When materials used in restorative dentistry, such as a glass-ionomer cement or a compomer, were applied to dentin, ion exchanges occur between the material and the dentin. This work is based on an assessment in vitro of the ion exchanges occurring over time between (i) a glass-ionomer cement and dentin and (ii) a compomer and dentin. An electron microprobe analysis, technique not previously used for such a study, permitted qualitative and quantitative analysis of the interface and of the peripheral dentin. Analysis of the distribution of the elements in the interface and nearby showed continuous, progressive exchanges between the glass-ionomer cement and the dentin and absence of diffusion between the compomer and the dentin.