Evaluation of free and total fluoride concentration in mouthwashes via measurement with ion-selective electrode

Abstract Background Mouthwashes are among the currently used oral hygiene products aimed at preventing and reducing dental caries. This is accomplished by a remineralization process, due to the presence of fluoride ions; however, mouthwashes should also contain an appropriate amount of unbound or free fluorides to provide bioavailability. The aim of this study was to compare active fluoride concentration and total fluoride concentration in mouthwashes. Methods Fluorine-containing mouthwashes from various companies and manufacturers (Colgate Total Plax Classic Mint®, Colgate Total Plax Gentle Mint®, Colgate Total Plax Fresh Mint®, Oral B Advantage®, Reach Fresh Mint®, Foramen®, Lacalut Sensitive®, Sensodyne®, Vesna F®, and Lacalut Fresh®) were selected as study objects. Fluoride measurements were carried out using the method of potentiometry. Results Free fluoride:total fluoride ratio was more than 80% for six samples and less than 63% for three samples. Two samples had more than 70% and less than 80% of unbound fluoride, respectively. Rinse containing sodium monofluorophosphate (Na2PO3F) had more than 50% of free fluoride, while the rinses containing amine fluoride (AmF) had 94%. The difference in activity can be explained by binding of fluoride ions by components contained in mouthwashes, such as coloring agents, polymeric compounds, etc. The lowest activity was observed for aluminum fluoride (AlF3) rinse, due to possible generation of strong fluoride complexes. This implies that fluoride ions will not be uptaken by tooth tissue and may even be washed away from it, compromising the efficacy of mouthwashes. Conclusions There is an urgent need to develop a method for evaluation of free fluorides in mouthwashes for proper updating of national and international guidelines.