Effect of a neutral citrate solution on the fluoride release of conventional restorative glass ionomer cements

This study investigates the effect of a neutral citrate solution on the fluoride release of 10 acid-base setting glass ionomer cements during 140 days at 37 degrees C.

Five disks of 10 acid-base setting restorative glass ionomers were prepared according to the manufacturer's instructions. These specimens were immersed individually in 25 ml of a 0.01 mol/l citrate solution with pH = 7. Over 140 days, the solutions were regularly renewed and the fluoride concentration eluted during each period was determined with a combined fluoride ion selective electrode.

The cumulative fluoride release was the result of an initial high release that ceased after some time and a long-term of low fluoride release. The long-term fluoride release was higher in neutral citrate solution than in water. For some formulations the short-term fluoride release also was higher in neutral citrate solution than in water suggesting that the polysalt matrix composition could be important in this respect.

The fluoride release process is due not only to a loss of relatively loosely bound fluoride in the cement matrix, but also to the release of strongly bounded fluoride inducing a long-term fluoride release. The effect of citrate on the fluoride release process may increase depending on the acid (polyacrylic acid versus copolymers of polyacrylic acid) used for the polysalt formation in the hardening cement. Depending on the competition between the polyacrylate anion and the citrate anion for the metal cation extraction the fluoride release process may be retarded.