Loss of surface enamel after acid etching procedures and its relation to fluoride content.

The etching of an enamel surface with a strong acid causes loss of surface contour together with a roughening of the enamel, which is necessary for proper adhesion of the bonding agent. It is known that the fluoride concentration plays an important role in the reduction of enamel solubility. The objective of this investigation was to measure the bulk enamel loss because of acid etching with phosphoric acid, with special emphasis on the fluoride content of tooth enamel. It was shown that fluoridated enamel has a high acid-resistant layer 2 to 4 microns in thickness. In some teeth the enamel is locally so resistant that, even after a 3-minute etching period, practically no material is removed. Since considerable amounts of topically applied fluoride ions are known to leak out, it is advisable to omit fluoride application shortly prior to the bonding procedure.