A scanning electron microscope study of factors influencing etch patterns of human enamel

Facets were ground and polished in the outer third of the enamel thickness from 25 caries-free human molar teeth to produce enamel sub-surfaces cut perpendicularly to the prism direction. Under static conditions of acid dissolution, using 0.25 M formic, acetic or lactic acid solutions adjusted to pH 4.0, prism cores were preferentially dissolved. The predominant honeycomb acid-etch pattern, which showed an elevation of prism sheaths relative to adjacent unetched enamel surfaces, is interpreted as due to the precipitation of dissolution products. Vigorous agitation of the acid media caused preferential dissolution at prism junctions, a change of acid etch pattern attributed to the breakdown of diffusion barriers and accelerated dissolution rates which would tend to enhance the loss of enamel tissue from sites of greatest porosity, that is, the prism junctions. Therefore, the establishment of diffusion barriers with the potential for recrystallization of dissolution products may be a contributory factor in the formation of the honeycomb topography.