Lattice Imperfection of Carbonate-containing Hydroxyapatite

Abstract

The mineral component of bone or tooth is hydroxyapatite containing a small amount of carbonate ions. The crystallinity of biological apatites is one of the important factors which affect its chemical stability.
In this study, the cause of lattice imperfection of carbonate-containing hydroxyapatite has been investigated by means of variance and Fourier analyses of X-ray diffraction line broade- flings. The variance (i. e., mean-square breadth) of diffraction line profiles increased in proportion to carbonate contents in carbonate-containing hydroxyapatite. Among the factors which contribute to the variance, the"mistake"of lattice was much more effective than the crystallite size. For instance, about 90% of variance was effected by the mistake of lattice while only 10% was effected by the crystallite size, as shown in Table 4. In tooth enamel, there were more mistakes in direction of the a-axis than the c-axis.
These results lead to the speculation that the lattice imperfection of carbonate-containing hydroxyapatite or biological apatites are caused by the disorders in atomic arrangement due to substituted carbonate or other ions.