<<Prev Intra-oral Bisecting Angle Technique Next>> Introduction This technique is used in areas where the parallel technique is impossible due to poor access, making the angle between tooth and film more than 15 degrees. Using this technique, a true image of the tooth length and width is obtained. Principle In any 90-degree arc, there is one angle that will allow an x-ray beam to cast an accurate shadow of the tooth on the film. The best analogy is that of a tree in the desert. When the sun rises, the shadow of the tree is longer than the tree. At some point in the morning the shadow and the tree are the same length. This is the bisecting angle. The sun continues to rise until, at its zenith, the shadow is very short. In the afternoon the same sequence occurs in reverse. Therefore in the 180-degree arc of the sun during the day there are two bisecting angles. For this to work three angles are calculated.   Angle A is the long axis of the tooth. Angle B is the angle of the film. Angle C is the angle that bisects angle A and B. The beam is then directed at 90 degrees to angle C.     Comment This technique is essential for the incisors and canines in both jaws and preferable, but optional, for the maxillary premolars and molars (see extra-oral near parallel technique).   Example 1 - To Radiograph the Mandibular Canines and Incisors Position the dog in dorsal recumbency, with the palate parallel to the tabletop. Place the film carefully in the mouth, so that all of the target tooth will show on the film. Hold the film flat with mouth props or swabs. Calculate your angles and direct the beam (at approximately 45-degrees) onto the plate. Bisecting angle technique - oblique lateral - for 304 canine tooth   Note that to show all of a canine tooth without superimposition, the beam needs to be angled slightly out to in (i.e. from rostro-lateral to medio-caudal). This is lateral oblique. However, it is good practice to take a second lateral bisecting angle view. This will show pathology that may not be visible on a lateral oblique bisecting angle view. The apex of this 304 canine has been missed due to incorrect angulation Example 2 - To Radiograph the Maxillary Canines and Incisors Position the dog in sternal recumbency and place pads below the head, to keep the palate parallel to the table. Place the film in the mouth so that all of the target tooth will show on the film. Hold the film flat with mouth props or swabs. Calculate your angles and direct the beam at approximately 45-degrees to the plate. Bisecting angle technique for maxillary cuspid (canine) in the cat. Courtesy of Dr Verstraete   Bisecting angle technique - oblique lateral - for 104 canine tooth     When taking radiographs of upper canine teeth, angle slightly out to in (i.e. from rostro-lateral to medio-caudal) to avoid superimposing incisors at the apex of the tooth. As with the mandibular canine, a second lateral bisecting angle view will provide information that may not be visible on one view. Fractured upper canine of a young dog with immature, thin walls and an open apex   Example 3 - To Radiograph the Maxillary Premolar (Carnassial) Position the dog in sternal recumbency and place pads below the head, to keep it stable. Place the film in the mouth, under the carnassial, so that all of the target tooth will show on the film. Hold the film flat, with mouth props or swabs. Calculate your angles and direct the beam over the medial canthus of eye onto the target tooth - this should be at approximately 45 degrees to the plate. NB - in cats this angle should be nearer 30 degrees to prevent superimposition of the zygomatic arch over the tooth roots and extra-oral near parallel may be easier. Intraoral bisecting angle for upper carnassial tooth   First view of bisecting angle technique - oblique lateral - for 108   Alternative view - slightly caudal - used if roots are superimposed           Radiograph of above technique   Radiograph of above technique     Take a second, and perhaps a third, radiograph with no change in the vertical beam angle, but move the tube head horizontally (i.e. slightly rostrally or slightly caudally). Multiple views of multi-rooted teeth are often required to limit the effects of superimposition of roots - either by the adjacent teeth or by another root of the same tooth. Radiograph of upper premolar 4 demonstrating poor positioning. Note superimposition of mesial roots and partial superimposition of caudal root on molar 1   <<Prev © 2002 eMedia Unit RVC v1.0 Next>>

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