RESUMEN
Electron microscopical observations of the size and shape of bone mineral crystallites have not been in complete agreement with X-ray diffraction findings. The two prevalent viewpoints consider bone mineral crystals to be either rod, or plate like in habit. There appears to be agreement that the smallest dimension of the crystals is about 5 nm, but there is discrepancy in the reported c-axial lengths. The method of dark field imaging is used to obtain a quantitative measurement of the c-axial length distribution in rabbit, ox and human bone: mean c-axial lengths 32.6 nm, 36.2 nm and 32.4 nm, respectively, show no significant difference at the 5% level to the mean c-axial length measured by X-ray line broadening. Both bright and dark field images strongly suggest that bone mineral has a plate like form. Reasons for past discrepancies are discussed.
Asunto(s)
Huesos/ultraestructura , Minerales , Animales , Bovinos , Humanos , Aumento de la Imagen/métodos , Microscopía Electrónica , Conformación Molecular , Conejos , Difracción de Rayos XRESUMEN
Under controlled machining, storage and testing conditions the tensile strength of longitudinally orientated specimens of cortical bone is measured over a range of 3 rates of strain. Coefficients of correlation and associated regression curves computed between the strength measurements and the results of a comprehensive photometric analysis of the histological microstructure indicate that naturally occurring cavities in the structure constitute the most significant sites of weakness. The observed strain rate sensitivity of their weakening effect suggests a mechanism of stress concentration to be operative. Clinical significance in such conditions as osteoporosis is indicated.