale. Plane 4: horizontal reference plane constructed by bilateral porion and left orbitale. Pitch, yaw, roll for four planes were measured three dimensionally. All the samples were measured two times by one judge at an interval of two weeks. The two times measuring results were evaluated with Intraclass correlation coefficient (ICC) for verifying reliability. The multiple sets of repeated measurement analysis were used to compare the four different planes. Based on ages, the samples were divided into two groups (group 1: ages 13 to 17, group 2: over 18 years), the mean and standard deviation of landmark coordinates measured with Dent as the origin point, the circumference formula was applied to calculate the change of landmark position generated by head rotation. Results: No significant differences of pitch, yaw and roll among the four planes (P=0.196, 0.314, and 0.341). One degree of pitch rotation made changes of porion and orbitale approximate 0.5 mm, and 1.6 mm, respectively. One degree of yaw rotation made changes of porion and orbitale approximate 1.1 mm, and 1.5 mm, respectively. One degree of roll rotation made changes of porion and orbitale approximate 1.2 mm, and 0.7 mm, respectively. Conclusion: There was no significant difference among the four horizontal planes constructed by any three points of bilateral orbitales and bilateral porions. It has the highest concordance using bilateral orbitales and one porion to construct horizontal plane in this study, probably the best option in clinical practice. Different head rotation generated different distance changes of anatomical landmarks.