Fluorapatite crystal. Composite coloured scanning electron micrographs (SEM) showing the growth of a fluorapatite, or calcium fluoride phosphate, crystal from a hexagonal rod (red) to a sphere (purple). This crystal has been grown in the laboratory for research into the use of fluorapatite as an ingredient in toothpaste to treat sensitive teeth. The fluorapatite transfers fluoride ions to tooth enamel, which is a composite of collagen and hydroxyapatite (calcium phosphate), repairing any damage. Magnification: x2080 when printed at 10 centimetres wide.