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]