How to Repair Incisor Tooth Avulsion Fractures in the Standing Horse

Incisor tooth avulsion fractures of the rostral mandible and premaxilla are a common occurrence in the horse. Most of these fractures can be repaired with interdental wiring in the standing, sedated horse using regional and/or local anesthesia.

1. Introduction

Fractures of the rostral mandible and premaxillary bones are common injuries in the horse. In fact, the mandible is the most commonly fractured bone in the equine head [1]. Most of these injuries are avulsion type fractures involving the mandibular or premaxillary incisor teeth that are often left attached only by surrounding soft tissue. These fractures are open and contaminated with saliva and feed material. This type of injury may be the result of the incisors being caught on a stationary object such as a feed bucket, followed by forcefully pulling back when the horse becomes startled. Less frequently, they may be caused by kicks, falls, or other forms of blunt trauma. The injury may appear quite devastating to the owner but most carry a good prognosis, both functionally and cosmetically, with appropriate therapy. Without repair, the result may be loss of teeth, osteomyelitis, jaw deformation, or loss of proper masticatory function.

The location and configuration of the fracture dictates the type of fixation chosen. There have been many described techniques for repair of mandibular and maxillary fractures including interdental wiring, intramedullary pins, lag screws, external fixation devices, intraoral acrylic splints, compression plates, or a combination of techniques. Interdental wiring with stainless steel wire is adequate for the majority of avulsion fractures located at the rostral mandible or premaxilla and can be performed on most horses standing with appropriate sedation and regional anesthesia. Performing the technique standing precludes the risks and cost of general anesthesia and allows repair in a non-hospital setting.

2. Materials and Methods

Diagnosis of fractures of the rostral mandible and premaxilla are usually obvious with physical examination alone. Common clinical signs are pain on attempting to perform an oral examination, difficult prehension, protruding tongue, salivating from the mouth, malalignment of the incisors, and a fetid odor if the fracture is a few days old. Even if the fracture is of some duration, repair can be successful because of the good blood supply of the area. Radiographs are usually not necessary for diagnosis of rostral fractures but may be useful to determine the extent of the fracture and whether tooth root damage has occurred. In addition to standard lateral, dorsoventral, and oblique projections, an intraoral view may be indicated and most useful. Palpation for symmetry of the temporomandibular joints should be performed. The temporomandibular joint may rarely be luxated or subluxated with mandibular fractures. Hydration status should also be evaluated, because some animals are unable to drink water properly. If the fracture was the result of a kick or other form of blunt trauma, caution should be taken for potential cranial injury.

Displaced fractures are candidates for surgical repair. Even non-displaced fractures may be unstable and would benefit from surgical repair. Sedation of the horse is necessary, because they must remain calm throughout the procedure. A combination of detomidine (0.01 mg/kg) and butorphanol (0.05 mg/kg) is usually adequate. Additional sedation can be added as needed. The repair is best performed with the horse standing in stocks, either cross-tied or using one of the commercial dental halters available to restrain the head. This is necessary to prevent dislodging of fracture fragments from their soft tissue attachments if the horse should move suddenly while stainless steel cerclage wires are pre-placed and secured [2]. A twitch may also be used if needed.

In addition to proper restraint and sedation, regional anesthesia is needed to desensitize the rostral mandible or maxilla. Peri-neural anesthesia of the mental nerve usually produces adequate analgesia for repair of rostral mandibular avulsion fractures. This is a branch of the mandibular nerve; it exits the mental foramen on the lateral side of the ramus of the mandible. The foramen can usually be palpated ~3 cm posterior to the commissure of the lips, under the tendon of the depressor labii inferioris muscle. A 22-gauge, 3.5-cm needle is advanced parallel to the mandible and 5 ml of lidocaine or mepivacaine is used to anesthetize the nerve [3]. An infraorbital nerve block produces anesthesia of the premaxillary region, allowing repair of fractures in this area. This nerve emerges from the infraorbital foramen just under the nasolabialis muscle. The foramen can be located approximately midway and 2.5 cm dorsal to a line connecting the nasomaxillary notch and the rostral end of the facial crest. A 22-gauge, 3.5-cm needle is used to inject 5 ml of lidocaine or mepivacaine into the bony lip of the foramen [3]. Local anesthesia may be used to augment these nerve blocks if necessary. More extensive fractures may require a mandibular or maxillary foramen block.

Surgical repair using interdental wiring requires little specialized equipment. Small bone curettes, 14-gauge needles, 18-gauge stainless steel wire, wire twisters or pliers, wire cutters, a hand-held chuck, and Steinmann pins are sufficient equipment in most cases. A battery-powered drill with 3.2-mm bits may be beneficial if holes are needed in the mandible. It is also helpful to have a good surgical head lamp or an assistant holding a quality flashlight.

