Glass ionomer cement: evidence pointing to fluorine release in the form of monofluorophosphate in addition to fluoride ion

The fluoride ion released from glass ionomer cements into water is reportedly, in part, complexed with other elements present in the cement. When measured using ion selective electrode potentiometry (ISE) a decomplexant TISAB IV (T) is used to convert all fluoride to F− ion which the ISE can detect. In this study, an additional decomplexing procedure (H) designed to hydrolyse fluorine covalently bonded to phosphorus in the monofluorophosphate (MFP) ion into F− was also used. The soluble products from three glass ionomers were analysed by both techniques (H & T). Five 1×10 mm discs were each immersed in 10 ml of de-ionised water. This was changed and 4 ml analysed by T and 4 ml by H at 1, 2, 3, 6, 10, 13, 17, 21, 24, 28, and 31 days. H was greater than T for 161 of the 165 pairs (X2=74.7,p=<0.001). The total cumulative F release H (in μmol/g cement) at 31 days for AH2 was 122.3, s.d. 30.8; LG26 44.0, s.d. 1.55; LG30 10.0, s.d. 3.15 as compared T results of 100.1, s.d. 31.1; 30.3, s.d. 1.92; 3.7, s.d. 1.36, respectively. In all three cases the H was significantly greater than T (matched pair ‘t’ test with p=0.01 or less). H–T was show to have a very strong associative relationship with t1/2 (R2=0.98 or greater P<0.001). Evaluating the ratio of P:F in the cements in comparison with the ratio of additional F measured by H to that measured by T produced a relationship log[(H−T)/T]=0.28×log[P/F]−0.45 with R2=0.999. It is concluded that glass ionomers release more fluorine than is detected by ISE using TISAB IV. If this F is in the form of MFP this may be released more completely into saliva than F as F−, release of which is substantially reduced by Ca2+, since calcium monofluorophosphate is more soluble than CaF2.