A very informative article about the development of molar teeth and several disorders in molars and tusks has been written by D.A. Fagan, J.E.Oosterhuis, and A. Roocroft (Colyer Institute). Click here to read the entire manuscript.
Molar development
Written by Willem Schaftenaar
Dental formula in elephants
The molars in elephants differ from other mammalians. In each side of the mandible and the maxilla a single molar tooth develops at a time. This molar consists of lamellae that are compressed together to form one dental element, which slowly progresses in forward direction, pushed as it is by a new molar that is developing caudal to the functional molar. During their entire life span, an elephant develops only 6 molars on each side of the mandible and upper jaw.
The lamellae are fused together with cement and at the grinding side covert with enamel. The different length of the lamellae give the molars its irregular shape at the grinding surface, which is extra supported by the difference in hardness between enamel and dentine.
During the development of molar teeth, two processes are very important:
Dentinogenesis: the formation of dentin.
Amelogenesis: the formation of enamel.
Any disturbance in these processes may result in malformation or poor quality of that molar, which is manifested as dental dysplasia. Such an abnormal molar may be weak and prone to deformity, malposition and malocclusion. This can lead to food impaction and consequently infection of the peridontal structures.
The condition of the molar teeth is important for the physical condition of the elephant. The body mass of both breeding and non-breeding female zoo elephants shows a cyclic undulation with peaks separated by many years, and correlated with the total surface of the functional the molar teeth (Schiffmann 2018).
Molars are important for the estimation of the age of an elephant. The numbers of the lamellae are quite specific for the sequential number of the molar. These numbers differ slightly between Asian and African elephants. So, by counting the lamellae of the presented molar, the sequential number of that particular molar tooth can be estimated.
The lamellae of molars that have not yet erupted are loose. The same applies for molars in the embryonic stage.
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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)
Age estimation
This table shows when a new molar erupts and at which age this particular molar is replaced by a new one. When the number of lamellae has informed us about the sequential number of the molar tooth, we can simply look at this table to estimate the age of the elephant.
The final molar tooth that appears is the 6th one, that erupts at the age of 40 years. When this molar is gone (usually between 60 and 80 years), no new molar develops and the elephant will have no proper molars to mastigate its food.
This radiograph shows the tusks and the molar teeth in the skull of a young elephant. Each tusk has a large, distinct pulpa chamber (Courtesy: Basel Zoo).
This radiograph shows you the mandibles. As indicated on the picture, each side contains a very small erupted molar on the left side, followed by another (erupted) molar in the middle and finally a large molar on the right side. (Courtesy: Basel Zoo).
The erupted molar in the middle consists of 6 lamellae. This means that it is the second molar tooth that has developed in this elephant. There is still a small remnant of the first molar. The 3rd molar is at the point of eruption. The dentition of the jaw on the X-ray corresponds with the dentition of the jaw preparation. Both elephants was approximately 2,5 years old.
Molar tooth disorders
Molar tooth disorders are quite common in elephants, especially in the older ones. The progressive changes of the molars make them prone to malpositioning. Pathological changes during the development of the molar before it erupts, can result in a deformed or rotated tooth.
Like in all animals with teeth, the quality of the food correlates with the quality of the teeth. If the speed of the abrasive wear is faster than the mineralization, the pulp of the molar tooth can become exposed. Insufficient abrasive wear (for example if the diet contains insufficient branches) will result in the opposite: long molar teeth, which often often are rotated.
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A loose piece of an old molar in this 40 yrs-old Asian elephant caused pain, which became manifest by the animal's reluctance to eat hard food items. Video: Willem Schaftenaar
Sometimes, especially when there is a certain degree of molar mal-positioning, the peridontal area can because infected. This is a painful condition which may lead to reduced appatite or selective food consumption, avoiding hard items.
An example of mal-formation and rotation of the molar tooth in an Asian elephant.
Click here to read a case report about this condition. Courtesy: Christian Schiffmann
Excessive abrasive wear of the molar teeth in this elephant had opened the pulp cavity of the anterior lamella of this lower molar tooth af an African elephant. Courtesy Peter Kertesz.
Insufficient abrasive wear or disturbed pre-eruption molar development has resulted in excessively long molar teeth in this 60 yrs-old female Asian elephant. As a result the animal could not masticate her food properly, which was expressed by the poorly digested, long fibers present in the feces. The photo in the middle was taken a few years after the first one.
Molar extraction and shortening
The extraction of a molar tooth in an elephant is quite challenging. The indication for an extraction is usually mal-positioning and abnormal abrasive wear of the tooth, which has a negative impact on the elephant's well being. Click here to watch the video about the extraction of the mal-positioned molar tooth in a female Asian elephant.​
This photo shows the extracted molar tooth. The cut in this tooth was made to get sufficient grip on the tooth for the extraction. Note the abnormal abrasive wear on the anterior side of the molar
​In another adult Asian elephant the lower molar had been worn down insufficiently and this obstructed the normal chewing action. By using a special pneumatic oscillating saw and chisel the length of the molar was reduced sufficiently to restore the normal chewing activities.
The photos show stills from a video (https://www.youtube.com/watch?v=lUHzCxL8FhI); note the special designed gingiva protector, a high potent vacuum cleaner and the oscillating saw in use. The short video fragment shows the end result of the shortened molar tooth.
References
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Biology, Medicine, and Surgery of Elephants. Fowler & Mikota, 271-290.
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Fagan DA, Oosterhuis JE, and Roocroft A. Captivity Disorders in Elephants: Impacted Molars and Broken Tusks. Colyer Institute, San Diego (Ca) USA.
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Kertesz P. 1993. A colour atlas of Veterinary dentistry and oral surgery. Wolfe Publishing. ISBN 0 7234 1542 0.
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Schiffmann C, Hatt J-M, Hoby S, Codron D, Clauss M. 2018. Elephant body mass cyclicity suggests effect of molar progression on chewing efficiency. Mammalian Biology, Volume 96, May 2019, Pages 81-8.
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Lucha the elephant visits the dentist (youtube.com)
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Molar issues
