Demystifying veterinary oral trauma image interpretation

I'm lost when it comes to oral trauma films. I'm so confused figuring out what is fractured in this patient. Help me, please!” Veterinary dentists and radiologists field this request frequently. Practitioners faced with patients with fractured jaws know the alignment is off but often cannot determine where the pathology emanates from. Let's explore this imaging conundrum further.

Blunt trauma from falls, motor vehicle accidents, fights with other animals and strikes in the face injure dogs' and cats' oral cavities. The resulting damage can be classified as maxillomandibular (maxillofacial) and non-maxillomandibular (dental, periodontal or both). Imaging is essential to diagnose and plan therapy. Skull images, including dorsoventral, lateral, and right and left oblique projections, are recommended for starters. Once the area of injury has been pinpointed, intraoral images are often needed for further definition. Computed tomography (CT) imaging also can be very helpful.

Maxillas

Trauma to the incisive, palatine, zygomatic, lacrimal, frontal and nasal bones of the maxilla are not as common as mandibular fractures in dogs and cats. Fortunately, many maxillary fractures are nondisplaced and require only soft tissue management (Photos 1 and 2).

Photo 1: A lacerated and fractured feline hard palate from a motor vehicle accident. (Photos courtesy of Dr. Jan Bellows.)

Photo 2: A radiograph of the cat in Photo 1 revealing a non-displaced maxillary fracture. The tooth roots are not involved. Note the right canine complicated crown fracture.

The key to interpreting whether a tooth root is also fractured is to follow the fracture line for gross root involvement (Photos 3 and 4). If the tooth root or roots appear fractured, extraction is indicated.

Photo 3: A maxilla fracture in a dog from a horse kick.

Photo 4: A radiograph of the dog in Photo 3 revealing a maxilla fracture (arrows delineate fracture line). Note the proximity to the secondary tooth roots.

Tooth luxation

Lateral luxation of the canine teeth causes displacement from fracture of the labial or the palatal or lingual alveolar bone. The trauma creates a partial or complete separation of the periodontal ligament. Radiographically, the periodontal ligament space usually appears widened on one side and compressed on the other (Photos 5A and 5B).

Photo 5A: A left maxillary canine tooth luxation.

Photo 5B: A radiograph of the patient in Photo 5A revealing increased periodontal space secondary to alveolar fracture. The arrows are pointing to the increased periodontal space.

Mandibles

Acute mandibular trauma is common in dogs and cats, resulting from motor vehicle accidents, falls and fights (Photos 6 and 7).

Photo 6: A rostral mandible fracture, resulting from trauma.

Photo 7: A radiograph of the dog in Photo 6 reveals rostral displacement of the left mandibular incisors and fracture of the right second incisor. All of these teeth were extracted.

Regrettably, iatrogenic mandibular fractures occur during extraction procedures when the underlying bone is weakened by pathology (Photo 8).

Photo 8: An iatrogenic fracture during extraction of a deciduous fourth premolar. Note the amount of bone loss present along the distal root of the deciduous fourth premolar, predisposing the jaw to fracture.

Unilateral mandible deviation, if present, is toward the side of the injury if caused by a fracture (compared with TMJ rostral dorsal luxations where the deviation is away from the affected side). Dropped jaws occasionally occur from bilateral fractures.

The mandibular symphysis is a joint that can become separated from trauma. Radiographs help determine whether there is a minimal separation of the symphysis or a perisymphyseal fracture that may require further care (Photos 9A and 9B).

Photo 9A: Symphyseal separation in a cat.

Photo 9B: A radiograph of the cat in Photo 9A revealing that the teeth do not appear to be involved in symphyseal separation.

The direction of the mandibular body fracture needs to be further evaluated to plan therapy and determine prognosis. Favorable (stable) fractures are oblique with the fracture line running in a rostroventral direction where masticatory muscle forces oppose the fracture segments. Unfavorable (unstable) fractures occur when the fracture line runs in a caudoventral direction, where the muscular forces displace the fracture segments (Photo 10).

Photo 10: An unfavorable caudoventral mandibular fracture. Note the roots of the fourth premolar are present.

Mandibular body fracture radiographs must also be evaluated for tooth crown and root involvement. Generally, teeth that are also fractured with pulp exposure are either treated endodontically or extracted (Photos 11 and 12).

Photo 11: A mandibular fracture extending into the first molar in a 7-month-old dog. Note the periapical lucencies of the mesial and distal roots indicating endodontic involvement (arrows).

Photo 12: A right-sided mandible fracture along the rostral border of the first molar. Note the advanced periodontal disease affecting this tooth, necessitating extraction.

Temporomandibular area

Fractures around the temporomandibular joint (TMJ) area can be difficult to interpret radiographically. Positioning is critical to obtain a diagnostic image of the joint (Photo 13A). Dorsoventral views are helpful together with raised lateral views to complete the study (Photos 13B and 13C). To produce diagnostic images in cats, the head is positioned laterally and then the nose is raised 15 to 20 degrees. In dogs, the nose is raised 5 to 10 degrees dorsally.

Photo 13A: The lateral aspect of the TMJ in a cat: 1) coronoid process, 2) zygomatic arch, 3) zygomatic process of the temporal bone, 4) mandibular ramus, 5) condylar process, 6) articular eminence, 7) typanic bulla, 8) mandibular fossa, 9) retroarticular process; 10) angular process. 

Photo 13B: A normal radiograph of a TMJ in a dog.

Photo 13C: A condylar process fracture.

Joint luxation

TMJ luxation presents as a deviaton of the mandible toward the contralateral side of the luxation in contrast to mandibular fractures, which present with an ipsilateral deviation. Luxation of the mandible is usually in a rostrodorsal direction but may also be in a caudal direction.

When assessing TMJ luxation, it is important to know if there is a fracture of the TMJ and surrounding areas. Joint luxation without fracture can be treated by closed reduction under general anesthesia using a dowel between the carnassial teeth. While closing the mandible, push caudally until the condylar process slips back into place (Photos 14A, 14B, 14C, 14D and 14E).

When there is a fracture in the area and closed joint repositioning is not possible with further injury, open surgery with or without bonding of the canine teeth for stabilization is recommended.

Photo 14A: A cat skull specimen of the TMJ: 1) retroarticular process, 2) mandibular fossa, 3) condylar process, 4) angular process.

Photo 14B: A radiograph of a right caudoventral luxation of the TMJ (red circle).

Photo 14C: The clinical appearance of a cat with its mandible deviated toward the left secondary to right-sided TMJ luxation.

Photo 14D: A radiograph of right rostrodorsal luxation of the TMJ (red circle) from the patient in Photo 14C. The green circle indicates a normal TMJ on the left side.

Photo 14E: Correction of right-sided TMJ luxation in the patient in Photo 14C. The green circles indicate normal conformation on both sides.

Suggested reading

Hammond G, King A, Lapaglia J. Assessment of five oblique radiographic projections of the canine temporomandibular joint. Vet Radiol Ultrasound 2012;53(5):501-506.

Dr. Jan Bellows owns ALL PETS DENTAL 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: dentalvet@aol.com.