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 event -- with a missing incisor -- is
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 incisors -- three 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 cavity --
containing the nerve and blood vessels -- the 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 ferret's 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
neighbor's 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
[Posted in FML issue 3511]