Nano forms of hydroxyapatite, other calcium phosphate compounds, and additional bioactive inorganic materials will be prepared by a newly developed method, employing either a spray drying or a flame pyrolysis technique in such a way that (1) target particle sizes over a wide range can be obtained, (2) compounds with both low and high solubilities can be prepared, and (3) the prepared particles would not be exposed to any solution environment after their formation and therefore would retain their original, highly reactive surfaces (Aim1). Due to their small sizes and high reactivity, the prepared nano materials are expected to have a range of clinical applications. Two of which will be evaluated in Aims 2 and 3. Aim 2 will focus on evaluating the effectiveness of nano forms calcium fluoride (CaF2) as the source of fluoride (F) for remineralizing tooth enamel carious lesions using (1) an in vitro model to understand the relationship between CaF2 particle size and F deposition, (2) an in vivo saliva and plaque model to compare oral F retention produced by the nano CaF2 and currently used NaF rinses, and (3) an in situ demineralization/remineralization model to evaluate the remineralization effects of the nano CaF2 rinse. Aim 3 will evaluate the effectiveness of nano sized calcium phosphates and calcium fluoride in reducing dentin permeability, a property closely associated with dental hypersensitivity.