Objectives: To compare the microhardness and ion content of three glass-ionomer cements (GICs) during setting and up to 15 days, to composite resin-based material in vitro, and after 5 to 10 years in vivo. Method and materials: Disks of three GICs, EQUIA Fil, Riva Self Cure, and Ketac Molar were examined in vitro for microhardness using Vickers indentations after 15 to 60 minutes, 24 hours, and 8 and 15 days, and compared to composite material, Spectrum. The ion content of the GIC and composite was analyzed using the energy dispersive spectroscopy program of a scanning electron microscope. A primary second molar restored with GIC normally exfoliated after 5 years, and a third molar restored with GIC extracted due to periodontitis after 10 years, were sliced through the restoration buccolingually, and the microhardness of the restoration and of the dentin was measured. Results: In comparison to composite material, the Vickers value for the GICs were similar or better after 24 hours to 15 days. The amount of fluorine was three times higher in EQUIA Fil and Riva Self Cure in comparison with Ketac Molar, after 20 days. After 5 years in vivo, the microhardness of GICs was similar to dentin and after 10 years it was significantly higher than that of the dentin. Conclusion: The microhardness of GICs was comparable to composite material after only 24 hours. In vivo the microhardness of GICs increased and after 10 years in vivo it was higher than that of the dentin. After 20 days the amount of fluorine was still high in Riva Self Cure and EQUIA Fil. Keywords: fluorine, glass-ionomer cement, inorganic ions, microhardness