MANAGEMENT OF ORAL TRAUMAor‘PUTTING HUMPTY TOGETHER AGAIN…’

Dr WAYNE FITZGERALD, BVSC MACVSC (Vet. Dentistry)Reservoir Veterinary Clinic226 Spring Street, Reservoir, Vic. 3073

In attempting to treat fractures of the Maxilla or Mandible the forces of gravity, muscles and mastication; and the function of occlusion place these fractures into a different category to conventional orthopaedic surgery.

The innervation and vascularity of these structures is rich and as a result healing times are short and infection resistance is high. Vital structures such as canals and tooth roots occupy much of the bone’s integrity and along with function must be taken into consideration when choosing a method of repair.

Fracture of the bones of the head may result from trauma and/or pathology such as advanced periodontal disease. Our first priority aim is to restore occlusive function thus allowing the animal to eat and drink.

Essential to the management of these cases is a working knowledge of the anatomy and the biomechanics of the head. It is very useful to have access to a skull of the species you are working with as a reference for making assessments of the injuries, radiographs and assessing possible treatment options.

Because of the complexity and over-riding nature of the bones and other structures in the head, it is difficult to obtain clear diagnostic radiographs with screen films in cassettes. Intraoral films are often required as they reduce the superimposition problems and improve detail.

The nature of the fracture/s and the forces acting upon the mandible which affect the displacement of fractures, influence the placement of our fixative devices.

These forces are: gravity, mouth closing muscles (temporal, masseter and pterygoid muscles) and opening muscle (digastricus m.) and they often cause over-riding of fragments.

As an example, a fracture of the mid-horizontal ramus might behave like these, depending on the fracture type:

The tension-band side of the mandible is the alveolar border and as long as the ventral border is intact, interdental wiring alone is often adequate.

Most fractures will be compound with vital, or devitalized, teeth complicating the picture. Fractures often include the dental alveoli.

On the plus side, the blood supply to the head is very generous and healing is often quite rapid.

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It is generally considered necessary to extract those teeth involved in the fracture site, especially if unstable, because of exposure of large areas of periodontal attachment and devitalization of the endodontic system. On the other hand, stable teeth may be very useful as ‘spacers’ in a fracture line and as points of attachment of fixative devices, so make this decision after evaluating your treatment options. After healing, the tooth could either be extracted or root canal therapy could be performed.

Except for size, the canine and feline mandibles are similar. The lower canine tooth occupies almost the entire width of the mandible and 65-75% of it lies in its alveolus.

It is not acceptable practice to drill through tooth roots when placing fixation devices.

The mandibular canal is found in the ventral third of the body of the mandible. It contains the mandibular artery and vein, and the mandibular alveolar nerve. Cause it no harm!

Most of the muscles of mastication insert on the vertical ramus and the caudal portion of the mandible.

Exposures:

Oral approach is best for fractures rostral to the last molar,

Extra-oral approach for the ventral half of the body of the mandible.

Principles:

Keep the method of repair as simple as possible, use the minimum number of implants,

Preserve soft tissue attachments,

Provide drainage whenever severe contamination or trauma is involved,

Remove abscessed or loose tooth, especially when in the fracture site,

Avoid tooth roots and the mandibular canal, and

Avoid the soft tissues in the space between the mandibles, this includes the tongue’s frenulum.

Ancillaries:

Oxygen tent,

Steroids to reduce swelling,

Tracheostomy *, and

Pharangostomy.

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Temporary tracheostomy is often useful to clear the oral cavity during the treatment and also permits free movement of the mandible to check occlusion.

Treatment Options:

Tape muzzles can be used for temporary fixation and prevent drying of the mucus membranes of the oral cavity. They can also be used to support internal fixation and sometimes for stable, non-displaced fractures.

Fractures rostral to the molars tend to heal rapidly and a tape muzzle alone may be satisfactory. The likelihood of a malocclusion is greater with this method than with the other fixative devices.

However, they are difficult to place and maintain on cats and the brachycephalic dog breeds where stay sutures may be useful.

Wires, pins, plates & screws.

With or without an acrylic bond assistance, orthopaedic stainless steel wires of 24, 22 and 20g sizes are the most useful materials in oral fracture repair.

