Focal demineralization of the enamel of permanent teeth was studied in 104 schoolchildren aged 9 to 12 over the course of prophylaxis (cleaning the teeth with fluorine-containing toothpastes). The parameters checked up were the intensity of coloring, size and electric conductivity of the spots, and the rate of remineralization of the enamel of permanent teeth. For a year a strong correlation between the tested characteristics of the enamel and saliva was observed. Some age-specific characteristics of permanent teeth enamel were detected. Age group of 11 to 12 years should be distinguished in prophylactic and control groups, because it is at this age that all the tested properties of the enamel are the most liable to change: electric conductivity, permeability, and remineralization rate. This period seems to be characterized by a specific reaction of all systems and organs of the body to environmental exposures. Remineralizing prophylaxis was found to be the most effective at the age of 9 to 10 years. The findings permit us emphasize the contribution of fluorine contained in the Blendax fluorine-containing toothpaste used by the children to the major components of the pathologic process (white spots) and enamel remineralization at the stage of its maturation.