The fracture site should be thoroughly lavaged with water or dilute povidone iodine, and a small curette should be used to debride the fracture line of feed material, blood clots, and small fragments of bone. The latter is especially important to prevent sequestra formation. Alternatively, a gauze sponge can be used to "floss" the fracture line to remove particulate matter. Loose teeth should be preserved unless obviously devitalized. Many loose teeth will survive, or if necessary, they can be removed at a later date. Applying direct pressure on the teeth is usually all that is necessary to reduce the fracture, and retention wires are placed using stable teeth on either side of the fracture. On younger animals, this may be accomplished by inserting a 14-gauge needle just below the gum line between two stable incisors to function as a sleeve through which to pass wire. It may be necessary to tap on the needle with pliers to advance it through the gum. On older horses, a chuck and Steinmann pin may be necessary to accomplish this. It is important to make the holes below the gum line to prevent the wires from slipping. A strand of 18-gauge stainless steel wire is passed through the needle from the lingual side to the buccal side. The needle is removed, and the procedure is repeated on the fractured side. If slipping of the wire is a problem, which may occur on immature corner incisors, a groove can be cut in the tooth with a file. A minimum of one wire (or preferably two wires) is used on either side of the fracture with overlapping of the wires if possible.

These wires should be staggered between incisors. Wires are usually used in an encircling pattern. The wire should be kept tight at all times and care taken not to kink the wire, which may weaken or break it. Tightening the wire completes the repair. While tightening, it is important to pull on the wire while twisting to prevent breakage of the wire before the fracture is compressed. The knot should be bent to prevent trauma to the oral mucosa. Fractures involving the corner incisor and a significant portion of the hemi-mandible may require additional caudal support. It may be necessary to use a Steinmann pin or drill bit to make a hole through the mandible to anchor the wire. On an older animal, the canine tooth may be used if present. The same technique may be required on both sides of the mandible if a larger portion of bone is involved. Fractures of the premaxilla are repaired in a similar manner.

This method of repair does not follow the rule of complete rigid stability, but because of an excellent blood supply, these fractures heal sufficiently in 6 - 8 wk, at which time the wires can be removed. After surgery, the wires should be checked routinely and re-tightened if they become loose. If a wire should break, stability of the fracture site should be evaluated. If the fracture is still unstable, the wire may need to be replaced. If two wires have been used and the fracture is stable, replacement of the broken wire is not necessary. Routine use of antibiotics is not required but may be indicated on an individual basis if severe contamination or excessive soft tissue trauma has occurred [4,5]. Phenylbutazone should be given for several days after the injury to help control pain so the horse can eat comfortably. Most horses start eating shortly after the fracture is repaired. If not, a pellet gruel or bran mash may be offered for a few days. If the animal does not actively eat and drink for several days, they should be monitored for dehydration, and appropriate therapy should be initiated if necessary. The mouth should be rinsed daily with water to remove feed material from the fracture site and from around the wires. Rinsing the mouth should be continued until the mucosa has healed.

3. Results

Most fractures of the rostral mandible and maxilla are amenable to repair in the standing, sedated horse. The surgical technique used is the same as that used under general anesthesia, and the final result should be similar. Prognosis of uncomplicated fractures repaired by interdental wiring should be considered good to excellent. Short-term complications mainly involve loosening or breaking of the wire fixation. Some of these may be prevented by proper wire handling to reduce kinking and correct twisting of the wire to complete the knot. Brachynathism in foals has been reported after surgical repair of bilateral fractures of the mandible [6]. This is probably not a fault of the technique but occurs because growth of the foal's jaw is impeded by the fixation.

4. Discussion

Rostral avulsion fractures of the mandible and premaxilla are virtually always open and contaminated. Many of these may go unnoticed for several days. Surgical repair of a long bone fracture presented in this manner is destined for failure. With proper repair, rostral mandibular and premaxillary fractures of this nature carry a good prognosis because of the excellent blood supply of this region. In animals with deciduous teeth, it is difficult to determine and relate to an owner exactly what to expect when the permanent teeth erupt. Eruption may be normal, or if damage has been done to the permanent tooth buds, the tooth may not erupt or may erupt abnormally.

The goal of surgical treatment is to restore normal occlusion to the incisors and stabilize the fracture so the animal can function properly while the fracture heals. Interdental wiring is adequate in most cases. This technique requires little specialized training, is inexpensive, does not require specialized equipment, and usually does not require general anesthesia, and the complication rate is low.