The anticaries effect of professional fluoride application has been associated with the formation of calcium fluoride-like products ("CaF2") on dental surface, which may function as a slow release fluoride reservoir. Among professional fluoride products, fluoride gel and varnish are the most important, and have different soluble fluoride concentrations, pHs and vehicles. Although the concentration of fluoride formed on enamel after the use of both is similar, the retention of these reaction products is unknown. Also, it is unknown the capacity of these reservoirs to enhance dental biofilm fluid with fluoride. Moreover, the effect of the varnish application time on these parameters is unknown. Therefore, the aim of this study is to compare the capacity of fluoride gel and varnish to form fluoride reservoirs on enamel and increase dental biofilm fluid fluoride concentration with time. Rapid biofilm-forming individuals will be selected to participate and divided into 4 experimental groups: 1. Negative control: no treatment; 2. Varnish 4 hours: fluoride varnish will be applied and kept on teeth for 4 hours; 3. Varnish 24 h: fluoride varnish will be applied on teeth and kept for 24 h; and 4. Gel: Fluoride gel will be applied on teeth. Microbiopsies of enamel will be obtained by a microbiospy technique to assess fluoride concentration before, 7 and 28 days after the treatments. Dental biofilm will be collected before and 3, 7, 14 and 28 days after treatments. Fluoride concentration on enamel and in the biofilm fluid will be determined by an ion-specific electrode. Data will be analyzed statistically comparing the groups and collection times.

Inclusion Criteria:

• Good general health
• Good oral health
• At least 5 teeth in each hemiarch
• All 4 superior incisors in the mouth
• Rapid biofilm forming

Exclusion Criteria:

• Pregnancy
• Intake of medication that reduces salivary flow
• Chronic diseases
• Smokers
• Orthodontic appliances
• Dental prosthesis
• Allergy to fluoride varnish components