Interactions between glass ionomer cement and alkali metal fluoride solutions: the effect of different cations

This study examines the effect of different cations in equimolar alkali metal fluoride solutions on their interactions with glass ionomer cements. Uptake of both fluoride and cation were measured together with change in solution pH and morphological changes in the cement surface. Two cements were used; AH2, a dental restorative cement containing both fluorine and alkali metal (Na) as glass components and LG30, which contained neither. Discs of cement 1×10 mm were set in moulds at 37°C for 1 h then, stored in water for 3 days at 37°C. Discs in each test group (N=5) were immersed in 10 ml of solutions of either NaF, KF, or RbF, all containing 900 ppm F−, control discs were stored in water, all at 37°C for 24 h. Solutions were analysed for F− by ISE potentiometry, Na+ by the same technique and K+ and Rb+ were analysed by atomic absorption spectrometry. Uptake was obtained by difference between solution used for immersion and the control solution. Solution pH was measured potentiometrically. The surface roughness of the discs was measured by linear stylus profilometry. Fluoride ion uptakes for AH2 were 451 μmol/g NaF, 378 KF, and 318 RbF. The comparable figures for LG30 were 202, 161, and 159. Differences between cements were all statistically significant and also between solutions pairings except for the KF/LG30 vs. RbF/LG30. Uptake of cations was equimolar for AH2/NaF, AH2/RbF and LG30/KF but M+ : F− ratios were significantly above unity for AH2/KF and LG30/NaF and significantly below unity for LG30/RbF. The pH changes were all positive and were significantly higher for AH2 than LG30 and for RbF compared to the other fluoride solutions for each cement (probably because of its lower initial pH). The final pH of all solutions were less than 1 pH unit from neutral (pH7). The AH2 cement test discs all showed significant increase in roughness (Ra) compared to control discs stored in water whereas the LG30 discs showed no such difference. Regression analysis showed a significant positive correlation between fluoride uptake and Ra. It was concluded that changing the alkali metal cation influenced all four variables examined (F− uptake, M+ uptake, pH change and extent of cement surface roughening).