In a two-year pragmatic clinical trial, the effect of the mineralizing agent was evaluated on permanent teeth of the first eruption group among Finnish children (7-years old at the beginning of the study) with a low prevalence of DFS. In the test group (n = 123, biweekly mouthrinsing with a 2% solution of mineralizing agent and 0.2% NaF solution) the percentage reduction in increment of both EFDS and DFS was high, whereas in the control group (n = 123, biweekly mouthrinsing with placebo and 0.2% NaF solutions) the incidence for symptoms of caries disease did not differ from that normally found in this age cohort. Positive clinical effect of tested solution was age-related and was associated with remineralization of old and inhibition of occurrence of new EFD lesions.