Introduction

Non-domestic pets, whether small mammals or more exotic "zoo" animals, present owners and caretakers with the challenge of providing an environment and diet that approximates their natural conditions. Zoos are making great strides in these areas, designing housing that looks and feels like a natural habitat. Dietary needs are being well supplied with regard to nutrients, but it is often difficult to provide the consistency and texture of their natural foods. Providing these needs can be even more difficult for private owners that choose to own non-domestic pets.

There is a tremendous variety and variability in animals, their dentition and anatomy. They suffer from many of the same problems as domestic pets. Add to these the additional problems that can develop due to housing and enclosures, and behavioral problems that develop due to the stress of captivity.

Dentistry on exotic animals tends to play a relatively small role in most private general practices. However, many people own exotic pets and they suffer from a number of dental and oral problems.

Zoo Animals

Zoo animals can provide some interesting and fun variety to veterinary practice. In the U.S. there is very little demand for zoo animal care in private practice, since most zoos employ their own veterinarians. Many zoos prefer to have human dental practitioners work on their animals' teeth rather than veterinary dentists. The highest profile dental procedures are root canal treatment or extraction for treatment of dental trauma. Many of the carnivores find ways to fracture their canine teeth, exposing the pulp chambers and resulting in eventual pulp necrosis. Root canal treatment on these patients is relatively routine for the veterinary dentist...just larger. 120mm endodontic files are available for these patients, and many of the materials and equipment has been nicely modified to accommodate the large pulp chambers of these patients.

Non-carnivores rarely suffer from dental trauma. In addition to periodontal disease, antelopes and marsupials commonly develop an osteomyelitis, known as "lumpy jaw", that is thought to begin from oral trauma in animals fed a dry coarse hay.

Small Mammals--General

Small mammals and "pocket pets" are quite common. Many dental problems in these animals are related to husbandry or dietary problems and are often resolved through routine maintenance or extraction. These are relatively simple procedures and are generally performed by general practitioners or exotic animal specialists, so we rarely see them in dental referral facilities. General anesthesia, antibacterial management, and pain management often play a more important role with small mammals than the actual dental procedures themselves.

Anesthesia of small mammals is extensively covered in the literature and is beyond the scope of this paper except for a few comments. General anesthesia is often accomplished using combinations of injectable drugs such as diazepam or midazolam, butorphanol or buprenorphine, ketamine, acepromazine, and xylazine. Inhalant gas such as isoflurane can be administered for longer procedures or more profound anesthesia. Endotracheal intubation is the best way to deliver inhalant anesthesia. Many of these pets can be challenging to intubate; endoscope-guided endotracheal tube placement may be helpful. For many procedures, gas can be delivered with a face mask. Working in the mouth makes this difficult, however for short procedures a small mask that fits over the nose can provide inhalant anesthesia while still allowing access to the oral cavity. Whenever anesthetized patients do not have an endotracheal tube in place, extreme care should be taken to protect the airway from aspiration of debris. Also, rabbits and rodents are obligate nasal breathers; if a modified face mask is used over the nose to provide inhalant anesthesia, care should be taken to avoid hyperextension of the head or occlusion of the nostrils.

In addition to pre-operative analgesia, post-operative pain control and supportive care are crucial when treating small exotic mammals. It may be helpful to send them home on a short course of a non-steroidal anti-inflammatory, such as meloxicam, to encourage quicker return to function. It is vital that these species do not go for prolonged periods of time (i.e., greater than 12 hours) without eating. There are critical care hand-feeding diets available herbivores and carnivores that should be sent home with the owners to hand-feed if necessary.

Ferrets have teeth that are very similar to cats. The most common dental problem we treat in ferrets is traumatic fracture of the canine teeth. We rarely see small rodents such as rats, mice, hamsters and gerbils for dental treatment. They are less prone to problems due to their brachyodont (small crown-to-root ratio) cheek teeth. These teeth, (although not their hypsodont incisor teeth) have complete apical closure and stop growing coronally early in life. In addition, they have relatively short life spans and are inexpensive, unfortunately bringing the economics of treatment into play. Other rodents such as chinchillas and guinea pigs, that have continuously growing cheek teeth, are more commonly afflicted with dental-related disease. This is also true of lagomorphs.

Rabbits

Rabbits are relatively commonly seen in private practice in the U.S. Lagomorphs are distinguished from rodents in that they have 4 upper incisor teeth. There are no canines, 3 upper and 2 lower premolars, and 3 molars on both the upper and lower jaws. The incisors have thick enamel on their labial (front) aspect and mostly the much softer dentin on the palatal and lingual (back) surfaces. The enamel is much harder than the dentin and much more resistant to wear. As abrasion and attrition wear the tooth, this differential wear-resistance results in a sharp labial edge shaped like a chisel. Although the maxillary arch is wider than the mandibular arch, the occlusal plane of the cheek teeth is flat due to the rabbit's lateral mandibular excursions during mastication.

All their teeth grow continually throughout the animal's life. The apex remains open ("aradicular") and the teeth have long anatomic crowns and short roots ("hypsodont"). The continuous tooth growth causes most of the lagomorph's dental problems. When the teeth do not wear normally against the opposing dentition or by masticating an appropriately coarse diet, the crowns become functionally impacted against other teeth...those of the opposing dentition. The result is that the roots then grow apically. Apical growth can result in perforation of the ventral mandibular cortex or the maxillary alveolar bone into the orbital area.

