THE CRYSTAL CHEMISTRY OF CARBONATE APATITES AND THEIR RELATIONSHIP TO THE COMPOSITION OF CALCIFIED TISSUES

¹ The Ohio State University, Columbus, Ohio.

It is concluded that rigorous calculation of structural formulas for dental enamel will not be possible until analytical procedures have been devised for determining three different types of water (including hydroxyls). The higher organic content of dentin and bone will greatly increase the analytical difficulties when attempting to obtain quantitative information on the types of water present. Differential thermal methods may aid in the solution of these perplexing problems.

Inasmuch as the atomic ratios Ca :P :C are not constant for calcified animal tissues, and likewise are not constant for the carbonate-apatite mineral, francolite, calculations based upon the hypothetical compound 3Ca₃(PO₄)₂ CaCO₃ are necessarily anomalous. But the variability of the Ca :P :C ratios does not constitute a valid reason for assuming that more than one crystalline phase is present, and no direct evidence for the existence for a second phase exists.

On the basis of the proposed structural hypothesis for francolite, it is possible to obtain crystal chemical calculations which account for the isomorphic substitution of carbon in the lattice of apatite. Presumably, similar conditions obtain for dental enamel and probably also for dentin and bone.

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