Colyer Institute- Captivity Disorders in Elephants Impacted Molars and Broken Tusks

Gefangenschaftskrankheiten beim Elefanten

Captivity Disorders in Elephants
Impacted Molars and Broken Tusks

D.A. Fagan, J.E.Oosterhuis, and A. Roocroft.

DEVELOPMENTAL PROCESSES OF MOLARS

The elephant's molar dentition, perhaps surprisingly, features several unique characteristics, notably the manner in which each molar tooth is created by the fusion of a dozen or more successive dental plates ( see Figure 3). A predetermined number of these enamel plates are formed as embryonic denticles evolving from the replicating dental lamina. These still-developing plates or tooth buds are shaped like small human hands ( see Fig. 4). They are composed of tooth forming cells, which differentiate into the basic odontoblastic components of mammalian teeth, and in due course, manufacture the enamel, dentin and cementum necessary to create a single dental plate ( see Fig. 5). As this progression of individual plates matures, they fuse together to create a " package of dental plates", which then becomes the molar tooth. Many developmental dental maladies such as supernumerary teeth, gemination, and crown or root dilaceration can and do occur at this stage of development resulting in the eventual malocclusion of a deformed or nonfunctional tooth. This process has been described by many authors including Colyer, Kingdon, Mitchell and Van der Merwe. For a more detailed definition of gemination and related terms, see Ferreira et al. Briefly, however, gemination arises when two tooth buds fuse together to form a single tooth, and dilaceration refers to a marked angular curvature or distortion in the normal anatomical form of the crown or root portion of the tooth.

Fig. 2. An African elephant photographed in its native environment with a broken tusk.

Fig. 3. A view of the 15 "Enamel Plates" of a single elephant molar tooth in various stages of development. The 1st "Enamel Plate" of this Asian mandibular molar is located in the upper right of this photo, and has begun the process of being fused together with cementum to "Plates" number 2,3, & 4. Plates number 5,6,7, & 8 are positioned in sequence of formation according to size, which is an indication of their age. Plates number 9 thru 15 are arranged to present a clear indication of how they form with the sequential growth of additional little finger-like projections of enamel slowly fusing together as they elongate to eventually form another single hand shaped enamel plate. The various sets of six sequential molar teeth, which characterize elephant dentition are thusly composed of from 8 to 20 sets of "Enamel Plates" - with Dentin deposited internally, and fused together with Cementum as indicated in fig. 5.

Fig. 4. A close up View of "Enamel Plate 12" seen in fig. 3. Notice the very slight swelling ( arrow ) formation at the lower left boarder of this "Plate". This is the beginning of another "finger". The formation of dentin is known as Dentinogenesis, and the formation of enamel is known as Amelogenesis. It is at this early stage of molar development, before mineralization is complete, that various types of Dental Dysplasia can and do occur. Any disturbance of sufficient severity to interfere with ameloblastic function during formation of the enamel matrix (the apposition of enamel) can result in abnormal molar development like : enamel hypoplasia, enamel hypocalcification, and amelogenesis imperfecta. Dentinogenesis imperfecta and Osteogenesis imperfecta are manifestations of mesenchymal dysplasia that are familial and genetically dominant.

The molars, contained in the massive tuberosity of the elephant's maxilla or body of its mandible, are composed of a number of parallel plates or vertical laminae of enamel surrounded by dentin and cementum. The enamel, by virtue of its superior hardness, is less susceptible to abrasive attrition during mastication, and eventually remains standing above the more easily worn dentin and cementum, resulting in an uneven occlusal grinding surface. Each of the individual dental plates is joined throughout the body of the molar tooth, which thus creates a tooth with 15 to 30 functional apical openings (see Fig 6 ), and a "grinding surface" on the mature molar, which permits it to function with its opposing tooth much like two opposing course farrier's rasps providing the elephant with a most efficient masticatory apparatus. On the occluding or grinding surface, the pattern formed by these worn enamel plates distinguishes the Asian elephants' molars with a squashed ovoid pattern, from the African elephant with a distinctive diamond pattern (see Fig 7). In fact, it is this pattern of the molars which provides the origin of the African elephant's scientific name Loxodonta - from the Greek word loxos - meaning oblique.

