Dentes molares:
 
Grasping that ferrets are obligate, primary carnivores, that is, mammals
that primarily eat animal prey and are physiologically required to do so in
order to survive, it might seem incongruous that after millions of years of
evolution they would still possess molars.  For example, many felids have
lost their molars, and in many instances, cats are not as carnivorous as
ferrets (or rather, their polecat progenitors).  It is precisely because
ferrets are obligate, primary carnivores that they retain their molars;
they are an important aspect of the dental apparatus used to render animal
flesh, and are not designed to grind food.
 
Ferrets have two upper and four lower molars.  The 1st maxillary molar
(= M1/, upper molar, maxillary grinder, cheek tooth) is turned roughly
perpendicular to the rest of the dental arcade, and is reduced compared to
the rest of the dentition.  It is essentially shaped like an irregular oval
with a slightly pinched "waist." The portion nearest the vestibular surface
(= buccal surface) supports a pair of cone-like cusps, with the lingual
portion flatter and having a slightly raised rim.  The 1st mandibular molar
(= M/1, lower first molar, sectorial tooth; carnassial, cheek tooth) is
modified into the lower carnassial.  The blade is divided into two points
separated by a deep notch.  The distal portion of the carnassial is
flattened into a ledge, supporting a cusp that is aligned with the medial
portion of the maxillary molar.  The 2nd mandibular molar (= M/2, lower
second molar, cheek tooth, grinder) is greatly reduced; even in large males
it is usually only about an eighth of an inch in diameter.  The molar is
roughly shaped like the head of a pin, with a single cone-like cusp on top.
The 2nd mandibular molar sits directly behind the lower carnassial, and
aligns with the distal part of the upper molar.
 
The cone-like cusps of the upper and lower molars are offset to each other,
so they line up like the serrated jaws in a pair of pliers.  However, the
teeth are not designed to grip, nor are they designed to grind.  Rather,
they are designed to be a miniature anvil and hammer, perfect for crushing
small bones, hard insect and crustacean exoskeletons, snail shells, and
other hard objects that may contain nourishment the ferret is obliged to
obtain.  This is accomplished elegantly by ferrets, which use extreme
biomechanical force to drive the small point of a cusp into the material,
shattering it in the same general location as being sheared by the
carnassial.  As the ferret slices the flesh and impacts a bone, it will
slide down the blade of the carnassial and come to rest against the cusps
on the molars.  The molar cusps stabilize the bone, preventing it from
moving as the pointed cusp of the upper molar is driven into the surface
by the powerful jaw muscles.  This occurs in the rear of the jaw, where
the biomechanical forces are the greatest.  Small long bones, such as
those found in frogs, birds, rodents and rabbits, are shattered into tiny
fragments that remain imbedded in surrounding tissue, and are safely
swallowed.
 
In wild polecats, the molars will exhibit moderate wear, with the cusps
losing their points in older animals.  In contrast, this is not the case in
pet ferrets fed dry kibbled or extruded foods.  Dry foods cause extensive
wear to the molars for three basic reasons; the foods are very hard, they
are solid rather than being essentially hollow, and they are not cushioned
from direct impact with the teeth.  Dry foods are guaranteed to be 10%
moisture or less, which is instrumental in the creation of a hard, crunchy
food that can remain in the bowl for days without worry of purification.
There is no question that some of the foods consumed by wild polecats are
harder than these dried foods; nonetheless, it is also true that few of
those hard foods become the single component of a life-long diet.  Part
of the problem is that ferret teeth never evolved the strength to consume
a hard diet for long periods of time; the enamel shell surrounding the
dentine core is rather thin.  This is exacerbated by two other factors.
First, the hard foods wild polecats may consume are essentially hollow;
that is, they are composed of a hard shell surrounding a softer interior,
such as bones, insects, and snails.  When the jaws apply pressure, the bone
(or exoskeleton) collapses inwardly, which results in less wear than caused
by crunching a solid food pellet possessing "homogenized hardness."  The
problem is exacerbated by a lack of cushioning, such as when muscle and
connective tissue surrounds a bone.
 
For the zooarchaeologist, the result is that it is a simple task to
differentiate between wild polecats and pet ferrets, based wholly on the
wear to the molars.  In pet ferrets, the maxillary molar is brutally
impacted by commercially manufactured dried foods, and is severely worn by
the time the ferret is three or four years old.  Few ferrets older than
four years of age retain cusps on their molars; indeed, it is quite common
for the crowns to be completely worn away, exposing the internal dentine
structure.  In many cases, the maxillary molar is so worn that the tooth
breaks at the "waist", or even to the point that the only remaining
portions of the molar are the exposed roots.  This is also seen in the 2nd
mandibular molar, which is so commonly worn to the roots that in many pet
ferret skulls, all that can be seen is the rod-like root, sticking out of
the jawbone to the level of the gum line.  In all of the black-footed
ferret, steppe and European polecat, New Zealand feral ferret, and pet
domesticated ferret skulls I have examined, this type of extreme wear is
only found in pets fed hard commercial foods.
 
Molars are also subject to gingival and periodontal disorders, and the
2nd mandibular molar is frequently lost as a result.  Occasionally, a 2nd
mandibular molar will become impacted, that is, it cannot normally erupt
because of overlying bone or an adjacent tooth, but this is relatively
infrequent.  With extreme wear comes microfractures, which provide access
points for the bacteria which cause caries; not uncommonly found in the
molars.  On occasion, the molars will be malformed.  This is especially
true in the maxillary molars, which can exhibit a wide range of morphology.
On very rare occasions, the maxillary molar will be lost; a condition more
commonly seen in the case of the 2nd mandibular molar.
 
Adult ferrets have a total of six molars; two each in the maxillary
quadrants, and one each in the mandibular quadrants.  Dentes molares
(= M, m, molar, grinder, cheek tooth, posterior tooth, postcanine tooth,
grinding tooth, sectorial tooth, carnassial)
[Posted in FML issue 3519]