Bob Church’s Article on Why Kibble Destroys Teeth

Why Kibble Destroys Teeth

By Bob Church


Google Doc Version

This article was written in regards to ferrets, but applies exactly to skunks also.

Q: “I can’t understand why if cats and dogs can eat kibble without hurting their teeth, ferrets can’t. Can you answer why or why not?”

A: Ferrets are not cats, nor are they dogs, and every vet that makes that assumption will ultimately come to rue the decision. It is a remarkable thing that people can accept the huge leap that a ferret’s physiology is different enough from a cat or a dog to make elements of their vet care unique, but still cannot make the short tippy-toe that a ferret’s dietary physiology can be subtly different as well. It’s the equivalent of faith-based science: decide what you want to believe, find a few references to support it, and then dogmatically and energetically combat any critical inquiry suggesting a ferret’s diet needs improvement.

I would like to add that my critical appraisal of ferret food is not an effort to drive kibble makers out of business.

Far from it-using commercial foods is perhaps the only viable dietary resource available to most ferret owners. My only goal is to ultimately present such a strong argument and overwhelming evidence of kibble’s shortcomings that ferret owners will demand healthier foods made for a ferret’s specific and unique needs and kibble makers will listen and make them available. Ferrets deserve better food, made for THEM, not for us, nor for cats or dogs. And while this fight for a better food is sometimes perceived by some antagonists to be as dangerous as those looming windmills of days gone past, the real danger is in the misguided intentions of a number of Alonso Quijanos that populate various corners of the ferret world.

It doesn’t really matter if Don Quixote only had good intentions in his heart; what matters is the harm done to the innocents surrounding him. It is not enough to be able to show a food can meet a ferret’s basic nutritional requirements; it also MUST NOT DO HARM to the creature consuming it.

Specific Ways Kibble Harms Teeth:

1.) Scale is everything in the animal world. A human can trip on a crack in the sidewalk, fall, and break a limb, but a ferret can fall from a person’s shoulder, and just act like the invisible Dookie Monster is after them. The reason, extremely simplified, is in the relationships of mass, speed, and kinetic energy. Without making the attempt to elucidate physics without being able to refer to twenty 8x10s with circles and arrows and a paragraph on the back of each one that explains what it is, lets just say that ferrets have small mass, so in a fall they have smaller kinetic energy than big mass people. At the height of most shoulders, the kinetic energy produced in falling does not typically exceed the design load of a ferret’s musculoskeletal system, so ferrets can fall proportionately fantastic distances compared to a human, only to pop up to dook again. This is important, and not just to the ferret falling off the shoulder. The forces acting on teeth have a similar scaling effect. To imagine this effect in your mind, envision a lion, cat, and ferret consuming identical kibble. The kibble will wear away identical amounts of tooth enamel in all three species, all other factors being equal (they aren’t really, but for the sake of argument, assume they are). The difference is that a lion’s carnassial (the sectorial, or cutting tooth) is extremely thick and large compared to the one in a ferret, so it can lose a great deal of tooth enamel and dentine before the loss becomes a problem. Scale that piece of kibble so that it is as large to a lion’s tooth as a regular piece of kibble is to a ferret’s, and the wear rate will change, coming closer to the rate seen in our pets. If they all eat the same size of kibble, the wear rate will be lowest in the lions, followed by the cats, and then the ferrets. This allows predictability for “kibble-wear” for any size kibble and any species of animal. In the case of the cat and the ferret, because the kibble size is more or less identical, the wear rate depends on tooth size. In other words, because ferret teeth are smaller than cat teeth, the tooth wear rate is increased out of proportion, even though both species are consuming the same size of kibble.

