Calcium Pre-rinse Enhances Fluoride Reactivity with Enamel and Root Dentin

Objectives: A pre-application of calcium is able to enhance fluoride retention in dental biofilm, but it is unknown if this approach could also improve the reactivity of fluoride with enamel and root dentin, forming loosely-bound fluoride reservoirs, which was tested here.
Methods: Enamel and root dentin slabs (4x4 mm) were cut from bovine teeth and polished flat. All slabs surfaces were isolated with wax leaving only the enamel or root dentin surface free for reaction. Slabs were randomized into 3 treatments (n=6 for each substrate): 1. Negative control, not treated; 2. Treatment with a 0.05% sodium fluoride solution (226 ppm F), preceded by a treatment with a 150 mM sodium lactate solution (active control); 3. Treatment with the 0.05% sodium fluoride solution, preceded by a treatment with 150 mM calcium lactate solution (experimental). Slabs were immersed in each treatment for 5 min, at 160 rpm. Loosely-bound fluoride products were extracted using 1M KOH for 24h. Fluoride concentration in the alkali extracts was determined using an ion-specific electrode. Data was analyzed by ANOVA considering the factors substrate (enamel or dentin) and treatment (α=5%).
Results: Pre-treatment with calcium, when compared with the active control, significantly enhanced fluoride reaction with enamel (from 0.21±0.11 to 5.4±3.0 μg F/cm²) and root dentin (from 0.56±0.13 to 1.8±0.8 μg F/cm²). The negative control group presented the lowest fluoride concentration (enamel=0.07±0.03; dentin=0.06±0.01 μg F/cm²), with no difference between enamel and dentin.
Conclusions: The results suggest that a calcium pre-application enhances fluoride reactivity with biofilm-free enamel and root dentin surfaces.