Maxillo-facial injuries resulting from hit-by-car trauma can result in both soft and hard tissue damage.
Maxillo-facial injuries resulting from hit-by-car trauma can result in both soft and hard tissue damage. The clinician's first assessment must evaluate the patient for life threatening conditions. Hemorrhage, both internal and external, must be controlled. Any injuries to the airway and damage to the lung tissue must be evaluated and treated. Often concussive forces of the head lead to neurogenic shock. This needs to be rigorously treated with steroids and mannitol and volume replacement. Any open fractures of the extremities need to be initially prepped and cleaned and conservatively bandaged and splinted until the animal is stable. Antibiotics are immediately started and any blood volume loss needs to be corrected. Patient stabilization is the primary initial concern.
Signs of maxillo-facial injuries are initially assessed by observing the pet. Facial symmetry needs to be evaluated from the front and side of the animal. Any compression fractures of the temporal bone need to be compared with any abnormal neurological findings. Head tilting to one side could be a sign of ipsilateral vestibular damage, a ruptured tympanic membrane or fracture of the mandibular condyle-temporal fossa. Lateral displacement of the mandible or inability to close the lower jaw can be visualized. An animal often presenting with this is, in addition, copiously salivating. The presence of epistaxis, and schleral hemorrhage might indicate trauma to the underlying facial bones. Often shearing injuries can avulse the soft tissue from the underlying bone. Injuries to the lips, muzzle and nose are very common.
If the animal permits, a further inspection of the oral cavity should be carried out. Fractured or avulsed teeth need to be carefully identified. Open pulp exposure will lead to contamination and infection with eventual tooth devitalization. At times, the fractured crowns might appear normal however on palpation, they are mobile. The fractured portion of the crown is being held only by gingival tissue. Obvious mobile segments of teeth can indicate a fracture of the underlying supporting alveolar bone. Often lacerations of the associated soft tissue are visible. The tongue or inside buccal mucosa often are traumatized by the teeth. At times the crowns can break off and lodge within the soft tissue wound. The buccal mucosa should be assessed for evidence of ecchymosis, perforation or full thickness tissue damage.
Once the animal is stabile, anesthesia is induced. Any open oral wounds should be lavaged and the soft tissue sutured with absorbable simple interrupted sutures. This author favors 4-0 gut with a J-1 cutting needle since it hydrolyzes within 10-14 days. Monofilament is preferred over polyfilament absorbable sutures due to reduced tissue drag.
Fractured teeth that have open pulp chambers depending on the tooth importance (the canines, and upper and lower carnassial teeth being the most important), should be either extracted or receive a vital pulpectomy. The latter treatment should be considered in animals less than 5-years old with freshly exposed pulp chambers of more important teeth. Pulpectomies should also be considered when the tooth in question is in close association with a mandibular fracture and an extraction of the affected tooth would leave a space void and difficulty in jaw stabilization. The procedure involves removing 5 mm of the contaminated coronal pulp and covering the freshly excised tissue with CaOH powder and quick setting paste. This is then restored with a glass ionomer and a composite material. The so treated tooth should be reevaluated radiographically in 6 –months to determine the tooth's vitality.
Skull radiographs in conjunction to intraoral dental films need to be taken. If there is any suspicion of a traumatic malocclusion, the TMJ bilaterally should be imaged. The more common TMJ luxations are of the dorsal cranial position. On clinical evaluation, the lower jaw moves laterally to the contralateral side. If it is a caudal ventral luxation the jaw will lateralize to the ipsilaterally affected TMJ. The latter is often causes by cranial-caudal trauma to the mandible. Often the fossa is fractured as the condyle is driven caudally.
Fractures of the vertical mandibular ramus are often at the juncture to the horizontal ramus since the more dorsal portion or coronoid is protected by the maxillary zygoma. The bone is extremely thin at this site and a fracture difficult to stabilize with internal fixation. Stabilization of caudal fractures and reduced TMJ luxations are either done with a tape muzzle or by fusing the canine teeth. The teeth are first acid-etched, rinsed and dried. A bonding agent is then applied and light cured. The teeth are fused in a partially opened position with a composite resin. The opening is just enough to allow the tongue to pass through it, therefore allowing the animal to lap soft food. Initially the client is instructed to help syringe food in the patient's mouth for the first week. Alternatively an esophagostomy tube can be placed at the time of surgery.
The primary concern of the oral surgeon is to reestablish occlusion of the upper and lower jaws if there is any traumatic displacement. First aligning the teeth will allow the proper alignment of the underlying fractured bones which are attached to the teeth. Fractures of the upper jaw pose specific problems of stabilization since the palatal and maxillary bones are thin and incapable of holding screws and plates. Any facial deviations caused by their fracture must be stabilized by utilizing a combination of interosseous or interdental wiring techniques and acrylic splinting. The splint can be kept in place by directly bonding it to the pre-etched teeth similar to above. It can also be kept in place by priorly placing interdental wires and a then covering them with the acrylic. Significant trauma to the dorsal naso-maxillary bones with disruption of the turbinates can lead to subcutaneous emphysema. This rarely requires intervention since spontaneous resolution occurs post operative to the fracture repair
Fractures of the mandible lend themselves to acrylic and wire stabilization. Although plates and screws can be used in edentulous areas, when the teeth are present an increase risk of perforating the roots and creating chronic draining tracts exist. Often when tooth roots are within the fracture site it becomes necessary to extract the tooth in part or totally. A partially hemisected tooth followed by a vital pulpectomy can serve as an abutment tooth for purposes of an acrylic splint retention and stabilization. It also allows for a functional tooth after the oral trauma has healed.
