Résumé
Periodic fringes corresponding to six different lattice planes have been observed in apatite crystals of human normal alveolar bone by transmission electron microscopy. Three of these sets of fringes have spacings less than 3.5 Å corresponding to the Scherzer resolution of the microscope used. The (0002) lattice plane of hydroxyapatite of 3.4 Å d-spacings, the(211¯1) lattice plane with a d-spacing of 2.81 Å, and the(303¯0) lattice plane with a d-spacing of 2.72 Å have been identified. The (0002) and(212¯1) lattice planes have been observed for the first time in bone microcrystals. Some of the crystals studied were characterized by a mean width/thickness ratio of 6.91, typical of platelike habit, whereas observations of crystals aligned along the⟨12¯10⟩ and⟨12¯11⟩ directions showed a needlelike habit. The mean length of the bone apatite crystals was 470 Å. A dark line similar to the one observed in enamel and dentine crystals was also seen. The bone microcrystals observed have shown a high sensitivity to beam damage.