Fluoride Controlled-release System for Initial Lesions of Caries

Study Design:A randomized, triple-blind crossover clinical trial study was performed to evaluate the bioavailability of intraoral fluoride in biomarkers of exposure (biofilm and saliva) after the use of mouthwash with experimental fluoride for one week, with wash-out periods between them. The biofilm was collected 1 hour (h) and 12h after toothbrushing and the use of mouthwash, and saliva was collected 1h (T1 - T60 min) and 12h. The data was obtained by potentiometry (ion selective electrode) for fluoride in these samples. The pilot test was performed with three participants before the study begins.

Experimental mouthwashes:The participants were allocated randomly to use the following experimental mouthwashes: P - placebo (without F); 100% sodium fluoride (NaF) (225 ppm) - positive control; 50% nanoencapsulated fluoride (225 ppm, 50% free NaF + 50% nanoF); and 100% nanoF (225 ppm) (Savoy SA - São Paulo, Brazil). All mouthwashes were packed in similar containers and had the same color and flavor. They were coded by an independent investigator not involved in the trial.

A simple randomization was performed taking into account a cross design. The unit of randomization was "mouthwash", so all mouthwashes had the same chance of being selected. The design of the study was created for each participant and for each new one another draw was made.

Clinical stage:First, the participants were submitted to dental prophylaxis and scraping to remove all biofilm and dental calculus. They used a placebo mouthwash for 7 days. Then, the Whitford protocol was followed [17]. Briefly, the subjects were instructed to rinse 10 ml of the mouthwash 2 times / day (morning and evening) for 1 min after toothbrushing (a non-F dentifrice was used throughout the study). On the seventh day, the subjects were instructed to brush only the occlusal surfaces, rinse the mouthwash 2 times and do not use dental floss, to allow biofilm accumulation. After going to bed, they abstained from eating or drinking anything except water, did not brush their teeth or use the mouthwash. The next morning, after 12 hours of last brushing and mouthwash, and fasting, the first samples of stimulated saliva and biofilm (upper and lower right hemi-arch) were collected. Then, the volunteers brushed the occlusal surfaces and rinsed 10 mL of the mouthwash for 1 min. Soon after, saliva samples were collected in the following times: t1, t5, t10, t15, t20, t30, t45 and t60 minutes. Later, 1 hour after the mouthwash, the biofilm samples (left side) were collected.

The stimulated saliva (chewing on a silicone) was collected for 2 min, posteriorly the saliva samples were centrifuged at 6,000 rpm for 10 minutes in order to separate the saliva debris. The biofilm was collected from all tooth surfaces, in both buccal and lingual areas, using a 3S hollenback spatula, from which the samples were immediately transferred to an eppendorff tube, centrifuged, subsequently dried at 60 °C for 4 h and then weighed.

Determination of the concentration of fluoride:The samples were analyzed by the hexamethyldisiloxane (HMDS) facilitated diffusion method of Taves [21] modified by Whitford [22]. The analyzes were performed with a fluoride specific electrode (model 9409; Orion Research) and a potentiometer (model EA 940; Orion Research, Cambridge, MA, USA) (Model 720 A Orion). Fluoride standards (1-100 nM) were used to prepare calibration curves.

Statistical analysis:Statistical analysis were performed in software R considering α = 0.05. The Shapiro-Wilk and Kolmogorov Smirnov tests were applied to evaluate the normality of the data. The comparisons of F concentration in saliva and biofilm between groups were performed by repeated measures ANOVA after the Bonferroni test. The AUC measure (area below the curve) was calculated to indicate the efficacy of F retention in the saliva over the long term by taking the F concentration values in the time interval from 12h to 60 min after the last rinse. The relationship between fluoride concentrations in biofilm and saliva was determined using Spearman's correlation coefficient. The data was calculated on Graph Pad Prism (version 6) and Statistical Package (SPSS) version 23.