Methods: The pH and titratable acidity (TA) of common dietary acids were determined by hydroxide titration to pH 7.0. Buffers of citric acid pH 3.8, tartaric acid pH 3.1 and acetic acid pH 2.4 were prepared with a TA of 110mM, 78mM and 1.0M to be representative of orange juice, white wine and vinegar respectively. Lactic acid pH 4.5, TA 19mM, was used to mimic a caries acid challenge. HA powder was pre-treated for 2min with water or a solution of sodium fluoride (NaF) at 300ppm F- then exposed to the relevant acidic buffer for 2mins. The resultant supernatants were analysed for orthophosphate (o-PO4) by ion chromatography. Enamel solubility reduction (ESR) studies using a NaF silica toothpaste were based on the US Food and Drug Administration testing procedures method #33, modified to use both lactic and citric acid.
Results: The quantities of o-PO4 dissolved from the HA following pre-treatment with water were 69, 168, 181 and 379mg g-1 HA for lactic, citric, tartaric and acetic acid respectively (n=3). Corresponding o-PO4 releases following the F- pre-treatment were 26, 52, 78 and 167mg g-1 HA. The increase in HA demineralisation correlated with a reduction in pH whilst the degree of fluoride protection, as a percentage, remained comparable. ESR showed that fluoride conferred a protective effect against demineralisation of enamel against both lactic and citric acid of 14 and 25% reduction respectively.
Conclusion: Fluoride helps protect HA and human enamel against demineralisation caused by acidic buffers representative of dietary acids in these studies. These results in vitro suggest that fluoride can protect against dietary acids in vivo.