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Odontodes, the ancestors of teeth, looked like placoid scales of recent sharks. Odontodes consisted of a dentine cone with a pulp cavity and covered by a hypermineralized tissue like enamel or enameloid. They were attached to the integument by a bony base.
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Figure 1: Odontodes, the ancestors of teeth, looked like placoid scales of recent sharks. Odontodes consisted of a dentine cone with a pulp cavity and covered by a hypermineralized tissue like enamel or enameloid. They were attached to the integument by a bony base.

Mentions: Teeth are highly mineralized appendages found in the entrance of the alimentary canal of both invertebrates and vertebrates. They are associated mainly with prehension and processing of food, but they also frequently serve other functions, such as defense, display of dominance and phonetic articulation in humans. Generally, when speaking of teeth we usually refer to the dentition of vertebrates. Teeth with the basic microscopic anatomy similar to that of recent vertebrates first appeared at Ordovicium, approx. 460 million years ago. Some jawless fish developed superficial, dermal structures known as odontodes 5, 6 (Fig. 1). Those small tooth-like structures were located outside the mouth and served various functions, including protection, sensation and hydrodynamic advantage. The encroachment of odontodes into the oropharyngeal cavity created the buccal teeth, which covered the entire surface and later were localized to the jaw margins. Dietary habits and ecological adaptations have driven the teeth of vertebrates to acquire numerous anatomical forms and shapes, as represented by incisors, canines, premolars and molars 7.

A Curriculum Vitae of Teeth: Evolution, Generation, Regeneration

Koussoulakou DS, Margaritis LH, Koussoulakos SL - Int. J. Biol. Sci. (2009)

Bottom Line: Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity.In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased.These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors.

Affiliation: University of Athens, Faculty of Biology, Department of Cell Biology and Biophysics, Athens, Greece.

ABSTRACT
The ancestor of recent vertebrate teeth was a tooth-like structure on the outer body surface of jawless fishes. Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity. In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased. Teeth form mainly on the jaws within the mouth cavity through mutual, delicate interactions between dental epithelium and oral ectomesenchyme. These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors. Congenital disturbances in tooth formation, acquired dental diseases and odontogenic tumors affect millions of people and rank human oral pathology as the second most frequent clinical problem. On the basis of substantial experimental evidence and advances in bioengineering, many scientists strongly believe that a deep knowledge of the evolutionary relationships and the cellular and molecular mechanisms regulating the morphogenesis of a given tooth in its natural position, in vivo, will be useful in the near future to prevent and treat teeth pathologies and malformations and for in vitro and in vivo teeth tissue regeneration.

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