By
D.A.Fagan, D.D.S., M.S.Edwards,Ph.D., and J.E.Oosterhuis,D.V.M.

Abstract: The need for reliable nutritional information is fundamental to the task of maintaining both the systemic health and the reproductive capability of all species. For most animals, the oral cavity represents the entry mechanism to the digestive system, and when this masticatory apparatus fails to function properly, systemic collapse is not far to behind. This discussion of the anatomy, physiology, and common disability of animal dentition and masticatory function provides an overview of the inescapable interdependence between these two often dis-associated scientific disciplines.

A little more than one hundred years ago, a British dental surgeon interested in the issue of oral disease in animals, visited most of the world's most prestigious Natural History Museums and numerous lesser known facilities and private collections, conducting research and gathering documentation. He subsequently compiled his data, and published his findings in the form of a textbook titled "Variation and Disease in the Teeth of Animals." On page 690 of that text, he describes his findings with the words:

"The conclusions I have arrived at after my investigations into the (oral) disease in animals are as follows:

1. The disease starts as an injury to the gum margin caused by food. This injury may be of a traumatic or chemical nature; when traumatic, the food in the process of mastication penetrates the soft tissues; when chemical, the products of stagnant food injure the epithelial surface and thus expose the deeper tissues to infection.

2. The bone lesion is a progressive rarefying aesthetes commencing at the margin of the bone, and there is no evidence to support the claim, made by some writers, that the initial bone changes are of an atrophy character.

3. The disease is caused by an alteration in the character of the diet of the animal either of a physical or chemical nature -- in other words, by a departure from natural diet and conditions.

Expressed in biological terms, the disease is due to an alteration in the environment of the mouth."

In spite of enormous sums of money and effort spent during the intervening 100 years in an attempt to understand, control and eliminate oral disease, these words "an injury to the gum margin caused by food" still describes one of the most common diseases and disorders found among animals in captivity. Why is this so? Why is it that the situation still remains so commonplace, under appreciated, over looked, and misunderstood?

All animals depend upon the successful operation of a uniquely designed masticatory apparatus for their survival. If or when, this apparatus ceases to function properly, it's owner is immediately faced with a variety of potentially compromising difficulties. Very quickly this individual's status in its group's social hierarchy is in jeopardy.

The oral cavity is the entry mechanism to the animals digestive system. Without the ability to efficiently capture, modify into bite-sized chunks, and consume adequate portions of proper nutrients, the entire biochemical system of the animal soon ceases to function adequately. Furthermore, displaying evidence of a systemic medical or dental weakness, disability or disease jeopardizes the animal's status even further. The result is that most exotic and/or free ranging animals tend to hide all of their medical ailments as long as possible. The disease process then has the opportunity to progress to its natural conclusion. What began as a slight oral infection may ultimately invade the individual's entire body by spreading to adjacent tissues, through normal passageways to nearby organs, and through the blood stream to the animal's entire system. As a result, the primary functional manifestations of oral disease in exotic animals are usually systemic disorders, such as an acute interstitial nephritis; kidney failure; bacterial endocarditis and/or arthritis, rather than localized facial or oral pain.

Untreated oral disease in exotic animals results in major systemic physical disorders, including the inability or disinclination to reproduce. The clinical practice of veterinary dentistry with exotic animals spans the entire scope and breadth of traditional human medicine and dentistry, all of veterinary medicine, and the rapidly developing field of companion animal veterinary dental practice. Exotic animal dentistry is a very diverse and challenging field of interest. It is time to share information known to participants of that discipline with concerned investigators in other realms of scientific inquiry. This is necessary in order to increase awareness of the clinical consequences of various nutritional and dietary choices, and thereby eliminate a few more of the etiological factors which contribute to chronic oral disease. This is the essential mandate of Preventative Medicine.

