The ABCs of veterinary dentistry: "J" is for jaw fractures

When a dog or cat presents with a jaw fracture, trepidation often sets in-not unlike watching “Jaws” the movie. Ready to step into the waters of jaw fractures and symphyseal separations? We'll hold off on temporomandibular joint fractures until “T” is for TMJ disease. For now, let's embrace jaw anatomy, terminology and a few straightforward concepts.

The maxilla

The maxillary bones form the lateral parts of the face and the part of the hard palate that holds the canines and upper cheek teeth. The maxilla articulates with the incisive bone rostrally, the nasal bone dorsally, the vomer bone medially, and the lacrimal and zygomatic bones caudally.

The palatine bone forms the bony part of the hard palate together with the maxillary and incisive bones. The incisive bone located rostrally holds the upper incisors and forms about one-sixth of the hard palate.

The hard palate separates the oral and nasal cavities. The primary palate is the incisive portion of the palate and associated soft tissues. The secondary palate includes the remaining hard and soft palatal structures. Firmly attached heavily keratinized mucosa covers the hard palate.

The mandible

The large bones articulating with the skull that support the lower teeth are the mandibles. Each mandible is composed of a horizontal body and a vertical ramus. The body supports the lower teeth. The ramus has three processes (coronoid, condylar and angular). The condylar process articulates with the cranium in the temporomandibular joint (TMJ). The mandibles are connected to each other by a strong fibrocartilaginous joint at the mandibular symphysis.

Jaw fracture pointers

Keep in mind that jaw fracture repair options include simple suturing, external fixation, plates and screws, elastics, interfragmentary wiring and acrylic splinting. But let's look at some particulars.

• Generally, the lower jaw deviates toward the side of the fracture (Figures 1A and 1B).

Figures 1A & 1B. A cat's mandibles deviated toward the left, secondary to a right-sided mandibular fracture. (All photos courtesy of Dr. Jan Bellows)

• Determining whether the fracture is favorable or unfavorable is important in deciding which method of fixation is best. Attached jaw muscles either compress (favorable) or distract (unfavorable) the fractured segments.

Favorable mandible fractures run dorsocaudal to ventrocranial. These fractures compress because of the upward pulling of the masseter and temporalis muscles, and downward and caudal pulling of the digastricus. Stabilization of the tension surface may be all that is required for bony healing.

Unfavorable fractures run dorsocranial to ventrocaudal and distract the fracture fragments. The alveolar crestal bone is considered the tension surface, while the ventral cortex is considered the compression surface (Figure 2).

Figure 2. An illustration of favorable and unfavorable jaw fractures.

• Unless you've had advanced training, avoid plating jaw fractures for fear of compromising tooth roots. Also avoid placing intramedullary pins into the mandibular canal. The mandibular canal carries the neurovascular structures-it's not an intramedullary canal.

• Removing teeth (or parts of teeth) in the fracture line is usually a good idea (Figures 3A-3C and 4A and 4B).

Figure 3A. A radiograph of an immature right mandibular first molar in the fracture line.

Figure 3B. The immature first molar.

Figure 3C. The healed fracture site before removal of wires and splint.

Figure 4A. A left mandibular fracture between the first and second molars.

Figure 4B. Repair with hemisection and vital pulp therapy of the first molar, orthodontic buttons, a splint and an external fixator.• For many minimally displaced jaw fractures, you can use a tape muzzle or loose-fitting commercial muzzle that allows for food lapping to stabilize the area.

• External fixators work well in many mandibular fractures (Figure 5).

Figure 5. An external fixator used to complement repair of the above first and second molar fracture (Figures 4A and 4B).

• Mandibular symphyseal separations are not true fractures. The symphysis is a joint. If needed, the separation can be stabilized with suture, wire or light cured composite (6A-6I).

Figure 6A. A symphyseal separation.

Figure 6B. An 18-ga needle used to feed suture around the left rostral mandible.

Figure 6C. Suture placed around the right mandible.

Figure 6D. Suture exiting ventral to the symphysis.

Figure 6E. A stabilized, realigned symphysis.

Figure 6F. The appearance at suture removal one month after surgery.

Figure 6G. Application of acrylic to a symphyseal separation in another cat patient.

Figure 6H. An acrylic splint to stabilize separation during healing.

Figure 6I. The healed separation after splint removal four weeks after surgery.

• Midline maxillary fractures without displacement often only need to be sutured (Figures 7A-7C).

Figure 7A. A maxillary defect secondary to fracture.

Figure 7B. The sutured defect.

Figure 7C. The healed fracture.• Maxillary fractures with displacement often need much more then suturing the tissues overlying the hard palate (Figures 8A-8D).

Figure 8A. A rostral maxillary fracture in a 4-month-old Weimaraner puppy after being kicked in the face by a horse.

Figure 8B. The sutured defect with placement of orthodontic buttons and elastics for apposition and realignment.

Figure 8C. An acrylic splint placed over buttons and elastics, which was removed after three weeks.

Figure 8D. The appearance of the dog at 2 years of age before maxillary canine teeth restoration.

Time to stop jawing and start doing!

Jaw fractures don't have to be overwhelming when you concentrate on creating a stable means of fixation to maintain alignment and quick return to function. Feel free to contact your local veterinary dentist (avdc.org) for help.