Although diamine silver fluoride (AgF: (NH3)(2)AgF) stains teeth black, it is known as a very effective agent to prevent the dental caries progress. In order to find another fluoride that has a similar anticariogenic effect without changing tooth color, we prepared ammonium hexafluorosilicate (SiF: (NH4)(2)SiF6), in which the silver of AgF is replaced with silicon. In this study, the anticariogenic effect of SiF was evaluated using bovine teeth. Fluoride solutions, SiF, AgF, acidulated phosphate fluoride (APF), and sodium fluoride (NaF), were applied to bovine enamel and dentine blocks, and the depth of demineralization was measured after exposure to a demineralizing solution for 24 h. Also, fluoride was applied to a simulated dentine caries specimen to evaluate the caries progress-preventing ability. For the dentine specimens, mineral loss (&UDelta; Z) was also measured with microradiography. We found that SiF treated enamel showed better acid resistance than specimens treated with NaF or APF. AgF treated enamel also showed similar acid resistance, but was stained black. SiF and AgF treated caries-affected dentine showed reduced demineralization when exposed to a demineralization solution for 24 h. Mineral loss (&UDelta; Z) was reduced to 85% and 75%, respectively. Although the acid resistance of the SiF treated teeth was inferior to that of the AgF treated teeth, we consider that SiF has good potential as anticariogenic agent, since it increased acid resistance without changing tooth color. (C) 2005 Springer Science + Business Media, Inc.