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Acidic demineralization of apatites studied by scanning X-ray microradiography and microtomography

Published online by Cambridge University Press:  05 July 2018

J. C. Elliott ,
F. R. G. Bollet-Quivogne ,
P. Anderson ,
S. E. P. Dowker ,
R. M. Wilson  and
G. R. Davis
J. C. Elliott*
Affiliation:
Institute of Dentistry, Queen Mary, University of London, Francis Bancroft Building, Mile End Rd, London E1 4NS, UK
F. R. G. Bollet-Quivogne
Affiliation:
Institute of Dentistry, Queen Mary, University of London, Francis Bancroft Building, Mile End Rd, London E1 4NS, UK
P. Anderson
Affiliation:
Institute of Dentistry, Queen Mary, University of London, Francis Bancroft Building, Mile End Rd, London E1 4NS, UK
S. E. P. Dowker
Affiliation:
Institute of Dentistry, Queen Mary, University of London, Francis Bancroft Building, Mile End Rd, London E1 4NS, UK
R. M. Wilson
Affiliation:
Institute of Dentistry, Queen Mary, University of London, Francis Bancroft Building, Mile End Rd, London E1 4NS, UK
G. R. Davis
Affiliation:
Institute of Dentistry, Queen Mary, University of London, Francis Bancroft Building, Mile End Rd, London E1 4NS, UK
*
*E-mail: j.c.elliott@qmul.ac.uk
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Abstract

The mineral in bones and teeth is an impure form of hydroxylapatite (HAP), the principal impurity being 2—5 wt.% carbonate. This mineral dissolves during remodelling of bone and also in dental caries as a result of the action of acids produced by osteoclasts and by bacteria, respectively. In enamel, demineralization proceeds with preferential loss of carbonate relative to phosphate. Surprisingly, in the early stages, the demineralization is subsurface. In order to facilitate the understanding of physical chemical aspects of these processes, we have undertaken studies of demineralization in model systems. We give three examples here. The first two used scanning microradiography in which the specimen is stepped across a 10—30 μm diameter X-ray beam. Intensity measurements allow calculation of the mineral mass per unit area in the X-ray path through the specimen. In the first experiment, porous HAP sections were separated from a reservoir of acidic buffer by a column initially filled with water (the diffusion length) and scanned with the X-ray beam perpendicular to the axis of the diffusion length. The rate of total loss of mineral along each profile was calculated from the scans. The rate of demineralization fell as the diffusion length increased. We believe the explanation is that the rate-controlling step is the diffusion of dissolved HAP away from the solid to the buffer reservoir. In the second experiment, demineralizing solution and water were pumped alternately, for equal lengths of time, past blocks of porous HAP or enamel. The X-ray beam was perpendicular to the exposed surface. As the rate of switching between solutions decreased, the mean rate of demineralization also fell. We propose that this effect is due to retention of acid in the pores of the HAP during the time when water flows, allowing further demineralization to take place during this time. The third study used X-ray microtomography, a form of 3D microscopy, to study the loss of mineral in compacted carbonate apatite powders. The powders were packed in six 10 mm internal diameter acrylic cylinders to a depth of 4 mm (after pressing). One end was covered with a porous polyethylene disc and each tube placed in acidic buffer for 70 days. Periodic examination by microtomography showed the development of subsurface demineralization. Infrared spectroscopy of the dissected-out surface layers showed preferential loss of carbonate over phosphate by comparison with deeper layers. Rietveld analysis of X-ray powder diffraction data showed changes in the crystallographic structures of the apatites between the initial and dissected-out apatite.

Keywords

dental enamelhydroxylapatiteteethdemineralizationX-ray microtomographyscanning microradiography
Type
Research Article
Information
Mineralogical Magazine , Volume 69 , Issue 5 , October 2005 , pp. 643 - 652
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2005

