Page 664 - ONLINE PROCEEDING BOOK WSAVA 2017
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664
An Urban Experience
Step 2: Film Placement within the patient’s mouth
There is an embossed dot on the  lm. The convex side of this should be placed towards the x-ray beam. In most  lms, this side is pure white. The opposite or “back” side of the  lm will usually be colored (purple
or green). Place the  lm in the mouth so that the entire tooth (crown and entire root surface) is covered by the radiograph. Remember, the roots of all teeth are very long. This is especially true of canine teeth, which are longer than you think. Always err on the side of having the  lm too far in the mouth to ensure you do not cut off the root apexes. The  lm should be placed as near as possible to the object (generally touching the tooth and gingiva) to minimize distortion.
Step 3: Positioning the beam head
There are two major techniques for positioning the beam head in veterinary patients. Both of these techniques are used daily in veterinary practice.
Parallel technique: This is where the  lm is placed parallel to the object being radiographed and perpendicular
to the beam. This is how standard (large)  lms are
taken. This gives the most accurate image. Unfortunately this is only useful in the lower cheek teeth in the dog
and cat. This is due to the fact that these patients don’t have an arched palate. The  lm cannot be placed parallel to the tooth roots because of the palate’s interference. Therefore this technique is not always possible.
Bisecting Angle Technique: This is the most common type of dental radiograph taken in veterinary
patients. This uses the theory of equilateral triangles to create an image that accurately represents the tooth
in question. To utilize this technique, the  lm is placed
as parallel as possible to the tooth root. Then the angle between the tooth root and  lm is measured. This
angle is cut in half (bisected) and the beam placed perpendicular to this angle. This gives the most accurate representation of the root.
If this angle is incorrect, the radiographic image will be distorted. This is because the x-ray beam will create
an image that is longer or shorter than the object imaged. The best way to visualize this is to think of a building and the sun. The building will create a 90 degree (right) angle to the ground. The bisecting angle in this case is 45 degrees.
Early and late in the day, the sun is at an acute angle to the building and casts a long shadow. In radiology this occurs when the angle of the beam to the object is too small and is known as elongation. At some point in the late morning and early afternoon, the sun is at a 45 degree angle to the building, which is the bisecting angle. This gives an accurate representation of the building height. As the sun continues up in the
sky, the shadow shortens. This occurs in veterinary radiology when the angle is too great and is known as foreshortening. Finally, at noon, the sun is straight up from the building, which gives no shadow.
The “Simpli ed Technique” as developed by Dr. Tony Woodward does not utilize direct measurement of any angle, instead relying on approximate angles to create diagnostic images. There are only 3 angles used for all radiographs in this system 20, 45, and 90.
Mandibular premolars and molars are exposed at a 90 degree angle, maxillary premolars and molars at a 45-degree angle, and incisors and canines at a 20 degree angle.
To initiate any radiograph, place the  lm in the mouth and set the positioning indication device (PID) perpendicular to the  lm. For mandibular cheek teeth, this is the correct placement. For the maxillary premolars and molars, rotate the beam to a 45 degree angle. For the incisors and mandibular canines rotate 20 degrees. For the maxillary canines an additional rotation 20 degrees lateral is necessary to avoid superimposition of the  rst and second premolars.
Step 4: Setting the exposure
If you are using a machine where you set the exposure manually, you will need to set up a technique chart similar to one for a standard (large) unit. The good news is that there is only one variable that needs to be adjusted. \
If you are utilizing the computer controlled system, set the buttons for the species, size of the patient, and tooth to be imaged. If you have correctly set the machine and the image is incorrectly exposed, the easiest way to adjust is to change the f setting. By pressing this button, you will see the numbers go up on both sides. The one on the left is the f number and the one on the right is the exposure time. If you continue to press the button it will continue to increase the exposure until you reach 9 when it will markedly lower and the f number will go back to
1. If the radiograph is overexposed (too dark) lower the
f number by 1. If it is underexposed (too light) increase the number by 1. Continue this process until you have the  lm that you want. Generally, the f number will be the same for all radiographs once you have discovered the correct setting for your machine start at that number in future sessions.
Step 5: Exposing the radiograph
Dental radiograph machines have a hand held switch to expose the radiograph. If it is possible, leave the room prior to exposing the radiograph. If it is not, stand at least 6 feet away at a 90 to 130 degree angle to the primary beam (meaning to the side or back of the tube head,
not in front or behind). Once everything is set, press the button. It is important to remember, that these switches are “dead man’s”. This means if you let up during the
42ND WORLD SMALL ANIMAL VETERINARY ASSOCIATION CONGRESS AND FECAVA 23RD EUROCONGRESS


































































































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