Inequality of water fluoridation in Southern Brazil—the inverse equity hypothesis revisited

The purpose of this ecological study was to investigate the association between social and economic indicators at the municipal level and the presence of water fluoridation and time when water fluoridation was implemented in the 293 municipalities of Santa Catarina State in Southern Brazil. Several social and economic indicators were obtained from official Brazilian agencies as well as from UNICEF. Questionnaires were sent to local authorities and to the local government water supply Company to obtain information about the presence or not of a fluoridated water supply and the year when fluoridation was implemented. Differences in social and economic indicators between municipalities with and without fluoridated water and between those that have had this service for different lengths of time were compared by the Mann–Whitney U test. In addition, multiple logistic regression analyses was performed to identify associations between social and economic indicators at the municipal level and presence and time of implementation of water fluoridation. Results indicated that larger populations are associated with municipalities with fluoridated water. Larger populations, higher child development indexes and low illiteracy rates are associated with a longer time since the implementation of water fluoridation. The finding that less developed municipalities delayed the provision of water fluoridation corroborates the inverse equity hypothesis.