Dental radiography: Small improvements to technique can make a big difference

Oct 01, 2008

Veterinary dental radio-graphy traditionally has been one of the most frustrating aspects of veterinary dentistry.

The bisecting-angle technique can be demanding and difficult to perform consistently. Positioning the patient, the sensor and the tube head to create quality images can be problematic, too. This article will provide some tips and techniques to help minimize common frustrations in veterinary dental radiography.

Parallel and bisecting-angle techniques

In traditional radiography, we commonly use the parallel technique to obtain images. For example, with a radial fracture, the limb is placed on the X-ray table. The tube head is positioned above the limb and pointed directly at it, and the film is tucked under the limb and parallel to the tube head.

Photo 1: The parallel technique can be accomplished only in the caudal to mid mandible in our companion-animal patients.
When we take views of the teeth in the dog and the cat, we can use only parallel positioning in the mid to caudal mandible. This is possible only because the soft tissue (lateral to the tongue in this location) allows the sensor to be placed parallel to the caudal cheek teeth and mandible intra-orally (Photo 1).

As we move rostral with our sensor, the mandibular symphysis gets in our way and prevents use of the parallel technique.

Photo 2: Demonstration of the bisecting-angle technique on a skull. The angle for canine tooth imaging in this patient is 70 degrees with a rostral to caudal oblique tube-head orientation.
In the maxilla, the palate provides a similar barrier. Therefore, the tube head and sensor must be positioned in a way that will allow projection of the tooth image on the sensor that will give the same result as a parallel technique. The technique that allows us to accomplish this is called the bisecting-angle technique (Photo 2).

Patient and sensor positioning

How do we position a companion-animal patient correctly to take veterinary dental radiographs? The answer lies in consistency.

Photo 3A: Wall-mount radiography unit demonstrating the location of the angle setting.
In order to minimize the variables in the steps to follow, positioning should be approached the same way in each patient, depending on whether we are taking views of the mandibular arcade or the maxillary arcade.

Photo 3B: Close-up of the angle setting.
Sternal recumbency is preferred by this author for taking views of the maxillary arcade. The angle setting on the tube head of all dental radiography units is measured based on degrees from the horizontal plane (Photos 3A and 3B). So, if you use this valuable tool to help obtain consistent quality veterinary dental radiographs, the positioning recommendations described make perfect sense.

Photo 4: Proper patient positioning for taking radiographs of the maxillary arcades.
In our example, the patient's head is elevated so that the palate is parallel to the table (Photo 4). The digital sensor is placed intraorally in an orientation parallel to the palate and the table.

Photo 5: Proper patient positioning for taking radiographs of the mandibular arcades.
For the same reasons, dorsal recumbency is preferred for obtaining mandibular images (Photo 5). With dorsal recumbency, the body of the mandible is positioned parallel to the table. The sensor again is placed parallel to the table in all but the caudal mandibular view where the parallel technique can be used.