Interarcade or mandibular-maxillary fixation is a useful technique in dogs and cats with unstable fractures of the mandible or TM joint. Aim to maintain the alignment of the ‘canine interlocks’. If the jaws are wired or bonded fully closed, fluid and nutrition must be given by pharangostomy tube; however if a gap is left between the incisors (mouth partly open) they will learn to adapt and can satisfactorily lap.

Direct bonding of teeth. Is used with alveolar segment fractures and with subluxated or avulsed teeth. It requires minimal material to fix the teeth making for better oral hygiene. A disadvantage is the lack of strength and the likelihood of materials fracturing because of poor anchorage from loosened teeth. Incorporating reinforcing wire improves the strength.

Orthodontic appliances. Brackets, for instance have some applications in fracture patients, however, generally wiring techniques are more useful.

Mandibulectomy in full or partial form may in some cases be indicated and is considered to be a salvage technique.

Materials:

Orthopaedic wire is still probably the most useful and practical implant material used in dental orthopaedics. It is very inexpensive and does not require costly ancillary equipment to use. Wire can be placed directly in bone, around fragments or around teeth

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Interdental wiring: it may be necessary to ‘notch’ the teeth or even bond the wire to the teeth. 22 to 20-gauge wire is generally satisfactory.

Transfurcational interdental wiring: the wire passes between the roots of the adjacent teeth.

Interfragmentary wiring: used in the repair of oblique and some multiple fractures. Wires are placed at right angles to the fracture line.

Bone defects can make wiring techniques difficult because of the need to place wires on the tension side of the fracture, which can cause collapse and malocclusion.

The Ivy and Stout methods of interdigital wiring are applicable to the dog and cat, but application depends on the health and integrity of the teeth adjacent to the fracture. The application of plastics to the wire can improve the stability of the wiring method, especially if there are bone fragments and does not further disrupt soft tissues.

The principles here are to include two or three teeth on either side of the fracture.

Ivy wiring method: Stout wiring method:

Wiring techniques.

Eyelet Technique (Oliver, Eby, Ivy). A versatile and easy to apply eyelet wiring technique. A 50mm length of wire is twisted around an instrument to make a small loop. The ends are passed through the interproximal space from the buccal side, one end is then passed around the mesial tooth and back through the next interproximal space. The other end likewise around the distal tooth. One end of the wire is then passed through or medial to the eyelet and the two ends are twisted to form a ‘button’. This produces a loop

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and a button to be used for supporting other wires, elastic loops, ligatures etc. After sufficient numbers have been made, the teeth are brought into occlusion and ligatures or elastics are placed between the uppers and lowers. This technique is especially useful when fractures are simple and ‘favourable’. It is less useful with grossly displaced fractures of tooth-bearing areas because of lack of arch rigidity.

Continuous Loop Wiring Technique (Stout). A series of eyelets on a single strand of wire is produced as follows: A wooden handle of a cotton-tipped applicator (spacer) is placed against the teeth to aid in forming the wire loops. A wire is placed around the most distal molar with both ends projecting towards the buccal side. The distal end becomes a horizontal buccal wire; the mesial wire end is the active passing wire to form the loops and should be longer than the other end. The ‘active wire’ is passed over the horizontal buccal wire and the spacer then back through the same interproximal space from which it emerged. It is drawn taught, finishing the first loop. It is then passed around the lingual surface to the next interproximal space …the procedure is repeated to form a quadrant of wire loops. The spacer is removed and the loops are twisted two or three times to form an anchor leg which is then turned apically. The disadvantages are the extensive manipulative technique, the restrictions imposed by dental anatomy or disease and the need to replace the entire section if a wire breaks.

Physical properties of wire management: because many fixation techniques require the use of wire, it is important to consider some of its physical properties. In the early days, gold, copper and silver wires were used and more recently, soft alloys. Today these have limited applications. Currently stainless steel wires of 0.016 to 0.20 inches diameter are used predominately. Its ductility and flexibility make it very strong as well as bio-compatible and corrosion resistant.Prestretching and ‘working’ the wire increases its hardness and increases its likelihood of breaking. Also, repeated heating makes it more brittle and likely to break, so leaving the spool intact and re-autoclaving it over and over again will weaken it. Air cooling instead of water cooling also adds to this problem. It is recommended to precut small amounts of wire and pre-autoclave these at most, twice and discard small amounts left over after use. This may seem wasteful, but it is better than the frustration of repeatedly breaking wires and having to replace them.For uniformity of technique the wires are twisted in a clockwise direction. When tightening a constant outward pull will stop the tendency for the wire to twist upon itself and ‘work harden’ which is a frequent cause of breakage. Intramedullary and Trans-mandibular pins:

The mandible is difficult to pin because of its curvature plus the other anatomical features previously described. The mandibular canine tooth obstructs direct rostral entry into the medulla. Caudal access is difficult without causing more soft tissue trauma. The method is less than useful with comminuted fractures.