BACKGROUND INFORMATION

There is quite a difference between performing the "traditional" endodontic procedure on the canine tooth of a marmoset (which is approximately the size of a straight pin), and performing the "traditional" endodontic procedure on the canine tooth of a 500-pound male African lion (which can have the internal volume of a 10-cc syringe), or performing the "traditional" endodontic procedure on the tusk of a 12,000 pound elephant (which may have a 3.5 liter dental pulp chamber ). Each case varies according to the species specific circumstances, including but not limited to, anatomy, habitat, diet, level of nutrition, and prevailing management practices of the individual animal. Clearly, the clinical management problems associated with elephants, are quite different than those associated with the treatment of birds of prey, antelopes or nocturnal carnivores.

Consequently, there are no "routine" veterinary dental procedures in exotic animals. Oral diseases observed in exotic species is usually the result of three primary factors: genetics, environment, and diet. Inappropriate diet and/or habitat contributes greatly to the normal wear and tear of any animal's masticatory apparatus.

From a practical point of view, the practice of exotic animal veterinary dentistry involves three basic processes: (1) determination of appropriate and comprehensive clinical care; (2) research to support the clinical treatment plan; and (3) education of concerned administrative personnel, veterinary medical professionals, handlers, keepers, and public.

The treatment of a male dromedary camel scheduled for the removal of both of his mandibular canine teeth should illustrate how these three issues are intertwined. The call for the removal of the teeth represents the call for clinical care. Research at a local museum revealed that the canine teeth of the camel comprise 80 percent of the architectural support of the anterior portion of the mandible. Thus, if the canines were removed, the camel would lose about 90 percent of the functional strength of this portion of the oral cavity. The next time he bit into anything solid, his mandible would most likely fracture. In this case, reduction of the clinical crown with partial pulpotomy solved the problem and eliminated the call to remove the teeth. The responsible clinician must not only continually educate themselves, but the other veterinarians involved with the case, the zoo management personnel, the animal's keepers, as well as all of those individuals responsible for developing and/or prescribing diet and habitat alternatives.

As a result of utilizing these three processes, a cohesive team can be developed with all members focused in the same direction, and working as a single unit. Attaining a "functional team effort" is a necessary element of comprehensive dental care. It is the most practical method of maintaining the oral health of the animal, and is absolutely essential to preventing and detecting future dental disease. This requires a good deal of time, effort and preparation, but the payoff is clearly apparent and rewarding.

Veterinary dentistry is, by necessity, a cross-disciplinary field. As a result of the enormous diversity in morphology, size and shape of the oral structures of exotic animals, the application of information and solutions from many medical fields is necessary. Solutions that are no longer appropriate in human dental practice may be the most appropriate for use in a particular exotic animal procedure. This is not because these are lesser solutions, but because they are the solutions that lend themselves more specifically to the unique circumstances of that individual animal's morphology and /or problem.

CONCERNING THE DENTITION

The teeth encountered by a veterinary dental clinician represent as many variations and extraordinary forms as there are different species. The alligator has a very simple cone-shaped tooth, whereas the leopard seal has a row of pre-molars shaped like Poseidon's three-pronged scepter with beautifully sculptured miniature flame-shaped enamel cusps.

Invertebrate Dentition
Not all members of the invertebrate class have teeth, but when teeth are present, they are analogous to the teeth of vertebrates because they are usually oral organs that perform the same function as the denticles of vertebrates. They are not homologous with the teeth of vertebrates, however, because they may not have the same tissue of origin or even a similar structure (for example, the claw of a crab). The dentition of invertebrates varies in number from none to one (the claw of the lobster) to over 40,000 in the mouth of a snail.

Vertebrate Dentition
The teeth of vertebrates are generally confined to the oral cavity in the bones and cartilage of the head and face, or in the esophagus in some of the snakes. Vertebrate denticles come in an enormous variety of sizes, shapes, and quantities. They vary in number from zero in the anteater, to 1 in the narwhal, to 6 in the elephant, to 32 in man and the old world monkeys, to more than 100 in some cetaceans. Regardless of their quantity, they can all still be characterized as one of the four functional forms noted below. This is even true with respect to the "denticle" or beak characteristic of avian species. The eagle may only have one hooked "tooth" attached to the end of its stiff upper lip, but that "tooth" still performs as the lone functional denticle of this animals masticatory apparatus .

