SummaryGlass ionomer cement (ASPA®) was inserted in unconditioned class V cavities or in contact with polished ground surfaces of enamel and dentine in twelve teeth. Ground sections of all teeth were examined by microradiography, and four of the sections submitted to electron probe microanalysis. A narrow outer zone of increased radiopacity in the dentine walls was explained by a 5−10% increase of Ca and P. In some sections this zone covered a partly demineralized subsurface zone. The concentrations of F and Al in enamel and dentine were ∼0.3% and 1.5%, respectively, decreasing to<0.1 % at a distance of 16–80 μm (F) and 8–24 μm (A) from the surface. Both F and Al penetrated deeper into the dentine than into the enamel. Decreased Zn values, sometimes concomitant with increased Ca, P and Mg values, were in some instances observed in an outer narrow zone of the dentine walls. It is assumed that like silicate cement, glass ionomer cement must have anticariogenic properties, due to uptake of F and Al in ca