In this work, we studied the dissolution of three different refractory compositions belonging to the ternary system SiO2-CaO-MgO into two Simulated Lung Fluids (SLF). The initial powder mixtures were uniaxially pressed and then sintered at 1300-1400 °C. The sintered samples were immersed for times from 1 to 21 days into a given SLF at 37 °C. The samples were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The dissolution of Ca2+, Mg2+ and Si4+ into the SLF was quantified by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The in vitro studies suggested that all the considered materials had a potential to show a diminished biopersistence in vivo, due to reasons that depended on their chemical and phase composition.