Department of Oral Pathology and Oral Radiology, Institute of Dentistry, University of Turku, Lemminkäisenkatu 2, 20014, Turku, Finland.
Department of Oral and Maxillofacial Diseases, University of Helsinki, Helsinki, Finland.
BMC Oral Health. 2021 Dec 29;21(1):670. doi: 10.1186/s12903-021-02029-6.
Cone-beam Computed Tomography (CBCT) is widely used for preoperative 3D imaging of lower third molars. Hence, for this imaging indication, the present study aimed to define the minimum field-of-view (FOV) size and its optimum placement, to decrease radiation exposure, and highlight the need of computer-assisted FOV centering technique for dental CBCT devices. To facilitate proper placement of image field, lower second molar was chosen as reference.
The retrospective study included 50 CBCT-scans of 46 patients with mean age of 34 years. Based on the lower second molar, a three-dimensional coordinate was formed and the location of mandibular canal (MC) and the dimensions and locations of the lower third molars, and possible associated pathological findings were assessed. Accordingly, the FOV size and position for third-molar imaging were optimized, while ensuring encompassment of all relevant structures.
The minimum cylindrical volume, covering lower third molars and MC, was 32.1 (diameter) × 31.6 (height) mm, placed in relation to the second molar crown, top 2.2 mm above cusp tips, anterior edge 6.7 mm in the front of the most distal point of the crown, and lingual edge 7.9 mm on the medial side of the lingual wall.
The optimized FOV for lower third molars was smaller than common standard small FOVs. We recommend using FOV volume 3.5∅ × 3.5 cm for third molars without associated pathology. Accurate FOV protocols are essential for development of new CBCT-devices with computer-assisted and indication-specific FOV placement.
锥形束 CT（CBCT）广泛用于下颌第三磨牙的术前 3D 成像。因此，对于这种成像适应证，本研究旨在定义最小视野（FOV）大小及其最佳位置，以减少辐射暴露，并强调需要计算机辅助 FOV 定位技术用于牙科 CBCT 设备。为了便于正确放置图像区域，选择下颌第二磨牙作为参考。
这项回顾性研究包括 46 名患者的 50 个 CBCT 扫描，平均年龄为 34 岁。基于下颌第二磨牙，形成了一个三维坐标，并评估了下颌管（MC）的位置以及下颌第三磨牙的尺寸和位置，以及可能存在的相关病理发现。因此，优化了用于第三磨牙成像的 FOV 大小和位置，同时确保涵盖所有相关结构。
最小的圆柱形体积，覆盖下颌第三磨牙和 MC，为 32.1（直径）×31.6（高度）mm，放置在第二磨牙冠的关系，在牙尖顶部上方 2.2 毫米，前边缘在牙冠最远端点前方 6.7 毫米，舌侧边缘在舌侧壁内侧 7.9 毫米。
优化的下颌第三磨牙 FOV 小于常见的标准小 FOV。我们建议对于没有相关病理的第三磨牙使用 3.5∅×3.5cm 的 FOV 体积。对于具有计算机辅助和适应证特定 FOV 定位的新型 CBCT 设备，准确的 FOV 方案至关重要。
