Introduction

Head trauma often results in fractures to the mandible or maxilla. The dental arcade occupies a large area of these bones and complicates fracture management. Treatment of fractures needs to take into account not only the bony damage but also damage to the teeth and soft tissues of the jaw and the requirement for patient nutrition during fracture healing.

Fracture Identification

Most jaw fractures are easily identified with obvious facial deformations or defects visible and/or palpable. These fractures are often combined with significant soft-tissue trauma and are extremely painful. Fractures caudal to the dental arcade or within the mid-facial region are less easy to appreciate, and imaging is required to evaluate the whole skull prior to planning repairs. Radiography of the head can be challenging to interpret, and computed tomography (CT) is a useful modality to supply further detail, especially of the more caudal regions.

In general, facial fractures should be repaired as soon as the patient is stable. This allows concurrent soft-tissue injuries to be addressed and improves patient comfort, facilitating nutritional support and minimising analgesia requirements.

Principles of Fracture Repair

The principles of fracture repair in the jaw are the same as those for fractures in other regions, but there are some major differences. The mandibles of dogs and cats do not have medullary canals.¹ The cortex of the mandible surrounds cancellous bone and supports the alveolar neurovascular structures; however, there are no haematopoietic cells available to promote fracture healing. The integrity of soft tissue attachments to the rostral mandible is important for revascularisation during healing of mandibular fractures and should be preserved wherever possible.¹ The maxillofacial bone, on the other hand, is only a thin lamina with a greater vascularity in relation to surface area, and this bone heals much faster than its counterpart.¹

Teeth occupy a large portion of the mandible and maxillofacial bones and often suffer damage during facial trauma.² Tooth fracture or pulp cavity exposure causes pain and morbidity if left untreated. Previously it was recommended that all teeth within a fracture line should be removed; this has, however, been challenged, and current recommendations are not to remove teeth unless they are fractured or loose and cannot be stabilised.³ Indeed, preservation of teeth within the mandible is associated with favourable outcomes, providing adequate stabilisation has been achieved.³

An "inside-out" approach has been recommended for treatments to jaw fractures. The bone is treated first, followed by the teeth (as related to the underlying bone) and then the soft tissue, and finally dental restoration procedures are undertaken.³

Anaesthetic Considerations

Appropriate surgical access to the jaw can be challenging. In simple fractures where realignment of the jaw is easily assessed through fracture reduction, an endotracheal tube can be passed as normal. In more complex fractures requiring assessment of occlusion intraoperatively, tracheotomy or pharyngotomy is necessary to allow intubation.

Goals of Surgery

The priority of surgical treatment is maintenance of dental occlusion with rigid skeletal fixation. Malocclusion will not only affect function of the jaw following surgery but will lead to abnormal forces acting against fixation devices, leading to fixation failure. Reapposition and rigid fixation without further vascular trauma and appropriate soft tissue management including debridement of severely affected tissues create the optimal environment for healing without infection. Perioperative antibiotic administration is still recommended since the vast majority of jaw fractures are open to the oral cavity and therefore contaminated by their very nature. Arguments for continuing the course therapeutically can often be justified.

Biomechanics of the Mandible and Maxilla

During mastication, bending forces are the primary forces acting on the mandible. Maximum tensile stresses are present at the alveolar (oral) surface whilst maximum compressive stresses are on the aboral surface.⁴ After mandibular fracture, distraction of the oral margin occurs, and this is magnified by contraction of the powerful muscles of mastication. All fixation devices are strongest in tension, and they should ideally be placed along the alveolar border of the mandible. In dogs and cats, the tooth roots occupy almost 2/3 of the bone adjacent to the alveolar border, limiting the bone area available for implant placement.

In general, the maxilla is subject to much less strain than the mandible, and repair of maxillary fractures will depend on the region fractured. If the area fractured does not provide much support to the skull and is not causing severe compromise to the patient, conservative management may be preferred. In some cases, fibrous unions develop, but these are likely to achieve a satisfactory functional result, providing dental occlusion is maintained.

Techniques for Fracture Repair

Techniques available for repair of jaw fractures include:

 Long-term mouth closure - occlusion is maintained and biologic osteosynthesis occurs. A 5- to 10-mm gap is left between the upper and lower incisors to allow lapping of liquid diet and water.

 External coaptation (muzzle)

 Interarcade wires

 Interarcade acrylic bonding

 Primary fracture repair

 Interfragmentary and cerclage wire fixation

 Interdental wire and acrylic splinting

 External skeletal fixation

 Intramedullary pinning

 Bone plating

 Salvage procedures - partial mandibulectomy/maxillectomy

For mandibular fractures, a ventral approach is used whilst an intra-oral approach is preferred for access to the hard palate or maxillary dental arcade.

Postoperative Care

All patients should receive liquid food for 4–7 days following surgery, and hard food should be avoided until the fracture has healed. Tube feeding may be necessary for certain patients. In patients with oral wounds or where intra-oral fixation has been applied, daily mouth washing should be performed.

Postoperative Complications

Complications are generally the same as for other fractures, but they have the added problems associated with the dentition. Osteomyelitis, delayed union, non-union, malocclusion/malunion, sequestrum, oronasal fistula, and dental abnormalities may develop. Complications have been reported to be as high as 34% in mandibular fractures in dogs and 24.5% in mandibular fractures in cats.^5,6

References

1.  Roush JK, Howard PE, Wilson JW. Normal blood supply to the canine mandible and mandibular teeth. Am J Vet Res. 1989;50:904–907.

2.  Soukup JW, Mulherin BL, Snyder CJ. Prevalence and nature of dentoalveolar injury among patients with maxillofacial fractures. J Small Anim Pract. 2013;54:9–14.

3.  Abubaker AO, Papadopolous H, Giglio JA. Diagnosis and management of dentoalveolar injuries. In: Fonseca RJ, Turvey TA, Marciani RD, eds. Oral and Maxillofacial Surgery. Vol II, 2nd ed. St. Louis, MO: Saunders; 2009:104.

4.  Küppers K. Analyse der funktionellen struktur des menschlichen unterkiefers. Adv Anat. 1971;44:3.

5.  Umphlet RC, Johnson AL. Mandibular fractures in the dog. A retrospective study of 157 cases. Vet Surg. 1990;19:272–275.

6.  Umphlet RC, Johnson AL. Mandibular fractures in the cat. A retrospective study. Vet Surg. 1988;17:333–337.