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tvpjournal.com | September/October 2015 | TOday'S VeTerinary PracTice PracTical denTiSTry Peer reviewed 65 STEP 4. S ETTing ThE ExPoSuRE 1,2 if you are using a machine that requires manually setting the exposure, the correct setting needs to be determined. • For cats, generally there is one setting for the maxilla and one for the mandible, which are easily determined. For dogs, approximately 5 settings are available for use. • However, each system has its own unique settings and these settings are incredibly variable depending on whether a sensor, plate, or film is used. adjustments will be necessary, but after imaging several patients, practitioners develop a good sense for the appropriate settings. if you are using a computer controlled system, set the buttons for the species, flm/digital system, and tooth to be imaged. These settings are not perfect, so minor adjustments may be necessary. For experienced practitioners, setting based on time is generally best. STEP 5. ExPoS ing ThE RadiogRaPh 1,2 if it is possible, leave the room prior to exposing the radiograph to avoid radiation exposure. if this is not possible, stand at least 6 feet from the tube head (this minimum distance creates little to no exposure to radiation) at a 90- to 130-degree angle to the primary beam to limit radiation exposure. dental radiology machines have "dead man's" buttons: if you decrease pressure on the button during the exposure, it stops production of x-ray beams and the unit provides an error message. Make sure you hold the button down until the machine stops beeping before you start over. B A Figure 13. imaging the apices of the mandibular third premolar in cats: The patient is placed in dorsal recumbency and the sensor positioned perpendicular to the teeth and at least back to the frst molar; then the PID is positioned for a 45-degree bisecting angle laterally over the target teeth (a) to achieve the resulting image (B). note: interference from the caudal mucosa does not allow the sensor to be placed caudally enough to image the frst molar; therefore, the standard parallel technique image must also be exposed. B A Figure 14. extra-oral technique in cats: The sensor is placed underneath the patient's head, with the side of the mouth to be imaged against the sensor ( away from the PiD). The mouth is gently held open with a radiolucent mouth gag (not shown) and the patient rotated approximately 30 degrees past parallel (in the dorsal direction). The PiD is positioned to allow the root tips of the side of the mouth closest to the PiD to just miss the apices of the target teeth ( a). The resulting image (B) allows visualization of the roots without zygomatic arch interference.