Ohman A, Kull L, Andersson J, Flygare L
Department of Radiology, Sunderby Hospital, SE-971 80 Luleå, Sweden.
Dentomaxillofac Radiol. 2008 Dec;37(8):445-52. doi: 10.1259/dmfr/86360042.
To measure organ doses and calculate effective doses for pre-operative radiographic examination of lower third molars with CT and conventional radiography (CR).
Measurements of organ doses were made on an anthropomorphic head phantom with lithium fluoride thermoluminescent dosemeters. The dosemeters were placed in regions corresponding to parotid and submandibular glands, mandibular bone, thyroid gland, skin, eye lenses and brain. The organ doses were used for the calculation of effective doses according to proposed International Commission on Radiological Protection 2005 guidelines. For the CT examination, a Siemens Somatom Plus 4 Volume Zoom was used and exposure factors were set to 120 kV and 100 mAs. For conventional radiographs, a Scanora unit was used and panoramic, posteroanterior, stereographic (scanogram) and conventional spiral tomographic views were exposed.
The effective doses were 0.25 mSv, 0.060 mSv and 0.093 mSv for CT, CR without conventional tomography and CR with conventional spiral tomography, respectively.
The effective dose is low when CT examination with exposure factors optimized for the examination of bone structures is performed. However, the dose is still about four times as high as for CR without tomography. CT should therefore not be a standard method for the examination of lower third molars. In cases where there is a close relationship between the tooth and the inferior alveolar nerve the advantages of true sectional imaging, such as CT, outweighs the higher effective dose and is recommended. Further reduction in the dose is feasible with further optimization of examination protocols and the development of newer techniques.
测量使用CT和传统放射摄影（CR）对下颌第三磨牙进行术前影像学检查时的器官剂量并计算有效剂量。
使用氟化锂热释光剂量仪在人体头部模型上测量器官剂量。剂量仪放置在对应腮腺、下颌下腺、下颌骨、甲状腺、皮肤、晶状体和脑的区域。根据国际放射防护委员会2005年提议的指南，使用器官剂量来计算有效剂量。对于CT检查，使用西门子Somatom Plus 4 Volume Zoom，曝光参数设置为120 kV和100 mAs。对于传统X线片，使用Scanora设备，拍摄全景、前后位、立体（扫描图）和传统螺旋断层图像。
CT、无传统断层摄影的CR和有传统螺旋断层摄影的CR的有效剂量分别为0.25 mSv、0.060 mSv和0.093 mSv。
当采用针对骨结构检查优化的曝光参数进行CT检查时，有效剂量较低。然而，该剂量仍约为无断层摄影的CR的四倍。因此，CT不应作为下颌第三磨牙检查的标准方法。在牙齿与下牙槽神经关系密切的情况下，CT等真正的断层成像的优势超过了较高的有效剂量，建议使用。通过进一步优化检查方案和开发更新技术，进一步降低剂量是可行的。
