Comparison of salivary fluoride levels following the application of rice-based and commercial fluoride gels: a randomized crossover trial

Abstract

Salivary fluoride concentration is commonly used as an indicator of short-term fluoride exposure and clearance following topical fluoride application. Rice-based fluoride gels, formulated as rice-starch-HEC hybrid gels, may serve as alternative delivery systems; however, data regarding their salivary fluoride retention compared with standard commercial formulations remain limited. Therefore, this study aimed to evaluate the salivary fluoride retention of two novel fluoride rice-based gels in comparison with a commercial acidulated phosphate fluoride (APF) gel following professional application using a tray delivery method. A randomized, single-blind (participants), three-period crossover clinical trial was conducted in 32 healthy participants aged 18–30 years. Each participant received three different fluoride gel applications in a randomized sequence: a commercial APF gel (control), a fluoride non-glutinous rice-based gel, and a fluoride glutinous rice-based gel, with a 7-day washout period between treatments. Unstimulated saliva samples were collected at baseline and at 0, 5, 10, 20, 30, 45, and 60 min post-application. Fluoride concentration was measured using an ion-selective electrode. The area under the curve (AUC) and fluoride half-life (t½) were calculated to assess fluoride bioavailability and clearance rates. All three fluoride gel formulations produced an immediate increase in salivary fluoride concentration, with mean concentrations at 0 min ranging from 345.99 to 404.53 ppm, followed by a rapid decline over time. Salivary fluoride concentrations changed significantly over time ( p < 0.001), whereas no significant overall effect of gel formulation, gel-by-time interaction, sequence effect, or period effect was observed. AUC values did not differ significantly among the three formulations. At 60 min, mean salivary fluoride concentrations ranged from 4.94 to 5.62 ppm. The k and t½ also showed no statistically significant differences among formulations. The two rice-based APF gels showed short-term salivary fluoride concentration–time profiles, AUC values, and fluoride clearance parameters (k and t½) that did not differ significantly from those of the commercial fluoride gel. Salivary fluoride concentrations remained above the reference threshold for at least 60 min. However, further studies are needed to evaluate enamel fluoride uptake, CaF₂-like reservoir formation, acid resistance, and clinical anticaries efficacy. This study was registered in the Thai Clinical Trials Registry (TCTR; registration number TCTR20240707002) on 7 July 2024. The full registration details are available at: https://www.thaiclinicaltrials.org/show/TCTR20240707002 .