COMPARATIVE DEVELOPMENT OF THE CANINE TEETH IN WILD AND CAPTIVE BLACK BEARS, URSUS AMERICANUS PALLAS

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Abstract
Development of the canine teeth in continuously growing captive black bears, Ursus americanus Pallas, has been investigated by means of an intravital dye, alizarin red S, injected intraperitoneally in phosphate-buffered saline. The dye is deposited with the dentin and cementum, forming pigmented layers which delimit increments of growth. In continuously growing captives, the root of the canine tooth closes at the apex in about 3 years, whereas this does not take place in wild bears in southcentral Alaska until about the end of the sixth summer of life. In captive bears injected at 6-month intervals over a period of 3 years, the 6-month increments in dentin corresponded to those produced annually in wild bears. After the first autumn of life, up to which time wild and captive bears develop at the same rate, five 6-month periods of growth are required by both for completion of the canine root. This work confirms experimentally that the annual increments of dentin in the canine root of wild bears represent 6-month periods of growth, and that the canine teeth do not grow during the period spent in the den. It was confirmed also that a single layer of cementum is produced annually in the teeth of wild bears. The layers of cementum provide the best means for determining age of individual animals.