Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 84

This is the basic screen in all CT software and displays the three anatomical planes: axial, coronal and sagittal. The initial display is dictated by the orientation in space in which the patient was positioned during the scan. The operator may then tilt the volume in all three axes and reach any desired position in space, i.e. the position of the patient's head may be virtually altered after the scan was taken. An initial overall impression of the situation may be gained by exploring the scanned volume, using the 3D volume‐rendering module. At the outset, however, in order to discover if there are any relevant and unexpected details in the general area, a careful examination of each of the three planes for incidental findings is essential.

Fig. 4.16 Diagnosing resorption, cross‐sections. The lateral incisor #12(7) is tipped mesially. Cross‐sections are vertical cuts. Therefore in this case the cross‐sections cannot reveal the resorption to its full extent.

From this point on, the focus of the investigation is directed specifically to the impacted tooth/teeth. Many orthodontists will rely on the bucco‐lingual information, gleaned from a series of cross‐sectional cuts that are perpendicular to the curved panoramic cut. It is a common misconception that all the information in the bucco‐lingual plane should lie in these cross‐sections, which may often be 1 mm thick with 1 mm spacing from each other. In fact, this concept is a clear recipe for negligently failing to identify important information, because the angle of these sections cannot reveal all the relevant data (Case 3, Figures 4.16–4.18).

The MPR screen contains all the information and it is a very important tool. The first step to be taken is a thorough three‐plane scrolling of the ROI, with slice thickness set to a minimum (the voxel size), in the absence of sharpening filters. The ability to tilt one or more planes is an advantage in achieving the appropriate and more diagnostic cutting/slicing angle for visualization. The action that adds the ultimate level of diagnosis is viewing each involved tooth separately. It is necessary to tilt each tooth to a vertical position and to examine it while rotating it through 360° and covering every possible angle (Figures 4.14 and 4.17). Additional scrolling through the axials along the vertical tooth will complete the process. Similarly, if the impacted tooth is located at an almost horizontal angle, it is tilted so that its long axis is exactly oriented in the horizontal and sagittal posture. Using the same rotating tool, on this occasion the tool should be placed on the tooth axis in the coronal plane window (Figure 4.19c). After rotating the tool through 360°, additional scrolling through coronals along the tooth will complete the diagnostic information.