Mercury profile and speciation in human teeth restored

with dental amalgam by synchrotron microprobe

techniquesAnna Bernaus, Xavier Gaona and Manuel Valiente Grup de Tècniques de Separació en Química (GTS), Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain

Teethfilling is one of the most widespread applications of mercury. Normally, an alloy of Ag (66.7-74.5%), Sn (25.3-27.0%), Cu (0.0-6.0%) and Zn (0.0-1.9%) is mixed with elemental mercury (approximately 1:1 w/w) in order to obtain a very resistant amalgam. On the other hand, mercury is worldwide acknowledged as a hazard for both the environment and the human health [1]. The risk posed by this element is linked to two main parameters: its mobility and toxicity, which in fact are closely related and depend on the chemical speciation in which mercury is found.

Synchrotron X-ray microprobe techniques have been proposed for the direct observation of mercury and other elements present in human teeth restored with dental amalgams, to assess the elemental diffusion from tooth fillings and their possible uptake by the blood stream via the teeth pulp. µ-XRF (microscopic X-ray Fluorescence) analyses have been undertaken to identify elemental profiles distribution and qualitative trends on elemental associations in the tooth and µ-EXAFS (microscopic Extended X-ray Absorption Fine Structure) analysis have determined the speciation and molecular environment of Hg, in order to assess its possible solubility and mobility.

Introduction Experimental set-upMicroprobe analyses were performed at the synchrotron facility Hamburger Synchrotronstrahlungslabor (HASYLAB) in Hamburg (Germany) [2], at the bending magnet beamline L.

1. Polycapillary halflens

2. Fluorescence detector

3. CCD-camera

4. Sampler1

4

2

3

For µ-XRF analysis, the beam was monochromatized at 13 keV, and maps contained 11 × 11 points with a step size of 10 μm vertically and horizontally to provide the monitoring for mercury. µ-XAS analyses were performed by measuring Hg Lα1 (9988 eV) and Hg Lα2 (9897 eV) fluorescent line intensities.

The study of the local configuration around the mercury atom in the amalgam region was obtained through the Fourier transform and FEFF codes. Data treatment was performed by using the IFEFFIT data analysis software package [3].

DeviceSource energyMaximum CurrentMonochromator crystalsResolution (ΔE/E)Photon flux at sample positionSpot size at the sampleDetector

Geometry

T(K)

Bending magnet4.5 GeV150 mASi (111)

~10-4

some 109 phot s-1

15 µm (FWHM, diameter) Si (Li) and silicon drift detector45º beam - sample,45º sample - detectorRoom

References[1] U. Förstner, Integrated Pollution Control, ed. A. Weissbach and H. Boeddicker, Springer-Verlag, Berlin, 1998

[2] HASYLAB at DESY [online], www.hasylab.de

[3] Newville, M., IFEFFIT: interactive XAFS analysis and FEFF fitting. Journal of Synchrotron Radiation, 2001. 8: p. 322-324

µ-XRF analysis

Sample preparation

µ-EXAFS analysis

Fig. 2 Original teeth sample Fig. 4 Teeth slice

mounted for synchrotron analysis

Conclusions

Acknowledgments

The microprobe analysis showed a minimum diffusions of all elements (Mn, Fe, Cu, Zn, As, Br and Pb) throughout the tooth. A linear correlation between Hg, Cu and Br was identified.

Fig. 3 Longitudinal section of teeth sample inserted in a hard resin block

Fig. 7 Spatial distribution of Hg, Cu, Zn and Ca throughout the tooth structure (amalgam, dentine, pulp cavity and root), as fluorescence intensity (counts/s)

Fig. 5 μ-XRF elemental maps for Hg, Br, Ca, Fe, Mn, Pb, Zn, Cu and As and Zn on a thin section (100 μm2 area) in the amalgam region. White colors shows the higher count-rate for each element (arbitrary units)

Fig. 6 Pair correlation diagrams of different elements relative to Hg, from the μ-XRF maps of the averaged studied samples, as fluorescence line intensity (counts s-1)

Fig. 1

a) b) c)

Experiments revealed synchrotron-based microprobe techniques as a powerful tool to provide unique information in micro spatial areas of dental hard tissues. Elemental correlations show significant relationships between mercury and other elements present in the amalgam. These amalgam components do not diffuse in the tooth. Nevertheless, the study is limited to assess future medical considerations on dental restorations. In this concern, further investigations will be undertaken at the amalgam-dentine and amalgam-enamel interfaces, taking into consideration the medical history of each dental specimen.

This work was supported by the European Community - Research Infrastructure Action under the FP6 "Structuring the European Research Area" Programme (through the Integrated Infrastructure Initiative "Integrating Activity on Synchrotron and Free Electron Laser Science")Contract RII3-CT-2004-506008, and the research project CTQ2005-09430-C05-01/PPQ, of the Spanish Ministry.

Analysis of the alloy particles reveals the interaction of elemental mercury into a Ag3Sn phase, as well as the presence of O2 indicating the possible interaction of mercury with the environment and its transformation with time.

Hg-O

Hg-Ag3

Hg-Sn

Fig. 8 Steps in the analysis of an EXAFS spectrum: (a) fit of background of the normalized spectrum, (b) background-subtracted EXAFS function in the k space, and (c) radial distribution of the Fourier transform