Substances frequently used in caries prevention have been studied with regard to their influence on the occurrence and rate of lesion repair. Single and periodical addition of fluorides and diphosphonates were compared in short, and long-term experiments. Diphosphonates, which are now used as anticalculus agents in tooth pastes, have an inhibitory effect on remineralization. Therefore, the use of diphosphonate-containing toothpastes should be dissuaded for children. Multiple application of low concentrations of fluorides are preferable to single high concentration treatments. In the latter case a rapidly formed, very insoluble precipitate in the surface layer pores prevents complete lesion repair.