Kinetics of fluoride release from glass components of glass ionomers.

OBJECTIVES: To compare the F release from glass ionomer glasses (GICs) into water changed periodically with release into an unchanged "sink" [Williams JA, Billington RW, Pearson GJ. The glass ionomer cement: the sources of soluble fluoride. Biomaterials 2002;23:2191-200]. To evaluate the effect of replacing Ca wholly or partially by Sr. To compare two different methods of decomplexing F containing species. METHODS: All four glasses contained Al, Si, P, O and F. Glass AH2 (Advanced Healthcare Ltd.) had Na and Ca, LG26 (Advanced Healthcare Ltd.) had Ca, LG26Sr (ULTRASET project) had Ca and Sr, and LG125 (ULTRASET project) had Sr. Glasses were tested: after ball-milling, after washing in dilute acid, and W mixed with 35% acetic acid to form a "pseudo-cement". F(-) release was from 130mg samples into 10ml of deionised water changed at 1, 3, 7, 14, 21, 28, 35, and 42 days. Analysis was carried out: (a) using ISE without decomplexing, (b) using TISAB buffer, and (c) acid hydrolysis+TISAB (after Hattab). RESULT: The cumulative release rates from all glasses and treatments are linear with respect to t(1/2) with r=0.97 or greater (p=<0.001). F release into a "sink" showed no such correlation. The higher release rate from AH2 is more than accounted for by its higher F content. Most F release is not complexed except of AH2. AH2 has 20% of complex fluoride from raw glass, 44% from acid-washed glass and 51% from pseudo-cement. More fluoride is released after acid treatment from all 4 glasses, these are on average 4.4 times higher from acid-washed glass and 5.3 times higher from pseudo-cement. For TISAB fluoride release, LG26Sr is 26% more than LG26. Hattab fluoride>TISAB fluoride only for raw glasses. CONCLUSIONS: Changing water produces diffusion controlled kinetics. Acid treated will increase the complex fluoride from AH2. Replacing Ca by Sr enhances F release rate slightly.