Distribution of fluoride in glass ionomer cement determined using SIMS

The uptake by glass ionomer cement of ions (particularly fluoride) from solutions in which the cements have been immersed has been extensively reported. The distribution of these ions has not been determined. The aim of this study is to use SIMS to investigate the levels of ions within the cement at different depths below the immersed surface of the cement. K+ and F were the ions studied and uptake was into a cement containing neither K nor F (LG30) and one containing F (AH2). XPS, which is very much a surface technique, was used in confirmatory role with respect to the SIMS analysis. Cement discs were made from LG30- and AH2-based cements. After maturation for 72 h these were immersed in 0.275% KF solution for 24 h. SIMS analysis indicated appreciable surface F concentration on LG30 and on AH2 an enhanced F concentration. In contrast, K was not detected on the LG30 surface and only at a low level on AH2. These results were confirmed by XPS. Using the ion beam of the SIMS to sputter away cement enabled the F depth profile on LG30 to be measured to 10 microm. Over this distance the F content drops from 6.2 mmol/g at 0.2 microm from the surface to 0.2 mmol/g at 10 microm. No K was detected down to 13 microm from the surface. From the results of this study, it can be concluded that SIMS is an appropriate tool for further investigation of the distribution of ions uptaken by glass ionomer cements.