North American pet ferrets with fractured teeth = 30.0%.
Feral New Zealand ferrets with fractured teeth = 4.6%.
Wild polecats (all combined) with fractured teeth = 0.0%.
93.8% of all animals with fractured teeth were pet ferrets.
 
There are several ways you can identify and count a fractured tooth
depending on the degree and position of fracture, if the fracture extends
through the tooth, if it is a slab fracture, or if it is a crack, chip,
or spall.  Most fractures in ferret teeth do not extend entirely through
the tooth, but are instead are cracks into or through the enamel, chipped
tips of canines and premolars, and various degrees of spalled enamel.
Sometimes a fractured tooth is the result of extreme dental wear
(attrition) which has weakened the tooth until it fractures, usually
between the roots.  If the tooth has been shattered and the damage was
not caused by diet-mediated wear, it nearly always was a canine tooth.
A few canine teeth had large slab fractures, probably the result of a
high-energy impact, such as from a fall or accidental kick, or perhaps
from cage biting.  In the majority of carnivores, slab fractures are most
commonly seen in the carnassials, but in mustelids they generally involve
the canines.  Slab fractures occur when a portion of the crown breaks off
the tooth, removing a large portion of enamel and exposing the dentine;
occasionally the pulp chamber is involved.  Sometimes the fragment
extends under the gums, involving the roots.  It is called a slab
fracture because the fragment looks like a slab of tooth.  In this study
the pulp chamber was never exposed in ferret canines with slab fractures,
but a large area in the front of the tooth was damaged.
 
Interestingly, not a single slab fracture to a cheek tooth was seen in
the entire study, including bone-eating polecats and feral New Zealand
ferrets.  This is important because some vets suggest the type of slab
fractures seen in carnassials from dogs that chew bones will occur to
ferrets if also allowed to chew bone; these data suggest ferrets are not
dogs.  This finding doesn t exclude the possibility that a slab fracture
will happen to a ferret s carnassial, it simply means it is a very rare
event and wasn t sampled.  I feel a slab fracture can occur to a ferret s
carnassial under the right circumstances, especially one that displays
extreme wear.  There is a point where the dentine wears faster than the
surrounding enamel and shallow dish-like shape forms in the crown.  In
these heavily worn teeth, pressure on the enamel portions could
potentially cause slab fractures from ANY reason.
 
Generally speaking, one of the reasons dogs frequently suffer from slab
fractures in their carnassials and ferrets generally don t is situated in
the biomechanics of their jaw attachments.  Dog jaws have a comparatively
short temporal-mandibular joint (TMJ) seated in a short groove, but the
TMJ in ferrets is comparatively quite large, and is seated in a deep,
long groove that essentially locks it into place.  When a dog bites a
hard object with a lot of force, the lower jaw can slightly dislocate
and slip to one side, producing lateral forces that can chip off a slab
of tooth in a fashion similar to chipping off flakes of obsidian to make
an arrowhead.  Tooth enamel and dentine, like bone, are bioceramics; they
are governed by the same rules of physics that apply to fracturing glass
and stone, and they break in exactly the same manner.
 
In contrast, ferret jaws are locked into place and the force required to
cause the jaw to slip laterally is generally greater than is needed to
fracture the TMJ and dislocate the jaw (ferret jaw dislocations are very
rare compared to other carnivores, and generally are the result of some
type of damage to the TMJ).  The point is that a slab fracture requires
lateral force applied to the top AND side of the tooth exactly the same
type of lateral force applied to the edge of a stone to remove a flake,
or slab.  Because a ferret s jaw is constructed to prevent that sideways
force, it is rare for their carnassials to break in that manner.  There
were a couple of cases in this study where one of the points of a
carnassial was spalled (the enamel flaked off, but little damage to the
underlying dentine), but in those instances other teeth displayed
fractures that suggested the damage was due to a fall or other trauma.
 
Pet ferrets have a tooth fracture rate of 30.0%, significantly greater
than rates seen in feral New Zealand ferrets, wild polecats, or even the
averaged rate for mammals in general.  In one four-year-long British
study of 350 ferrets, the fracture rate was 0.9%.  Feral New Zealand
ferrets had a tooth fracture rate of 4.6%, which is roughly the average
from several studies of small carnivores (fracture rates varied from 2%
to 12%), but the rate may have been artificially inflated by the methods
used for trapping and killing.  A British study of otters had a 19% rate
of both fractured and missing teeth (the two values were lumped together
because the researchers were collecting data from necropsies, not from
cleaned skeletons), with a carnassial fracture rate of 2.5%.  Wild felids
were found in a study of skeletons to have a dental fracture rate of 15%
to 24% and 29% of wolves in the same study had fractured teeth.  For
quite a long time it was thought that large animals that ate large prey
had higher tooth breakage rates than small animals that ate smaller prey.
The idea was that the struggle with larger prey opened the carnivore to
a greater risk of injury.  This idea has been mostly falsified in recent
years when it was realized the risk of having a broken tooth was better
correlated to age.  This hypothesis suggests the older the animal, the
more accumulated damage to the teeth hence the higher fracture rates.  In
this study, dental fractures were correlated with age, meaning that the
longer a ferret lives, the more dental problems are seen.  If injury is
accumulative, as is currently the accepted paradigm, then sidetracking
damage will reduce the long-term destruction of teeth.  This is exactly
what is done when you initiate a daily tooth-brushing regime with yearly
tooth cleaning.
[Posted in FML issue 4520]