With the success of water fluoridation, it was reasoned the topical application of fluoride might also result in fluoride uptake and incorporation into the teeth; and that some benefit may also be achieved with less frequent applications of higher concentrations of fluoride. Bibby7 initiated many early studies on both dentifrices and topical fluorides but these studies were not entirely successful. A review of these and many other dentifrice studies was published by GK Stookey in a paper presented at a conference entitled "Clinical Use of Fluorides."8 There were about eight early studies using a combination of sodium fluoride with calcium abrasive systems, but none of them resulted in significant reductions in dental caries.9-14 The most likely explanation was the incompatibility of the abrasive system with the sodium fluoride active, since it could react with the calcium of the abrasives and form calcium fluoride.15 Calcium fluoride is not reactive with the enamel surface, and this lack of reactive ionic fluoride most probably resulted in the failure of these early formulations to prevent caries. In 1954, the first report of a clinically effective fluoride dentifrice was made. This dentifrice contained stannous fluoride combined with a heat-treated calcium phosphate abrasive system.16 This SnF2–Ca2P2O7 combination was provisionally accepted by the ADA's Council on Dental Therapeutics with category B classification in 1960.17 Upon completion of additional studies showing its therapeutic effect, the dentifrice was given a category A classification in 1964.18 This recognition of preventive value led to continued investigations for improved formulations with different active agents and abrasive systems. The search for more effective products continues to this day.