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Transmandibular pinning with or without wiring can be useful in unilateral and rostral (to the molars) fractures. Must be rostral to avoid entrapment of the tongue and its frenulum.

Percutaneous pins:

External fixators can be used in conjunction with percutaneously inserted pins or screws to provide stabilization of fragments of both mandible and maxilla. An advantage of this type of fixation is that little iatrogenic soft tissue damage is required, it is also useful with unstable and/or bilateral fractures and when bone has been lost.

Threaded pins are less likely to loosen, and pre-drilling with a slightly smaller drill or pin will make placement easier and more accurate. Place the pins with the mouth closed and the teeth occluded. Care with heat production when drilling bone as (heat) necrosis will allow the pins to loosen.

Make sure the fixator pin ends have been blunted.

Acrylic fixators are easier to use than the conventional Kirschner apparatus because the pins do not have to be all the same length or perfectly aligned.

The difficulties encountered with this type of fixation is the displeasing appearance, the risk of them catching on furniture etc and that the owners will have to keep them clean.

Plates, Wire mesh and Screws:

In theory these should provide rigid fixation; however their application requires substantial iatrogenic soft tissue damage and are difficult and time consuming to place. Contouring and molding to shape may be difficult.

The cost of materials is high, as is the ancillary equipment list.

In practice it is difficult to place these appliances because of the anatomy and contouring the plates to attain good occlusion is often required. Plates must be placed ventrally in the mandibular body to avoid tooth roots. It is not always possible to avoid the mandibular canal with screw placement but it might be argued that the contents of the canal are already damaged by the initial ‘insult’.

In the repair of these fractures, the method of choice will always be the one that achieves the best stabilization with the least amount of soft (and hard) tissue disruption.

Fractured teeth

Exposed dentine is sensitive and porous, it is recommended to restore enamel deficits with a composite material.

If the enamel bulge is lost, for instance from the upper carnassial tooth, the result is chronic insult to the gingival sulcus and this results in periodontal disease. Restoration with a composite is possible but normal chewing forces

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can undo this work. A dog’s chewing forces, which are 8 times that of man, can even dislodge a crown.

Endodontic exposure is, at least initially, painful. We often see our patients presented with a fresh pulp exposure and the owners have to be convinced that it is painful. Relating it to them personally sometimes works! Our patients are very adept at masking painful conditions, this being part of their survival instinct.

We have only two choices with the treatment of fractured teeth: extraction or endodontics.

Fracture of the alveolus …teeth avulsion

Fracture of the lateral wall of the maxillary canine tooth alveolus is a common presentation resulting in lateral displacement (avulsion) of the tooth. These are often stable when reduced and interdental wiring with some composite to keep in place is usually satisfactory.

If ‘caught short’ in an acute canine tooth avulsion, it may be possible to temporarily hold it in place with a rubber band in a figure of 8 and a few sutures.

Endodontic treatment of the tooth can be done at the time, or left to a time more appropriate to the patient.

Fracture of the maxilla

These are often not as obvious as mandibular fractures and may be quite ‘stable’. Few require fixation especially if displacement is minimal, they also heal rapidly.

If malocclusion, marked deformity or obstruction of the nasal passages is present, intervention is necessary.

The soft tissues surrounding these bones provide good support and nutrition. Problems occur when this relationship is compromised. Postponing surgery until the soft tissue swelling has resolved is helpful.

Sometimes a blunt probe inserted through the nose or small percutaneous K-wires will help elevate depressed fragments.

Acrylic splints or palatine plates, interdental wiring alone, or to an intraoral splint, can be used to stabilize some maxillary fractures.

Use finer gauge wires (22-24 gauge) if using interfragmentary wires because of the ease of placement and adjustment.

Be aware that leaving small detached, non-vital bone fragments may lead to chronic rhinitis or sinusitis.

Transverse fractures of the rostral maxilla will be unstable and interdental wiring will often be fixative.

