Abstract: The invention consists of a system comprising a measuring device of shape adapted to the tooth, which with yellow, green and blue color grades the current pH value in the patient's tooth film and in which the green color indicates the optimum pH value for the formation of caries-counteracting fluorapatite. Three types of color-matching tubes of toothpaste have compositions that contain fluoride and center the pH values of the tooth films on the green level. The system's measuring device shows by colorimetric means which toothpaste will at that precise time best promote the formation of fluorapatite in each of the three pH groups form which the device selects.