Topical application of titanium tetrafluoride has shown promise as an effective chemotherapeutic agent in combating tooth decay. The mechanism of action of such topically applied fluorides probably has both a chemical and a biological component. It is the objective of this project to investigate the chemical component of the mechanism. The initial approach will be to study the reactions of titanium tetrafluoride with powdered hydroxyapatite in aqueous media. Similar reactions will also be carried out with powdered dental enamel. The studies will then be extended to include the entire TiF4-Ca(OH)2-H3PO4-H2O system because in this way one can more closely approximate the conditions that obtain in the mouth. The products of these reactions will be identified by application of x-ray diffraction, scanning electron microscopic, infrared, atomic absorption, and wet chemical analytical methods.