Observations on structural features and characteristics of biological apatite crystals. 4. Observation on ultrastructure of human bone crystals.

In a series of studies to investigate the structural features of the biological crystals such as the tooth and bone, following the previous observations of the tooth crystal using an electron microscope, we examined the ultrastructure of the human bone crystals at near atomic resolution through the cross and longitudinal sections of the crystals. The materials used for this study were the normal bone tissue obtained from the buccal alveolar compact bone of the human mandible in the portion of the lower first molar. The small cubes of the bone tissue were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with the HITACHI H-800 type transmission electron microscope operated at 200 kV. Each crystal was observed at the initial magnification of 300,000 times and at the final magnification of 10,000,000 times and over. Using this approach, we showed the configuration of the hydroxyapatite structure in the cross and longitudinal sections of the bone crystals deposited within and between the collagen fibrils (intrafibrillar and interfibrillar crystals) in the bone tissue. Furthermore, using the same approach, we observed the crystal lattices of the hydroxyapatite structure appearing in the cross and longitudinal sections. We sincerely believe that the electron micrographs shown in this report are the first atomic images from the section obtained from the hydroxyapatite crystal from the human alveolar bone.