16 Feb 2015
Matthew Oxford
Job Title
Jaw fractures are a common traumatic pathology seen in our patients, as a result of road traffic accidents, falls, kicks and altercations with other animals, and can also be seen secondary to periodontal and endodontic disease, neoplasia and metabolic bone disease (Legendre, 2003).
The repair requirements differ from the fixation of fractures of the axial skeleton in a number of ways, and these differences are reflected in the preferred repair techniques. This article offers the reader an overview of some of the techniques available.
Jaw fractures represent a substantial challenge for repair in general veterinary practice because the “normal methods” available for orthopaedic repair have less application owing to the risks of iatrogenic damage. Bone plates and screws, intramedullary pinning, and even the placement of external fixation, have limited use because of the reduction in available bone for fixation as well as the proximity and complexity of numerous structures such as tooth roots and neurovascular bundles within bone canals.
However, this is balanced by the bones of the jaws not bearing weight, which means fixation techniques can be more focused on an anatomical reconstruction that provides a perfect occlusion for mastication. If occlusion is incorrect following repair, then abnormal forces can be placed on the temporomandibular joints (TMJ), which may cause significant long-term discomfort, with the potential for development of osteoarthritis.
Wire and acrylic splinting techniques, placed intraorally, provide an excellent fixation method, allowing for good anatomical reconstruction while minimising the risks of damaging orofacial structures. Maxillomandibular interdental bonding allows for a good anatomical reconstruction in complex trauma cases where other techniques are limited (Legendre, 2003; Niemiec, 2003).
The materials used for intraoral wire and acrylic fixation are not expensive, but their application requires practice. Combining interdental wiring with the use of acrylic or methyl-methacrylate splinting has been demonstrated to provide superior strength than either technique used alone (Kern et al, 1993). Intraoral splinting is minimally invasive, and allows comfortable repair for simple fractures of the mandibular symphysis through to complex bilateral mandibular body fractures.
Mandibular symphysis separation is a very common traumatic injury seen in cats, accounting for 73 per cent of jaw fractures (Piermattei et al, 2006). The commonly published technique has some drawbacks, and it is worthwhile highlighting these given the prevalence of this type of injury.
The standard technique for repairing symphyseal separations is to make a small skin incision on the ventral aspect of the mandible, passing cerclage wire around the rostral mandible, and tightening with a ventrally placed wire twist (Figure 1; Fossum et al, 2002; Scott, 1998). This technique is reasonably simple to carry out, but its downsides are:
A technique less commonly used, but that provides some significant advantages, is to place an interdental wire and acrylic splint between the mandibular canine teeth.
For this technique, composite or acrylic retainers are placed on the buccal aspect of the mandibular canine teeth. A figure of eight wire is then placed around the base of the crown of the mandibular canine teeth, with the knot positioned caudal to the crown of one of these. The wire is tightened to oppose the symphysis, but excessive force is not required as this will promote incorrect angulation of the canine teeth, which will rotate the mandibles. Apposition and correct occlusion is the priority. The wire is then covered in acrylic or composite, which provides a more comfortable surface that is less likely to damage opposing oral soft tissues, and which also adds additional strength to the repair.
The wire and acrylic/composite splint is left in place for four to six weeks and then removed. At removal, there is often some gingivitis where the splint has been overlying the gingiva, but this will resolve within a few days without any further treatment (Figure 5).
For more complex fractures of the mandible, a similar technique of wire and acrylic splint application can be used.
Again, the aim is to produce an accurate anatomical reconstruction, with a perfect occlusion that will promote the early return to normal mastication. Splints can be placed unilaterally or bilaterally, and their extent is determined by the position and stability of the fracture.
Some important considerations must be taken into account during splint application regarding where it can be placed. During normal mouth closure, the normal arrangement is for the maxillary arcades to sit on the buccal aspect of the mandibular arcades. Therefore, splint placement on the mandibles should be focused on the lingual aspect. For the maxilla, the splint is placed predominantly on the buccal aspect. This will allow for the normal scissor action of the dental arcades, and for normal mouth closure postoperatively.
Before fracture repair takes place, it is often useful to place an oesophagostomy feeding tube. This will guarantee early postoperative nutrition.
Another useful consideration is for pharyngostomy intubation, which removes the endotracheal tube from the operative site and allows for the intraoperative assessment of occlusion more easily.
For wire and acrylic splint placement, the teeth must first be scaled to remove gross calculus and then polished with a non-fluoridated paste. The crown surfaces to be used for splint placement should then be etched with a phosphoric acid gel and bonded, which will allow more secure bonding of the acrylic. Any exposed bone surfaces should be debrided to remove any granulation or necrotic tissue.
