ENAMEL OF SHARK'S TEETH

¹ School of Dental and Oral Surgery, Columbia University, New York, N. Y.

1. Tomes noted that enamels of plagiostome fish, osseous fish, marsupials and placental mammals present resemblances which are far stronger than their differences. 2. In sharks there is an enamel organ formed from ectoderm, as in mammalian enamel formation. The ameloblasts are concerned in calcification of the matrix. 3. In studying the teeth of sharks the 2 tissues on the teeth, dentin and enamel, which are homologous with the tissues of other vertebrate teeth, are seen. 4. Radiographs of shark teeth show that there is a marked difference of density of the 2 tissues, entirely comparable to mammalian teeth. 5. The direction of calcification of shark's enamel is somewhat like the pattern of human enamel as described by Diamond and Weinmann and is correlated with the appearance of luster on the surface, which progresses from tip of tooth to its base. 6. In microscopic examination of a thin ground section marked differences in the morphologic appearance of the 2 tissues and a sharp line of demarcation at the dentino-enamel junction due to difference in refractive index of the tissues are seen. 7. In decalcified sections the dentin matrix has numerous projections into the enamel, but the enamel matrix stains differently from the dentin matrix. The delicate strands projecting into the enamel matrix are definitely related to the dentin matrix, but this is also seen in marsupial enamel. The spindles of human enamel are vestigial. 8. The evidence from paleontology indicates that shark's teeth are the forerunners of the teeth of modern vertebrates. Thus, from a consideration of all the evidence we conclude that the outer layer covering the teeth of the shark is a form of enamel.

This article has been cited by other articles:

				M. L. Moss, S. J. Jones, and K. A. Piez Calcified Ectodermal Collagens of Shark Tooth Enamel and Teleost Scale Science, August 28, 1964; 145(3635): 940 - 942. [Abstract] [PDF]