Treatment of periapical abscesses and osteomeyelitis in rabbits (Proceedings)
Periapical abscesses of incisor and cheek teeth are common in pet rabbits. Penetration of bacteria into the alveolus occurs most commonly secondary to acquired dental disease and is often associated with fracture. Due to the proximity and relationship of the reserve crown and maxillary and mandibular alveolar bones, periapical abscess frequently involves surrounding bone and soft tissues, producing osteomyelitis.
Much of the pathophysiology and clinical expression of periapical infection is poorly understood in rabbits. Dental abscesses in rabbits are unusual in that they seldom produce hyperthermia, can become very large without producing apparent discomfort, and tend to encapsulate and progressively destroy surrounding bone.
Location depends upon the affected dental structures, and in rabbits most commonly involves mandibular CT1-3. These abscesses typically present as soft tissue masses associated with the ventral or lateral aspect of the mandible. Periapical infections of CT4-5 are fortunately less common, as surgical management of this site is much more difficult due to the presence of the masseteric muscle, and risk of fracture of thin mandibular bone during surgical debridement.Abscesses of rostral maxillary teeth may present as swellings associated with the lateral maxilla. Abscess of maxillary CT3-6 present a more severe potential scenario, as the apexes of these teeth are closely associated with the orbital fossa. The reserve crown and apex of maxillary CT3-6 lie within a unique bony structure called the alveolar bulla. Periapical infection of one or more of these CT allows tooth fragments and purulent material to fill the bulla. If the thin dorsal cortical bone of the alveolar bulla is perforated, purulent material can accumulate in the retrobulbar space producing exophthalmia and a true retrobulbar abscess.
Treatment of uncomplicated periapical infections
A number of anecdotal reports of successful treatment of simple periapical abscess using various treatment protocols have been reported, but retrospective analysis of treatment options and outcomes is lacking. Due to the nature of abscess in rabbits and frequency of associated soft tissue infection and osteomyelitis, antibiotic therapy alone cannot be expected to carry an acceptable success rate in any except very early, mild cases (see antibiotic therapy below). Unfortunately, most rabbits with periapical abscesses do not present early in the course of the disease, where the only evidence might have been detected on high quality radiographs of the skull.
Simple single surgical opening of the abscess capsule and flushing is anecdotally associated with high failure rate, as this technique does not include removal of the capsule and diseased teeth and debridement of infected bone and soft tissues. Improved success rates have been reported utilizing a number of more advanced techniques including:
1. Aggressive surgical debridement with removal of affected teeth and bone, followed by marsupialization, and repeated flushing and gentle debridement, plus instillation of antibiotic gel and/or granulation-stimulating products until the wound heals by second intention;
2. Aggressive surgical debridement with removal of affected teeth and bone, followed by insertion of AIPMMA beads and primary closure, +/- repeated surgical debridement until healed;
3. More conservative debridement followed by packing of the wound with antibiotic soaked gauze until the wound heals by second intention;
4. Varying degrees of surgical debridement with or without marsupialization, and packing of the wound with honey or sugar solutions until the wound heals by second intention.
It is impossible to compare the merits of these approaches without an understanding of the variability of severity of periapical abscesses in rabbits. While less aggressive surgical techniques may be adequate for simple periapical abscesses of one or just a few teeth, the success rate in cases of widespread osteomyelitis is expected to be lower.
The author prefers technique (1) above, which is described in detail: Removal of the entire capsule is facilitated by incising the skin over the abscess and then carefully dissecting the intact capsule from surrounding tissues, taking care not to enter the abscess cavity. Once the capsule has been isolated up to the point where the abscess connects with bone, the capsule is incised and removed along with the purulent material. A specimen for culture and sensitivity can be collected from the capsule wall at this point. Any remaining debris or material is removed, and the infected or necrotic cortical bone debrided to the point of bleeding with a bone curette or rongeurs. Any affected tooth fragments are removed at this point, and the site thoroughly flushed. Marsupialization is performed with 3-0 or smaller non-absorbable suture material. Marsupialization produces a less appealing cosmetic outcome, but allows daily debridement, flushing and packing with antibiotic ointments. Most owners can be taught how to assume most of the care, with frequent veterinary rechecks to evaluate progress. Sutures are often removed 10-12 days post-surgery, and the wound allowed to granulate by second intention.