Dental Directions:
When considering the teeth, imagine you are facing the ferret, gazing
directly at their mouth. The maxillary dental arch is dorsal (or
superior), and the mandibular dental arch is ventral (or inferior). The
tooth surface you see when the ferret opens its lips, which curves to
follow the teeth towards the back of the mouth, and which faces outward,
is called the vestibular surface (= labial, buccal). The part facing the
tongue (or the inside of the mouth), which also curves to follow the teeth
towards the back of the mouth, is called the lingual surface (palatal, if
maxillary teeth). The mesial surface is the edge of the teeth that faces
towards the 1st incisor (= towards the median sagittal plane). The distal
surface is the edge of the teeth that faces towards the back of the mouth
(away from the median sagittal plane). The occlusal surface is the part
of the tooth that faces the other teeth (the cutting or grinding part).
The apex is the tip of the root, so the apical surface is the part of the
tooth facing the roots (the bottom of the tooth). The cervical surface
is essentially the neck of the tooth, where the root meets the crown, and
can extend a short way under the enamel.
Dental Shorthand:
Teeth are assigned to one of four regions: the Right Maxillary, the Left
Maxillary, the Right Mandibular, and the Left Mandibular quadrants. All
animal teeth are named by dentition, side, arcade, position, and type of
tooth, such as the "permanent right mandibular 2nd incisor". Since this
is such a long description, odontological shorthand has developed over
the years, (which is definitely NOT standardized! There are nearly as
many variants as authors). "R" or "L" means "right" and "left",
respectively. Incisors are shorted to "I", canines to "C", premolars to
"PM" or "P", and molars shortened to "M". The letters used for tooth types
are also used to identify the dentition; lowercase "c" means the tooth is
a deciduous canine and uppercase "C" means it is a permanent canine (some
shorthand methods use a lowercase "d" to distinguish deciduous teeth; dI,
dC, dPM). Individual teeth are numbered, starting at the edge closest to
the midline or front of the mouth (= median sagittal plane) and proceeding
towards the back of the mouth. The number is placed to the right of the
letter, and is subscripted for mandibular teeth and superscripted for
maxillary teeth. Thus, "deciduous right maxillary 2nd incisor" is
shortened to Ri2/ and "permanent left mandibular 1st molar" becomes LM/1.
When using a text program that does not allow sub-or superscripting (like
most email), placing a slash under or over the number will indicate jaw
position, which is also a good idea when writing out the formula by hand
(thus, "2/" is a superscripted 2, and "/2" is subscripted 2). In addition,
sometimes a short dash is made over a lowercase letter to insure clarity.
When the number is neither sub- or superscripted (C1), it means the tooth
is found in both the upper and lower jaws; but this isn't seen as often.
Dental Formulae:
The dental formula (= natural dentition, complete dentition) can be
written in many ways (like dental shorthand, standardization of dental
formulae has eluded odontologists). However, all use the standard
incisor-canine-premolar-molar sequence, which is the sequence of the
teeth in the jaw. The most complicated method lists all teeth in both
arcades (illustrated here with the ferret deciduous dentition):
pm3 : c1 : i3-4 : i3-4 : c1 : pm3 16
----------------------------------- = -- = 28-30
pm3 : c1 : i3 : i3 : c1 : pm3 14
You will notice the number of upper incisors indicated by "3-4". This
simply means the ferret may have 3 or 4 maxillary deciduous incisors
(the "28-30" means the ferret can have between 28 and 30 deciduous
teeth). This is a hard formula to write, requiring several passes on
the keyboard and subject to becoming a confused mess if the pagination
is off a tiny bit, so it often simplified as:
pm3/3 : c1/1 : i3-4/3 : i3-4/3 : c1/1 : pm3/3 = 16/14 = 28-30
However, since both sides of the jaw are symmetrical, there is no need
to write both down, so the deciduous dental formula for the ferret is
simplified:
i3-4/3 : c1/1 : pm3/3 = 16/14 = 28-30
Finally, in the last simplification, it is assumed the reader can do
simple mathematics, and the numbers are dropped, leaving the most commonly
encountered dental formula for the deciduous dentition of the ferret being:
i3-4/3 : c1/1 : pm3/3 = 28-30
The dental formula for the ferret's permanent dentition:
I3/3 : C1/1 : PM3/3 : M1/2 = 34
Mind you, as earlier indicated, there are a LOT of different ways to
write the dental formula of mammals. This method is only one of many,
and while used in Colyer's and other comprehensive texts, it should not
be considered the best or only method.