2.) There is another factor that needs to be considered: the relationship of surface area to volume of the tooth. The larger the tooth, the more volume it has compared to surface area, which means small animals not only have smaller teeth, but also that those teeth have proportionately smaller volumes: they are “skinnier” or “thinner.” Simplistically, surface area equations are generally squared, while volume equations are generally cubed. A tooth is a lot like a Dove bar (ice cream covered by a hard chocolate shell) in that a thin shell of very hard enamel surrounds a softer interior of dentine. Because small teeth have smaller volumes, the amount of dentine within small teeth is proportionately less than that found in larger teeth. This means there is less tooth material (enamel AND dentine) to grind away in smaller teeth. Put simply, kibble grinds away ferret teeth at faster rates than in larger animals not simply because their teeth are smaller, but because they have proportionately less volume of dentine when compared to the teeth of larger carnivores.

3.) The direction of the crystals of enamel, called prisms, in ferret teeth is not designed to resist the forces of chewing kibble. Enamel prisms are more-or-less needle-shaped (the middle is wider than the ends) and oriented so they best resist the forces of mastication, which is diet specific. Generally speaking, this is along the axis of the prism, not against it. Think of your leg bone; jump off a three-foot wall and the femur will not break. Fall off the same wall and land on a stone that places the same kinetic energy at right angles to the bone rather than along it’s length (axis), and the femur snaps.

In the ferret’s teeth, chewing stress extends from the wear facet (the part of the tooth that is worn when eating) down and across the tooth towards the root and jawbone, and the enamel prisms are arranged along those angled mediolateral side-to-side) lines of force. However, when a ferret eats kibble, all bets are off. Kibble does not cut like meat. When meat is compressed by opposing cutting teeth, it compacts and severs as the teeth scissor through the tissue. Some tissue is dragged back and forth on the teeth, but the friction is slight and the wear rate is low. Of great importance to the teeth is that the tissue compresses during eating, which imparts little impact to the tooth, and in some cases can even act as a shock absorber to dental tissues. However, when kibble is eaten, it doesn’t compress-it fractures and drags across the tops of the carnassials. Ever pick up a piece of sanding foam? That is exactly what kibble is like in microscopic cross section because it is extruded under heat and pressure, which forms numerous tiny air bubbles in the biscuit. At the low moisture levels of kibble (less than 10%), the biscuit is turned into “sanding foam,” and as it is dragged across the carnassials, it sands off the top part of the tooth. This changes the chewing stress on the tooth from “angled mediolateral”, the way it should be (from the wear facet to the opposite lower edge of the tooth), to “dorsoventral,” that is, from the tops of the carnassials towards the roots. Besides placing unnatural stress on the tooth, it eventually shifts the striking platform, the part of the tooth that is struck by the opposing one, from the side edge of the tooth to the top–greatly dulling it. As long as the enamel covering the tooth remains intact, the prisms will tend to point towards the object being chewed, which is the direction in which they are the strongest. Because the rate of wear is greatly increased, the prisms on the top of the tooth eventually yield, and the softer dentine below is exposed. Worse, when the enamel prisms on the top of the teeth are gone, it only leaves the shell of enamel on the sides of the tooth, and the enamel prisms in that area are generally angled mediolateral. Enamel prisms are very strong along their length, but weak across it, so they fracture under the stress and are more easily ground away. This is why the rate of tooth wear increases over time; it is slow when the top of the tooth is intact, but increases rapidly once the top enamel is worn through, only leaving the side enamel.

