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 met al fluoride solutions on their interactions with glass ionomer cements. Upt ake of both fluoride and cation were measured together with change in solut ion pH and morphological changes in the cement surface. Two cements were us ed; AH2, a dental restorative cement containing both fluorine and alkali me tal (Na) as glass components and LG30, which contained neither. Discs of ce ment 1 x 10 mm were set in moulds at 37 degreesC for 1 h then, stored in wa ter for 3 days at 37 degreesC. Discs in each test group (N = 5) were immers ed in 10 ml of solutions of either NaF, KF, or RbF, all containing 900ppm F -, control discs were stored in water, all at 37 degreesC for 24h. Solution s were analysed for F- by ISE potentiometry, Na+ by the same technique and K+ and Rb+ were analysed by atomic absorption spectrometry. Uptake was obta ined by difference between solution used for immersion and the control solu tion. Solution pH was measured potentiometrically. The surface roughness of the discs was measured by linear stylus profilometry. Fluoride ion uptakes for AH2 were 451 mu mol/g NaF, 378 KF, and 318 RbF. The comparable figures for LG30 were 202, 161, and 159. Differences between cements were all stat istically significant and also between solutions pairings except for the KF /LG30 vs. RbF/LG30. Uptake of cations was equimolar for AH2/NaF, AH2/RbF an d 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 al l positive and were significantly higher for AH2 than LG30 and for RbF comp ared to the other fluoride solutions for each cement (probably because of i ts lower initial pH). The final pH of all solutions were less than 1 pH uni t from neutral (pH7). The AH2 cement test discs all showed significant incr ease in roughness (R-a) compared to control discs stored in water whereas t he LG30 discs showed no such difference. Regression analysis showed a signi ficant positive correlation between fluoride uptake and R-a. It was conclud ed that changing the alkali metal cation influenced all four variables exam ined (F- uptake, M+ uptake, pH change and extent of cement surface rougheni ng). (C) 2001 Elsevier Science Ltd. All rights reserved.