North American pet ferrets with worn teeth  =  85.2%.
Feral New Zealand ferrets with worn teeth   =   2.3%.
Wild polecats (all combined) with worn teeth = 75.0%.
92.5% of all animals with worn teeth were pet ferrets.
 
North American pet ferrets with cage bite wear =  23.8%.
Feral New Zealand ferrets with cage bite wear =    0.0%.
Wild polecats (all combined) with cage bite wear = 0.0%.
100% of all animals with cage bite wear were pet ferrets.
 
From the moment the crown of a tooth erupts through the gumline (the
gingiva), it is exposed to an environment determined to wear it down.
This happens for a number of reasons, including (but not limited to)
teeth coming into contact with each other during chewing, tooth grinding
(pathological or behavioral), the abrasive quality of the food, the
hardness of the food, the abrasion of fur and foreign objects from
carnivory and grooming, water or air-borne environmental dirt and dust,
and object chewing (towels, toys, bones, Cheweasels, sticks, whatever).
Some ferrets, like humans, favor one side of the mouth for chewing, so
wear will be more pronounced on that side compared to the other.  In
zooarchaeology, dental wear is termed attrition and it subsumes all
factors that wear down teeth.  To differentiate different types of
attrition, I use the phrase dental attrition to describe natural tooth
wear; that is, the type of wear seen in wild populations whatever the
cause.  I use the phrase cage bite wear to describe the type of wear
caused from long-term cage biting and pulling in an attempt to escape.
I use the phrase dental abrasion to describe the type of wear caused by
eating a processed kibble diet, which is easily distinguished from the
wear seen in wild polecats and feral New Zealand ferrets that eat a wild
diet.
 
Cage bite wear is quite distinctive and is generally limited to the
canines and front premolars.  When the wear occurs to the canines it
removes enamel and dentine from the rear of the tooth and will actually
notch the canine, greatly weakening it.  When the wear occurs to the
front premolar, it is worn from the top and front, wearing down to the
roots, fracturing the tooth and causing it to be lost.  87.4% of the time
that I recorded a lost first premolar, the ferret also had obvious cage
bite wear to the canines.
 
Dental attrition, the wear normally seen in wild populations of polecats
and feral New Zealand ferrets, results in predictable wear facets on the
teeth and can be distinguished from all other types of chewing wear
based wholly on the angle and position of the wear facets.  As the upper
carnassial slides down over the lower one, the edges of the teeth strike
one another, forming a wear facet that extends from the top of the tooth
downwards at a steep angle.  This type of wear results in self-sharpening
teeth that slowly wear away in a cheek-to-tongue direction (buccolingual
wear).
 
In pet ferrets, a hard kibble diet causes dental abrasion that is
distinguishable from other types of attrition because the wear facets are
not at an angle, but are generally parallel to the plane of the mouth
(dorsoventral wear).  The kibble wears away the top of the crown, causing
a wear facet to form across the apex of the tooth.  Sometimes this wear
facet is distinctive, other times not so distinct, but it is always on
top of the tooth and is not seen in wild animals.  This type of attrition
is caused by the abrasive qualities of the hard kibble.  The wear occurs
at a much faster rate than the type of attrition caused from eating a
wild-type diet; my estimates indicate the increased rate of dental wear
is 3 to 4 times faster.  For those that can t believe kibble will
actually damage a ferret s teeth, they should talk to owners of dogs that
habitually chew tennis balls.  Something as pliable as a tennis ball will
wear the tops of a dog s teeth as flat as if it was done with a file.
Kibble is a lot harder than a tennis ball, ferrets eat it all the time,
and it likewise files down the tops of the teeth.
 
The wild polecat statistics offered are somewhat misleading; the numbers
are skewed because of the age of specimens in the sample; all were older
individuals that would naturally display more dental wear.  A larger
sample should place the wear between that for the feral New Zealand
ferret numbers (2.3%) and those for small mammals in general (4 to 6%).
Nonetheless, while the numbers are inflated, the wear facets are
distinctive of a wild population.  In contrast, statistical analysis
shows the numbers for the pet ferret population to be valid.  85.2% of
pet ferrets displayed significant dental wear, ALL classified as dental
abrasion; that is, flattened teeth caused by eating a kibbled diet.
 
Dental abrasion is a type of abnormal wear; it is not found in wild
populations, and it subjects teeth to wear and stresses the tooth was
not designed to bear.  What this type of wear does to the teeth has
significant consequences to the long-term health of the ferret s mouth.
The most profound problem is that the wear to the teeth is at a faster
rate than the teeth are designed to absorb.  This is especially noted
in the ferret s small molariform teeth, which frequently wear down to
the roots and fracture, causing them to be lost.  In ferrets, molars
do not come into contact with each other during chewing they are always
separated by a couple of millimeters or so (they are designed for
cracking objects, NOT for grinding).  As the carnassials wear down, the
molars start coming into contact with each other, greatly increasing the
physical forces normally placed on the teeth, intensifying wear rates and
micro-fractures that reduce tooth lifespan.  As the enamel crown is worn
away, the dentine is exposed.  Dentine is softer than enamel and, once
exposed, the rate of tooth wear significantly increases.  This is why
ferrets that don t appear to have dental problems can suddenly have
severe oral pathology within a relatively short period of time, requiring
significant professional intervention.
 
The idea that kibble helps keep a ferret s teeth clean is a myth; as
already discussed, dental calculus and periodontal disease are rampant in
ferrets eating nothing but kibble.  It doesn t clean the teeth because it
primarily impacts the contact surfaces and not the entire tooth.  That is
why teeth wear down so quickly compared to a wild diet: extremely hard
pieces of food are continuously impacting a single tiny point on a small
tooth.  This can actually be factored as a mathematical equation that
predicts the rate of wear for any particular brand of kibble based simply
on hardness and abrasive quality; it is not an illusion; it is a
mathematical certainty.
[Posted in FML issue 4519]