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X-ray diffraction analyses were carried out from pooled samples of old subgingival calculus. Also the concentration of Ca, Mg, Zn, Sr, Pb, Fe and Cu from these samples were determined by means of atomic absorption spectrophotometry. The comparison of the samples containing almost the same Zn concentration and two different concentrations of Mg (9 mg/g and 16 mg/g) showed an increase of 2.0.10 and 220 whitlockite reflections with an increasing Mg concentration. The increase of Mg concentration shifted whitlockite reflections suggesting a contraction of a-axis. The increase of Zn concentration showed an increase of 2.0.10 and 220 reflections indicating the fitness of Zn into the lattice of whitlockite. No changes of a-axis were detectable. When comparing all diffractograms and the results obtained from chemical analyses, the presence of Zn-MG-whitlockite proved evident.

This study was undertaken to determine the distribution and concentration of mineral in supragingival and subgingival dental calculus. Extracted incisors and premolars with attached dental calculus were used. After fixation the specimens were dehydrated and embedded in methylmethacrylate and 100-micrometers-thick ground sections were made. Microradiographs were produced and the mineral content in the sections was determined photometrically, using an aluminum step-wedge as a reference system. The distribution of the mineral varied considerably within the specimens and between different specimens. Supragingival calculus appeared heterogeneous and often stratified, containing areas that seemed to be non-calcified. The average mineral content was 37% by volume. By contrast subgingival calculus appeared homogeneously calcified, with an average mineral content of 58%. No differences in mineral content between surface areas and portions close to the tooth were seen. This indicates that once the calculus is formed no changes occur in the mineral content, i.e. no maturation occurs with age. Local variations in mineral content within the calculus might be explained by periodic differences in the fluid environment of the microbial plaque.

Selected area electron diffraction of sections and individual crystal fragments of human dental calculus has demonstrated that octacalcium phosphate, hydroxyapatite and whitlockite form the inorganic part of both supragingival and subgingival dental calculus. However, the major constituents in supragingival calculus are platelet-shaped crystals of octacalcium phosphate and needle-shaped crystals of hydroxyapatite, while bulk crystals of whitlockite is the predominant component in subgingival calculus. The subgingival samples seemed to be better crystallized than the supragingival ones. The results obtained by the electron optical and X-ray powder investigations are in good agreement.