Fluorapatite and Calcium Fluoride Bioavailability in Rat Dentin

The interaction between fluoride and dental structures may involve exchange with hydroxyl hydroxyapatite, with the formation of fluorapatite (FA) and calcium fluoride (CaF₂) precipitation, suggesting that the fluoride uptake may have different optimal biochemistry conditions.

Objectives: To evaluate the fluoride levels obtained in CaF₂ and FA samples extracted from rat dentin, with potential participation in dentin remineralization.

Methods: Standardized cavities in rat teeth were created, exposing dentin surfaces with areas strictly defined. The cavities were extended to the dentin in an area of 1 mm² in the superior and 2 mm² in the inferior teeth, with high rotation, after the animals had been anesthetized with thionembutal. The teeth were cut with a carborundum disk and washed with distilled/de-ionized water, subjected to evaporation with a paper filter, and dehydrated to 90^oC during 3 hrs. After dehydration, the cavities were filled with adhesive-coated tape and blue wax. The remainder of the tooth was waxed with red wax. After these procedures, the cavities were prepared, and the blue wax and coated tape were removed, with the aid of a microscope. The exposed cavities underwent microbiopsies with 0.3 mL KOH M during 24 hrs in agitation, being neutralized with 0.30 mL TISAB (HCl M). The obtained samples were used to determine the fluoride concentration in the CaF₂ form (n=58) through the selective electrode Orion 96-09. For analysis of the fluoride concentration in the FA form (n=58), the cavities were subjected to 0.30 mL HCl 0.5 M during 2 min in agitation after the CaF₂ sample preparation, being neutralized with 0.30 mL TISAB (20 g NaOH/L).

Results: The standard regression curves were calculated (R² = 0.998) by Log₁₀ mgF. The data obtained allowed us to quantify the levels of CaF₂ in dentin = 3.45 ± 0.25 mgF/cm² (c ± SEM) and FA = 1.64 ± 0.26 mgF/cm² (p < 0.0001).

Conclusion: Analysis of the data suggests that there is more CaF₂ bioavailability than FA in rat dentin, with potential participation in dentin remineralization.