ON THE SYMMETRY OF SYNTHETIC AND BIOLOGICAL HYDROXYAPATITE. J. Reyes-Gasga, M. Benaissa, D. Romeu, Instituto de Fisica, UNAM Apartado Postal 20-364, 01000 Mexico D. F., Mexico

Hydroxyapatite is an important calcium phosphate in biomaterials science since it is the principal constituent of tooth bones and cements. In this work we have made use of electron microscopy, electron diffraction, and image simulation to study both synthetic and biological hydroxyapatite. We have observed the systematic appearance of crystallographic forbidden spots in their electron diffraction patterns. Structural disorder, double diffraction, super and/or modulated structures and size effects are discussed as possible causes. Since we have found no samples in which they were absent, we believe their presence must be an inherent feature on the structure of hydroxyapatite.

We would like to thank L. Rendón, C. Zorrilla, S. Tehuacanero, P. Mexía, R. Hernández and J. A. Ramirez for technical help this work was supported by DEGAPAUNAM under project IN-106295.