Water Uptake and Solubility of Resin-Modified Glass Ionomer Cement (RMGIC)

To compare water uptake, diffusion coefficients and solubility of two commercial RMGICs, Rely X Luting (RX, 3M ESPE) and Fuji Plus (FP, GC), immersed in de-ionised water (DW) up to six months.

Methods:

Six discs (15mm diameter x 1mm thickness) were prepared for each material. Following setting in an oven at 37°C for 1 hour, discs were finished and then immersed in DW at 37°C . Percentage weight change with time was recorded and plotted against time^½. After six months, discs were removed from DW and placed in a desiccator in a drying oven at 37°C. Specimens were weighed at regular intervals, as for the water uptake process, to a minimum weight. Desorption data was also plotted as mean percentage weight loss against time^½. Solubility and diffusion coefficient (D) values were calculated.

Results:

Mean percentage water uptake ranged from 4.75 ± 0.28 for RX and 5.72 ± 0.30 (wt %) for FP after six months immersion. All materials appear to have reached apparent equilibrium. Apparent D values for water uptake and desorption were higher for RX than FP (eg 1.92 x 10^-11 m²sec^-1 versus 5.84x10^-12 m²sec^-1 respectively. Similarly, the solubility of RX was higher than FP.

Conclusion:

RMGICs contain a hydrophilic monomer (hydroxyethyl methacrylate, HEMA), which absorbs water when polymerised, to form hydrogel. The increased water uptake and solubility of RX may be attributed to the liquid containing a higher amount of HEMA.