The release of fluoride ions is one of the notable characteristics of GICs. It is present originally as a flux in the manufacture of the glass, and is released from the glass particles on mixing with the polyalkenoic acid. The presence of fluoride also has benefits in increasing translucency and strength and improving handling properties . The mechanism of release is complex and not fully understood. However, it is maximum in the first few days and decreases rapidly to a lower level over weeks, and maintains a low level over months. It has also been shown that GIC can be 'recharged' with fluoride, resulting in a subsequent short-term boost in release. Most of the fluoride is released as sodium fluoride, which is not critical to the cement matrix, and thus does not result in weakening or disintegration of the set cement. Resin-modified GICs show similar dynamics of fluoride release, although for both types of material the dynamics of release and the amounts released depend on the particular material and the experimental design [79, 89].
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