Symphyseal fractures are commonly dealt with by a full cerclage wire behind the canine teeth. Usually the wires are placed through an eighteen gauge needle which enters through the submandibular skin below the canines and exits at the muco- gingival line on the distal aspect of the canine. This loops over the symphysis and reenters into the needle tip which has been passed again from the ventral mandible up through the muco-gingival line on the distal aspect of the other lower canine. The wire ends are then twisted on each other until the symphysis is stable. Additionally an acrylic splint can be bonded between the canines for additional stabilization.
Any lip avulsions in association with Symphyseal fractures can usually be dealt with by reattachment of the lip by sling sutures passed around the incisal teeth and anchoring the lip to the underlying bone. If the incisor teeth have been fractured then predrilling the rostral mandible with a #2 round bur will allow a suture or wire to tack down the lip to the bone. Often in addition to the soft tissue avulsion the underlying incisal bone and teeth are fractured away from the symphysis. In this case a rostral mandibulectomy can be performed. The bone and teeth are excised off of the soft tissue and the gingiva is attached with simple interrupted sutures to the remaining mandible.
Avulsions of the teeth usually occur more frequently to the rostral canines and can either be partial or complete. The apex of the tooth is displaced and alveolar bone is often fractured. Mobility of the tooth requires radiographs to determine if there is root fracture concomitant to the fractured alveolar bone. Usually the radiographs show a disparity of periodontal space width from one tooth side to the other when a luxation is present. The sequella of a damaged apical blood supply is pulpal necrosis in the mature tooth. The immature tooth due to an open apex and a greater tendency to recover may only develop a partial pulp necrosis limited to the coronal aspect. This may lead later to internal changes of the tooth so further radiographic assessment should be recommended.
Luxated teeth are digitally reduced to a normal position. A wire / acrylic splint should be placed around the affected tooth and stabilized to the contralateral side during the initial alveolar fracture healing. The splint should not interfere with the animal's opening and jaw closing. The procedure of splint placement is as follows: Apply a "figure 8" 24 gauge wire around the reduced canine and the contralateral canine. Suture any soft tissue lacerations. Cleanse the crown after the tooth has been reduced. The tooth surfaces which will receive the acrylic are acid etched with 40% phosphoric acid gel for 1 minute followed by rinsing with water. On drying, this will leave a frosted appearance to the enamel. Acrylic is applied circumferentially around the reduced tooth and the contralateral anchorage tooth which is connected by an acrylic bridge formed across the palatal mucosa if it is a maxillary canine injury. A cold-curing acrylic without significant exothermia should be used for splinting (Pro-temp Garant-ESPE or Maxitemp Schein). The animal is sent home with a curved tip syringe and a dilute 1:100 chlorhexidine flush (1 cc of Nolvasan with 8 ounces of water). Normally the splint is removed in 4 weeks and the non-vital tooth is root canalled at this time.
Devitalization of the affected tissue is not uncommon as a complication to maxillo-facial injuries. In the case of the bone having been separated from its blood supply, a bone sequestrum may occur. If a bone sequestrum forms it needs to be excised to bleeding tissue. Non-healing draining tracts usually indicate deeper lying necrotic tissue. Dehiscence of suture lines can also occur due to tissue which has initially undergone trauma and subsequently devitalizes. Often repeat surgeries 7-14 days later are required after the non-vital tissue demarcates. In young animals distortion of the facial growth plates can occur due to premature traumatic closure. Adult tooth buds can be malpositioned and erupt in ectopic areas of the mouth due to the traumatic insult.
Oral trauma surgery should abide by the following principles: All lacerated soft tissue should be closed when possible over bone and not a void. The muco-gingival pedicle flaps necessary for this closure, should be carefully harvested with a good underlying blood supply. Care should be given to prevent any rough handling of the tissue edges. Any potentially compromised tissue should be excised. Tension along the suture line can be prevented by harvesting excess donor tissue. This is undermined and mobilized. If the traumatized palatal mucosa is the recipient site for the pedicle flap, the epithelium should be scarified to allow for proper attachment to it. This scarification can be accomplished by using a rough diamond bur in a high-speed handpiece.
Young animals with jaw fractures should be treated with as minimally invasive procedures as possible. This is due to fact that the non-erupted adult teeth and the poorly mineralized bone are not appropriately treated with orthopedic hardware. Using tape muzzles and tincture of time with close radiographic follow up can give excellent results.
If a fracture is poorly reduced, any maloccluding teeth need to be prevented from destabilizing the fracture healing. The traumatic malocclusion caused by teeth hitting into other teeth or into soft tissue, creates movement which prolongs the healing. If not corrected, this can lead to a non-union fracture. To prevent this from occurring, the insulting teeth are either extracted or crown reduced. The latter treated teeth then receive a vital pulpectomy / pulp capping. This technique is especially useful when treating the maloccluding canine teeth whereby extracting them would be considerably more invasive.