4.) If you ever spend some time looking at the ferret’s cheek teeth, you will note that from the side they look like shark’s teeth, and from the top they look like pinking shears. The shape of each serration in the side view (shark tooth view) of the cheek teeth approximates a pointed or gothic arch, one of the most stable of architectural forms. Bite forces are transferred from the cutting edge of the tooth, down the arch, and into the roots and jaw of the ferret. From the top of the tooth row, the “pinking-shears” side approximates a pointed arch, and the opposite side approximates a Roman arch–perhaps even more stable. In fact, if you really study the form of teeth, entire or in part and regardless of species, you will see they generally fall into one of six basic types of arches seen in both ancient and modern architecture. This is because the forces of mastication are very powerful, and arches are simple, elegant, and effectively transfer those forces down into the roots and jaws of the animal, or are dissipated throughout the tooth, rather in a single spot. These tooth designs have been tweaked by natural selection for millions upon millions of years, and are highly specialized biomechanical structures designed to do a specific job — to cut the flesh and bones of prey animals. In fact, while teeth are specific to genus and species, tooth components–the cones, arches, and root architecture–are so effective, there has been little change in the basic design for scores of millions of years. The ferret’s canines are “design duplicates” of jaw teeth in the T-rex, and the design of their cheek teeth can be found in early sharks; there is no such thing as copyright in tooth design. When a ferret cuts meat, the wear is primarily restricted to the cutting facets. When a ferret masticates kibble, the wear is generally confined to the tops of the teeth. As the tops of the teeth are worn away in ferrets that eat kibble, the arch structure is disrupted, changing how stress is distributed within the tooth. This may result in faster rates of wear, stress micro-fractures, or even catastrophic failure of the tooth. The stress is generally poorly conducted down worn teeth, which could result in inflammation of the periodontal ligament that holds the tooth in the jaw, reactive changes in the bone forming the socket, or even ultimately the loss of the tooth.

5.) Kibble is a hard substance, so ferrets chew it in a predictable manner on specific teeth. This makes tooth wear predictable. In the top jaw, the molar is the tooth in the very rear of the mouth; the one that looks like it was twisted sideways (called the first maxillary molar). When newly erupted, this tooth looks similar to a brassiere–two pointed cones connected with a narrow waist. In the lower jaw, the molar is a tooth that, in side view, looks like the head of a straight pin, topped with a very small cone (called the second mandibular molar). On the rear of the carnassial, or cutting tooth (called the first mandibular molar), abutting the second molar is a short, flat area topped with a small cone. These two cones are similar in size and shape to the cones on the upper molar, but are turned 90 degrees from the top ones. When the jaw closes, the cones on the upper molar and lower teeth interlock, but do not come into contact with one other. They come close, but are separated by a few millimeters. It doesn’t take a “socket scientist” to realize the orientation and spacing of the cones converts the rear of the jaw into a “nut cracker.” This is the part of the jaw used to break bones, crack insect carapaces, and otherwise fracture small hard objects like snail shells. The majority of ferrets use this part of the jaw, he “cracking teeth,” to render kibble into small enough fragments to swallow. The problem is, these teeth are small because they are not designed for grinding, but rather for cracking, and so are used infrequently when consuming a natural diet. What happens with pet ferrets is that they tend to crack the kibble on the back teeth until they are worn down to a point where they become sensitive to pressure, and then the ferrets transfer the task to the carnassials. Even so, the cracking teeth continue to wear down, and it is not unusual to find these teeth worn down to the roots, broken in half, or completely lost. These teeth are simply not structurally designed to process a food as abrasive as kibble. After transferring the bulk of the chewing to the carnassials, they also begin to wear down and become sensitive to pressure. At this point, the ferret may be 4 to 6 years old, and they start using the premolars in front of the carnassial to help masticate the kibble. These teeth are extremely small, and are designed for holding and ripping tissue, not crushing abrasive biscuits. They wear down very rapidly, and it is not unusual to find only the tops of the roots protruding from the recessed gums. At this point, the carnassials are the only teeth left to do the job, and they are used until the ferret dies. It is not an infrequent observation to see the carnassials ground down to just above or at the gum level in older ferrets.

