A warmed topical fluoride solution enhances KOH-soluble and -insoluble fluoride formation on tooth surfaces in vitro

In paediatric dentistry, topical application of fluoride is a vital routine preventive procedure. Therefore, it is important to identify more effective methods of fluoride application. This study investigated the effect of warmed topical fluoride solutions on human enamel. Several solutions (acidified phosphate fluoride (APF), 2% NaF or 0.2% NaF) were applied to human premolars for 5 min at 25, 37, 50, and 60 °C. KOH-soluble and -insoluble fluoride formation on the enamel surface was then measured. KOH-soluble fluoride formation increased proportionally with temperature. KOH-soluble fluoride levels at 60 °C were 1.7-, 2.6-, and 2.7-fold greater than at 25 °C for 0.2% NaF, 2% NaF, and APF, respectively. Also, KOH-insoluble fluoride incorporation into the enamel increased proportionally with the solution temperature. KOH-insoluble fluoride levels at 60 °C were 4.9-, 7.5-, and 2.8-fold greater than at 25 °C for 0.2% NaF, 2% NaF, and APF, respectively. The dissolution of enamel in APF at the time of topical application is a major clinical concern. Therefore, the dissolved calcium in the APF solution was assayed and found to be equivalent to enamel thicknesses of 0.007, 0.042, 0.045, and 0.05 μm respectively. The effect of increasing the temperature outside the tooth on the pulp temperature was monitored for 5 min. Pulp temperature increased by 3 and 8 °C using solutions at 50 and 60 °C, respectively, which was considered to be unlikely to have adverse effects on the pulp. The warming of topical fluoride solution, even slightly, can be a useful method to make the topical fluoride application more effective.