Ceramics-Silikáty 53, (1) 1 - 4 (2009)

The water loss behaviour of a clinical glass-ionomer dental cement has been studied with and without the addition of alkali metal chlorides. Dehydrating conditions were provided by placing specimens in a desiccator over concentrated sulphuric acid. Cements were prepared using either pure water or an aqueous solution of metal chloride (LiCl, NaCl, KCl) at 1.0 mol/dm³ . In addition, NaCl at 0.5 mol/dm³ was also used to fabricate cements. Disc-shaped specimens of size 6 mm diameter × 2 mm thickness were made, six per formulation, and cured at 37°C for 1 hour. They were then exposed to desiccating conditions, and the mass measured at regular intervals. All formulations were found to lose water in a diffusion process that equilibrated after approximately 3 weeks. Diffusion coefficients ranged from 2.27 (0.13) × 10⁹ with no additive to 1.85 (0.07) × 10⁹ m² /s with 1.0 mol/dm³ KCl. For the salts, diffusion coefficients decreased in the order LiCl > NaCl > KCl. There was no statistically significant difference between the diffusion coefficients for 1.0 and 0.5 mol/dm³ NaCl. For all salts at 1.0 mol/dm³ and also additive-free cements, equilibrium losses were, with statistical limits, the same, ranging from 6.23 to 6.34 %. On the other hand, 0.5 mol/dm³ NaCl lost significantly more water, 7.05 %.