Water uptake of soft lining materials from osmotic solutions

The water uptake characteristics of soft lining materials are of obvious importance in that they are expected to function in the oral environment. Results for Novus (Hygenic Corp., Akron, OH, USA) show a very high uptake from distilled water. Despite this high uptake, Novus appears to function satisfactorily in the mouth. High water uptake of soft lining materials has been attributed to the presence of water soluble impurities that, on immersion, form solution droplets; the driving force for the uptake being the osmotic gradient between the droplets and the external solution. Uptake should therefore be less from ionic solutions. The object of this study was to test the applicability of this theory to Novus and two experimental soft lining materials.

Water uptake of two experimental materials and Novus has been determined from distilled water and two saline solutions (0.45 and 0.9 M). After 196 days specimens were desorbed to constant weight and then subjected to a second sorption cycle.

Novus had the highest uptake from distilled water at approximately 18%, the experimental materials having an uptake approximately 7%. Desorptions were all rapid, minimum weight being reached within 1-2 days. Uptakes of the second sorptions from water were all higher. Uptake from saline solutions was approximately 12% for all materials, uptake from 0.9 M saline being the lowest. Second sorption results from solution were similar to the first.

The results obtained support the theory that the high water uptake of elastomeric materials is osmotically driven.