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TOday'S VeTerinary PracTice | September/October 2015 | tvpjournal.com PracTical denTiSTry Peer reviewed 64 the bisecting angle technique is used. The sensor/plate is placed in the same position as for the mandibular canines, with the tube head positioned 45 degrees laterally (Figure 13). 2,7,9 3. Feline maxillary cheek teeth: When using the standard intraoral bisecting angle technique, the zygomatic arch impedes visualization of the maxillary third and fourth premolars as well as the frst molar. While this author feels this does not signifcantly affect interpretation, if the practitioner wishes to view these teeth without interference, the extra-oral technique can be utilized. Place the sensor/plate on the table and, with the patient in lateral recumbency, place the patient's head on the sensor/plate with the arch to be imaged closest to the table (away from the beam). insert a radiolucent mouth gag to gently hold the jaws apart. angle the beam through the mouth to create a bisecting angle of approximately 30 degrees (Figure 14). remember that this image was created extraorally and must be labelled accordingly. 2,7,9 4. Mesial roots of the maxillary fourth premolar: The straight lateral 45-degree bisecting angle provides a good representation of the mesial roots but they will be superimposed (Figure 10). 2,9 if the practitioner wishes to view these roots separately, an additional angle—the tube shift technique —is necessary. The tube head is angled in the horizontal plane, and the mesial roots of the maxillary fourth premolar are split. To perform this technique, position the tube head for a straight lateral image (ie, 45 degrees in the vertical plane). Then rotate it distally or mesially, approximately 30 degrees in the horizontal plane. However, once the roots are split, it is imperative to be able to identify each root (see identifying buccal & Palatal Roots). Since the whole tooth cannot be effectively evaluated with the mesial tube shift technique, it is recommended that the caudal tube shift technique be used, creating a quality image of the entire tooth. If the distal root is imaged well, the palatal root is in the middle. Figure 12. Proper imaging of the maxillary canines: When the image of the maxillary canine is created with the P iD positioned directly above the nasal cavity (even with the correct 70-degree vertical angulation), the canine is superimposed over the maxillary frst and second premolars (a). To avoid this superimposition, the tube head is rotated approximately 20 degrees laterally (although more is acceptable) (B), which images the canine root over the nasal cavity, consisting of mostly air (c). C B i dentifying Buccal & Palatal r oots The classic way to determine the buccal from palatal root is to use the same lingual/opposite buccal (SLOB) technique. 3,10 The root that is more lingual (or palatal) is imaged in the same direction the tube is shifted, with the buccal root in the opposite direction. Therefore, with a distal tube shift, the palatal root will move caudally compared with the buccal root. With a mesial tube shift, the palatal root moves rostral in relation to the buccal root. There is, however, a much simpler way to identify the roots. If the tube head has been shifted mesial, the distal root of the fourth premolar is often imaged over the frst molar. In this case (figure 15, page 66), the mesiobuccal root is in the middle. When the tube head is shifted distally, the distal root is well visualized, away from the frst molar, with the palatal root in the middle (figure 16, page 66). i d t i A