Incisor overgrowth is a common presenting complaint. It is very obvious clinically as the teeth often curl around into the oral cavity or outside the mouth. This problem may be caused by a genetic malocclusion in which the lower jaw is too long compared to the upper jaw (mandibular mesioclusion, underbite, mandibular prognathism). This usually appears after the third week of life and has been reported to be an autosomal recessive trait that causes shortening of the maxilla. Much more commonly, however, it is secondary to cheek tooth overgrowth caused by eating a non-abrasive pelleted-food diet with insufficient coarse hay. As the teeth overgrow they are forced into malocclusion, which then affects the opposing dentition in a similar manner as attrition and occlusal abrasion is compromised. This forces the mouth into an anterior open bite, discluding the incisors and displacing them from their normal relationship that would otherwise wear them down adequately. (?? Add about occlusion at rest here) As the incisors overgrow, they deviate into bizarre positions. Corrective trimming of the incisors is generally only a temporary solution unless the cheek teeth are treated and the etiology addressed. Once the cheek teeth and etiology have been addressed, the incisors can be trimmed using a dental bur (while protecting the tongue) approximately monthly, or they can be extracted. Sometimes a corrective trimming of the incisor teeth, leaving the labial edge longer on the upper incisors and the lingual edge longer on the lower incisors, will allow them to re-engage to the opposing dentition and begin normal attrition.

Mandibular abscess is another common rabbit problem, and also usually related to dental disease. Periodontal disease and endodontic disease can cause this, as can cheek tooth overgrowth. Large unilateral, and sometimes bilateral, mandibular swelling usually indicates a chronic abscess filled with caseous material. Treatment requires extraction of the infected tooth or teeth, surgical excision (this is preferable to debridement) of the abscess, and packing the defect with antibiotic-impregnated methylmethacrylate beads, calcium hydroxide powder, or doxycycline gel. The prognosis is guarded.

Guinea Pigs

Guinea pigs are delightful little pets. Their teeth are also aradicular hypsodont teeth similar to the rabbit. In contrast to the rabbit, the maxillary arch is much narrower than the mandibular arch. The lower cheek teeth erupt toward the midline of the palate where they meet the upper cheek teeth that are erupting laterally towards the mandibles.

When they suffer from dental problems, the clinical course is sometimes speedy, and secondary infections are difficult to treat. They should be fed fresh guinea pig chow that can be supplemented with timothy grass hay. Overgrowth of the cheek teeth can cause oral discomfort and trauma to the tongue. Visualization of a guinea pig's premolars can be difficult due to their cheeks collapsing inward as the mouth is opened. Special small mammal cheek dilators and light sources mounted on small tongue blades greatly assist with oral examination, although an otoscope also allows some evaluation. Due to their eruption angle, overgrowth can cause the lower premolar teeth to grow completely over the tongue. Treatment involves "floating", or trimming the sharp overgrown crowns, while protecting the tongue and cheeks from trauma. The natural occlusal plane of 30-45 degrees should be re-established when possible. It is important to be careful to prevent aspiration of fragments during the procedure. Tooth overgrowth may be caused by a genetic malocclusion, or by other factors such as genetics, diet, trauma etc. In guinea pigs there may also be an association with vitamin C deficiency. Unless the cause of the overgrowth is addressed, recurrence is common. Extraction will resolve the overgrowth, but is difficult due to the small oral orifice. Also, opposing teeth may then overgrow due to the lack of opposing dentition. They are often brought for treatment when the condition is advanced, and the prognosis is generally poor.

Chinchillas

Overgrowth of the incisors and/or cheek teeth is very common in chinchillas. Dental overgrowth is associated with malocclusion, but this is very rarely due to primary malocclusion (genetic) and most commonly caused secondary to dental abnormalities. Similar to guinea pigs, the mandibular arch is wider than the maxillary arch. However, similar to rabbits the occlusal plane of the cheek teeth is flat. Most malocclusions are secondary, and can be caused by dietary problems (protein and mineral levels as well as non-abrasive diets), dental trauma, or dental infections. Chinchilla teeth constantly grow and must be worn down by abrasive foods and the opposing dentition. Without this wear, overgrowth can cause drooling or ptyalism sometimes referred to as "slobbers". However, other factors can also cause drooling such as esophageal obstruction, dental or oral foreign body, or general illness. Treatment involves trimming the teeth aggressively to the gingival margin, but if the underlying cause of the overgrowth is not addressed the problem will recur. The incisor overgrowth is most obvious and it is tempting to just trim them. However, the primary overgrowth problem is generally the cheek teeth.

Chinchillas are very susceptible to stress, including the stress of anesthesia and treatment.

Fish

Oral problems in fish tend to be relatively uncommon. Two conditions that we have treated are lip and oral tumors, and overgrowth of dental plates. Anesthesia solution (their normal aquarium water with tricaine methane sulfonate in solution) can be flowed over their gills. We prefer to place the patient in a container of the solution to effect, and then transfer them to a recovery container of pure aquarium water as needed to lighten the depth of sedation. The dental plates can be reduced and shaped with a cross-cut fissure dental bur. The patient needs to be lifted from the water during dental high-speed handpiece use unless the handpiece exhausts the pressurized air remotely.

References

1.  Gorrel C, Verhaert L. Dental diseases in lagamorphs and rodents. In: Gorrel C. Veterinary Dentistry for the General Practitioner. Edinburgh: Saunders; 2004

2.  Johnston DE, Ed. Exotic Animal Medicine in Practice. Trenton: Veterinary Learning Systems; 1991

3.  Kertesz P. A Colour Atlas of Veterinary Dentistry and Oral Surgery. London: Wolfe; 1993

4.  Wiggs RB, Lobprise HB. Veterinary Dentistry: Principles and Practice. Philadelphia: Lippincott-Raven; 1997