The influence of plaque on reaction mechanism of MFP and NaF in vivo.

A modified Intra-oral Cariogenicity Test was used to study the influence of plaque on the reaction mechanism of sodium monofluorophosphate (MFP) or sodium fluoride (NaF) in either sound or demineralized enamel in vivo. Volunteer students, wearing mouth appliances holding enamel blocks, rinsed their mouths with MFP or NaF solution (1,000 ppm F-) three times a day. The amount of loosely-bound and acquired fluoride was determined after an experimental period of five days in plaque-covered, demineralized (PCD); clean, demineralized (CD); plaque-covered, sound (PCS); and clean sound enamel (CS). While no measurable loosely-bound fluoride could be found after MFP treatment, NaF caused deposition of a significant amount of alkali-soluble fluoride in all experimental groups. After MFP rinses, fluoride concentration in the enamel was increased in the following order: CS, PCS, CD, and PCD. After NaF treatment, demineralized enamel exhibited a higher fluoride acquisition when compared with sound enamel. Plaque had a minor effect on F- acquisition. It is concluded that demineralization of enamel enhances F- uptake from both NaF and MFP solutions. In the presence of plaque, F- acquisition was additionally increased only after MFP rinses in vivo.