The effect of lactic and acetic acid on the formation of artificial caries lesions.

Fluoride specifically adsorbed to hydroxyapatite reduces the rate of dissolution of hydroxyapatite. Since specific adsorption is a property which anions of all weak acids have in common, it is expected that the anions of lactic and acetic acid will be specifically adsorbed to hydroxyapatite too and in this way will cause a reduction in the rate of dissolution of hydroxyapatite. In order to investigate this, we used the experimental results from Featherstone and Rodgers (1981). Calculations of the rate of increase of the lesion depth in dental enamel per mmol. L-1 of the un-ionized acid revealed that lesion progress was pH-dependent and was lowest at that pH which corresponds with the pK-value of the relevant acid. It is concluded that the anions of lactic and acetic acid are specifically adsorbed to the enamel mineral and in this way reduce the rate of dissolution of the mineral. This suggests that a description of the development of an artificial caries lesion in mathematical terms should include the effect on the rate of dissolution of the mineral of specific adsorption of the relevant acid anions to the mineral.