The aim of this in vitro study was to evaluate the characteristics of four commercial dental composites: two dual-curing luting resin cements and two indirect composites for crowns and bridges. The novelty of the study consists in the use of combined characterization methods for the investigated materials, namely: after maintaining the samples in the water/ artificial saliva, besides sorption, the surface degradation of the samples was observed after their immersion period; thereafter, the immersion medium was lyophilized and then the percentage of residual monomer found in the medium was determined by HPLC. After 44 days, small concentrations of monomers have been determined in the aqueous/saliva extracts. SEM images show that the samples from each class of material, with a higher content of inorganic filler, exhibit a larger erosion of the surfaces after contact with water compared to the other two samples that show a larger erosion of surfaces after contact with saliva than with water. The surface of the dual-curing resin cement with a higher content of inorganic filler is the smoothest from the samples exposed to saliva, instead the other resin cement is the roughest, as shown by AFM analysis. The overall observation reveals that the samples kept in saliva are rougher than the ones kept in water. Smooth surface materials of both classes of materials ( with a higher content of inorganic filler) have absorbed a higher amount of water / saliva compared to materials with a rougher surface.Water sorption in the composite resins is influenced by the hydrophilicity of the monomers, the nature and size of the inorganic filler particles, and the quality of the matrix / filler interface.