Abstract
Acid resistance of the surface enamel in human deciduous and permanent teeth after etching with 30% phosphoric acid was investigated by atomic absorption spectrometry, electron probe microanalysis, scanning electron microscopy, and Knoop microhardness tests. The surface enamel containing a higher Ca concentration did not show a lower acid dissolution, but that with less dissolved Ca occupied wider areas of the ‘prismless’ structures. Surface ‘prismless’ enamel, therefore, tended to have stronger resistance to phosphoric acid than surface prismatic enamel, but the acid-influenced layer that contained ‘prismless’ structures was weak against physical forces. The results suggest that the surface ‘prismless’ layer forms a barrier against enamel caries and acid etching. With acid etching and bonding techniques, the ‘prismless’ layer which interrupts adhesive penetration of resin to the underlying prismatic enamel will be apt not only to adhere poorly to the resin, but also to break away with the resin.
