Kinetics of fluoride release from zinc oxide-based cements

Considerable attention has been given to the release of the cariostatic flu oride ion from glass-based dental cements (dental silicate and glass ionome r). In these, the total available fluoride content is not precisely known s ince fluorine is distributed between the cross-linked aqueous salt matrix, partially dissolved glass, and undissolved glass. In analogous cements base d on zinc oxide the fluoride is added as highly soluble SnF2. The object of this study is to compare the F- ion release profiles of commercial zinc po lycarboxylate and zinc phosphate containing 4.4 and 3.6% SnF2, respectively . Mixed cements were clamped in split ring moulds to produce discs of 10 mm x 1 mm. after storage at 37 degreesC for 1 h. Each was weighed and immerse d in 10 ml of deionised water. When this changed, at 13 time intervals up t o 98 days, the fluoride content was measured using an ion selective electro de. The mean (N = 3) values obtained were expressed cumulatively [F] in mu mol F ion/g cement. The total EF] released was 1 1 1 for the zinc polycarbo xylate and 286 for zinc phosphate compared with total F in the cements of 5 61 and 464, respectively. When the cumulative [F] was plotted versus t(1/2) close associations were found for both cements. For the polycarboxylate th e regression line [F] = 10.6t(1/2) + 9.9 fitted well over the whole 98 days (R = 0.997). For the phosphate a better fit regression line was obtained u sing results upto 32 days only; [F] = 36.8t(1/2) - 8.4 (R = 0.999). For t > 32 days results increasingly deviated from this line. These results fitted a regression line of the form [F] = 81.7 log(c) t - 87.3 (R = 0.9997). Com parisons are made with data from previous authors both for zinc phosphate c ement and glass-based cements and with diffusion theory of F ion release. I t is concluded that zinc-based cements provide some indications of how glas s-based cements may behave over long periods of release and that zinc phosp hate is the material of clinical choice for orthodontic cementation if maxi mal fluoride release is the prime criterion. (C) 2001 Elsevier Science Ltd. All rights reserved.