Longitudinal microradiography: a non-destructive automated quantitative method to follow mineral changes in mineralised tissue slices

Abstract

This paper presents a new powerful method, longitudinal microradiography (LMR), with which it is possible to follow the mineral content in a de- or remineralizing carious tooth sample as a function of position on the surface of the mineralizing tissue independent of the sample thickness. Planoparallel tooth slices (thickness 300-400 microns) are cut parallel to the labial tooth surface and then fixed on a PMMA holder. Repeated microradiographic images of the same tissue slice together with an aluminium step wedge are made on photographic film at different times of mineralisation. The images are scanned under a densitometer with a microcomputer and the mineral content per unit tooth area at the same discrete tooth-slice surface positions is calculated (maximum predefined area is 5 mm x 5 mm, 15 x 15 positions). The change of mineral in one tooth slice per unit tooth surface area can be calculated at different times of mineralisation locally, as well as averaged over the total tooth-slice surface area. The SD in average mineral change is 0.009 kg m-2, which corresponds approximately to the mineral loss involved with a 8 microns deep tooth enamel carious lesion. All results are stored on disc. In an example, the enamel surfaces (6 mm2) of five human tooth enamel slices were exposed to an acetic acid buffer solution (pH 4.8) containing Ca, P and F. The mineral content variations in the enamel sample were followed in time by longitudinal microradiography. Mineral content evaluation shows in all cases a gradual increase in mineral loss. 3D plots of the mineral loss per unit area against tooth surface position at different stages of demineralisation of the same sample show an excellent uniform local behaviour in time with all tooth slices.