Rat
Rescue :: Dental
disease in Exotic Small Mammals
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: Sandhole
Veterinary Centre, Snodland, Kent, ME6 5LG. He is an Exotics
specialist with a soft spot for chinchillas.