Specific Findings of the Study:

People may recall some years ago I solicited donations of ferret foods from all over the world. I measured the hardness, brittleness, and abrasiveness of the foods on scientific devices designed for the purpose. The data startled me; ALL kibbles were roughly equal in all three qualities, and any differences could be explained by storage and handling conditions. I was prompted to look into the issue because I had noticed a profound difference in tooth wear rates between kibble-eating ferrets and those on a natural diet. There is nothing like getting your buttocks smacked with a 2×4 to get your attention, so I started a long-term investigation of the connection between kibble and worn teeth. I couldn’t ethically release my findings on the kibble until I knew what it did to a ferret’s teeth, so even though I asked for the kibble years ago, I am only now feeling confident enough to discuss my findings in the open. In fact, I am now so secure in those findings that I am willing to provide the FML with a synopsis of my conclusions. Mind you, I could write several dozen detailed posts explaining point by point why my investigation is valid, but I will spare you that exercise and just tell you what I concluded.

a.) ALL kibbles have a combination of hardness, brittleness, and abrasiveness that increases the rate of tooth wear between 3 to 5 times faster than seen in pet ferrets consuming a natural diet, polecats, black-footed ferrets, or New Zealand feral ferrets. In practical terms, this means a 3-year-old ferret may have as much tooth wear, or more, as a 9 or 10-year-old ferret eating a natural diet.

b.) The tooth wear caused by kibble is not “normal wear sped-up.” Normal tooth wear in a ferret’s carnassial is from the cutting facet towards the opposite, lower part of the tooth (angled mediolateral). This type of wear is actually a self- harpening feature of the tooth, so that even though the tooth is worn, it maintains a sharp cutting edge. Because kibble is an unyielding substance, it erodes the top part of the tooth, which shifts the angle of the cutting facet, making the edge blunter, rounder, and more like the grinding tooth of an omnivore.

c.) Tooth wear damage was not of a linear type that can be graphed like a straight line. Rather, wear rates were initially slow to a point (about 2 to 4 years of age), and then they rapidly increased. Inspection of the teeth provided the answer:

the initial slow rate was correlated to the time it took for the surface enamel on the top of the tooth to be worn away, and the increase in rate occurred when the softer dentine core of the tooth was exposed. In practical terms, this means the teeth look more-or-less normal for a couple of years, and then they suddenly seem to wear away at a much faster rate. Kibble causes an “s-curve” type of dental wear: initially slow, it rapidly increases as the dentine is exposed, and then slows down as the tooth is worn to the gum line.

d.) There is zero evidence that consuming a kibble diet will keep the teeth of ferrets clean. In fact, the opposite was found to be true; most ferrets consuming kibble had as much dental tartar, or more, as those consuming a wet diet (wet cat food, chicken baby food, a/d, etc.). Pet ferrets consuming a natural diet, polecats, black-footed ferrets, and New Zealand feral ferrets had very little dental tartar. This correlation is not hypothetical, nor is it theoretical; it is observational. It is simply laying the skulls on the table and counting the ones with dental tartar, and then checking back to see which animal ate kibble and which ate a natural diet.

e.) The only aspect of the tooth that hard kibble actually cleans are the parts that come into contact with the food. In a large animal with a broad tooth, this may result in limited cosmetic scouring of parts of the sides of the teeth, but it results in little gumline or below gumline cleaning–the place where cleaning is important. In an animal with a narrow tooth, such as the ferret, the amount of plaque removed from the tooth by kibble is minor and mostly relegated to the biting surface.

f.) I have developed a way of roughly assessing age in pet ferrets based simply on dental wear caused by kibble. In all ferrets, tooth wear is greatest in the back of the jaw, where a ferret attempts to use their tiny molars to crack the kibble. If the wear is primarily seen on the rear teeth, the ferret is between 1 and 3 years of age. The wear then progresses to the carnassials, when the ferret is between 2 and 5 years of age. Between 3 1/2 and 6 years of age, significant wear is seen on the premolars. After 6 years of age, the carnassials begin to be significantly worn, and tooth loss, mostly molars and incisors, is common. From 6 to 10 years of age, the tops of what were once serrated teeth are now flattened like the grinding teeth of small rodents.

