On inhibition of dental erosion

Abstract

Objective. To examine the erosion-inhibiting effect of different concentrations of hydrofluoric acid. Materials and methods. Thirty-six human molars were individually treated with 10 ml of 0.1 M citric acid for 30 min (Etch 1), acid was collected and stored until analysis. The teeth were randomly divided into six groups and then individually treated with 10 ml of one of six dilutions (from 0.1–1%) of hydrofluoric acid. The teeth were then again treated with citric acid (Etch 2). The individual acid samples from Etch 1 and 2 were analyzed for calcium by flame atomic absorption spectroscopy and difference in calcium loss was calculated. Results. The highest erosion inhibiting effect was obtained in groups with the highest concentrations of hydrofluoric acid, where the pH was lowest, below pKa of 3.17, thus the hydrofluoric acids being mainly in an undissociated state. Discussion. Diluted hydrofluoric acid is present in aqueous solution of SnF₂ and TiF₄ (which are known to inhibit dental erosion): SnF₂ + 3H₂O = Sn(OH)₂ + 2HF + H₂O and TiF₄ + 5H₂O = Ti(OH)₄ + 4HF + H₂O. It is also known that pure, diluted hydrofluoric acid can inhibit dental erosion. Teeth treated with hydrofluoric acid are covered by a layer of CaF₂-like mineral. This mineral is acid resistant at pH < 3, because it was formed at this pH. Conclusion. The erosion-inhibiting effect is due to formation of an acid resistant mineral, initiated by tooth enamel treatment with hydrofluoric acid. Hydrofluoric acid is different in having fluoride as a conjugated base, which provides this acid with unique properties.