Effect of monovalent ions in glass ionomer cements on their interaction with sodium fluoride solution

The effects on surface morphology of glass ionomer cements following exposu re to 0.2% NaF solution were studied. The effect of cement on the solution was also evaluated. The four cements were chosen to contain Na and F, Na al one, F alone and neither Na nor F to show any interactions produced by havi ng the same ion in both the cement and solution. Four glass ionomer cements were formulated so that they differed only in respect of the glass compone nt. AH2 (a glass used in dental restorative cement) contained both Na and F , MP4 (a glass used in orthopaedic cement) contained Na, only, LG26 (a glas s used in surgical cement) contained F only and LG30 (an experimental contr ol glass) contained neither F nor Na. Discs of cement were set in moulds at 37 degrees C for 1 h, then matured in water for 3 d. Each test disc was th en immersed in 10 mi 0.2% NaF for 24 h at 37 degrees C whereas control disc s remained in water. The test and control disc surfaces were assessed quali tatively using electron microscopy and quantitatively by linear profilometr y generating roughness values (Ra). Test solution pH was measured before an d after cement immersion. Inspection of the electron micrographs showed con siderable disruption of AH2 and LG26 test surfaces compared to 1:heir contr ols whereas MP4 and LG30 showed similar surfaces for test and control. Stat istical analysis of the Ra values showed that AH2 and LG26 test surfaces we re significantly rougher than their controls as well as LG30 and MP4 test s urfaces, which were not significantly different from their controls. All Na F solutions show pH increases; those for AH2 and MP4 were significantly hig her than those for LG26 and LG30. The F-containing cements were subject to surface disruption whereas F-free cements were not. The Ra values of test s urfaces correlated strongly (r = 0.998) with the F uptake of the cements (d ata from a previous study) but it was not possible to ascribe the causality to this association. The pH changes appear to be influenced by whether or not Na is present in the cement. The resultant pH values are too near to ne utral for pH alone to explain the surface disruption observed. In addition, it is concluded that the changes in OH ion concentration are too low to pe rmit F-/OH- interchange as a possible explanation for F uptake by these cem ents. (C) 1999 Elsevier Science Ltd. All rights reserved.