Mandibular fractures usually occur secondary to trauma, although pathologic fractures during dental procedures are not uncommon. A traumatic aetiology means that serious concurrent injuries are common requiring prompt clinical attention, notably to the brain, maxilla and chest. An expanded discussion of head trauma and preoperative stabilisation is presented in the next lecture 'Fractures of the Skull and Maxilla.' However, it is important to note that management of life threatening injuries and normalisation of patient physiology is paramount before surgical stabilisation of mandibular fractures. This discussion will focus on principles of dentistry and fracture biomechanics for the surgeon.

Palpation of the jaw inside and outside the mouth can assist oral visual assessment. Fractures are often open with obvious mucosal defects. Perioperative broad-spectrum antibiotic administration is recommended.¹ however, providing the surgical reduction is mechanically stable, infections are less common due to the excellent blood supply of the mouth. Any instability of the fracture repair will create the conditions ideal for infection.

Imaging involves the use of either intraoral film to acquire views of the arcade or conventional radiographic views (lateral and dorsoventral skull, and lateral oblique views). Complex fractures are best visualised with computed tomography.

Without a thorough understanding of the dental components of treating oral disease, iatrogenic oral pain is a possible sequel. Small animals, especially dogs, appear to cope well with chronic oral pain but that does not mean that the impact of that discomfort on an animal's welfare is not as distressing as our own. Therefore, a discussion of the important dental attributes of successful mandibulo-maxillofacial trauma treatment is indicated.

The principles of fracture repair are:

 Functional reduction, utilising techniques which preserve blood supply, that provide rigid fixation and therefore an early return to function.²

 Restoration of normal occlusion is paramount.

 Maintain teeth in fracture lines unless they are diseased. Monitor those teeth clinically and radiographically. If disease develops, extraction or endodontic treatment is indicated.³

 Prevent damage to remaining teeth.

When these principles are not adhered to, patient morbidity can result including pain, infection and inappetence. Complications of surgical repair are high at 34%, the most common being malocclusion and osteomyelitis.⁴

Unless teeth in the fracture line are loose or fractured, they should not be removed. Tooth removal changes the mechanics of fracture alignment and inherent fracture stability making repair more difficult. It creates a fracture gap, blood supply to the fracture is disrupted during teeth removal and healing is impaired. In fractures with coexisting periodontal disease, treatment of the periodontal disease during fracture repair is indicated.

Mandibular fractures are approached ventrally.¹ The healing of the mandible is similar to long bones. Some fracture instability leads to indirect bone healing with a fracture callus. Direct bone healing occurs under conditions of anatomic reduction and rigid fixation. The mandible can be considered as a long lever arm. Muscles of the mandible all insert on its caudal aspect, and chewing forces act on the mandible's cranial aspect causing a predominant bending force in a mandibular fracture. This force is in tension at the alveolar surface of the fracture with some compression at the ventral surface. Utilising principles of fracture repair, to counter this bending force, implants need to act as a tension band along the alveolar surface. However, because the teeth sit at this location, the biomechanically preferred location of implants requires some modification to neutralise this bending force. Tooth impingement by implants is to be avoided.

Treatment options:

 Maxillomandibular fixation. Tape muzzles can provide dental interlocking, a simple treatment option providing occlusion is maintained with a gap between the incisors to allow lapping of a temporary gruel diet. Useful during pre-operative stabilization and may be successfully applied as the primary repair technique in young animals. Bis-acryl composite bridging can be applied between maxillary and mandibular canines. Complications of these techniques include dermatitis, aspiration pneumonia, dyspnoea and overheating.³

 Circumferential wiring. Useful for mandibular symphysis fractures. Orthopaedic wire is applied around the rostral aspect of both mandibles assisted by large bore needles. The wire is twisted ventral the mandibles to sit underneath the skin for four weeks.

 Interdental wiring and intraoral splinting. Orthopaedic wire is placed subgingivally beneath the crown (enamel part of the teeth) of at least two teeth on each side of the fracture line. The wire construct is covered by bis-acryl composite resin.

 Intraosseus wiring. Used only for fractures that have inherent stability and can share loading forces when reapposed and compressed by a wire. Therefore, wiring is not appropriate for use in comminuted fractures requiring buttress fixation¹ or those that cannot be anatomically reduced. The biomechanical limitations of this fixation method should be fully appreciated.¹ The wiring must be placed so that its acts as a tension band to create interfragmentary compression. The primary wire is placed on the tension surface (alveolar side of mandible) following the lines of tension. A second wire provides additional stability and prevents shear or rotation of the fragments around the primary wire. This secondary wire is placed perpendicular to the fracture. 1–1.25 mm wire is most often used.¹ Place 5–10 mm from the fracture edge. Boudrieau.¹ recommends placing drill holes angled towards the fracture to ensure that the wire on the far side of the bone becomes taught during tightening. Principles of orthopaedic wire use must be followed.² Complications of wiring are usually the result of poor case selection or technical failures in wire placement. Broken principles of wire placement or tightening cause loosening and repair failure.

 External skeletal fixators (ESFs) are a simple and effective technique for managing mandibular fractures of the rostral two thirds of this bone, especially where buttressing, or management of soft tissue injuries, is required.¹ ESFs do have limitations to their use. Complications of ESFs are often secondary to early pin loosening.

 Miniplates (titanium) are standard of care in humans and are becoming more common in small animals.⁵ Veterinary cuttable plates can also be used. They are useful for buttressing bone defects and the thin thread pitch of their screws provides adequate purchase in the thin bone.¹ Their small size and number of screw holes per unit length means screws can be placed between tooth roots. Screws can additionally be angled. If non-locking plates are used, accurate contouring is required or screw tightening will result in a shift in the planned construct and an occlusion abnormality. Principles of miniplate fixation are similar to wiring - two plates are required in the mandible. A plate is placed along the alveolar surface to resist bending and act as a tension band. A secondary plate is required on the ventral surface to resist shear and rotation.¹ A larger plate can be used for the ventral plate if large loads or buttressing requires a stronger construct.

Postoperative care includes feeding soft food and avoidance of chewing on firm objects. Internal implant exposure can be managed by implant removal if the fracture has healed, or a mucosal flap if it has not. The implant must be stable if it is left in situ. If the implant is unstable, despite a lack of fracture healing, then implant removal is indicated.

References

1.  Boudrieau RJ. Mandibular and maxillofacial fractures. In: Tobias, Johnston, eds. Veterinary Surgery Small Animal. Saunders; 2012:1054–1077.

2.  Boudrieau RJ. Fractures of the mandible. In: Johnson AL, Houlton JEF, Vannini R, eds. AO Principles of Fracture Management in the Dog and Cat. AO Publishing; 2005:98–115.

3.  Reiter AM, Lewis JR, Harvey CE. Dentistry for the surgeon. In: Tobias, Johnston, eds. Veterinary Surgery Small Animal. Saunders; 2012:1037–1053.

4.  Umphlet RC, Johnson AL. Mandibular fractures in the dog. A retrospective study of 157 cases. Vet Surg. 1990;19(4):272–5.

5.  Boudrieau RJ, Kudisch M. Miniplate fixation for repair of mandibular and maxillary fractures in 15 dogs and 3 cats. Vet Surg. 1996;25(4):277–91.