Orthodontic Treatment of Impacted Teeth. Adrian Becker
standing teeth in cross‐section, thereby providing bucco‐lingual positional information on the tooth and any associated structures in a plane at right angles to that seen on the periapical radiograph. Due to the thickness of bone traversed, detail is much poorer, unless there is expansion owing to a large cyst or a bucco‐lingually displaced tooth.
Fig. 4.1 The angle of the central ray in a true occlusal view of the lower jaw depends on the area of interest.
Source: Reproduced from previous edition. Adrian Becker, The Orthodontic Treatment of Impacted Teeth, 2nd ed., 2007 with the kind permission of Informa Healthcare – Books.
In order to produce a true occlusal view in the anterior region of the mandibular arch (Figure 4.1), the head will need to be tipped back further and the tube pointed at the symphysis menti, at an angle of 110° to the occlusal plane, in line with the long axes of the incisor teeth. To achieve the same for the molar teeth, the 90° angle to the occlusal plane will need to be augmented by a 15° medial tilt of the tube, to compensate for the characteristic slight lingual tipping of these teeth [3]. This means that, ideally, the radiograph should be performed individually for each side, in order to capture each molar in its long axis and its true occlusal view.
Maxillary arch
Maxillary anterior occlusal
In the maxillary arch, the nose and forehead interfere with the positioning of the X‐ray tube close to the area to be viewed. The best that can be achieved by positioning the tube close to the face is an oblique, anterior, maxillary occlusal view of the teeth, which is perhaps better described as a high or steeply angled periapical view (Figure 4.2). This view will shorten the apparent length of the roots and will be a far cry from the cross‐sectional view that is so easy to achieve in the mandibular arch. The central ray passes through cancellous bone rather than the compact bone that is found in the mandible, so detail is usually good, although not as clear as with the periapical view.
Fig. 4.2 A diagram showing incisor inclination, receptor position and central X‐ray beam, differentiating the periapical view, the anterior (oblique) occlusal view and the true vertex occlusal view.
Source: Reproduced from previous edition. Adrian Becker, The Orthodontic Treatment of Impacted Teeth, 2nd ed., 2007 with the kind permission of Informa Healthcare – Books.
True (vertex) occlusal
A true (vertex) occlusal 2D view of the anterior maxilla [4] needs a very long exposure time and it is for this reason that the method has never been popular. It is therefore almost with a collective sigh of relief among professionals that the method has been totally superseded by the introduction of volumetric cone beam computerized tomography (CBCT) scanning. The CBCT imaging modality, which can give much more information with little or no increase in radiation dosage, is discussed towards the end of this chapter.
Extra‐oral radiographs
The panoramic view, while not showing detail to the same degree as a periapical radiograph, has the advantage of simply and quickly offering a good scan of teeth and jaws, from the temporo‐mandibular (TM) joint on one side to the TM joint on the other. It is probably true to say that today orthodontists are in general agreement that this radiograph gives the most qualitative information to act as a starting point from which to proceed to other forms of radiography, in line with the demands of the particular situation in any given case.
True and oblique extra‐oral views (Figure 4.3a–c) and the variously angulated oblique occlusal radiographs all provide information that may be used to complement the periapical radiograph, particularly when tooth displacement is severe. However, the use of any oblique radiograph, be it a single periapical, an occlusal or a lateral jaw radiograph, for the accurate localization of a buried tooth may frequently be misleading. This being so, two incipient dangers exist. First, a surgical procedure may be misdirected and a flap opened on the wrong side of the alveolar process. Second, misinterpretation of the tooth’s position may lead the operator to consider there to be a very favourable prognosis for biomechanical resolution when in fact the tooth may be in a completely intractable position. In such circumstances, therefore, the choice of treatment will be inappropriate.
In view of these and other shortcomings, these cases are now diagnosed and treatment planned using CBCT imaging and the only extra‐oral radiographs still in use, to complement panoramic radiographs, are the lateral and PA cephalometric projections.
Three‐dimensional diagnosis of tooth position
As dentists, we are used to seeing periapical radiographs of individual teeth and, provided that the teeth concerned are erupted and in the line of the arch, these radiographs have many advantages. However, in this view the X‐ray tube is not directed in either the true horizontal, true vertical or true lateral plane. Aside from radiography of the mandibular posterior teeth, the tube is always tipped at an angle to one or more of these planes. For an erupted tooth this is unimportant, since the third dimension is supplied by direct vision within the mouth. However, while it gives a good 2D representation of the tooth, this view has limited value when visualization of an unerupted tooth is required in the three planes of space.
Fig. 4.3 (a) The periapical view shows an impacted left maxillary central incisor, due to an inverted, unerupted, supernumerary tooth. The deciduous tooth is over‐retained. Accurate diagnosis of the height of the impacted tooth in the alveolus is not possible to determine from this view. (b) The anterior maxilla seen on a lateral cephalometric radiograph shows the high impacted central incisor (arrow) and its bucco‐lingual location, facing the labial vestibular sulcus. (c) The parallel intra‐oral photographic view at surgical exposure. The radiograph has been laterally inverted to simplify comparison.
Courtesy of Dr D. Harary.
Parallax method
By following the principles involved in binocular vision, two periapical views of the same object, taken from slightly different angles, can provide depth to the flat, 2D picture presented by each of the radiographs individually (Figure 4.4) [5–7]. This is of considerable help in distinguishing the buccal or lingual displacement of the canine, which is low down and fairly close to the line of the arch, and is performed in the following manner (Figure 4.5):
1 A