Shokri Abbas, Miresmaeili Amirfarhang, Farhadian Nasrin, Falah-Kooshki Sepideh, Amini Payam, Mollaie Najmeh
1 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Dental Research Center, Hamadan University of Medical Sciences, Hamadan, Islamic Republic of Iran.
2 Department of Orthodontics, Faculty of Dentistry, Dental Research Center, Hamadan University of Medical Sciences, Hamadan, Islamic Republic of Iran.
Dentomaxillofac Radiol. 2017 Jul;46(5):20160180. doi: 10.1259/dmfr.20160180. Epub 2017 Apr 12.
This study aimed to assess the effect of head position on the accuracy of transverse measurements of the maxillofacial region on CBCT and conventional posteroanterior (PA) cephalograms. The second objective of this study was to find skull positions with the greatest and smallest effect on transverse measurements in the maxillofacial region.
PA cephalograms and CBCT scans were obtained from 10 dry human skulls in 7 positions, namely the central position, 10° and 20° rotations, 10° and 20° tilts and 10° and 20° tips. The CBCT scans were converted to PA cephalograms on which distances from six landmarks, namely the nasal cavity, zygomatic arch, jugale, antegonion, condylion and zygomaticofrontal suture to the mid-sagittal plane, were measured on both sides using Dolphin two-dimensional software. The paired t-test was used to compare the mean values separately in each position (for each landmark) with the gold standard (central skull position). The interclass correlation coefficient and the Bland-Altman plot were used to compare the mean values measured by two observers.
The mean values of the distances measured on CBCT PA cephalograms were greater than those measured on conventional PA cephalograms; this difference was statistically significant for some landmarks (p < 0.005). The rotated position (as compared with the central position) caused the greatest change in values for most landmarks on both sides (p < 0.005).
The CBCT PA cephalogram was more accurate than the conventional PA cephalogram, and landmarks farther from the midline exhibited greater changes on cephalograms compared with those closer to the midline. Patients are at risk of improper positioning when undergoing extraoral radiography such as PA cephalograms. Changes in head position may affect the transverse measurements and thus the treatment plan.
本研究旨在评估头部位置对锥形束计算机断层扫描（CBCT）和传统后前位（PA）头颅侧位片上颌面区域横向测量准确性的影响。本研究的第二个目的是找出对上颌面部区域横向测量影响最大和最小的颅骨位置。
从10个干燥的人类颅骨获取PA头颅侧位片和CBCT扫描图像，共7个位置，即中心位置、10°和20°旋转、10°和20°倾斜以及10°和20°倾斜。将CBCT扫描图像转换为PA头颅侧位片，使用Dolphin二维软件在两侧测量6个标志点（即鼻腔、颧弓、颧颌点、下颌角点、髁突点和颧额缝）到正中矢状面的距离。采用配对t检验分别比较每个位置（每个标志点）的平均值与金标准（颅骨中心位置）。使用组内相关系数和Bland-Altman图比较两名观察者测量的平均值。
CBCT PA头颅侧位片上测量的距离平均值大于传统PA头颅侧位片上测量的距离平均值；对于某些标志点，这种差异具有统计学意义（p < 0.005）。旋转位置（与中心位置相比）导致两侧大多数标志点的值变化最大（p < 0.005）。
CBCT PA头颅侧位片比传统PA头颅侧位片更准确，与靠近中线的标志点相比，远离中线的标志点在头颅侧位片上表现出更大的变化。患者在接受如PA头颅侧位片等口外放射摄影时存在定位不当的风险。头部位置的变化可能会影响横向测量，从而影响治疗计划。
