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
[Posted in FML issue 3509]
|
