This is the fourth article of a five-part dvm360 series focusing on how to use an intraoral dental system as an adjunct to great patient care.
In veterinary radiology, a question arises with some regularity—is that "lesion" you see on the film real pathology, or is it an artifact? Artifacts are undesired alterations in data introduced by improper technique, a technological glitch or a combination of the two. The issue can become critical to a patient's health, and in veterinary dentistry it frequently means the difference between tooth extraction or no treatment.
The right and left mandibles are rostrally joined with fibrous tissue. This symphysis is a joint that does not fuse even in older patients and usually appears as a radiolucent line on a radiograph (Photo 1A). This line may be misinterpreted as a mandibular fracture, which would be incorrect because the connection is fibrous, not osseous. Symphyseal interdigitation may also be confused with pathology (Photos 1B and 1C). Symphyseal separation usually occurs secondary to trauma. The increased width of radiographic lucency and asymmetry in symphyseal separation decreases the confusion between symphyseal separation and normal (Photo 1D).
Photo 1A: Radiolucent line represents mandibular symphysis (white arrow).
Photo 1B: Radiographic appearance of symphysis artifacts secondary to image elongation (white arrows). Note fractured incisors.
The mental foramina
Foramina are round or ovoid circumscribed radiolucent structures, which may or may not have a radiopaque edge. In the rostral mandible, there are three mental foramina that occasionally cause interpretation issues—the rostral, middle and caudal foramina. The middle mental foramen is the largest, usually located at the level of the second premolar in the dog and rostral to the third premolar in the cat (Photos 2A and 2B).
Occasionally, one or more of the radiolucent foramina is superimposed over the mandibular premolar root apices, mimicking periapical pathology (Photo 2C). To determine if the "lesion" reflects true disease or superimposition, the area can be reimaged by positioning the X-ray generator tube head rostrally or caudally to the original placement. This will visually separate the apparent mental foramina from the root apex if the tooth is normal (Photo 2D). If the tooth truly has a periapical lesion, the radiolucency remains fixed to the apex regardless of the tube position. Further evaluation of the lamina dura and periodontal ligament space is needed for correct interpretation (Photo 2E).
Photo 2A: Mandible of a cat demonstrating the mental foramina.
Photo 2B: Middle (white arrow) and caudal (green) mental foramina in the cat's left mandible.
Photo 2C: Diffuse right mandibular periapical lucency consistent with endodontic pathology.
Photo 2D: Oval radiolucency, representing the middle mental foramen, ventral to the mesial root of the right mandibular second premolar in a dog.
Photo 2E: On repositioned radiograph, radiolucency moves away from the root apex. Note that the caudal mental foramen now appears apical to the mesial root of the third premolar.
Superimposition of radiopaque and radiolucent structures
Often, the dense, compact bone of the alveolar walls contrasted with the trabecular bone surrounding the canine or maxillary incisor apices appears as chevron-shaped lucencies (Photo 3A). This radiolucent "chevron effect" may give the appearance of endodontic pathology.
To differentiate this artifact from true endodontic pathology (Photo 3B), evaluate the periodontal ligament space and lamina dura around the root apex. Comparison of pulp chamber width with contralateral teeth, as well as clinical examination for pulpal exposure and transillumination, can be helpful (Photos 3C and 3D). Generally, periapical lesions of endodontic origin will appear more circular on radiographs compared with chevron-shaped lucencies and there will be a loss of the radiolucent continuity of the periodontal ligament space and radiodensity of the dura.
Photo 3A: Normal chevron-shaped lucency (white arrows) around the right maxillary canine apex. This radiolucent "chevron effect" may give the appearance of endodontic pathology.
Photo 3B: Periapical lucency consistent with endodontic disease.
Photo 3C: Normal chevron-shaped radiolucencies (arrows) surrounding the maxillary first incisors and the right second incisor in a dog. Note the lamina dura and periodontal ligament space (radiodense lines) are intact around the entire root.
Photo 3D: Localized periapical radiolucencies continuous with the bone, consistent with bone loss due to endodontic pathology. The left second and right first incisors (red arrows) are affected—note the enlarged pulp chambers compared with the contralateral teeth. Green arrows indicate normal chevron-shaped radiolucency of the right second incisor.
The nasal surface of the alveolar process of the maxilla (Photo 4A) is often radiographically superimposed over the apex of the canine and the premolars (Photo 4B). The created radiolucency, which at times appears bordered by radiodense lines, may be confused with periapical pathology.
To determine if the area of the described maxillary radiolucency is due to normal anatomical structures or specific tooth pathology, multiple images should be exposed and compared. If the radiolucency moves forward and backward relative to the tooth root, the artifact is not in the same plane as the root and considered normal anatomy. If the rostral and caudal tube shift test shows the radiolucency moves relative to the root, meaning it is in the same plane, then true pathology needs to be investigated further (Photos 4C and 4D).
Photo 4A: The nasal surface of the alveolar process.
Photo 4B: Normal radiograph of a left maxilla in a cat.
Photos 4C and 4D: Right and left maxillary fourth premolars and first molars. Radiolucency surrounding the distal roots of the fourth premolars created by local anatomical structures. Note the furcation resorption (red arrow in Photo 4C).
Mandibular canal overlay
The mandibular canal contains a radiolucent neurovascular bundle. It is located above the ventral border of the mandibular body, extending toward the roots of the molars, premolars and canines (Photo 5A). The superimposition of the radiolucent periodontal ligament spaces of the apices over the radiolucent mandibular canal can give the appearance of periapical endodontic disease (Photo 5B). Repositioning the tube head in a more acute ventral-dorsal or dorsal-ventral position will "move" the root apex away from the canal to better visualize the area (Photo 5C).
Fortunately, veterinarians don't have to interpret these enigmas alone. Some professional veterinary websites encourage veterinarians to post their interesting films and dental cases online to share with the veterinary community. In addition, many telemedicine services employ dental specialists to read films. With plenty of practice and expert input, you'll eventually be able to interpret dental radiographs with confidence.
Photo 5A: Normal-appearing right mandibular canal in a dog.
Photo 5B: Red arrows show suspicious periapical lucency.
Photo 5C: Apices move away from the canal, indicating normal anatomy.
Dr. Jan Bellows owns Hometown Animal Hospital and Dental Clinic in Weston, Fla. He is a diplomate of the American Veterinary Dental College and the American Board of Veterinary Practitioners. He can be reached at (954) 349-5800; e-mail: email@example.com