Maxillary and mandibular fractures

After nearly 7 years of writing articles for this feature, I must confess that I approach writing on this subject with a degree of trepidation. Mandibular and maxillary fractures represent no less than a “battlefield” of strongly held beliefs when it comes to appropriate therapy. Orthopedists view the mandible and maxillae as “modified long bones” into which can be placed all kinds of metallic implants, whereas veterinary dentists view the mandible and maxillae as a milieu of vessels, nerves, and, most importantly, tooth roots or budding permanent teeth. The idea of violating these precincts with cold, hard steel brings them to apoplexy! In the finest political tradition I will try and find common ground between the warring factions!

One thing that is beyond argument is that jaw fractures are a common occurrence, accounting for 1.5% to 3% of all fractures in dogs (1–4) and 15% to 23% of fractures in cats (1,5) with vehicular trauma being the most common cause. Most patients are young, having a mean age of 3 y (2), and almost 50% of affected dogs are < 1 year of age (1,3). Mandibular symphyseal fractures are the most common in the cat accounting for 73% of jaw fractures in this species (1), while fractures in the premolar region are most common in the dog accounting for 31% of mandibular fractures (2). Most jaw fractures are open with varying degrees of contamination and infection (1,2). Perhaps more surprisingly, less than half were classified as comminuted in one survey (2). A distinct subset of jaw fractures involves pathologic fracture associated with gingival disease, especially in older small breed dogs. These fractures truly are the prevue of the dentists and are beyond the scope of this discussion.

The good news is that, perhaps due to the young age of most patients, healing of many jaw fractures, with the exception of the aforementioned pathologic dental disease fractures, is rapid (1–3). Many are functionally healed in as little as 2–3 wk with a reported average healing time between 5.5 and 6.3 wk (5).

The complication rate of treatment for jaw fractures, however, is high at 34% (2). Nearly 2/3 of those complications involved dental malocclusion or osteomyelitis.

Diagnosis of mandibular or maxillary fractures is usually straightforward. While radiography can be helpful, it can also be confusing, as overlaying bones and tissues may obscure the detection of lesions. Dental radiography is the best solution to this problem; however, there is no substitute for a thorough examination of the jaw with the animal under general anesthesia. This process will provide a clearer understanding of the fractures that are present and the overall stability of the jaw.

Treatment of jaw fractures has the sole goal of reestablishing dental occlusion and jaw function. The most beautiful reduction of the fracture line matters not if the teeth don’t fit! Assessing occlusion intraoperatively is greatly aided by placing the endotracheal tube via a pharyngostomy incision. The incision can also be used to place a feeding tube in the uncommon event that the postoperative stability of the fracture repair requires it (1).

With the goal of optimum occlusion, an adhesive tape muzzle is a simple, inexpensive and effective way of treating many fractures (1,3). The muzzle is applied with the canine teeth in perfect occlusion and with allowance for the animal to open the mouth no more than 0.5–1 cm. The interdigitation of the canine teeth provides stability to the jaw, as does the animal’s limited ability to open the jaw. The tape muzzle is a good option in minimally displaced fractures that have a potential for rapid healing, but it is equally effective in comminuted, unstable mandibular fractures where it is difficult to provide a stable surgical fixation, or in fractures to the vertical ramus of the mandible where the surgical approach is difficult (1,3). Tape muzzles may also be used to provide temporary support for a surgical repair; their biggest failing being the inevitable moist dermatitis that develops under and around the tape. Nursing care can help to minimize this and the problem quickly resolves when the tape is removed (1,3).

The most popular repair methods use various wiring techniques. Surgical wire can be used in hemicerclage fashion between fracture fragments, cerclage techniques can be used, most notably in fractures of the mandibular symphysis, and wire can be wrapped around teeth adjacent to the fracture to provide stability. Interdental wiring is a simple, effective procedure with few drawbacks other than the accumulation of food particles between the wire and gumline and the accompanying gingivitis. The technique relies on the presence of stable teeth on either side of the fracture and, indeed, the complication rate in fractures where adjacent teeth are damaged or missing has been noted to be much higher (2).

