全景X线片上下颌第三磨牙区域角度测量的准确性及变形评估
Accuracy of angular measurements and assessment of distortion in the mandibular third molar region on panoramic radiographs.
作者信息
Dudhia Raahib, Monsour Paul A, Savage Neil W, Wilson Richard J
机构信息
Queensland X-Ray, Brisbane, Queensland, Australia.
出版信息
Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011 Apr;111(4):508-16. doi: 10.1016/j.tripleo.2010.12.005.
OBJECTIVE
The objective of this study was to examine distortion on panoramic radiographs by assessing the accuracy of angular measurements in the mandibular third molar region on panoramic radiographs using computed tomography (CT).
METHODS
Images from patients referred to a radiology practice for low-dose CT scans of their lower third molars were used in this study. The angle between the long axes of the second and third molars was assessed on panoramic radiographs and the corresponding CT images. Apparent tilting of the tooth across the arch on the panoramic image and the bucco-lingual inclination on CT were also recorded and compared.
RESULTS
Eighty-eight patients had 163 mandibular third molars. The mean difference between the panoramic measurements and the CT measurements was -1.44 degrees, indicating that on the panoramic radiograph the third molar appeared less mesially inclined on average. This pattern was present in most cases, but in 64 cases the third molar appeared more mesially inclined on the panoramic radiograph. It was not possible to predict the direction of the discrepancy based on the radiographic findings. The discrepancy between the 2 measurements was greater if the third molar appeared tilted across the arch on the panoramic image, and tilted teeth showed a higher bucco-lingual inclination on reformatted CT images.
CONCLUSIONS
Distortions inherent in panoramic imaging because of projection geometry produce discrepancies in the angular measurements in the mandibular third molar regions on panoramic radiographs. Interpretation of third molar angulation from panoramic radiographs is often unreliable and may not accurately reflect the true orientation of the tooth. Apparent tilting of the tooth across the arch on the panoramic radiograph exacerbates the problem and appears to correlate with the bucco-lingual inclination of the third molar as visualized on reformatted CT images.
目的
本研究的目的是通过使用计算机断层扫描（CT）评估全景X线片下颌第三磨牙区域角度测量的准确性，来检测全景X线片上的失真情况。
方法
本研究使用了因低剂量CT扫描下颌第三磨牙而转诊至放射科的患者的图像。在全景X线片和相应的CT图像上评估第二和第三磨牙长轴之间的角度。还记录并比较了全景图像上牙齿在牙弓上的明显倾斜以及CT上的颊舌向倾斜。
结果
88例患者有163颗下颌第三磨牙。全景测量值与CT测量值之间的平均差异为-1.44度，表明在全景X线片上第三磨牙平均看起来近中倾斜度较小。大多数情况下都是这种模式，但在64例中，全景X线片上第三磨牙看起来近中倾斜度更大。根据影像学表现无法预测差异的方向。如果第三磨牙在全景图像上看起来在牙弓上倾斜，那么这两种测量之间的差异会更大，并且倾斜的牙齿在重组CT图像上显示出更高的颊舌向倾斜度。
结论
由于投影几何形状，全景成像中固有的失真会导致全景X线片上下颌第三磨牙区域角度测量出现差异。从全景X线片解读第三磨牙的角度通常不可靠，可能无法准确反映牙齿的真实方向。全景X线片上牙齿在牙弓上的明显倾斜会加剧这个问题，并且似乎与重组CT图像上显示的第三磨牙颊舌向倾斜度相关。
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