Fractures of the mandible

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Unilateral fractures are common and can usually be fixed with wire alone or in conjunction with acrylics. The wire may be placed interdentally or via stab incisions, through the bone (missing the tooth roots) and tightened over the mucosa. Screws with a figure of eight wire would, if placed correctly, be satisfactory.

Comminuted fractures are more difficult, are usually open and contaminated and caused by more high-energy trauma. A tape muzzle may be satisfactory if relatively stable and well aligned. Three to 5 weeks should be satisfactory.

External fixators may also be suitable, with the rostral pin also being transmedullary.

Fractures caudal to the teeth are less often diagnosed and are more difficult to manage because of inaccessibility. Fractures of the vertical ramus rarely cause malocclusion and often don’t need more than a tape muzzle or mandibular-maxillary wire for 2-3 weeks. This reduces pain and approximates the fragments.

Fractures at or ventral to the condylar process may be treated likewise but inter-arcade wiring may assist. The ventral border is thicker and easily exposed and internal fixation may be suitable. Avoid the mandibular artery.

Bilateral fractures of the caudal mandible are not uncommon and because of the marked displacement, are more difficult to manage. Emergency care is a tape muzzle. Pharyngeal entubation is helpful with treatment and visualization. Unilateral fracture techniques can be adapted and sometimes a plate in the non-comminuted side converts a bilateral into a ‘unilateral’ fracture.

Pathological fractures occur more frequently in the mandible than in any other bone. Periodontal disease in the aged, smaller breed dogs is largely responsible for this statistic.

Iatrogenic fractures are usually unilateral as a result of dental extraction attempts in diseased bone.

Dogfights may also place undue stress on disease compromised tissues.

Avoid placing implants into adjacent diseased bone. Tape muzzles may be satisfactory.

Nonunion of mandibular fractures is rare but more common in association with periodontal disease where a fibrous union may form. In the older, toy breeds that are only eating soft foods, veterinary interference may not be indicated.

Soft tissue disruption may also contribute to this problem and infection and/or sequestration may be present.

Leaving periodontally or peripically diseased teeth in the fracture site may also lead to infection.

Separation of the mandibular symphysis

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This is the most common oral injury in cats (Harvey & Emily). Most can be well stabilized with an encircling wire of 22-20 gauge placed with a 20-18g needle as a wire-passer. If the fracture is comminuted, collapse of the symphysis with distortion of the angle of the canine teeth may occur. Wire plus an acrylic splint could be useful or a more complex wiring technique with the addition of a figure of 8 wire around the canines. If instability is a problem, then good occlusion can be attained by bonding the upper and lower canine teeth together for 2-4 weeks.

In large dogs, further stabilization can be achieved by inserting a small transmedullary pin ventral to the second premolar.

Fracture/luxation of the Temporomandibular Joint (TMJ)

Fractures can be difficult to define clearly on radiographs and to treat in the dog and cat because of relative inaccessibility and the small size of the bone into which implants can be placed.

If there is little or no malocclusion or if highly comminuted, try a tape muzzle for 4-5 weeks.

If pain is severe or persists on opening the mouth, consider excision (excision arthroplasty) of the mandibular condyle or the fragments.

Often the soft tissues are severely disrupted and stability is poor so some form of alignment-fixation is recommended to maintain alignment. Interarcade wiring for 4 weeks may be considered.

Luxation is seen more commonly in the cat than the dog and is frequently bilateral. Adjacent bone may be fractured as the joints are well protected.

If the luxation is rostro-dorsal, correction is aided by placing a wood dowel or pencil between the caudal teeth.

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Further reading:

A Colour Atlas of Veterinary Dentistry & Oral Surgery. Kertesz P. 1993. Wolfe Publishing.

Manual of Small Animal Dentistry. Crossley D.A. & Penman S. 2nd edn 1995. British Small Animal Association.

Maxillofacial Trauma. Alling, C & Osbon, C. Chapter 5: Maxillofacial Fracture Fixation Prostheses, Methods & Devices. Brindley, P.

Small Animal Dentistry. Harvey C.E. & Emily P.P. 1993. Mosby.

Small Animal Oral Medicine & Surgery. Bojrab, M.J. & Tholen, M. 1990. Pliladelphia.

Veterinary Dental Techniques. Holstrom S.E., Frost P. & Eisner E.R. 1992. W.B.Saunders

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