Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 79

When the orthodontist’s CBCT machine is ‘in‐house’, the imaging process is initiated with the software supplied by the machine manufacturer, or with third‐party software. When the patient is referred to an imaging centre, the imaging technician will produce a DICOM (Digital Imaging and Communications in Medicine) set, representing the international standard for image format and file structure for communication, handling, storing, and printing of medical and dental imaging and image‐related information. It will be handed over together with a viewer program supplied by the CBCT unit manufacturer, or with a third‐party software viewer preferred by the imaging centre. Often, however, more digitally savvy orthodontists may decide to use their own third‐party software to achieve the same ends. In this case only, the DICOM set is handed over and the orthodontists employ their own software.

Many orthodontists will prefer to patronize a professional imaging centre, who may offer a service to perform a work‐up of the case. The technicians at the centre are experts in specifically providing an accurate positional diagnosis of the tooth/teeth in the three planes of space and in relation to the adjacent teeth and other anatomical structures. The work‐up should be adequate to the task of analysing and discovering the existence of pathological entities, leading to the diagnosis of the cause of the impaction, a task for which this modality is second to none.

Secondary and online reconstructions can alter the patient position by tilting in any desired axis in space and slicing it in any direction and in any chosen slice thickness. The slices are not limited to straight cuts, with the panoramic view being the most popular curved cut. A thick panoramic view looks similar to the traditionally irradiated 2D panoramic view and it has the advantage that its form is without horizontal or vertical magnification and, therefore, without distortion. It is possible to avoid overlapping of individual teeth, especially in the premolar area, and there is no projection of other structures, such as the hyoid bone on the mandible or spinal vertebrae on the anterior region. The only information presented on the images is precisely what exists in the focal trough. The disadvantage of the reconstructed panoramic view is that artifacts found in the focal trough will be seen in the reconstructed panoramic view even if their source is outside the focal trough or even the FOV. If an extra‐large FOV is chosen, 3D orthodontic software has the capacity to produce standardized cephalometric views and the many other views needed for an orthodontic portfolio. A handful of devices have this capability. It is very important to note that all devices that enable this extra‐large FOV will perform this scan using half‐beam scan technology (up to 40% less radiation). The result is a normal‐ to low‐resolution scan, which in most cases will be sufficient for all the reconstructed views needed for the orthodontic portfolio. When zooming in on an impacted tooth and its surroundings, one might find it difficult to go into delicate details, like minor resorption, early‐stage invasive cervical root resorption (ICRR), etc.