Prototypic Eutherian Dentition:
Mammals are divided into three basic groups, more or less depending on
how they give birth. Prototherians (= monotremes) are egg-laying mammals
such as the platypus, and they lack teeth in the adult (the platypus
dental formula is considered to be 0/5 : 1/1 : 2/2 : 3/3 = 34).
Metatherians (= marsupials) are pouched mammals such as the opossum, and
they retain a primitive dental formula containing extra incisors and
postcanine teeth (the opossum has 50 teeth, including 10 upper and 8
lower incisors). Eutherians (= placental mammals) are mammals that
possess a functional placenta, and have a simplified dentition compared to
marsupials. The prototypical eutherian permanent dentition (generalized
mammalian dentition, ancestral eutherian dentition) is considered to be:
I3/3 =96 C1/1 =96 PM4/4 =96 M3/3 = 44
The prototypical eutherian deciduous dentition is:
i3/3 =96 c1/1 =96 pm4/4 = 32
Most species have some variant of this formula -- usually a reduction in
the number of teeth. The ferret is no exception, lacking an upper and
lower premolar, and an upper and two lower molars in the permanent
dentition. When numbering, there are rules for considering lost teeth;
premolars are lost from the front, and molars are lost from the rear.
This means the ferret lacks the maxillary and mandibular 1st premolar,
as well as the maxillary 3rd molar, and mandibular 2nd and 3rd molars.
This is a developmental loss of teeth, or hypodontia. Humans have likewise
lost teeth; the first two premolars are missing, but because of centuries
of dental nomenclature prior to the modern understanding of tooth homology,
the teeth in the 3rd and 4th position remain the "1st and 2nd deciduous
molars", and the "1st and 2nd permanent premolars". Knowing the prototypic
eutherian dentition is valuable for understanding extra or missing teeth
in a particular set of jaws, and is of great benefit in discovering
evolutionary relationships.
Gingivitis and Periodontitis:
Where gingivitis is -- in essence -- an infection or inflammation of the
gums (= gingivia), periodontitis is an infection of the outer tooth and
surrounding dental structures as a whole, including the gingivia, alveolar
bone, periodontal ligament, and tooth surfaces. Either can be localized or
extended, although periodontal disease generally attacks a larger area than
gingivitis. Periodontal disease is far more serious because it can result
in the loss of the tooth through the destruction of the supporting bone or
loss of the periodontal ligament. The exact mechanisms for the shift from
gingivitis to periodontitis are still under investigation, especially in
the ferret. However, it is clear gingival plaque plays a role, as does
the presence of tartar (= dental calculus, calcareous deposit, mineralized
plaque). Diet is also a major contributing factor from both the mechanical
and compositional aspect.
Plaque is a tenacious film composed of bacteria embedded in a food and
saliva matrix (roughly 70% is composed of bacteria, and 30% is composed of
matrix). It is commonly found on tooth surfaces, between teeth, and -- in
the case of an open gingival sulcus due to inflammation -- under the gums
adjacent to the bone and other periodontal structures. Plaque often
progresses into "materia alba"; the cheesy, white deposit on and between
the teeth, consisting of food and skin debris, and significant numbers of
bacteria. Over time materia alba will calcify, forming dental calculus,
which is a hard concretion typically found adhering to the teeth at the
gum line (in ferrets, dental calculi is rich is calcium phosphates, and
is often a form of bone-hard hydroxyapatite). In the presence of plaque,
materia alba, and/or dental calculus, other mechanisms -- including
autoimmune reactions, tobacco products, drug therapy and systemic diseases
(especially lymphoma) play a part in the transformation of a simple disease
into one which threatens the health of the mouth. Aleutian's Disease
may also be a factor in periodontal destruction in ferrets; advanced
periodontitis is often associated with the viral disease in ranched
American mink.
As the disease progresses, causing the gingivia and bone to withdraw, it
exposes the root (= long in the tooth). Ultimately, the tooth can lose so
much support that it will break or fall out. While this is more common in
the incisors and cheek teeth, it is not unheard of in the canines. Most
cases are treatable with antibiotics, changes to the ferret's diet, or
dental work. Ferrets with loose or discolored teeth, with obvious deposits
along the gum lines, or with bad breath which does not resolve in week or
so, should be evaluated by a veterinarian. While the loss of teeth and
dental structure is the prevailing consequence of the ailment, periodontal
disease may promote other bacterial disorders, such as cystitis, kidney
infections, or endocarditis.
