Water fluoridation is a strategy for caries control recommended by the WHO. In Brazil, it is regulated by law but this program has not been successfully implemented in the North region. This research aimed to collect data on the existence of external control (heterocontrol) in the ten largest municipalities in the state of Tocantins, Brazil, and to analyze fluoride concentration in the public water supply of these cities. The study was conducted from May-August/17, and its theoretical-methodological framework was a quantitative, descriptive and cross-sectional analysis. Water collections were carried out monthly, using sampling protocol of water collection of the network. Fluoride concentration in the waters was determined with ion specific electrode by the direct technique. It was verified that water fluoridation monitoring is only been done in Palmas, capital of the state, starting in 2016. Thirty-two percent of waters samples analyzed showed fluoride concentration to obtain the maximum benefit of reduction caries and 27.5% of them presented a high or very high risk of dental fluorosis. It is necessary to implement a program to control the concentration of fluoride in the water of the municipalities of Tocantins, in order to ensure that the population is not deprived of the anticaries’ benefits of the adjustment of fluoride concentration of the treated water.

*Original abstract online at http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1413-81232020000401507&tlng=pt