Two cycles of sorption/desorption of water or ethanol by light-cured dental resins of bisphenol A glycol dimethacrylate (Bis-GMA), bisphenol A ethoxylated dimethacrylate (Bis-EMA) urethane dimethacrylate (UDMA) triethylene glycol dimethacrylate and decanediol dimethacrylate (D(3)MA) were studied. The experimental curves m(t) = f(t) taken for the first water sorption by poly-Bis-GMA, poly-Bis-EMA and poly-UDMA showed a maximum. A maximum was also observed in the curve obtained for first sorption of ethanol by poly-Bis-GMA. In all other cases, the curves for sorption or desorption of water or ethanol showed Fickian behavior. The experimental data obtained for first sorption of water or ethanol were perfectly fitted to a new proposed equation, which predicts water or ethanol sorption with simultaneous extraction of unreacted the monomer. This equation gave us the possibility for the determination of the diffusion coefficient of the extraction of the unreacted Bis-GMA during the water and ethanol sorption, as well as the diffusion coefficient of the extraction of the unreacted Bis-EMA and UDMA during the water sorption. The maximum water or ethanol absorbed at equilibrium and the diffusion coefficient are determined from the second sorption/desorption cycle during which the extraction of the monomer is negligible. (C) 2007 Wiley Periodicals, Inc.