Degrees of saturation with respect to apatites in parotid saliva at various ph values

The purpose of the present work was to investigate the degrees of saturation with respect to hydroxyapatite and fluorapatite in saliva at various pH's. The data of ionic activities in parotid saliva were collected from the literature and the degrees of saturation with respect to hydroxyapatite and fluorapatite were calculated. It was found that parotid saliva was supersaturated with respect to both apatites above pH 5.5, unsaturated with respect to hydroxyapatite and concurrently supersaturated with respect to fluorapatite in the pH range 5.5-4.5, while it was unsaturated with respect to both apatities below pH 4.5. In the laboratory it has been found that when enamel is exposed to a liquid unsaturated with respect to hydroxyapatite and supersaturated with respect to fluorapatite, a caries-like lesion is developed. A liquid unsaturated with respect to both apatites leads to an erosion-like injury. It is concluded that the two chemical conditions leading to the two types of enamel lesions may both occur in the oral cavity.