The bisecting angle technique is used for imaging the maxillary incisors.7 In cats and most small-breed dogs, all six incisors can be exposed on one film. In large-breed dogs, left-and right-side
views may need to be radiographed separately, especially if using digital sensors. In certain dogs (particularly dolichocephalic
breeds), the lateral incisors may need to be imaged separately since they will be superimposed on the canines.9 In this case, move the tube head in the horizontal plane to properly image the lateral incisors.
As with the mandibular canines and incisors, the maxillary incisor roots curve backward to nearly a 45-degree angle in many
cases.8,9 This means the roots have markedly different angles than do the crowns. Since the roots are typically the area of interest,
remember to use the angle of the root and not the angle of the crown for your bisecting angle calculation.
To capture the maxillary incisors, place the patient in sternal recumbency with the neck extended and the head level with
the table. Place the film in the mouth so that the upper canines are resting on it and a small amount of the film is in front
of the incisors. Center the tube head directly in front of the patient's head, and angle it about 80 degrees to the film in
the rostrocaudal plane, which is the approximate bisecting angle for the distally curved roots (Figures 7A & 7B).
In some cases, the lateral incisor may be superimposed over the canine. Correct this overlap by keeping the tube head at the
same angle in the rostrocaudal plane and rotating it about 30 degrees laterally in the horizontal plane.
The technique for radiographing maxillary canines also uses the bisecting angle principle; remember to focus on the root rather
than the tooth. Each maxillary canine must be imaged on a separate film8,9 because the root of the maxillary canine lies over the maxillary first and second premolars in dogs and over the maxillary
second premolar in cats. If the canines are imaged by using one rostral view only, they will overlap with the premolars on
the image.8,9 Furthermore, it is important to remember that the apex of the canine root is near the mesial root of the second premolar.
So to image the entire root, the film needs to be placed distal to the second premolar.
For these views, position the patient in sternal recumbency with the neck fully extended. Place the film in the mouth between
the maxillary canines, with the front of the film behind the incisors but just in front of the canines. It is important to
place the back edge of the film at least to the level of the second premolar. Start with the tube head centered straight on
with the nose. In cats, the ideal angle for this radiograph is 80 degrees in the rostrocaudal plane and 20 degrees in the
lateral plane (Figures 8A-8C).10 Likewise in dogs, 80 degrees in the rostrocaudal plane is the ideal angle.11 The lateral ideal is less clear-cut, but an angle between 20 and 30 degrees appears to give the best image (Figures 9A-9C).11 The 80-degree rostrocaudal angle compensates for the backward sweep of the canines, and the 20-degree lateral angle removes
the premolar interference while minimizing distortion. (For a demonstration, see the video "Maxillary cuspid—dog" at
Maxillary molars and premolars
The techniques required to image maxillary molars and premolars are the most challenging of the veterinary dental radiographs.
This is especially true of the maxillary fourth premolars. A precise bisecting angle technique7 is needed to achieve a high-quality radiograph of these teeth.
Position the patient in sternal recumbency with the neck extended. The cusp tips of the teeth to be imaged should be resting
on the film, which is relatively flat against the palate. Center the tube head over the tooth to be imaged, and place it at
about a 45-degree angle to the film. Proper technique will produce an excellent image of the premolars (Figures 10A & 10B) and an acceptable image of the molars, but this technique does cause superimposition of the mesial and palatal roots of
the fourth premolar. In cats, this technique will give an excellent view of the second premolar and part of the third premolar,
but the zygomatic arch interferes with the maxillary fourth premolar, third premolar, and first molar (Figures 11A & 11B).