g.) Once I correlated dental disease and tooth wear to age at death, I found that if a ferret had significant dental problems by 4 years of age, the chances were 92% that they would die at about 6 years of age (+/- 1 year). In these ferrets, the most common reported cause of death reported by donators were “cause of death unknown” or lymphoma, but based on gross necropsy, nearly half clearly died from cardiac and gastrointestinal disease. In the relatively few instances where vets did a necropsy, there was not a single mention of the condition of the oral cavity, or it’s possible impact on the health (or death of the ferret. Cardiomyopathy was the most common cardiac problem I noticed, and gastric ulceration the most common GI problem (presumably caused by Helicobacter infections).

h.) These conclusions are based on more than 300 donated ferrets randomly collected throughout the USA, and compared to more than 600 pet ferrets consuming a natural diet, New Zealand feral ferrets, black-footed ferrets, and polecats. A number of the polecats, black-footed ferrets, and New Zealand feral ferret skeletons inspected were captive animals that consumed a kibble diet, and their dental problems approximated or matched those of the pet ferret population. This is clearly a problem of diet.

i.) The prevalence of tartar and periodontal disease in pet ferrets is not related to consuming any one food, but to a lack of consuming whole prey. While dental tartar existed in animals eating whole prey, the percentage was extremely insignificant compared to ferrets eating kibble or cooked foods. There was no significant difference in the prevalence of periodontal disease in ferrets consuming kibble compared to wet, cooked, or soft foods, although the severity of disease was higher in ferrets only consuming kibble. Ferrets that ate wet, cooked, or soft foods that were also allowed to eat whole adult mice 3 to 4 times a week, had periodontal disease at a slight-to-moderately increased rate compared to animals consuming a whole-prey diet.

j.) Based on all available evidence and the vast majority of reported research, the conclusion is that a kibble diet results in significantly increased dental wear rates and tooth destruction that negatively impacts the oral health of the ferret, and probably negatively impacts the ferret’s overall heath. While there has been little published research to link dental disease to bone and other systemic nfections, liver, gallbladder, kidney, gastrointestinal, or cardiovascular disease in ferrets, such links are commonly found across a large spectrum of mammalian carnivores, and the probability that such links will be found in ferrets is extremely high. Combined with the prevalence of periodontal disease caused by a lack of consumable whole prey and exacerbated by kibble, there is little doubt the damage caused by a kibble diet negatively impacts the health of nearly all American ferrets. All that remains is to quantify that damage.

Final Remarks:

One of the most frequent questions I get regarding diet is, “Why has my older ferret become anorexic?” Now you know a major reason. I just roll my eyes when I read the hysteria on rare ferret medical disorders that harm perhaps one or two ferrets out of a million, or even a hundred thousand, when the number one medical problem in ferrets is undiagnosed or misdiagnosed dental problems that affect more than 95% of the pet ferret population (of ALL ages). This means that if you own 10 ferrets, the chances are extremely good that at least 9 of them will have dental problems that I can detect in their bones and teeth.

Dental disease is insidious, unexpected, and extremely harmful. For all intents and purposes, your ferret could present as a healthy animal, yet may be harboring an underlying infection that years down the road may be responsible for their death.

The types of dental problems seen in ferrets has, in numerable species ranging from mustelids to primates, been positively linked to a host of diseases, including (but not limited to) bone infections, systemic sepsis, cardiomyopathy and heart value disorders, gastrointestinal disease, liver and gall bladder disease, kidney disorders, the formation of various kidney and bladder stones, and much, much more. Consuming kibble is either a primary reason, or a contributing reason for profound dental disease.

A major reason dental disease is so disregarded is that vets rarely inspect a ferret’s mouth unless they smell significant odor. The main problem with that approach is that by the time the odor is detectable, major disease, perhaps incurable problems, already exist. Because of this, dental disease and associated diseases in ferrets are tremendously under-diagnosed.