Hydrochemistry of mountain rivers in the Sierra de Velasco, La Rioja, Argentina: implications on dental fluorosis through statistical modeling

Dental fluorosis is a disease associated with prolonged intake of high concentrations of fluoride, mainly by drinking water consumption. In a rural region in NW Argentina, several localities are supplied for domestic use by surface waters with variable contents of dissolved F⁻ (from 0.3 to 3.1 mg L⁻¹) of geogenic origin. Dental fluorosis, from very mild to severe, has been registered in the population according to the spatial variability of dissolved F⁻. In this work, statistical models demonstrated that the concentrations of dissolved F⁻ that determine the occurrence of dental fluorosis (and its severity) depend on the concentrations of dissolved Ca²⁺. In children and adolescents, the probability of presenting this disease, at any degree, increases with age and dissolved F⁻; whereas moderate-to-severe degree is controlled by an inverse relationship between dissolved F⁻ and Ca²⁺. This last result was also obtained in the group of adults, for any degree of dental fluorosis. Thus, for a particular concentration of dissolved F⁻, as dissolved Ca²⁺ increases, the probability of developing dental fluorosis decreases. The findings of this work could be useful to adjust the current regulations, since guidelines of dissolved F⁻ in drinking water for different degrees of dental fluorosis are not considered, nor the relationship between F⁻ and Ca²⁺.