Fig. 5. This drawing of Shape, Development, & Abrasive Wear illustrates yet another unique characteristic of the elephant's molar dentition, which is the relative locations, and quantities, of the three primary components of all teeth - i.e.: Enamel, Dentin and Cementum. Customarily, mammalian dentition is composed of a "Mass of Dentin" with the root surface covered with a thin layer of Cementum, and its coronal portion covered with a thicker layer of Enamel. The elephant's Tusk is similarly formed. However, the elephant's molars are composed of a relatively large number of structurally positioned Enamel plates, fused together with a large quantity or "Mass of Cementum" with a relatively minor amount of Dentin contained within each of the Enamel plates. This is a unique and ingenious utilization of the three standard mammalian dental tissues to create a reliable, and very structurally efficient masticatory apparatus. (Modified from KINGDON 1971 & STERNDALE 1929 - with permission)

Fig. 6. A side view of a maxillary Asian molar tooth with a 9cm long pocket knife for comparison, and clearly demonstrating a functional, finished product of 17 enamel plates fused together with cementum to produce an elephant molar tooth. The functioning occlusal surface of this tooth is the irregular worn surface located diagonally at the lower left corner of the tooth. See fig. 12 for a better view of this chewing surface. See fig. 7 for a comparison with the African molar. Only about 1.5 to 2.0 cm. of this portion of the molar extends out of the alveolar ridge into the oral cavity, and only this small portion of the tooth is visible inside the mouth. The object in the upper left corner of the photo is the remnant of an exfoliated, worn out molar tooth commonly referred to as the elephant's dental "Cap". This last remaining portion of a molar represents that portion of the fully formed molar outlined within the black line in the upper right, root portion of the tooth in this photograph.

The molars of the African elephant are considerably larger than those of the Indian, and are well endowed with a more substantial portion of enamel for efficient mastication of a courser and harder diet. Their first or primary set of molars, sometimes referred to as the Milk teeth, gradually give way to a second set, which, in turn, are worn away, and lost by exfoliation to be replaced by a another molar as needed. This cycle of "eruption / use / wear / loss" occurs at somewhat predetermined intervals in order to insure the elephant with 60 +/- years of functional dentition. At each stages, as has been partially described by Hinton and others, deformity and mal-positioning can and does on occasion occur.

When abnormal molar positioning is present, food impaction can become problematic. The impacted food debris wedged into the abnormal spaces around the tooth decomposes, and results in localized infection of the surrounding periodontal structures. If not resolved, this initial infection spreads locally into the adjacent tissues creating a localized cellulitis, and in due course will eventually spread systemically through the animal's circulatory and lymphatic systems. Veterinarians generally concur that the intermittent, transient, bacteremia usually associated with chronic dental abscessation is not usually reflected in the elephant's blood profile, thus making it very difficult to evaluate the severity of the oral condition. Systemic infection in the elephant is always poorly monitored by hemo-analysis. If the offending tooth is not removed in a timely fashion, the masticatory function of the individual animal will eventually become impaired leading to poor nutrition in an animal already compromised by the presence of a developing infection. The inability to properly masticate food eventually leads to dietary deficiency, malnutrition with weight loss, and possibly an impaction colic. The combination of transient, intermittent septicemia with local infection and poor nutrition can have fatal consequences. Progressive masticatory malfunction is fairly easily monitored by routine inspection and/or analysis of the individual's fecal mass. Elucidation of factors relating to the animal's necessary dietary coefficient of abrasivity would seem to further clarify this concept.

Fig. 7. A drawing of the distinctive Occlusal Wear Patterns characteristic of Asian and African elephant molar dentition. It is this unique diamond shaped patten which provides the origin of the African elephant's scientific name Loxodonta - from the Greek word loxos - meaning oblique. (Modified from KINGDON 1971 & STERNDALE 1929 - with permission)

Introduction
Development Process of Molars
The Coefficient of Abrasivity in the Wild and in Captivity
"Gefangenschaftskrankheiten" And Molar Mal-Position
Fundamental Tusk Structure
Summary and References

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