A manual of dental anatomy : human and comparative / by Charles S. Tomes.

  • Tomes, Charles S. (Charles Sissmore), Sir, 1846-1928.
Date:
1904
Catalogue details

Licence: In copyright

Credit: A manual of dental anatomy : human and comparative / by Charles S. Tomes. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    newt, in which animals only this enamel-capped tip of the tooth projects far above the surface of the mucous membrane ; or it may cover a much larger proportion of the tooth, as in man. Perhaps the most usual condition is that the enamel invests the whole crown of the tooth, stopping short at aboiit the level to which the gum reaches, as in the human and most other mammalian teeth of limited growth. In teeth of persistent growth the enamel extends down into the socket as far as the base of the tooth ; in such cases it may embrace the whole circumference of the dentine, as in the molar teeth of many rodents, or it may be confined to one side only, as in their incisor teeth, where by its greater hardness it serves to constantly preserve a sharp edge as the tooth is worn away. The enamel is believed to be quite absent from many teeth ; thus the order Edentata, comprising sloths, armadillos, and ant-eaters, have it not; the Narvval, certain cetaceans, some reptiles, and many fish have none. But although it might appear an exceedingly simple matter to determine whether a tooth is or is not coated with enamel, as a matter of fact in practice it is not always easy to be certain upon this point. When the enamel is tolerably thick there is no difficulty in making sections which show it satisfactorily, but when it is very thin it is apt to break off in grinding down the section. And even when it does not, it is in such cases usually quite trans- parent and structureless, and the outermost layer of the dentine being also clear and structureless, it is very hard to decide whether the appearance of a double boundary line is a mere optical effect due to the thickness of the section, or is indicative of a thin layer of a distinct tissue, which might be either enamel or cementum, for very thin layers of cementum look very much like enamel. My own investigations upon the development of the teeth offish and reptiles have led me to suspect that rudimentary layers of enamel may exist upon many teeth on which their presence has not been recognised, for I have found that the formative enamel organs occur universally, at least they exist upon all tooth germs which liave ])cen adequately