The compressive, flexural, torsional and dynamic torsional strengths of polycrystalline hydroxyapatite sintered at a temperature of 1300 ~ C for 3 h were found to be 509, 113, 76 and 68 MPa, respectively. The mechanical properties of polycrystalline hydroxyapatite are compared with those of cortical bone, dentine and enamel. SEM observation of the fracture surfaces indicates a predomination of transgranular failures.

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Abstract. Mgs(CO3)4(OH)2(H20)4 (Dovez, Iran), monoclinic, P21/c , a = 10.105 (5), b = 8.954 (2), c = 8.378 (4)/I,, fi = 114.44 (5) °, Z = 2, Dr~ (flotation) = 2.25, Dx = 2.25 g cm -3. The H positions have been determined from three-dimensional X-ray data. The H atoms in the water molecules take part in a hydrogenbond system, while those in the hydroxyl groups do not.

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