The interdental wire base frame is then constructed, which will allow for the manipulation of the fracture fragments into the correct anatomical alignment. A self-cure acrylic can then be applied to the wire frame and crowns of the teeth. This will set hard, and maintain the rigidity of the repair.
The splint should again be left in place for six to eight weeks, at which time radiographic assessment of bone healing is usually carried out. If the jaw is sufficiently stable, the splint can be removed. Once removed, the teeth should be professionally cleaned again. At removal, there is often some gingivitis where the splint has been overlying the gingiva, but this will resolve within a few days without any further treatment.
Maxillo-mandibular interdental bonding is particularly useful in cats with jaw trauma, owing to the reduced crown surface from splint placement, and the tight occlusion between the maxillary and mandibular premolars and molar teeth. The main benefit of the technique is the ability to recreate a perfect occlusion despite often complex jaw fractures. It is a useful technique both for fractures and for TMJ luxations. Again, pharyngostomy intubation and the placement of an oesophageal feeding tube are useful preoperative considerations.
The teeth are prepared as before, with acid etch and bond and then correctly aligned for occlusion. The amount the mouth is held open requires some judgement and experience: too close together and food cannot be taken into the mouth; too far apart, and the mechanisms for swallowing can be affected, and the bond strength to the canine teeth can be reduced. Some authors advocate a 2mm overlap although I prefer to overlap the crowns by approximately 50 per cent.
With the teeth in correct alignment, the crowns are bonded with either acrylic or composite materials, creating two pillars around the four canine teeth. The material can again be shaped for comfort (Reiter, 2004; Figure 8).
Postoperatively, the cat would normally be able to eat sloppy food successfully through the opening. If this is not possible, then the feeding tube should be maintained as required.
Dental trauma should always be mentioned when discussing craniofacial trauma. It is often overlooked at the time of initial presentation, but dental trauma can have a significant contribution to pain, both at the time of injury and postoperatively if treatment isn’t carried out.
Dental trauma will also affect the type of treatment that can be provided. Teeth traumatised at the time of craniofacial trauma should be extracted or should be treated with endodontic treatment if preservation of the teeth is required (Figure 9).
Figure 1. The traditional method for repair of a mandibular symphysis separation (Fossum et al, 2002). To stabilise mandibular symphyseal fractures, use a 16 gauge or 18 gauge hypodermic needle to place the cerclage wire.
Figure 2. Typical caudal injuries seen associated with mandibular symphysis separation. 2a. Condylar fracture (arrowed). 2b. Fracture of the caudal mandibular body.
Figures 3a and 3b. Recent repair of a mandibular symphysis separation using cerclage wire. Note the relative rostrocaudal displacement of the mandibular canines, along with the buccal angulation of the right mandibular canine owing to a caudal mandibular fracture.
Figures 4a and 4b. This cat had a symphyseal separation, along with a caudal fracture at eight months of age. Now eight years old, the chronic malocclusion and malalignment of the jaws is clearly evident, including an iatrogenic posterior crossbite.
Figure 5a. Preoperative photo of the mandibular symphyseal separation. 5b. A figure of eight wire is placed around the base of the crowns of the mandibular canine teeth. 5c. The wire was covered with restorative composite to provide additional rigidity and to protect the oral soft tissues from the wire.
Figure 6a. This cat presented with a symphyseal separation along with a ventrally displaced oblique fracture of the left rostral mandible, following a fall from a tree.
Figures 6b and 6c. The fracture was repaired with a wire and acrylic splint. Wire twists were used to maintain appropriate spacing between the teeth before the acrylic was applied
Figure 7a. This seven-month-old dog was presented with bilateral rostral mandibular fractures along with a left side caudal mandibular body fracture (see arrows).
Figures 7b and 7c. The fractures were repaired using a bilateral wire and acrylic splint to stabilise the rostral mandibular fracture portion. The caudal fracture was minimally displaced and well maintained in the masticatory muscles and so a soft muzzle was used postoperatively to maintain the dental interlock to stabilise this caudal fracture.
Figures 7d and 7e were taken eight weeks postoperatively, following splint removal. They demonstrate an acceptable postoperative occlusion, with no significant tooth-tooth contact or soft tissue trauma.
IMAGES: Anderson Moores Veterinary Specialists
Figure 8. Examples of maxillo-mandibular interdental bonding. 8a. Used to treat a symphyseal separation and midline palatal fracture. Note here the use of pharyngostomy intubation. 8b. Used to treat a temporomandibular luxation.
Figure 9. This radiograph of the cat seen in Figure 4 demonstrates evidence of pulp necrosis and periapical pathology as a result of complicated crown fractures of both mandibular canine teeth.
