ABSTRACT: Effect of Pre-treatment with Dilute Hydrofluoric Acid on Enamel Solubility

It is reported in another paper (Rölla et al. this meeting)) that pre-treatment with an aqueous solution of 0.1% hydrofluoric acid (HF) reduced the solubility of human teeth in 0.1M citric acid and in 0.01M HCl to the same extent as 0.4% stannous fluoride (SnF2). The pH of the aqueous solution of SnF2 is 3 and the fluoride is thus present as dissociated and non-dissociated HF. It was suggested that 0.1%F as HF was the part of the SnF2-molecule which reduces the solubility of teeth in aqueous SnF2, and that Sn2+ only provides a suitable pH for the reaction). Objective: To examine the solubility reducing effect on dental enamel by a series of aqueous solutions of HF. Methods: [HF] ranging from 0.1% to 1.0% was examined. Intact human third molars (n=36) were cut at the collum and the exposed dentin was covered with acid-resistant nail varnish. In six groups (n=6) the specimens were individually pre-treated with different concentrations of HF (10ml, 10min), rinsed briefly in deionised water and dried, treated (10ml 0.1M citric acid, 30min). The solubility of the enamel was determined by measuring [Ca2+] using atomic absorption spectroscopy. Enamel samples pre-treated with HF dilutions were examined by EDXA and SEM (Phillips type XL30 ESEM). Results: Pre-treatment with 0.1%HF reduced the solubility of dental enamel by 50-60%, whereas 0.2-1.0% HF gave reductions of 90-100. The pre-treated enamel was covered by a dense layer of a calcium fluoride-like material. Conclusion: It appears that the calcium fluoride produced in the presence of HF is acid resistant and may exert a protective effect against clinical erosion of the enamel.