Purpose: To determine the fluoride ion release/uptake of two conventional glass-ionomer cements (GICs) manufactured for use with the ART approach (Fuji IX GP, Ketac-Molar), as compared with that of a resin-modified GIC (Fuji II LC).
Materials and methods: 15 specimens of each material were prepared and placed in vials with artificial saliva and stored at 37 degrees C. The solution was replaced weekly for 6 wks, and the fluoride ions released were measured in ppm each week. After 6 wks, the 15 specimens of each material were divided into three equal groups and placed into three fluoride recharging agents (1.23% APF gel, 1.1% neutral NaF and 0.001% CaF2) for 4 min at 23 degrees C. Fluoride ion measurements of the recharged specimens were carried out at 1 day, 2 days, then weekly for another 6 wks.
Results: All freshly-mixed specimens showed the highest fluoride ion release after 1 week, then the release rates dropped quickly to become largely stabilized after 3 wks. After one 4-min exposure to APF gel the initial fluoride ion release increased significantly for all materials. The highest rates were during the first day, but then dropped very quickly to again become largely stabilized after usually 3 wks. Exposure to NaF and CaF2 did not usually result in significantly sustained fluoride ion release by any material. The order of release/uptake for all three agents was Fuji II LC > Fuji IX GP > Ketac-Molar. The mechanism of fluoride ion release after the application of different fluoride recharging agents is not clear. It may occur partly by washout of recharge agents that are retained in the pores and cracks of the restorative materials, for APF gel is viscous and difficult to wash off completely with deionized water; by erosion of surfaces by low pH agents, or by the subsequent release of fluoride ions from within the cement matrix.