X-Ray Diffraction Study on Remineralization Using Synthetic Hydroxyapatite Pellets

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Abstract
Crystallographic changes of the surface layer of synthetic hydroxyapatite pellets dissolved in acetate buffer (pH 4.0) were investigated by X-ray diffraction. In both agitated and nonagitated systems, the presence of a well-mineralized surface layer covering a demineralized lesion was substantiated by microradiography and electron probe micro-analysis. This X-ray diffraction study indicates that all reflections became sharper and the intensity of the (hk0) and (h00) reflections increased after dissolution. A Fourier analysis of X-ray line profiles revealed that crystallite size increased in both (001) and (hk0) directions and lattice imperfections decreased in the (001) direction. The addition of 100 ppm fluoride ions to the solution resulted in a marked reduction of the dissolution rate of apatites, and no significant improvement of crystallinity was observed. It is concluded that the phenomenon of subsurface demineralization might be the result of remineralization or recrystallization, and growth of the residual apatite crystals might be of major importance in the process.