Computer graphics of hydroxyapatite and beta-tricalcium phosphate.

Hydroxyapatite (HA) and beta-tricalcium phosphate (TCP) were studied by computer graphics with a personal computer. Crystal models of fluoridated hydroxyapatite and fluorapatite, in which F- ions are substituted into some or all OH- positions, were also drawn. Data on the structural coordinates of the hydroxyapatite and beta-TCP crystals were put into a protein graphics program in Angstrom units. The connection of each element, with front and rear, was displayed by the shade-line erasing method, and the solidity of the image was expressed by the degree of lightness from the light source. The colour tint was obtained by the Raster graphics method. A fine picture can be obtained with the photo program. Rotating the graphics freely around the X, Y, and Z axes gives a view from any direction. The computer graphics demonstrated visually that F- ions contribute to stabilize the hydroxyapatite crystal and that beta-TCP has an unstable structure due to 0.5 probability of Ca2+ ions and [PO4-Ca-Ca-Ca-PO4] zigzag chain.