Step 5: Exposing the radiograph
It is strongly recommended that everyone leave the room before exposing the radiograph to reduce X-ray exposure. If this is
not possible, stand at least 6 ft away and to the side of the tube head—not in front of or behind it—at a 90-to 130-degree
angle to the primary beam. Some practices use outdated human dental X-ray units. These units are not recommended because of
the increased radiation exposure (scatter) and, in some cases, the inability to achieve a short enough exposure time for direct
digital systems. Regardless of the type of unit used, regular inspections and radiographic monitoring should be performed.
Most dental radiography units have a hand-held switch. When exposing radiographs, if you release finger pressure on the switch
during the exposure, the production of X-rays will stop. On a manually adjusted dental radiography unit, this will result
in an underexposed or light radiograph, while on a computer-controlled dental radiography unit, an error message will illuminate,
and you must restart the process. Make sure to press the button until the machine stops beeping. When using a digital system,
this will be a short time.
OBTAINING RADIOGRAPHS OF SPECIFIC TEETH
The various types of teeth in dogs and cats are best imaged by using differing patient positions and projection angles.3,8,9 The techniques listed below are for mesaticephalic dogs and cats. Dolichocephalic and especially brachycephalic breeds may
require a slight to marked difference in angles.
Mandibular premolars and molars
Views of the mandibular premolars and molars typically use the parallel technique, which is the most basic veterinary dental
radiographic technique.6 An exception to this may be the first and second premolars in dogs and the third premolars in cats because in certain breeds
the interference of the mandibular symphysis makes exposing the apices of these teeth impossible with the parallel technique.8 The alternate technique for these teeth is discussed in the "Mesial mandibular premolar teeth" section.
For the parallel technique, place the patient in lateral recumbency with the arcade to be imaged up. Place the film parallel
to the teeth on the lingual surface of the teeth or mandible, and position the tube head perpendicular to both the teeth and
the film (Figures 3 & 5).
Mandibular incisors and canines
All six mandibular incisors and both mandibular canines can be exposed on the same film in cats and small-to medium-breed
dogs.8,9 In some cases, the exposure time may need to be decreased for the incisors, although the angle is the same. Large-breed
dogs (and also medium breeds if using digital sensors) will generally require one film for the canines and one for the incisors.9 The angle technique required for these views is a slight modification of the parallel technique.
An important point to consider when imaging the canines and incisors is that the roots curve backward to nearly a 45-degree
angle in many cases. Consequently, the roots and crowns have markedly different angles. Since the roots are typically the
area of interest, use the angle of the root (not the crown) for your bisecting angle calculation.8,9 Because of the anatomical angle of incisor and canine roots, the technique required for imaging these teeth is similar to
the parallel technique.
Also keep in mind that the length of canine teeth is often underestimated. The tip (apex) of the canine roots ends over the
mesial root of the second premolar. It is easy for a novice to miss the apices of the root. To ensure imaging the entire canine
tooth, place the distal edge of the film behind the second premolar.8,9
To capture the mandibular incisors and canines, place the patient in dorsal recumbency with the neck fully extended. Place
the film as parallel to the plane of the mandible as possible, so that the film covers the entire intended area. Center the
tube head on the patient's head, perpendicular to the film. Then rotate the tube head in the same vertical plane to an angle
about 75 degrees to the film. This should be an accurate bisecting angle for the roots (Figures 6A-6C).
In large-breed dogs, the small size of the dental film may require the incisors to be exposed separately from the canines.
In this case, the first view is taken with the front edge of the film sticking out just in front of the incisors. This film
will image the incisors. To image the entire canine root, place the film so that the back edge is beyond the level of the
second premolar. In larger breeds, this view does not typically image the coronal area of the incisors. Note that there may
be a difference in exposure for these two views.