From:
RRC
Date: 2001-08-09 06:56:00 UTC
Subject: Bob C: Ferret Dentition, part 4
[Note: I will be in Portland for the weekend, causing trouble for the
good ferret people out there. I will post the final part when I return,
next Tuesday.]
Dentes incisivi:
Incisors are nipping teeth, used for nibbling small tidbits off larger
chunks, as well as for holding, pulling and carrying objects. Ferrets
also use their incisors for grooming, pulling tufts of hair and dirt,
and chasing down fleas. Like human incisors, ferret incisors occlude
when the mouth is closed, with the upper teeth slightly overlapping the
lower teeth. In ferrets, the lower incisors are short, with a root that
is tremendously compressed laterally, and the corner, or 3rd incisor, is
the smallest tooth in the dentition. The upper incisors are larger, with
the corner incisor larger than the rest and possessing a short,
canine-like crown.
Ferret deciduous incisors are natal teeth; present at birth. However,
while present in the jaw, they remain embedded (= unerupted) in the
gums, so they are rarely seen (there are occasional, and even complete
litters where this is not true and the incisors can be seen (especially
the lower ones). They are, however, exceptions). Typically, there are
three maxillary deciduous incisors per upper quadrant, but many ferrets
have four on each side, or three on one side and four on the other. This
tendency for extra teeth is seen in the adult, where an extra upper
incisor is moderately common (just under 1% of ferrets have an extra
upper incisor). This extra tooth is called a supernumerary tooth (=
accessory tooth, polyodontia, heterotopic polydontia, supplemental
tooth), although technically, the term is only applied if the tooth is
also abnormal in shape. Strictly speaking, an extra tooth of normal
appearance is called a supplemental tooth, but the supernumerary term is
applied so frequently to ANY extra tooth that they are essentially
synonymous (an odontologist would probably disagree, as do I, but that's
life). Sometimes a deciduous incisor is retained, that is, it does not
fall out, which gives the appearance of a supernumerary tooth. This is
called "pseudopolyodontia," and usually the deciduous tooth falls out
later (this is normal with canines). Occasionally a deciduous incisor
can be retained for the life of the ferret. The opposite eventwith a
missing incisoris occasionally found, and is generally termed anodontia
(= missing teeth). Hypodontia (= less teeth than normal, oligodontia)
generally refers to the congenital or developmental absence of teeth,
and is a more specific term than anodontia. I tend to use anodontia
when I am not sure of the reason why a tooth is missing, hypodontia
when it is obviously a congenital or developmental reason, and avulsed
or extracted when those situations are apparent.
At about 46 days after birth, the first permanent incisors have erupted,
starting at the midline and second position. The 3rd maxillary incisor,
next to the canine, is partially caniform (= similar to the canine tooth
in appearance) and erupts around day 54. This upper corner incisor is
larger than the other incisors, and has a small canine-like hook. The
permanent mandibular incisors are typically crowded (= dento-alveolar
crowding); that is, there is not enough room for them to line up from
side to side, so generally the middle incisor is offset cranially (=
behind the 1st and 3rd incisors). This is so common in ferrets (and
mustelids in general) that it is not considered a malocclusion, but
rather a normal state.
In all the skulls I have studied, I have never seen dental caries (=
cavities) in the incisors, which should not be considered as meaning
caries cannot occur, but that it is infrequent. Anodontia is common,
particularly in older ferrets, and the incisors are probably most
commonly lost because of gum disease. On rare occasion, an incisor will
be fractured at the gum line, but unless it is a fresh break, it will
smooth over and mimic a worn incisor. If the ferret is a toy or cloth
chewer; that is, they chew rough or hard objects regularly, then
frequently the incisors will be worn down to gum level. Sometimes the
ferret will accidentally avulse (= pull out) one of the incisors while
tugging an object, or will lose one during surgery if they bite down on
hard objects entering the mouth. Ferrets will occasionally have damaged
tooth germs (= tooth buds) and two adjacent incisors will grow together,
creating a fused tooth (= twinned, connate), but this is uncommon.
While the loss of incisors may cause some loss of cosmetic appearance,
since they have only limited function in a wild animal and negligible
function in a pet, such losses are of minor consequence.
Adult ferrets have twelve incisorsthree each in four quadrants.
Incisors are found in the front of the upper and lower jaws; they are
the first three teeth in each half of the mandible, as well as the three
teeth in each half of the premaxilla, or incisive bone. (Synonyms
incisors = I, i, di, dentes incisivi, anterior tooth, cutting teeth,
nipping teeth. Specific names of incisors [from the centerline towards
the back of the mouth]: 1st = I, medial, central; 2nd = II,
Intermediate; 3rd = III, lateral, corner).
Dentes canini:
The ferret canine is a killing tool, designed to rapidly dispatch prey
animals by either crushing the skull at the base of the brain, or by
separating the upper cervical vertebrae, cutting the spinal cord. The
upper canines are larger and straighter than the lowers. Ferret canines
are exceptionally sharp, with an airfoil-like cross-section. This gives
the teeth great strength while reducing friction and drag during biting.
The ferret canine is large and well developed, and the maxillary canine
(= upper canine, eye tooth) is the longest tooth in the ferret's mouth.
