Objective: The objective of this study was to examine whether the recharging of glass ionomer materials with fluoride affects their strength. Methods: Three different types of glass ionomer materials were tested: Fuji IX (GC), FG; Fuji II Improved (GC), LC; and Reactomer (Shofu), RE. Specimens (6mm diam., 3mm thick) were prepared for each material using Teflon molds. LC and RE specimens were light-cured for 40 sec on the top and bottom surfaces. One hour after mixing or curing, the specimens were immersed in deionized water at 37°C up to 9 weeks. Fluoride recharging was done at 3 and 6 weeks after the start of immersion using an acidulated fluoride phosphate gel (Fluorident Gel, Stone Pharma.) as follows: the specimens were taken out of the deionized water and dipped into the gel for 5 min. They were rinsed with deionized water and immersed in the water again. Control specimens, which were not subjected to the recharging, were also prepared. The diametral tensile strength of specimens was determined one day after the start of immersion (baseline) and then 3 weeks after each recharging. Results: The strengths (MPa, Mean±SD, n=6) were as follows. At 6 weeks, the recharged vs. control specimens were 18.7±2.2 vs. 19.3±2.2 for FG, 28.8±3.4 vs. 28.9±1.1 for LC, and 35.2±6.2 vs. 36.1±5.6 for RE. At 9 weeks, results were 18.9±2.6 vs. 18.9±2.5 for FG, 28.0±4.2 vs. 28.1±4.6 for LC and 29.2±7.5 vs. 31.8±8.9 for RE. For all materials, the recharged specimens did not show significant differences (p>0.05) in strength after either the first or second recharging compared to the specimens without recharging. The strengths of specimens recharged twice did not significantly (p>0.05) differ from those recharged once. Conclusion: Under the experimental conditions tested, fluoride recharging of glass ionomer materials did not appear to deteriorate the strength of the materials.

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