Experimental setup for line positioning and scanning

The elemental analysis was performed by the μ-SRXRF 8-BM-B beamline at the Division of Advanced Photon Source, Argonne National Laboratory. The schematic setup is shown in Fig. 5. The incident beam energy of 16.3 keV was selected for Pb (Lα: 10.6 keV, Lβ: 13.2 keV) by the crystal monochromator, and the pixel size was determined by the pinhole. The processed tooth samples were first decontaminated by 50% alcohol and de-ionised water and then mounted properly by tape placed at the sample edge to the holding brackets that served as the image plane. An appropriate mounting should be flat in order to assure an even scan over the surface without scanning the tape. The image plane had an accuracy of 1 μm with a 2 axis (x,y) remote-controlled stage.

Actual (up) and schematic (down) experimental setup (http://www.stefan.vogt.net/research_interests.html).

The tooth samples were first scanned on a scale of 100 μm to obtain the mapping images. The data for each pixel with a colour scale for the mapping images were measured for 2 s for all nine images (three images for each one of the three samples), with 1 s being the measurement of the pixel itself and 1 s moving from pixel to pixel. The incisor sample had three mapping images with matrices of 61 × 41 pixels, 61 × 31 pixels, and 71 × 29 pixels, respectively. The three mapping images of molar no.1 had matrices of 61 × 13 pixels, 75 ×32 pixels, and 5 ×21 pixels, respectively, and those of molar no. 2 had matrices of 87 × 31 pixels, 62 × 30 pixels, and 61 × 31 pixels, respectively. Then, the mapping images of the metal elements were obtained via appropriate fitting, and the three lines for each tooth sample were determined by the mapping image and the coordinates of the images. The corresponding line scanning on a scale of 50 μm was performed for the microdistribution evidenced on the tooth diagrams (Figs 1 and ​and3)3) inwardly along line 1 and line 3 and outwardly along line 2. The lines were determined after consulting the dentist, reviewing a few previous studies,^[10,14,22] and taking the anatomy of the teeth into account. The total scanned length of the incisor sample was 6, 6, and 7mm for line 1, line 2, and line 3, respectively;while that of molar no. 1 was 4.4, 7.4, and 7.5mm, and that of molar no. 2 was 5.6, 7.6, and 6.1mm for line 1, line 2, and line 3, respectively. The intensity of Pb signal at different position was acquired. The microdistribution information through this very plot of intensity was inferred against position.