From:
RRC
Date: 2001-08-08 00:17:00 UTC
Subject: Bob C: Ferret Dentition, part 2
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 C1/1 PM4/4 M3/3 = 44
The prototypical eutherian deciduous dentition is:
i3/3 c1/1 pm4/4 = 32
Most species have some variant of this formulausually 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 isin essencean 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,
andin the case of an open gingival sulcus due to inflammationunder 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
mechanismsincluding 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 Colyers 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