A micro-Raman spectroscopic study of hydrazine-treated human dental calculus

Hydrazine has been used to remove organic components and to isolate the mineral(s) from human calculus. Micro-Raman measurements were performed on the mineral phase. After the hydrazine-treatment, not only a large reduction in fluorescence but also an increase in Raman signal was observed. The treatment was essential in minimizing thermally-induced chemical changes which could otherwise occur to the original calculus mineral due to the intense laser light. The Raman spectral features of the mineral were nearly all identical among the Raman spectra obtained at many randomly-selected sites by the micro-Raman microbe with a lateral resolution of approximately 1 micron, and were consistent with those of impure hydroxyapatite containing CO3(2-) and HPO4(2-). The spectra contained typical hydroxyapatite bands including PO4(3-)bands of the v1, v2, v3 and v4 modes and one OH- stretch band. Other minor bands due to the CO3(2-) v1 and v3 modes and bands possibly due to the HPO4(2-) v1, v2 and v4 modes were observable by the technique despite the hydrazine-treatment that could in principle remove the HPO4 and CO3 ions from the mineral. In comparison with pure synthetic hydroxyapatite, the intensity of the OH- stretch band relative to that of the PO4(3-) v1 band was approximately 70% weaker, and the bandwidth of the phosphate v1 band was 200% broader, reflecting various crystal imperfections presumably present in the calculus mineral.