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References

Anderson, P., Levinkind, M. and Elliott, J.C. (1998) Scanning microradiographic studies of rates of in vitro demineralization in human and bovine dental enamel. Archives of Oral Biology, 43, 649—656.CrossRefGoogle ScholarPubMed
Anderson, P., Elliott, J.C., Dowker, S.E.P. and Bollet-Quivogne, F.R.G. (2003) Scanning microradiography — a digital 2-D X-ray imaging technique. G.I.T. Imaging and Microscopy, 5, 22—24.Google Scholar
Berner, R.A. (1978) Rate control of mineral dissolution under earth conditions. American Journal of Science, 278, 1235–1252.CrossRefGoogle Scholar
Bollet-Quivogne, F.R.G., Anderson, P., Dowker, S.E.P. and Elliott, J.C. (2005) Scanning microradiographic study on the influence of diffusion in the external liquid on the rate of demineralization in hydroxy-apatite aggregates. European Journal of Oral Sciences, 113, 53–59.CrossRefGoogle Scholar
Davis, G.R. (1998) Faster tomographic fan-beam back-projection using Cartesian axes pre-projection. Nuclear Instruments and Methods in Physics Research Section A, 410, 329–334.CrossRefGoogle Scholar
Davis, G.R. and Elliott, J.C. (2003) High definition X-ray microtomography using a conventional impact X-ray source. Journal de Physique IV, 104, 131–134.Google Scholar
Dowker, S.E.P., Anderson, P., Elliott, J.C. and Gao, X.J. (1999) Crystal chemistry and dissolution of calcium phosphate in dental enamel. Mineralogical Magazine, 63, 791–800.CrossRefGoogle Scholar
Elliott, J.C. (1994) Structure and Chemistry of the Apatites and Other Calcium Orthophosphates. Elsevier, Amsterdam.Google Scholar
Elliott, J.C. (1997) Structure, crystal chemistry and density of enamel apatites. Pp. 54–72 in: Dental Enamel (Chadwick, D. and Cardew, G., editors). CIBA Foundation Symposium, 205. John Wiley & Sons, Chichester, UK.Google Scholar
Elliott, J.C, Anderson, P., Gao, X.J., Wong, F.S.L., Davis, G.R. and Dowker, S.E.P. (1994) Application of scanning microradiography and X-ray microtomography to studies of bones and teeth. Journal of X-ray Science and Technology, 4, 102—117.CrossRefGoogle ScholarPubMed
Gao, X.J., Elliott, J.C, Anderson, P. and Davis, G.R. (1993) Scanning microradiographic and microtomographic studies of remineralisation of subsurface enamel lesions. Journal of the Chemical Society, Faraday Transactions, 89, 2907–2912.CrossRefGoogle Scholar
Hallsworth, A.S., Robinson, C. and Weatherell, J.A. (1972) Mineral and magnesium distribution within the approximal carious lesion of dental enamel. Caries Research, 6, 156—168.CrossRefGoogle ScholarPubMed
Hallsworth, A.S., Weatherell, J.A. and Robinson, C. (1973) Loss of carbonate during the first stages of enamel caries. Caries Research, 7, 345—348.CrossRefGoogle ScholarPubMed
Larson, A.C and Von Dreele, R.B. (1986) GSAS, General Structure Analysis System. Los Alamos National Laboratory Report, LAUR 86–748.Google Scholar
Morgan, H., Wilson, R.M., Elliott, J.C, Dowker, S.E.P. and Anderson, P. (2000) Preparation and characterisation of monoclinic hydroxyapatite and its precipitated intermediate. Biomaterials, 21, 617—27.CrossRefGoogle ScholarPubMed
Nowotny, H. and Heger, G. (1986) Structure refinement of lead nitrate. Acta Crystallographica, C42, 133–135.Google Scholar
Weatherell, J.A., Deutsch, D., Robinson, C. and Hallsworth, A.S. (1977) Assimilation of fluoride by enamel throughout the life of the tooth. Caries Research (Supplement 1), 11, 85–115.CrossRefGoogle ScholarPubMed
Wilson, R.M., Elliott, J.C. and Dowker, S.E.P. (1999) Rietveld refinement of the crystallographic structure of human dental enamel apatites. American Mineralogist, 84, 1406–1414.CrossRefGoogle Scholar
Wilson, R.M., Elliott, J.C, Dowker, S.E.P. and Smith, R.I. (2004) Rietveld structure refinement of precipitated carbonate apatite using neutron diffraction data. Biomaterials, 25, 2205–2213.CrossRefGoogle ScholarPubMed