This paper review the effects of orthophosphoric acid and other acidic agents on dental enamel. The effects of other treatments such as proteolytic agents or of mixture able to remove the lipids are also described. Specific problems are related to the dentine treatment. Acids and chelators should be avoided, because of the dentine tubules, the odontoblasts and pulp. We review also the problem of the smear layer, the surface of the carious dentine and the consequences for dental treatment. Researches which are still in progress are reported including the use of enzymes and alcali gels submitted to feeble electrolysis, this latter being able to prepare dentine, cementum and bone surfaces in order to increase the adhesion of biomaterials.