Message Number: YG6228 | New FHL Archives Search
From: RRC
Date: 2001-08-09 06:52:00 UTC
Subject: Bob C: Ferret Dentition, part 3

Wear Rates and the Influence of Caging

While enamel is the hardest substance in the body, it does not follow
that it is impervious to wear. Because of its brittleness, it fractures
like glass, chipping or cracking like the edge of your fine bone china
when clanking against your stainless steel faucet. This chipping quality
allowed prehistoric peoples create tools from teeth, simply by working
the edges like flint or obsidian. Because the layer of enamel on the
teeth is so thin, it can be rubbed off (= abraded) when chewing hard
objects. It is a simple task to look at the lingual edge of the canines
and separate cage biters from those ferrets that do not tug or pull at
caging wire. The difference between the two? As cage biters hold the
wire behind their canines, the wire will slip up and down, acting like
sandpaper on the backs of the teeth. The enamel is thin at this
location, and quickly wears through, exposing the dentine.

That is what the dentine is for, and why the pulp chamber and root canal
slowly fill in with dentine. In the wild polecat progenitor, teeth wear
down at a fairly standard rate for any single locality (the wear rates
are not comparable from different geographic locations). During this
time, dentine is being deposited within the tooth, so if a tip chips
off, or the enamel is worn away, the crown remains supported. In wild
populations, the wear rates generally do not exceed the life of the
tooth. That is NOT the case in domesticated ferrets. During cage biting,
the rear of the canines get a lot of wear, which tends to rub through
the enamel and expose the dentine. Why is this bad? First, canines
behave like tubular supports; they are very resistant to stress
longitudinally (that is, down their length). However, they are weak
laterally (that is, perpendicular to the tooth). It is sort of like a
cardboard tube which supports your weight if you stand on the end, but
crushes if you stand on the middle. Cage biting causes a lot of lateral
stress, which creates microfractures in the enamel and—over time—weakens
the tooth and promotes a catastrophic fracture. Second, anytime material
is removed from the side of the tooth, you weaken it at that point. This
type of fracture can usually be distinguished from broken teeth
resulting from falls in that the tooth will usually have worn areas
where the wire abraded the enamel, and the fracture is more-or-less
snapped straight across the dentine. Between the loss of enamel and the
microfractures, it is a miracle ferrets don't fracture more canine
teeth. There isn't a lot you can do about the microfracturing, but
plastic coated wire on the cages tend to reduce the abrasion. The best
solution is to increase the out-of-cage time. If that isn't possible,
consider building a larger cage, or covering the wide mesh with window
screening (from the inside). Ferrets who bite cages tend to do it most
of their lives, and it may have nothing to do with housing conditions.
Chrys is a free-roaming, late-alter male ferret who broke the left upper
canine as a juvenile, while cage biting. He has lived as a free-roamer
for the last five years, yet a couple of weeks ago, when caged for a
trip to the vet, he immediately started cage biting as if not a single
day had passed.

Cloth or toy chewing also results in a great deal of wear on the tooth,
especially in the canines and incisors. This type of wear is generally
from the biting surface towards the apex, or on the vestibular side of
the tooth. It can be on one side of the jaw only; ferrets, like people,
can favor one side of their mouth. This is a hard habit to break because
many ferrets are obsessive chewers. If this trait is a neurotic behavior
or just an extension of chewing instincts is unknown. However, I have
recorded several instances where I have found severe dental calculi on
the teeth, which were obviously worn by chewing cloth objects. It MAY be
that ferrets start obsessively chewing cloth when their gums are
irritated. However, it could be just as likely to result from dietary
imbalances, or just be neurotic behavior. I have had a couple of ferrets
that were adopted when they were older, who were cloth chewers. You
could hear Sam Luc chew terry cloth from across the room. However, when
I started giving the my ferrets bones, well-hydrated cartilage, and
tough meats to chew, they slowly stopped the behavior and started
chewing things less destructive to their teeth.

Wear Rates and the Influence of Diet

Ferret teeth are designed to render animal flesh into small pieces that
the ferret can swallow whole (= bolt). Ferrets have small, diminished
molars, but they are not designed to masticate; rather, they are used
like pliers or nutcrackers to crunch hard objects in the diet, such as
crawfish, snail shells or insects. Indeed, the ferret cannot masticate.
First, the teeth are formed into cutting blades which cannot grind food,
and second, the way the jaw is hinged to the skull allows an
opening/closing motion only. The result is, ferrets simply cannot chew
their food; they cut it into small chunks and swallow them whole. With
muscle tissue, this isn't a problem; the ferret simple cuts off a chuck
using their carnassial cutting teeth, then they bolt it. But what
happens when a ferret eats a hard dry piece of extruded food? The same
thing; they use their cutting carnassials to break the kibble into
pieces small enough to swallow. The problem is, most extruded foods are
significantly harder than muscle tissue.

The result to the teeth is devastating. The enamel on the carnassials
rapidly wears away, leaving the dentine portion exposed. This is pretty
hard, but not as hard as the enamel, so it wears away even faster. I
have seen carnassials, the large cheek teeth shaped like the blades of a
pairs of scissors, worn down as flat as molars. Abscessing is common,
and periodontal disease rampant. Ironically, the use of hard foods has
been long promoted for gingival health; the hard particles are supposed
to keep tartar under control. However, in ferrets, the result are teeth
worn down two or three times as fast (or more!) as the dentition in wild ferrets.

There is no real cure. If you get the dry food wet, the cooked
carbohydrates simply turn to mush and you run the risk of tartar.
However, feeding a softer diet isn't so bad if you also supply nature's
dental floss; the tough connective tissue that holds muscles together.
The parts of your steak that you trim and toss away are perfect for
gnawing, and result in clean teeth. You can also offer commercially
prepared chewing objects, such as chewweasels, or or boiled rawhide (it
MUST be boiled until it remains soft and pliable). Chicken backs, necks,
and beef ribs are very good at cleaning teeth; they have the additional
benefit of being a nutritious snack for the ferret.

Eruption Sequence, Deciduous Teeth:

Jaw: Tooth: Eruption (days after birth):

Maxilla i1 Embedded; does not normally erupt
Mandible i1 Embedded; does not normally erupt
Maxilla i2 Embedded; does not normally erupt
Mandible i2 Embedded; does not normally erupt
Maxilla i3 Embedded; does not normally erupt
Mandible i3 Embedded; does not normally erupt
Maxilla i4 0 to 3
Maxilla c1 20
Mandible c1 20
Maxilla pm3 20
Mandible pm3 20
Maxilla pm4 20
Mandible pm4 20
Maxilla pm2 28
Mandible pm2 28

Eruption Sequence, Permanent teeth:

Jaw: Tooth: Eruption (days after birth):

Maxilla I1 46
Mandible I1 46
Maxilla I2 46
Mandible I2 46
Maxilla C1 50
Mandible C1 50
Mandible M1 50
Maxilla M1 53
Maxilla I3 54
Maxilla PM2 60
Mandible PM2 60
Maxilla PM3 60
Maxilla PM4 60
Mandible PM3 67
Mandible I3 68
Mandible PM4 74
Mandible M2 74

Bob C