Chemical events during tooth dissolution.

The aims of the present survey were to describe some aspects of (a) enamel solubility in relation to pH and to the fluoride concentration, (b) chemical changes which occur during enamel dissolution, and (c) enamel resistance with an attempt to relate chemical events to clinical observations. The solubility of enamel powder increases dramatically with a decrease of pH. As long as the fluoride concentration in solution is high, the amount of enamel dissolved is low. When fluoride occurs only in the solid phase, the solubility is only slightly affected. Two clinically distinct lesions have been described in dental enamel: the erosion lesion, characterized by a dissolution of enamel from the surface; and the caries lesion, in which the enamel surface layer, accumulating fluoride, remains relatively intact, while the subsurface enamel dissolves. It was concluded that any dissolution of enamel is caused by an undersaturation with respect to enamel apatite. When whole enamel dissolves, the saturation with respect to fluorapatite determines whether a well-mineralized surface layer remains, i.e., whether the dissolution results in an erosion or a caries lesion. The degree of supersaturation with respect to fluorapatite determines the uptake of fluoride in the surface layer and its mineral content. It was observed that different areas of the enamel surface possess different degrees of resistance. A satisfactory explanation for the resistance has not been given.