The uncontested roles in arresting the phenomena of demineralization and in favoring remineralization, and also the intense anti-microbial activity make fluoride almost one of the most exclusive option when necessary preventive measures are required in the appearance of dental caries or therapeutic in the situation of incipient dental caries. If the right dose of fluoride appears to bring only benefits, its increasing leads to the appearance of phenomena of acute or chronic intoxication. The dental fluorosis appears as a following of the fluoride overdose through exaggerated ingestion during the formation of dental tissues. At the level of the teeth affected by fluorosis, in the initial stages of appearance of dental caries appears to be inhibited by the existence of an increased quantity of fluoride in the surface layers. The more advanced stages of fluorosis which go with the exposure of the subsurface de-mineralized and irregular enamel, represent susceptible areas for the appearance and progress of dental caries. The clinical case presented in this paper gives an example of the modality of evolution of the dental cavity lesions at the level of severely fluoride affected teeth.