Hexahedrally based crystals in human tooth enamel.

Mg-containing calcium phosphate crystals including pseudocuboidal, rhombohedral shapes and groupings of quadrangular blades cubically arranged were found in human tooth enamel by scanning electron microscopy and by electron probe microanalysis. In caries-free old enamel, these hexahedrally based crystals measuring 0.5-2.5 microns in length were observed in some crevices of tufts and lamellae. The crystals were rarely seen in the inner crevices of caries-free exfoliated deciduous enamel and none could be seen in sound young enamel. In brown-coloured old enamel possessing arrested caries with lamellae, some of the lamellae contained crystals measuring 0.1-1.5 mu in length adjacent to half-dissolved prisms. These crystals, identified as Mg-containing whitlockite, will grow during a long period after eruption of the tooth or during the enamel caries process.