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Bovine enamel was exposed to buffered lactic acid in hydroxyethylcellulose, hydrochloric acid or orthophosphoric acid during different periods. The resulting surface roughness was determined by a laser speckle technique, by a mechanical profilometric instrument, and from SEM stereomicrographs by applying these techniques to the same samples. The methods are compared. The results correspond reasonably well. Exposure of the enamel to hydrochloric acid or orthophosphoric acid gives a large increase of the surface roughness during the first 30 sec; further exposure gives some decrease of the roughness. Exposure to buffered lactic acid for 7 days gives hardly any change in surface roughness.

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