Proceedings of the World Small Animal Veterinary Association Sydney, Australia 2007

Transcription

1 Proceedings of the World Small Animal Veterinary Association Sydney, Australia 2007 Hosted by: Australian Small Animal Veterinary Association (ASAVA) Australian Small Animal Veterinary Association (ASAVA) Australian Small Animal Veterinary Association (ASAVA) Next WSAVA Congress

2 ORAL TRAUMA REPAIR Dr Wayne Fitzgerald, BVSc MACVSc (Vet.Dentistry) Reservoir Veterinary Clinic 226 Spring Street, Reservoir, Vic In attempting to treat fractures of the maxilla or mandible, conventional orthopaedic surgical principles often have to be ignored or modified. The innervation and vascularity of these structures is rich and as a result healing times can be short and infection resistance is high. Vital structures such as tooth roots, canals and sinuses influence much of the bone s integrity and along with function must be taken into consideration when choosing a method of repair. Trauma and/or pathology such as from advanced periodontal disease are the commonest causes of fractures of bones of the head. We aim is to restore occlusive function 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. In this regard, it is 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 recommended to use intraoral, non-screen dental films. 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 three main forces are: Mouth closing (temporal, masseter and pterygoid muscles), Opening (digastricus m.) which often causes over-riding of the fragments, and Gravity.

3 2 The fracture type can be classified as favourable or unfavourable as demonstrated below: these forces may tend to close or open the fracture. The tension-band side of the mandible is the alveolar border and this is where interdental wires are placed. Most fractures will be compound with vital, or devitalized, teeth complicating the picture. Fractures often include the dental alveoli. It is generally considered necessary to extract those teeth involved in the fracture site, especially if mobile or devitalized. On the other hand, stable teeth may be useful as spacers in a fracture line and as points of attachment of fixative devices, so make this On the plus side, the blood supply to the head is very generous and healing is often quite rapid. 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 or the mandibular canal when placing fixation devices.

4 3 FRACTURE REPAIR Exposures: The intra-oral approach is best for fractures rostral to the last molar, whereas the extra-oral approach is suitable for the distal 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. Tape muzzles can be used for temporary comfort support post-trauma whilst stabilising the patient and to prevent drying of the mucus membranes of the oral cavity. They can also be used to support other fixations and, in some cases, to conservatively manage non-displaced fractures. Fractures rostral to the molars tend to heal rapidly and a tape muzzle alone may be satisfactory. However, the likelihood of a malocclusion is greater with this method than with the other fixative devices. Inter-arcade or mandibular-maxillary fixation is a useful technique in dogs and cats with unstable fractures of the mandible or TM joint. The aim is to maintain the alignment of the canine interlocks. If the jaws are to be wired or bonded in a fully closed position, fluid and nutrition must be given by pharangostomy tube. If an appropriate space is left between the incisors (mouth partly open) they will learn to adapt and can satisfactorily lap. Orthopaedic wire is still probably the most useful and practical implant material used in dental orthopaedics. It is inexpensive and does not require costly ancillary equipment to use. Wire can be placed directly in bone, around fragments or around teeth: Interdental wiring: it may be necessary to notch the teeth or even bond the wire to the teeth gauge wire is generally satisfactory. Transfurcational interdental wiring: the wire passes between the roots of the adjacent teeth.

5 4 Interfragmentary wiring: used in the repair of oblique and some multiple fractures. Wires should ideally be placed at right angles to the fracture line. Bone defects can make wiring techniques difficult as the wires need to be placed on the tension side of the fracture, this may cause collapse resulting in a malocclusion. The Ivy and Stout methods of interdental 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 bonded plastics to the wire and teeth will improve the stability especially with comminuted fractures. Importantly, these techniques do not further disrupt soft tissues. The principles here are to include two or three teeth on either side of the fracture; placing wires on the buccal side of the maxillary teeth and lingual side of the mandibular teeth. This allows for the interference of the scissor bite of these teeth. Ivy wiring method: Bonded plastics +/- wire The advent of materials that are inert to the adjacent tissues, cure quickly in a non-exothermic way or can be light cured, and can bond to the enamel; has added another dimension to how we can treat oral fractures. The plastic can be placed along the dental arcade; it can even bridge gaps where teeth or bone may be missing. If its integrity is to be supported, wires can be incorporated as described previously, or in the mandible they can be placed circumferentially around the ramus to stop the plastic bridge from being dislodged by the patient.

