The Effect of Ionic Solutions on the Uptake and Water-binding Behaviour of Glass-ionomer Dental Cements

Water uptake in two glass-ionomer cements stored in various aqueous ionic solutions has been studied following a 6-week storage period, and the bound/unbound water ratio has been determined. Both types of cement took up water with net uptake varying with the storage solution. Uptake was greatest with KCl and lowest for 0.9 % NaCl. By comparison with an immature (1 hour old) specimen of each cement, specimens generally showed a distinct increase in bound/unbound water at 6 weeks, though for specimens stored in 0.9 % NaCl, there was an apparent reduction in this ratio, which is attributed to greater dissolution than uptake in this solution. Specimens stored in the artificial saliva solution Biotene contained significantly lower amounts of unbound water after 6 weeks than in all other solutions. Water was thus shown to become bound within these cements during a relatively slow process, and a mechanism for this water-binding is proposed.