Fluoride release and uptake by glass-ionomers and related materials and its clinical effect

The anticariogenic effect of silicate cement is well known and considered a result of fluoride release. In several studies a similar fluoride release from conventional glass-ionomer cement (GIC) has been established. Therefore, an anticariogenic effect may be predicted from the GICs too. In my studies the fluoride release was studied by exposing the test specimens to a continuous flow of running tap water. At certain time periods the specimens were transferred for 1 week in a small amount of deionized water (5 ml). The determination of the fluoride content of the solution showed the fluoride release of the material at that time. There was an initial 'burst' effect of fluoride release and then the release gradually decreased, settling at a constant level. The long-term release from conventional GICs was shown to remain on the same level for at least 8 years. The amount of the constant release did not differ much between different brands. Resin-modified GICs released fluoride to the same extent and in the similar way as conventional GICs whereas polyacid-modified composites ('compomers') did not show an initial fluoride 'burst' effect. To study the fluoride binding ability of GICs, specimens which had been exposed to running water for different periods of time were treated with a 50 ppm fluoride solution. After this 'recharging' GIC and resin-modified GIC specimens released more than twice the amount of fluoride released before the treatment. The fluoride treatment had no effect on polyacid-modified composites or on fluoride-containing composites or on the amalgams. To get an impression of the clinical effect of GICs a questionnaire was handed out to practitioners attending courses in the Nordic countries and in Australia during the period 1991-1992 which resulted in 954 answers. Among other questions, the dentists were asked if they had observed caries and gingival inflammation in association with GIC and composite fillings. According to the opinion of most dentists caries and gingival inflammation had never or only seldom been observed in association with GIC fillings whereas most dentists had observed these complications often in connection with composite restorations.