The predominant feature of most mouths is generally the teeth. A tooth is a small, bone-like structure usually found attached to or imbedded in the jaws. Teeth serve a number of important functions including: capture of food, deglutition in some fishes and snakes, incising of food into bite-sized pieces, crushing of food to begin digestion through insalivation, weapons for protection, primary tools (e.g. the beaver), sexual stimulants, and for the facilitation of some reproductive behavior.

The original architectural form of the primitive tooth-like projection, or denticle, is that of a solitary cone. Embryologically, all denticles originate from ectoderm and are therefore considered to be specialized dermal structures like hairs and fingernails. As a consequence, dentition is highly susceptible to variations and abnormalities of the nutrients necessary for the development of dermal organs. Teeth are composed of a combination of three dental tissues: enamel - the white, compact, and very hard calcium crystalline rods that cover and protect the crown of the tooth; dentin (ivory) - the most common substance or tissue of teeth that consists of a solid organic substratum, infiltrated with calcium hydroxy apatite salts, and permeated by numerous branching tubules that contain processes of the cells that line the tooth's pulp chamber (odontoblasts); and cementum - the thin layer of acellular bony tissue covering the root of the tooth which differs from ordinary bone in that it contains no Haversian systems.

All teeth can be divided into three functional parts: a clinical crown, or portion protruding into the mouth above the soft tissue of the jaw. A root, or portion covered with cementum that is used to attach the tooth to the jaw bone; and a neck, the region where the enamel ends.

By modification in response to functional demands, teeth have evolved into four functional forms which may be classified structurally. The incisor is a wedge-shaped form with a long, conical root used to cut objects. The canine is an elongated conical form that is used to puncture, hold, or tear objects. The premolar is a transitional form with a crown usually composed of two or three small cones fused together usually with one or more long roots. The molar is a broad, squarish form designed to grind or crush objects and with a crown composed of multiple small cones called cusps.

How Teeth are Attached
The teeth of vertebrates are all attached by one of four basic methods. (1) A fibrous membrane is present in sharks and rays. (2) An elastic hinge functions for most fish, although some fish and reptiles utilize the third method. (3) Ankylosis, or a continuous ossification between the tooth and jaw bone with no intervening membrane. The ankylosis method is divided into three styles depending upon how the tooth relates structurally to the surrounding bone (that is, on a pedestal, to the side of the jaw, or in a socket).

The ankylosis method of attachment is common to all mammals and some reptiles. It involves the use of an intervening ligamentous structure called the periodontal ligament. This ligament is embedded into the cementum layer of the tooth on the one end and extends to anchor the tooth to the surface of the surrounding specialized bone, called the alveolar process, on the other end. The unique feature of this method of attachment is that the alveolar bone is invaginated to intimately surround the entire root of the tooth in order to form a bony socket or crypt that is architecturally very sound. It is a very sophisticated suspension apparatus which has more in common with a wrist or ankle joint than with the other types of tooth attachments. Of interest is the fact that the continuously growing incisor teeth of rodents and elephants have this ligamentous attachment, although the dental pulp tissue of elephants does not contain nerve fibers.

This periodontal ligament represents a very effective method of absorbing and distributing the forces of mastication without undue injury to the surrounding bone. It is because of the unique relationship between the periodontal ligament and the surrounding bone that mammalian teeth can be easily repositioned or relocated within the jaw by the light forces induced with orthodontic appliances.

Sudden, sharp, or excessive forces to the tooth can, and in fact occasionally do, injure the ligament, much like a similar force would injure or "sprain" an ankle joint. The muscles of mastication in humans are capable of closing the mouth with about 250 to 300 pounds per square inch of biting force. When this load is applied suddenly onto the cusp tip, perhaps 1/100th of a square inch in cross section, it is not at all unlikely to develop a local stress of 25,000 to 30,000 psi --- certainly enough to injure the ligament or fracture a tooth. In the larger or stronger carnivores the load is proportionately greater.

