Dental disease in Exotic Small Mammals

At our Practice we see a large number of small mammals with symptoms of dental disease both as first opinion cases and as referrals from other practices. This article deals specifically with dental disease in Chinchillas (Chinchilla Langier). Degus (Octodon degus) and Guinea Pigs (Cavia porcellus).

The most common presentations include weight loss, anorexia, cachexia (chronic wasting), excess salivation (slobbers), small faeces or absence of faeces. An ocular (eye) discharge or a discharge from the nose may also be evident. The incisions (front teeth) are commonly overgrown and there may be a history of repeated burring or clipping of these teeth as an attempted treatment for the anorexia. On careful palpation the jaw of these presenting animals may be irregular and painful. Sometimes the animal will grind its teeth, a sign of pain in these species. There is often a poor dietary history which will be addressed later.

One of the most important points to stress is that a detailed oral examination of a conscious small mammal is nigh on impossible. This is especially true of the species dealt with in this article. Guinea pigs often have food in their mouths at the time of examination (in fact if they don’t it is a worrying sign), chins and degus resent oral examination vigorously. Anaesthesia is often required to thoroughly examine the oral cavity and this allows the clinician to perform skull radiography, arguably the most informative diagnostic tool in small mammal dentistry. This is because most dental disease processes in exotic small mammals are concerned with the tooth “roots” which are encased in bone and therefore not visible on a dental examination. In fact, many animals with severe dental disease have mouths that look essentially normal on casual examination of the anaesthetised patient.
Dental Anatomy

Guinea pigs, chinchillas and degus have the dental formula of 2 x I 1/1 C 0/0
P 1/1 M 3/3 (where I = incisors, C = canines, P = premolars and M = molars). The premolars and molars act as a functional unit to grind food and the incisors are used for prehension and cutting of fibrous foodstuffs. All teeth grow continuously. There is no true anatomical root. The lower (mandibular) cheek teeth are arched toward the tongue and overgrowth can lead to tongue entrapment. The upper (maxillary) cheek teeth are angled outward (laterally). Angulation of the teeth provides an effective surface for grinding thin fibrous food material and when eating this high silicate foodstuff, rapid tooth wear occurs and new growing tooth replaces the wear caused by grinding. In the wild these animals spend a long time eating low quality grasses which are high in silicates (the precursors of glass). This continual grinding prevents overgrowth of the teeth.

Diet and dental disease

Captive bred specimens are larger than their wild counterparts and it is established that a proportion of cases of dental disease can be attributed to genetic causes. However, by far the most cases of dental disease in Guinea pigs, chinchillas and degus results wholly or in large part from inappropriate diets. Specifically a lack of dietary fibre is implicated. Most modern “complete” diets are complete in that they contain adequate protein, carbohydrates, fats and trace elements. However, their sole use leads not only to problems with obesity but also does not allow these animals to spend the large amount of time chewing and wearing their molar teeth that they require to grind down their continually growing back teeth. This can lead to spur formation and entrapment of the tongue by the diagonally growing lower molars. This can be picked up and treated by a detailed examination of the mouth. All the time however, a more sinister development is occurring which is all together more difficult to treat.

If less time is spent chewing, the exposed parts of the teeth elongate. This puts pressure on the teeth which slows eruption, but tooth growth continues at a slow rate. Essentially what happens next is that the cheek teeth grow backwards, invading the structures of the skull. The teeth can grow into the nasal sinuses causing respiratory infections or towards the eyes causing weepiness. The lower teeth invade the jawbone causing bony changes and sometimes abscess formation (common in rabbits). The net result of this growth is that the mouth is progressively forced open. The front teeth elongate as they do not meet any more and becomes progressively more difficult for these animals to eat (try swallowing with your mouth open!). This leads to the condition known as slobbers where saliva spills onto the skin often causing a fetid smell. Clients often notice this and the fact that the incisors are growing and present these animals for incisor trimming. In fact the incisors are growing because they are not meeting as a result of the mouth being forced open by the overgrown back teeth. Skull radiography is the only way to accurately quantify if this has occurred and to what extent. All too often, animals are referred to this practice with histories of repeated anaesthetics with no radiography performed.

Treatment

To sum up, difficult at best. Most presented cases have advanced disease. Aggressive burring of the cheek teeth may be attempted. If abscesses have formed, these need specific treatment. Eye infections require antibiotics. Otherwise force-feeding and anti-inflammatory drugs are required. Quality of life needs to be assessed on a regular basis and weight monitoring with faecal output are useful indicators of appetite. The liquid anti-inflammatory drug meloxicam (Metacam: Boehringer Ingleheim) is well tolerated in these species. It has the advantage of being very palatable (it tastes like honey) so is well accepted also. Often patients require life long treatment. Secondary problems associated with anorexia (e.g. intestinal stasis where the guts shut down and stops moving) also need to be addressed. Often euthanasia is required in patients that fail to respond.

Prevention

As always, better than cure. The diet of these animals needs to resemble their diet in the wild. They are not like dogs and cats that get a bowl of food twice daily and that’s it. Their anatomy and physiology is specifically set up to deal with ingestion of large quantities of lower quality foodstuffs in order to meet their nutritional requirements. This means lots of good quality hay. Timothy hay is usually the beat. The fibre requires lots of chewing and keeps the intestines moving which is essential for health. 1 to 2 tablespoonfuls maximum of concentrate mix is the recommended daily allowance; the rest should be good quality hay with occasional treats. Offer the hay in a hayrack to prevent contamination with faeces. This also provides environmental enrichment, as the animals have to work a little harder for their food. Twice yearly veterinary checkups allow careful palpation of the cheek teeth. Also monitor weight and faecal output on a regular basis so that any symptoms can be managed early in the course of disease.

Pictures courtesy of Mark Rowland

Normal Chinchilla and Degu showing roots of molar (back) teeth
in normal anatomical position :

Chinchilla

Degu

Degu and Chinchilla with elongation of roots of molar teeth forcing mouth open causing the front teeth (incisors) to overgrow as they no longer meet :

Chinchilla

Degu

Slobbers (excess salivation) in a Guinea pig:

References

BSAVA Manual of Exotic Pets 4th edition
Hillyer, Quesenberry: Diseases of Ferrets, Rabbits and Rodents 2nd edition
O Malley: Clinical Anatomy and Physiology of Exotic Species
Carpenter: Exotic Animal Formulary 3rd edition

About the Author

Mark Rowland BVSc cert Zoomed MRCVS is in practice at: Trinity Vet Centre, Hermitage Walk, Hermitage Lane, Maidstone, Kent, ME16 9NZ. He is an Exotics specialist with a soft spot for chinchillas.