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Inorganic components and the fine structures of marginal and deep subgingival calculus attached to human teeth.

Inorganic components and the fine structures of marginal ledge-type and deep subgingival spiny deposits in human old dental calculus were investigated by scanning electron microscopy and energy dispersive electron-probe microanalysis. The ledge-type deposits consisted of the extra- and intracellular calcifying deposits, large plate-shaped crystals, and bacillus-shaped deposits composed of hexahedrally based crystals. The spiny deposits were mainly formed by aggregations of the bacillus-shaped deposits. In the outer and middle layers of the spiny deposits, the Ca, P, and Mg concentrations were all significantly higher than those of the ledge-type deposits. A consideration of the crystal shapes and Ca, P, and Mg molar ratios reveals the following differences. Calculus components of the ledge-type deposits contained crystal types quite similar to sandy grain-shaped hydroxyapatite (HAP), plate-shaped octacalcium phosphate (OCP), and hexahedral Mg-containing whitlockite (WHT). On the other hand, in the spiny deposits, the Mg-containing WHT type comprised a large proportion of the calculus; the HAP type was found in the outermost and inner layers; and no OCP type was detected.