THE MASTICATORY APPARATUS

The manner in which all these teeth, in all these different species, come together is referred to as their method of articulation, or interdigitation, or occlusion. It is this articulation that enables the individual denticles to operate as a unique functional apparatus that structurally occupies the upper end of the animal's digestive system. This apparatus comes in a wide variety of sizes and shapes designed to do an infinite variety of operations. For the veterinary dental clinician, however, some generalization is in order to summarize the matter. It may prove helpful to think of the masticatory apparatus as if it were a picket fence. The owner inherits basically three things:

1. The size, shape, and number of pickets or teeth (the dental formula: 0 to 40,000).
    
2. The length and shape of the fence or jaw bone (for example the short curved jaw of the Boxer dog versus the long thin jaw of the Caiman alligator).
    
3. The way the fences fit together (the temporomandibular joint, and the occlusion).

It is all more complicated than this, of course, but the multitude of details available from numerous texts on comparative anatomy and osteology are not relevant here. What is needed here is an awareness that all of the individual elements of this complex apparatus must be supported by a diet which provides all if the essential required nutrients necessary to form, develop and function as designed.

The masticatory apparatus in all vertebrates functions in response to the balanced interplay between three independent, but related, biological entities:

1. The teeth, or the number of pickets along the fence.
    
2. The temporomandibular joint, or the hinge that facilitates the articulation of the fences.
    
3. The major muscles of mastication, or the movers of the fence along the hinge axis during articulation.

DIAGNOSIS
The term "diagnosis" originates from a Greek word meaning to distinguish or to discern. For the clinician, it refers to the process of identifying a disease by analysis of the signs and symptoms presented by the patient. The procedure for making a diagnosis includes the following four primary steps:

1. Collection of the facts.
    
2. Analysis of the data for relative importance.
    
3. Correlation between synthesized data and descriptive features of suspected diseases.
    
4. Selection of the disease that best explains the collected facts and apparently disturbed physiologic processes of the patient.

The process of diagnosis usually results in the identification of a specific disease. It is well to remember that a name is only a shorthand method of describing a set of signs and symptoms or characteristics of a particular diseased state. The word diagnosis describes not just a "disease identified," but the diagnostic label itself tends to lead the clinician to the treatment alternatives and causative agents associated with or limited to that specific diagnosis. If the diagnosis is incorrect, the clinician can be severely misled. Consider a spontaneously bleeding gingivitis diagnosed as acute necrotizing ulcerative gingivitis as opposed to hemophilia. The patient is best treated if the clinician is focused upon the clinical facts collected, not just on the name of the disease selected.

CONCLUSION
Oral disease in animals results from an extremely diverse variety of environmental, dietary, and genetic circumstances. The clinical appearances of the disease process can vary considerably within a single species and may vary enormously from one species to another, particularly considering the contrasts between environments and diets. In spite of all this potential for diversity, from a practical point of view, the vast majority of disorders associated with the masticatory apparatus of animals belong to one of four basic groups, which tends to imply specific categories of treatment planning and/or causative agents.

1. Developmental and congenital defects (includes dental caries).
    
2. Maxillofacial trauma.
    
3. Periodontal disease.
    
4. Trauma to the teeth.

Although dental treatments can be relatively complex, their successful implementation is a matter of preparation, and the specific details of treatment are available in numerous references. Today, the clinical practice of veterinary dentistry must concern itself with the growing discipline of disease prevention; and as a consequence, the importance of accurate diagnosis is imperative. It is essential to remember that the role of diet and nutrition is an absolute essential requirement of all phases of development and function of an animals masticatory apparatus.

REFERENCES

Beard GB, Beard DM: Geriatric dentistry. Vet Clinics North Am Small Anim Pract 19 (1): 49-74, Jan 1989.

Colby, R. A., and Kerr, D. A.: Color Atlas of Oral Pathology. Philadelphia, J. B. Lippincott Co., 1971.