An excellent review of periodontal disease in various wild and captive
species can be found in Colyer's Variations and Diseases of the Teeth
of Animals (A. E. W. Miles and Caroline Grigson, eds. 1990 Cambridge
University Press, revised edition). Miles and Grigson report periodontal
disease in wild mustelids has never been found, yet the disease is
extremely common in captive and pet mustelids, including American mink,
polecats, ferrets, and other species. I have noticed a similar trend;
several skulls of polecats once housed in zoos showed extensive periodontal
disease, reactive bone and dental calculus, yet skulls from feral ferrets
and wild polecats showed very little evidence of the disease. Indeed, the
paucity of wild animals displaying evidence of gingival and periodontal
disease, compared to the plethora of captive animals suffering from the
affliction, suggests the common factor to be a human-designed diet (I
consider it to be a triggering mechanism). Modern zoos, which feed their
captive predators a more natural "meat and bone" diet, have reported
significant reductions of periodontal disease. Historically, soft diets
have been associated with periodontal ailments, and an emphasis has been
placed on feeding ferrets a hard food as a preventative. However, little
attention has been given to the various food components in the diet, or
even to the initial definitions of "soft", "semi-moist" and "moist"; were
they minced meats or cereal based?
Obviously, periodontal disease is a highly complex problem and suggesting
any single factor as being the cause would be simplistic. However, even
if the exact mechanism for shifting gingivitis towards periodontitis is
unproven, there is still a strong correlation of the disease to diet, as
well as to deposits of plaque, materia alba and tartar, and reducing such
deposits would have benefit. This would include restricting access to
soft, sticky fruits and reducing total starchy carbohydrates (especially
cereals). Rubbing a tartar-control dentifrice on the teeth on a weekly
basis may have value, although I am unaware if the fluoride is a danger
or not (I would appreciate veterinarian comments regarding the dangers of
ferrets ingesting small amounts of fluoridated toothpaste). Additionally,
augmenting the diet with hard or fibrous "chewing" foods, such as hard
gelatin products, dog biscuits, or even bone may be of help (in one
instance, laboratory ferrets with a high incidence of periodontal disease
showed a marked improvement after the addition of beef ribs to the diet).
The addition of bone to a ferret's diet is controversial and usually
results in comparisons to domestic dogs choking on chicken bones. It is
difficult to understand how a report of a dog bolting a chicken bone can be
contrasted to a ferret gnawing the end off a chicken femur that can hardly
fit into their mouth, but the comparison is common. The ferret's polecat
progenitor evolved eating bones of this size, and while the occasional
ferret may have a problem, that is insufficient reason to oppose a practice
with established positive benefits. On occasion, human infants drown
during bathing, but few fuss-budgets suggest mothers stop bathing their
children. Rather, extra care is suggested, which is good advice when
feeding bone. Far more ferrets have died from being trapped behind
furniture, from being accidentally stepped on, or even from chewing
electrical cords than have had confirmed deaths from bone. Zoo
dietitians routinely feed obligate carnivores a "meat-and-bone" diet,
and complications caused from bone ingestion are extremely rare. You
just have to be careful, feed bones which must be gnawed rather than
bolted, and allow the ferret time to learn how to eat the new food. In
terms of risk, eating bone is clearly safer than inoculations.
Cooked chicken necks and backs, and beef ribs and vertebrae are excellent
treats; they don't splinter like long bones, they cannot be swallowed in
large enough chunks to cause blockages, they allow the ferret access to
chewable bone, and they are large enough to be easily located for later
disposal. Round bones from beef or pork steaks are also good, especially
if they still contain marrow. The harder bones are too large and hard for
the ferret to chew, but if you leave small amounts of meat on the bone
(fibrous connective tissue or gristle is especially good), it will still
help clean the ferret's teeth as they pull and tug on the tissue. It is
carnivorian dental floss. Nonetheless, if you have questions regarding
the feeding of bone to your ferret, consult your veterinarian. Just point
out that ferrets are not dogs if those "dog swallowing chicken bone"
anecdotes are brought up.
Bob C
[Posted in FML issue 3505]
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