Water absorption of methacrylate soft lining materials.

The water absorption of soft methacrylate prosthetic materials is very high compared with rigid methacrylates and is not at an equilibrium value even after 6 yr. This very high and prolonged uptake can be explained qualitatively in terms of the presence of water soluble impurities which form sites for the formation of water droplets. These droplets grow until the osmotic and elastic forces balance; this mechanism can be accompanied by creep or even rupture under the osmotic pressure. Desorption on the other hand, is rapid and obeys diffusion laws, giving diffusion coefficients of 5-7 X 10(-8) cm2 s-1.