Collins, L. H., and Crane, M.: Internal Medicine in Dental Practice. Philadelphia, Lea & Febiger, 1965.

Colyer, J. F.: Dental Disease in Its Relation to General Medicine. London, Longhans, Green & Co., 1911.

Colyer, J. F.: Variation and Diseases of the Teeth in Animals. London, John Bale, 1936.

Dean MC, Beynon AD: 80. Tooth crown heights, tooth wear, sexual dimorphism and jaw growth in hominoids. Z Morphol Anthropol 78 (3): 425-40, 1991.

Donovan, GP: A brief review of ageing techniques for toothed cetaceans within the context of marine parks. In: Symposium on Endangered Marine Animals and Marine Parks. Cochin, India. 12-16 January 1985. Papers for Presentation. Volume I: Marine Mammals. Marine Biological Association of India, Ernakulam, India,1-17, January 1985.

Ela, KM: Zoo animal dentistry: another breed of patient. Dental Hygienist News 4 (1): 13, Winter 1990.

Ellis, R. G.: The Classification and Treatment of Injuries to the Teeth of Children. Chicago, Year Book Publishers, 1960.

Fagan DA: Diet consistency and periodontal disease in exotic carnivores.
Proceedings of the First Annual Dr. Scholl Nutrition Conference. A Conference on the Nutrition of Captive Wild Animals, December 5 and 6, 1980, Lincoln Park Zoological Gardens, Chicago, 241-259, 1980.

Fagan DA: Diagnosis and treatment planning. Vet Clinics North Am Small Anim Pract. 16 (5): 785-99, Sep 1986.

Fagan, D. A.: The Pathogenesis of Dental Disease in Carnivores. In Proceedings of the American Association of Zoo Veterinarians, 1980.

Goldman, H. M. (ed.): Periodontal Therapy, St. Louis, C. V. Mosby Co., 1964.

Gual SF, Suarez De Gual MC: Periodontal disease in wild mammals; A captivity related problem? Veterinaria - Mexico 27 (2): 165-173, 1996.

Hance SR, Bertone AL: Neoplasia. Vet Clinics North Am Equine Pract 9 (1): 213-34, Apr 1993,
Hennet PR, Harvey CE: Natural development of periodontal disease in the dog: a review of clinical, anatomical and histological features. J Vet Dent 9 (3): 13-9, Sep 1992.
Kerr, D. A., Ash, M. M., and Millard, H. D.: Oral Diagnosis. St. Louis, C. V. Mosby Co., 1959.

Page, R. C., and Schroeder, H. E.: Periodontitis in Man and Other Animals. New York, S. Karger, 1982.

Nizel, A. E.: Nutrition in Preventive Dentistry: Science and Practice. Philadelphia, W. B. Saunders Co., 1972.

Robinson, PT: A literature review of dental pathology and aging by dental means in nondomestic animals - part I. Journal of Zoo Animal Medicine 10 (2): 57-65, 1979.

Robinson, PT: A literature review of dental pathology and aging by dental means in nondomestic animals - part II. Journal of Zoo Animal Medicine 10 (3): 81-90, 1979.

Schnebitz, H., and Wilkens, H.: Atlas of Radiographic Anatomy of the Horse and Dog. P. Parey, 1968.

Stafne, E. C.: Oral Roentgenographic Diagnosis. Philadelphia, W. B. Saunders Co., 1963.

Sorrin, S.: Habit: An Etiological Factor of Periodontal Disease. Dental Digest, 41:291, 1935.

Tiecke, R. W., Stuteville, O. H., and Calanera, J. C.: Pathologic Physiology of Oral Disease. St. Louis, C. V. Mosby Co., 1959.

Watson AD: Diet and periodontal disease in dogs and cats. Aust Vet J 71 (10): 313-8. Oct 1994.

Zontine, W. J.: Canine Dental Radiology and Radiographic Development. J. Am. Vet. Radiol. Soc., 16(3):75-83, 1975.

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