Scanning Microscopy


The morphology and chemical composition of two subgingival calculus samples, which were composed of magnesium-whitlockite with a Mg/Ca molar ratio of approximately 0.1 as shown by X-ray powder diffraction, were analyzed semiquantitatively using energy-dispersive spectroscopy (EDS) combined with scanning electron microscopy (SEM). The Ca/P molar ratio values for 33 EDS-analyzed materials ranged from 1.24 to 2.03 with an average of 1.49, and the (Mg+Ca)/P molar ratio values ranged from 1.43 to 2.28 with an average of 1.63. The average Mg/Ca molar ratio was 0.10, a value very close to that obtained by X-ray diffraction analysis.

The EDS-analyzed materials were grouped morphologically into three types; Type A materials were typical rhombohedral crystals, Type B were crystals of ill-defined form or small crystallite aggregations and Type C materials had a small granular structure or were amorphous. The values of (Mg+Ca)/P molar ratio for Type A ranged from 1.57 to 2.28 and averaged 1.81, those for Type B ranged from 1.43 to 1.56 and averaged 1.48, and those for Type C ranged from 1.46 to 2.06 and averaged 1.62. Type A crystals had higher molar ratios while Type B crystallites had values similar to that of whitlockite. Type C materials covered the ranges of both Type A and Type B.

These results show that the materials resembling whitlockite morphologically did not have the (Mg+Ca)/P ratio of whitlockite and vice versa. This suggests that whitlockite crystals may substitute some ions for PO4 as well as Mg for Ca to a larger extent than thought previously, and that care is needed in the identification of these materials.

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