AbstractA 3‐year experimental toothbrushing study was conducted in a natural fluoride area in Denmark to evaluate the anti‐caries effect of a 2 % sodium monofluorophosphate dentifrice. In a previous report the results for the total population of 1,407 schoolchildren, representing a broad age‐span (7–12 years), at the commencement of the study in 1970 were given. In the present report results are presented for two subpopulations of “8‐year‐olds” and “11‐year‐olds” at the commencement of the study. Differential analysis of the effect of the, test dentifrice on defined types of surfaces for the two subpopulations is given. The evaluation was performed using both the conventional DMF‐indices and the recently published ECSI‐Index6. The evaluation showed that the test dentifrice had a valuable anti‐caries effect in both age groups, above and beyond the effect of the waterborne fluoride. Proximal surfaces were affected most baneficially by the active agent both in relative and absolute terms. However, an appreciable caries‐preventive effect was also found on