aetiological evidence for the failure to erupt of the first mandibular molar on the right side. In order to enhance the 3D view, a combination of mild bone peeling, clipping and sculpting away part of the lingual cortical bone was executed (Animation 4.1 on this book’s website). Two additional animations (Animation 4.2 and Animation 4.3) will enhance the perception of the case. The latter animation shows how, by tilting the chin upwards (in the SW) and thereby placing the molar in a vertical position, animation becomes more informative (orthodontic treatment by Dr Ronen Zoizner).
The lesser density of the bone in the upper jaw makes the situation there much more favourable for obtaining good‐quality imaging of the impacted teeth, while maintaining tooth volume.
It is important to note that the 3D transparent view tends to deceptively show tooth volumes to be smaller than they are and, as such, should be treated with caution.
Automatic tooth segmentation
This procedure, based on artificial intelligence (AI), is already in use (Figure 4.15). At the time of writing it is a third‐party service, which will undoubtedly be added to the CBCT software by the manufacturers. This is an excellent feature because it saves time and effort, but should only be used to obtain a general impression. Presently it is not accurate enough in relation to tooth volume. In the not too distant future, however, it is expected to improve, as with most applications that depend on AI. Tooth contact or minor resorption will need to be confirmed, preferably in the MPR screen.
Fig. 4.15 Automatic segmentation, artificial intelligence (AI) driven. The software algorithm automatically segments the teeth and bone for each jaw separately and the inferior alveolar canal. A viewer that can run on a PC or a smartphone will allow each entity to be coloured, rotated in all axes and moved separately, as well as being removed and much more.
Courtesy of ORCA Dental AI.
Multi‐planar reconstruction
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.
Case 3: Diagnosing Resorption
The left‐hand image in Figure 4.16 represents the anterior portion of a reconstructed panoramic view, depicting a typical, palatally impacted and strongly tipped canine. At the same time, the root of the lateral incisor is tipped mesially. The right‐hand image in Figure 4.16 shows a row of eight serial cross‐sectional cuts across the root of the lateral incisor, presenting a suspicion of root resorption, due to the proximity of the canine crown. Because the cross‐sectional cuts are always vertical on a reconstructed panoramic view, the tipped root of the lateral incisor cannot be sectioned to reveal the resorption to its full extent. The MPR screen (Figure 4.17) is the place to look for the extent of the resorption. The coronal (Figure 4.17c) and sagittal (Figure 4.17b) planes are tilted to bring the lateral incisor long axis to a perfect vertical posture. The rotating tool is placed on the tooth axis in the axial (Figure 4.17a) plane. The tool is then rotated 360°, thus depicting its outline at every possible angle. The window in Figure 4.17d is recording the resorption in the disto‐palatal aspect. The tool continues on its way around the tooth axis and in Figure 4.18 a resorption in the palatal aspect is recorded, indicating the breadth of the resorption lesion. There is, indeed, no substitute for this diagnostic ability in the aspect of the tooth long axis (orthodontic treatment by Dr Ronen Zoizner).
Case 4: Multi‐planar reconstruction for an incisor that is almost horizontal
The clinical aim was to learn why the right central incisor had refused to erupt, and to establish its exact location and anatomy and assess its proximity to other teeth and structures. The right central incisor was horizontally and sagitally re‐aligned in the axial (Figure 4.19a) and sagittal (