6 5 In smaller dogs and cats, dental composites may be suitable but they can be too brittle in practice; this is not true of the acrylic: Protemp Garant which is applied from a self mixing applicator, it cold cures in a few minutes and can be gradually built up to form the required cover; when hard, it can be easily shaped with a Goldie bur on a slow speed handpiece. 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. Trans-mandibular pinning with or without wiring can be useful in unilateral and rostral (to the molars) fractures. Importantly, the pins must be fairly 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 the 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. Heat production when drilling bone must be considered as 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 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 and Screws In theory these should provide rigid fixation; however their application is rarely applicable in our patients as they require substantial iatrogenic soft tissue damage to place. 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 and it is not always possible to avoid the mandibular canal.

7 6 The fixative method chosen should always be the one that achieves the best stabilization with the least amount of soft (and hard) tissue disruption. AND SPECIFICALLY Fractured teeth Exposed dentine is sensitive and porous, it is recommended to restore enamel deficits with a bonded composite material. If the tooth s enamel bulge is lost the result is chronic insult to the gingival sulcus resulting in periodontal disease. Restoration with a composite is possible but normal-chewing forces can undo this work. Endodontic exposure is painful, but as our patients mask pain very well, we often see patients presented with fresh teeth fractures that appear unaffected. 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 supported by composite is usually satisfactory support. If caught unprepared, they can be temporarily held in place with a rubber band in a figure of 8 and a few sutures. Endodontic treatment of the tooth can be done at a time appropriate to the patient. Fracture of the maxilla Because of the box construction of the maxilla, these are often not as obvious as mandibular fractures and may be stable not requiring fixation, 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 may be 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.

8 7 Fractures of the mandible Unilateral fractures are common and can usually be stabilised with wire +/- with acrylics. The wire may be placed interdentally or via stab incisions, through the bone (missing the tooth roots) and tightened over the mucosa. 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 mandibularmaxillary 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 interarcade wiring may assist. The ventral border is thicker and easily exposed and internal fixation may be suitable. Bilateral fractures of the caudal mandible are not uncommon and because of the marked displacement, are more difficult to manage. A tape muzzle makes great emergency care. Pharyngeal intubation is helpful with treatment and visualization. Unilateral fracture techniques can be adapted and sometimes stabilizing the noncomminuted side converts a bilateral into a unilateral fracture. Iatrogenic fractures are usually unilateral as a result of dental extraction attempts in diseased bone. Dog fights may also place undue stress on disease compromised tissues. Non-union of mandibular fractures is rare but more common in association with periodontal disease where a fibrous union may exist. In the older, toy breeds that are only eating soft foods, veterinary interference may not be indicated. Separation of the mandibular symphysis This is the most common oral injury in cats (Harvey & Emily). Most can be well stabilized with an encircling wire of gauge placed with a needle as a wirepasser. Collapse of the symphysis with distortion of the angle of the canine teeth may occur in some cases and may indicate that the wire is too tight. Adding acrylic to the wire is useful to add stability; a more complex wiring technique with the addition of a figure of 8 wire around the canines may also help. If instability is a problem, then good occlusion can be maintained by bonding the upper and lower canine teeth together for 2-4 weeks. Fracture/luxation of the Temporo-Mandibular Joint (TMJ) Fractures can be difficult to define clearly on radiographs and to treat. If there is little or no malocclusion or if highly comminuted, try a tape muzzle for 4-5 weeks.

9 8 If the luxation is rostro-dorsal, correction is aided by placing a wood dowel or pencil between the caudal teeth. Luxation is seen more commonly in the cat than the dog and is frequently bilateral. If pain is severe or persistent, 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 such as inter-arcade wiring is recommended to maintain alignment.