Contrary to myth, canines are not typically used for eating; watch your
ferret eat kibble and you will notice the food is processed with the
cheek teeth.  Polecats use canines to pull meat from bones, or to carry
food or prey, but they use the cheek teeth to process it.  If you see a
broken canine in a pet ferret, it is extremely doubtful it was broken
when eating bone simply because it is not used to eat kibble OR bone.
When killing prey, polecat canines are typically thrust through the
skull or vertebrae, and in fulfilling that function, they are rarely
damaged.  They are designed to pierce the bones of the skull and
vertebral column like the hardened tip of a spear through armor.
Canines are not typically broken by pressure along the longitudinal axis.
Rather, like long bones, pressure perpendicular to the length of the
tooth is the real danger (falls are an exception, where the energy load
exceeds design parameters).  What this means is that the canines are
designed to impact bones of a size found in animals that polecats evolved
eating (rabbit-sized and smaller), but are NOT designed to resist the
lateral pressure from a ferret tugging at the steel bars of a cage.
Tugging on cage bars, even if covered in plastic, creates a series of
microfractures and cracks, and wears away the enamel, reducing overall
tooth strength.  Over several years, the canine develops a series of
exfoliations, cracks and splits in the enamel, severely weakening the
tooth.  As discussed earlier, weakened teeth break, and if it happens
when a bone is being chewed, well, no one blames the years the ferret
spent tugging at the cage.
 
The teeth that are at risk from eating bone are the carnassials (cheek
teeth), used to slice and crush various tissues.  The upper carnassial
is a sharp-edged saw-toothed shaped tooth that slides against the lower
carnassial with a fit so close that it cuts tissue like poultry scissors.
The carnassials are almost solid dentine and enamel, with only a small
pulp chamber and root canal.  Dentine and enamel are made of the same
stuff used in bone construction--hydroxyapatite.  However, teeth contain
less moisture than bone, and the minerals are laid down in very compact
prisms.  Thus, teeth are actually harder than the bones their owners
evolved eating.  In short, a ferret's teeth are designed to chop up the
bones contained within the bodies of the animals the polecat progenitor
evolved eating.
 
Here is a question you should intuitively be able to answer.  What
happens when a ferret bites down on a piece of bone that is harder than
expected?  Well, what happens when you bite down on a hard bit of bone?
It hurts!  You stop chewing, and spit the chunk of bone out of your
mouth.  Ferrets do the same thing; they are not mindless automatons that
continue to chew through pain.  If the ferret's tooth breaks when eating
bone, chances are it was already damaged.  You can bet the ferret,
ignoring sudden and severe pain, didn't insist on plunging their teeth
through unyielding bone until they fractured.
 
Have you ever had grease-stained hands and used a pumice soap to cleanse
them?  Trabecular bone serves the same function in carnivores.  The tiny
spicules of bone that form the trabeculae rub the teeth, scrubbing off
layers of saliva, food particles, and bacteria that calcify into plaque.
This effectively eliminates buildups that turn into dental tartar, or
calculus.  Moreover, the tiny particles of bone actually polish the
tooth, helping to smooth out those rough areas that are the footholds of
caries-causing bacteria.  Colyer found that only 2% of wild carnivores
eating a natural diet had significant deposits of plaque or calculus.
Ferrets have problems with plaque because the carbohydrates in modern
ferret foods react with saliva, providing a great deal of sugary food for
oral bacteria, as well as supplying a matrix supporting calcification.
Trabecular bone in the diet not only scrubs off the offending white
matter, but it also polishes the tooth by smoothing cracks and fissures,
making it harder for soft foods to stick to the enamel.
 
Dry, extruded foods are advertised to serve a similar function, but there
are at least four important differences.  First, kibbles are composed of
a significant amounts of starch, so even though the crunchy nature of the
food is advertised to scrape off plaque, it also supplies the building
material for new problems.  This is why ferrets that eat nothing but
kibble still have problems with plaque.  Second, the particle size of
dry foods is larger than most of the spicules making up trabecular bone,
increasing the abrasiveness of the dry food.  The teeth of ferrets that
eat nothing but dry, extruded food have extremely worn teeth (dental
abrasion); any carpenter knows 60-grit sandpaper is used to remove
material, while 400-grit sandpaper is used for smoothing and polish.
Third, because the particle size is larger, the "polishing" scratches
are larger as well, giving bacteria--and plaque--more places to stick.
Dental technicians are well aware that after teeth are mechanically
scraped of plaque, it is very important to follow up with a good
polishing.  Last, and most important, it is a myth that kibble cleans
teeth; studies have shown then chewed, kibble breaks apart and falls
away, only cleaning those immediate areas that come into direct contact
with the food; that is, the tips of the tooth crowns.  Even "dental"
diets do a poor job of cleaning teeth and require brushing for good
results.
 
Bob C
[Posted in FML issue 4158]