Plate repair of mandibular/maxillary fractures offers the greatest stability in most cases but provides this in exchange for the greatest risk of disruption of tooth roots and neurovascular structures. Plates allow minimal latitude in terms of where the screws are placed making it difficult to avoid these structures in the adult and nearly impossible to avoid non-erupted teeth in the young dog. Another challenge associated with plate repair of jaw fractures is that the “tension” side of the mandible is the alveolar margin. Basic orthopedic principals mandate that the plate is placed as close to the tension side of a bone as possible so that the fracture line is brought into apposition under tension by application of the plate. However, the risk of impinging on tooth roots or neurovascular structures is increased the closer one gets to the alveolar margin. By placing the implant away from the tension side, the stability of the repair is less; however, given the relatively moderate forces encountered in the jaw compared with the strength of the implants, this is usually not a serious concern (1,3,6).

Longitudinal placement of an intramedullary pin within the mandibular medullary canal has been described, but is a technique that is best avoided. It is nearly impossible to place a pin of any size in this position without seriously compromising the teeth and neurovascular structures. In this vein, the placement of a pin has been associated with an unacceptably high complication rate, specifically nonunions (2).

Perhaps the places where orthopedists and dentists come the closest to agreeing are with external skeletal fixators on the orthopedist side and intraoral splints or dental bonding on the dentist side. External skeletal fixators allow the maximum flexibility in terms of pin placement and the wide array of available pins adds additional versatility. Specifically, minifixation pins (Imex Veterinary, Longview, Texas, USA) come in diameters as small as 0.035 mm with end threads and a roughened pin profile for improved holding power in acrylic or epoxy connecting columns. Smaller sizes of positive profile external fixation pins are also now available to improve strength and holding power of the construct. While conventional connecting bars may be used in simple unilateral fractures treated with external fixation, many jaw fracture repairs will utilize acrylic or epoxy connecting bars. These allow the connecting bar to be shaped to the profile of the mandible or maxillae and allow maximum flexibility in pin placement. As with any external fixator, the biggest potential complication is pin loosening, which is even more common in the soft, thin bone of the jaw. Fortunately, the healing of most jaw fractures is rapid enough that this is usually not a practical problem (1,3,5). Application of an external fixator will permit the animal to eat soft foods without difficulty, but in selected cases, the option of feeding via a pharyngostomy tube may be used.

The use of dental bonding or intraoral splints has become popular with veterinary dentists and represents a non-invasive way of stabilizing some fractures (7). Intraoral splints usually rely on the presence of intact teeth on either side of the fracture site and are best applied to mandibular fractures, especially those rostral to the molars (7). The teeth are commonly scaled and polished to reduce the possibility of incorporating plaque and tartar beneath the splint material. Acid etching of the teeth with a phosphoric acid gel is performed to improve adherence of the bonding material to the tooth enamel. Suturing of gingival lacerations can be accomplished at this time and interdental wiring between teeth on either side of the fracture line can help to provide accurate reduction, add additional stability to the repair, and reinforce the overlying acrylic bonding material (7). Bonding material, commonly used in humans for temporary crown construction is applied over the teeth on either side of the fracture. Alternatively, bonding the top and bottom canine teeth together on both sides with the mouth held slightly open is another technique that provides stability, preserves blood supply, and ensures proper occlusion while allowing the animal to lap water and eat a soft diet (3). The intraoral splints can be chipped off or may be removed with dental burrs after healing has been completed (3,7). The most common complication with intraoral splinting is gingivitis due to accumulation of food material between the gums and splint. This can be controlled by rinsing the mouth after meals and by the use of a chlorhexidine-containing mouthwash (7).

Partial mandibulectomy is a technique that can be used in cases of severe comminution or where non-unions or malunions result from initial therapy (4).