whitlockite and calcium-phosphate--monobasic--anhydrous

The residues of 5 samples of powdered human enamel, each subjected to 5 sequential equilibrations at 37 degrees C with either 17 or 4 mmol/l phosphoric acid, were examined microscopically. With 17 mmol/l acid, both brushite and monetite were found after 1 equilibration but, after further equilibrations, brushite was no longer present and the abundance of monetite crystals increased. Formation of monetite probably contributed to the lower metastability of this system compared to similar low-pH systems at 25 degrees C, where monetite does not form. Neither brushite nor monetite were present after equilibration with 4 mmol/l acid. Whitlockite was identified by transmission electron microscopy and electron diffraction in all residues. In the 4 mmol/l systems, the ionic activity product (IMWH) for magnesium whitlockite, Ca9Mg(HPO4)(PO4)6, became constant after 1-3 equilibrations, at a mean value of 3.6 (+/-0.51 SE).10(-105), which may reflect saturation with respect to this solid. For the 17 mmol/l systems, higher values of IMWH, and supersaturation with respect to monetite, were interpreted as evidence for persistent metastability due to slow crystal growth of whitlockite and monetite. It is concluded that neither brushite nor monetite are likely to form within carious lesions, but the results are consistent with the known association of whitlockite with caries.

Topics: Calcium Phosphates; Crystallography, X-Ray; Dental Enamel; Dental Enamel Solubility; Electron Probe Microanalysis; Humans; Microscopy, Electron; Osmolar Concentration; Phosphoric Acids

Plasma sprayed coatings of tetracalcium phosphate, magnesium whitlockite and three types of hydroxyapatite, varying in degree of crystallinity, were evaluated with light microscopy, scanning electron microscopy and backscatter electron microscopy (BSE) after implantation periods of 1, 2 and 4 wk in rat femora. BSE revealed that both tetracalcium phosphate and semi-crystalline hydroxyapatite underwent distinct bulk degradation and loss of relatively large particles. Amorphous hydroxyapatite showed a gradual surface degradation, indicated by a transition zone varying in grey level between that of the coating and bone tissue, while degradation was negligible with the highly crystalline material and magnesium whitlockite. Degradation appeared to be related to bone apposition, since more bone seemed to be present on amorphous hydroxyapatite and tetracalcium phosphate, as compared to highly crystalline hydroxyapatite and magnesium whitlockite coatings. At the interface between bone and magnesium whitlockite, a seam of unmineralized bone-like tissue was frequently seen with light microscopy, while few areas with bone contact were present. X-ray microanalysis revealed that both the magnesium whitlockite coating and the unmineralized bone-like tissue contained substantial amounts of aluminium which, in addition to possible influences of magnesium, may have caused the impaired mineralization. The results of this preliminary study indicate that, with regard to early bone formation, amorphous hydroxyapatite coatings seem to be beneficial over highly crystalline coatings. However, further experiments should be performed to give conclusive data on (i) the statistical significance of the differences in bone apposition rate, and (ii) the long-term behaviour of both amorphous and highly crystalline coatings in bone and their relation to implant performance.

Topics: Aluminum; Animals; Biocompatible Materials; Bone Regeneration; Calcium; Calcium Phosphates; Durapatite; Electron Probe Microanalysis; Femur; Male; Microscopy, Electron; Phosphorus; Prostheses and Implants; Rats; Rats, Wistar; Sulfur

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.

Topics: Calcium Phosphates; Dental Calculus; Durapatite; Humans; Hydroxyapatites

All biological calcium phosphates form in various neutral aqueous solutions containing [CaCl2] = 1 or 3 mM, [MgCl2] = 0-9 mM, [Na2HPO4] = 0.1-90 mM and NaCl (total 300 mosM) kept quiescently at 37 degrees C for 21 days. In all solutions containing 1 mM Ca and in solutions with [Ca] = 3 mM and [PO4] less than 10 mM, heterogeneous nucleation of octa-calcium phosphate (for Mg/Ca less than or equal to 1) or brushite (for Mg/Ca greater than 1) was observed; the former transforming to apatite with time. In contrast, homogeneous nucleation of an unstable amorphous calcium magnesium phosphate occurred in solutions with [Ca] = 3 mM and [PO4] greater than or equal to 10 mM, transforming to apatite, to brushite, and to whitlockite (and newberyite) depending on Mg/Ca and [PO4] values.

Topics: Apatites; Calcium Phosphates; Chemical Precipitation; Crystallization; Durapatite; Hydrogen-Ion Concentration; Hydroxyapatites; Magnesium; Magnesium Compounds; Phosphates; Solutions; X-Ray Diffraction