[Semiquantitative in vitro study of the etching of human enamel: scanning electron microscopy observations].

The efficiency of etching using lactic, citric, hydrochloric and phosphoric acids has been studied with the scanning electron microscope on 557 human enamel surfaces. A semiquantitative assessment has been performed with reference to Silverstone et al.'s classification (1975) as regards the demineralization stages of enamel prisms and to Sheykholeslam and Buonocuore's 6 points scale as regards the etching degrees. Lactic and citric acids proved ineffective. Hydrochloric and phosphoric acids were efficient between 20 and 50% concentrations. A 1 minute etching seems optimal. A long-continued etching induces crackling of the surface enamel layer into patches which do not stick properly to the underlying enamel. Only the removal of the hypermineralized surface layer (using a diamond wheel) allows to obtain microporosities evenly distributed all over the sample surface. A mechanical treatment of enamel surfaces prior to etching is necessary especially when temporary teeth or "mature" (between 5 and 50) or "aged" (over 50) teeth are concerned.