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.

This procedure requires significant owner commitment and aftercare, but is associated with higher successful outcomes.

Management of complicated periapical abscesses

Retrobulbar abscess

These abscesses are most commonly diagnosed when increased pressure behind the eye globe or true panophthalmitis is present, and consequently when the only option is enucleation of the eye globe. Enucleation allows an easier, dorsal surgical access to the alveolar bulla for careful debridement and flushing. True marsupialization and repeated debridement of this site is difficult and not recommended due to the deep orbital fossa, the potential exposure of the optical nerve and the optic foramen, and for aesthetical reasons.

Ideally, proper diagnosis of abscessation of the alveolar bulla is made before the development of a retrobulbar abscess, and therefore before the eye globe is compromised and can be saved. Options for management of this type of abscess are: a) approach to the alveolar bulla via lateral maxillotomy and b) extraction of the diseased teeth and management of the abscess via the oral cavity and tooth socket.

Extraoral (lateral) approach as for abscesses of the mandibular cheek teeth is extremely difficult due to the presence of the zygomatic arch, which prevents access to the abscess site, true marsupialization and repeated debridement and flushing. The intraoral approach to the alveolar bulla through the tooth socket after extraction of the diseased maxillary cheek tooth/teeth is possible, but difficult due to the small oral cavity and tooth socket.

The lateral approach to the alveolar bulla is performed by exposing the ventral margin of the zygomatic arch, and elevating the cranial portion of the proximal end of the masseteric muscle. A small portion of the ventral zygomatic arch is burred away with high-speed dental equipment in order to approach the lateral aspect of the alveolar bulla, which is gently penetrated with the burr. The fenestration of the alveolar bulla must be large enough to introduce a small Volkmann's spoon to allow debridement and thorough flushing, and eventual introduction of AIPMMA beads. The muscular fascia of the masseteric muscle is sutured with the zygomatic portion of the zygomatic muscle after surgery, and the subcutaneous tissue and the skin sutured routinely.

In cases where the diseased tooth or teeth are missing, or have been extracted, there is high risk of introduction of food into the alveolar bulla through the tooth socket during chewing, and loss of AIPMMA beads. In most cases, it is difficult to impossible to adequately suture the gingiva to close the tooth socket. In these cases, it is recommended to attempt to close the defect with dental resins designed for this purpose.

Oral access to the bulla via the socket of the missing/extracted tooth or teeth is performed with endoscopy to help facilitate visualization of placement of a catheter for flushing and removal of food and purulent material. It is impossible to completely debride the bulla, as it is wider than the tooth socket itself, and access via the small oral cavity of the rabbit is challenging. Placement of small AIPMMA beads is difficult, but has been reported. Again, continual introduction of food into the bulla and loss of beads is possible without primary closure of the socket. Suturing of the gingiva is extremely difficult. Another option is introduction of dental resins to close the defect.

Advanced osteomyelitis

The degree of osteomyelitis is difficult to judge with plain radiography. Diagnosis is enhanced tremendously with computed tomography (CT). A complete understanding of location and extent of diseased bone helps plan surgical intervention. Extensive osteomyelitis may require techniques such as hemi-mandibulectomy.

Antibiotic therapy for treatment of periapical abscess

As mentioned above, antibiotic therapy alone cannot be expected to achieve success in any but the mildest cases of periapical abscess. Antibiotic therapy is, however, and important adjunct to surgical management. Selection of antibiotics should be made based on culture and sensitivity, with the understanding that many dental pathogens in the rabbit are anaerobic bacteria.

Optimal length of therapy is unknown, but may be associated with the ability of surgery to remove infected hard and soft tissues. Most advocates of less aggressive surgical techniques recommend long-term (weeks to months) antibiotic therapy. The author prefers to prescribe a shorter course of antibiotics 7-14 days, except in cases where aggressive surgical debridement was not possible, for example, widespread osteomyelitis.

References

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Capello V, Gracis M. Surgical treatment of periapical abscessations. In: Lennox AM (ed); Rabbit and Rodent Dentistry Handbook. Blackwell Publishing (Formerly ZEN), 1005. p 249-272.

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Divers SJ. Mandibular abscess treatment using antibiotic-impregnated beads. Exotic DVM 2000; 2(5): 15-18.

Capello V. Personal communication. AEMV Conf. 2007.

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Martinez-Jimenez D, Hernandez-Divers SJ, Dietrich U, et al.: Endosurgical treatment of a retrobulbar abscess in a rabbit. JAVMA 230:869-872, 2007.

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