The aim of this research was to determine the correlation between dental caries and socioeconomic conditions in the State of Paraná, Brazil. Caries prevalence was estimated for each city in the State by gathering data on the DMFT index (in 12-year-old schoolchildren) supplied by the State Health Department. Official socioeconomic data for the municipalities were also presented. Ordinary least squares regression analysis was performed, and significant correlation coefficients were observed between the dental caries index and various social development indicators. Maps highlighting the overlapping areas with poor outcomes for most of these variables were presented. The results showed a significantly lower DMFT index in cities with fluoridated water supply and a negative correlation between the caries index and the proportion of households with running water in cities with fluoridated water supply. This observation highlights the importance of fluoridated drinking water for the prevention of dental caries and as a measure to reduce the impact of socioeconomic inequalities on the prevalence of tooth decay.