The tooth is easily identified by its length and the presence of an
adjacent, non-pathological, permanent gap in the tooth row, called a
diastema. This gap provides space for the canines, allowing the jaws to
close and the upper and lower dental arches to come into contact. The
crown of the maxillary canine is roughly a centimeter in length, which
causes it to project below the upper lip, making the ferret look like a
sort of miniature, saber-toothed polecat. This length is directly
related to the depth of tissue and bone in the necks of polecat prey,
especially rats and rabbits. The canines are used to pierce the base of
the skull or the top of the vertebral column, causing nearly
instantaneous death to prey animals. While this certainly lessens the
terror and agony experienced by the victims of carnivory, it is actually
designed to prevent harm to the ferret (or more accurately, the polecat
progenitor). Polecats regularly hunt animals their own size and larger,
pursuing prey down narrow tunnels and into rocky crevices. In these
situations, the chance of a polecat being harmed by prey is very real.
To lessen the chance of injury, the polecats attacks fiercely and
rapidly, seizes hold of the prey with strong paws and legs, braces the
prey with powerful neck and back muscles, and then repeatedly bites at
the top of the neck and base of the skull. Death is usually quite rapid
(and merciful compared to most deaths by carnivores, which are usually
the result of slow suffocation or disembowelment; it is not unusual for
a moose to still be alive when the wolves start eating it). For the
canine to withstand the biomechanical forces of biting, piercing bone
and tough connective tissue, and the twisting and pulling from escape
attempts, it has to be strong and well rooted in a deep and
well-supported dental alveolus (= tooth socket). Indeed, the root of the
maxillary canine is longer than the crown and nearly extends to the eye socket.
Deciduous canines come in at about 20 days, and remain in place until
after the permanent canines have completely erupted (the permanent
canines begin erupting about 50 days after birth, and are in place a
week later). During this period, the ferret will commonly have
pseudopolyodontia during the time the deciduous canine is retained. The
pulp cavity of the canine is gradually filled in with dentine during the
life of the ferret, which changes the way light passes through the
tooth, making dentine-filled teeth appear more translucent than teeth
with a pulp cavity filled with blood vessels and tissue. Some people
attempt to age ferrets based on canine dental translucence, but because
the pulp cavity filling rate is dependant upon many variables, including
biomechanical stress, injury, nutrition, individual genetics, sex, and
neutering, the degree of error is so great that specific ages (=
absolute ageing) cannot be assigned. As a relative ageing tool (defining
one ferret as "older" or younger than another), the technique is
somewhat more accurate. The tooth can be pulled and the root sectioned
and stained, and seasonal deposits of cementum (= cementum annuli or
dental annuli) can be counted, which provides a fairly accurate
estimation of age, but since the technique is destructive and painful to
the ferret, it is not done prior to death.
Because the maxillary canines project so far out of mouth, they are
commonly injured in falls, and it is rare when a ferret enters old age
with the tips of their canines wholly intact. This tendency to crack or
break off the tips of the canines is exacerbated by caging; many ferrets
attempt to escape by biting or tugging at wire cages and can chip or
break their canines during the attempt. If the fracture opens the pulp
cavitycontaining the nerve and blood vesselsthe injury can result in
discoloration, cause a serious infection or abscess, or ultimately
result in the loss of the tooth (in rare cases, the infection can result
in general sepsis, killing the ferret). Ordinarily, the exposed nerves
and vessels withdraw upwards into the tooth, and the opened canal is
naturally filled in with dentine. On rare occasion, I have observed
dental caries in the canines, especially at the gum line. Plaque is
common, as is dental calculus. Stubby, broken, and even discolored
canines are common, and while they may lessen fitness in a wild polecat,
result in little or no consequence for pets.
On occasion, someone will use wire cutters to nip the canines in a
ferret, presumably to prevent biting. These can be identified by a roof
line appearance; that is, either side is cut at a bevel and meets at
the midline of the tooth. Less frequently, a rotor tool is used to cut
the canine, which leaves a nearly flat, featureless stub.
Microscopically, both are easily identified by the presence of tool
marks. Distinguishing between a job done by a veterinarian (or animal
dentist) or a nipping done by a non-professional can be easily
ascertained by looking at the cuts; if done medically, the edges are
well prepared, smoothed and polished. However, a rancher using wire
cutters generally leaves behind rough and sharp edges. Distinguishing
between accidental breaks and human cutting is done by looking for a
stepped, fractured appearance, lacking tool marks. Cutting canines to
prevent biting was once a very common and approved technique, and is one
of the ways zooarchaeologists use to positively identify ferrets in the
archaeological record. However, with modern training techniques and an
understanding of ferret behavior, such tactics are unnecessary and
should be avoided. Canines are the ferrets ultimate method of physical
defense, and clipping the teeth would constitute a death sentence for
the animal should they accidentally escape and met with a predator or
the neighbors dog. However, canines are commonly lost through accident
or disease, and cause little difficulty in well-housed pets.
Adult ferrets have a total of four canines; one each in four quadrants.
Dentes canini (= c, C, dc, canine, cuspid, eyetooth, anterior tooth, dog teeth)
Bob C