A continuous flow system for assessing fluoride release/uptake of fluoride-containing restorative materials

Objectives. The aim of this study was to develop a continuous flow system to mimic the kinetics of salivary flow in the mouth and to study the fluoride (F) release/uptake characteristics of both a conventional (Fuji IX) and a resin-modified glass ionomer (Vitremer) in such system. Methods. Five discs were made for each material. The disc was suspended in a drip chamber sustaining 2 ml of deionized water. The flow rate was controlled at 20 ml/h by an infusion pump. The F release in the drip chamber was assessed at designated time points for up to 6 days. The discs were subjected to 1 min exposures of 0.2% sodium fluoride (NaF); the F re-release was assessed for another 12 h. Results. Following a brief initial burst of F release, the rate decreased rapidly. Vitremer reached a steady low after 8 h, while Fuji IX reached a steady low after 90 min. Cumulative F release was measured from both the effluence and the drip chamber and showed that Vitremer released and took up more F than Fuji IX, both before and after F treatment. Cumulative amounts of fluoride in the drip chamber were much less than that in the effluence. The daily release rate patterns from the two materials were parallel. However, the hourly release rate of Vitremer decreased more gradually than Fuji IX. After sodium fluoride (NaF) treatment, F can be recharged easily and re-released rapidly within 90 min. Conclusion. This study indicates that the continuous flow method can be used to assess F release/uptake of the material. This method may represent a closer model to in vivo conditions.