More and more scientific evidence show that fluorides have a cariostatic action to the plaque-saliva-tooth interface during cariogenous dissolution. Fluorides slow down demineralization and enhance remineralization. Their action is optimal, in the oral environment, when used at low concentrations on a continuous basis. The use of the fluorinated toothpastes during brushing of the teeth is a simple, rational method of daily topics application of fluorine, largely used in the context of prevention of dental caries and which can even be regarded as a public health measure. The water ingestion fluorinated represents itself an excellent average of the local application of fluorine. Our work concerned a quantitative study of fluorine in toothpaste and drinking water, and comparative between the local product and the imported one for the toothpastes, and the mineral water and public supply. The standard method of fluorine based on the potentiometry and distillation has shown that 50% of the tested toothpastes contain adequate concentration so that a product of dental care fights against decay. The Tlemcen tap water contains acceptable fluorine content, but the mineral water, with an excessive contribution, can cause fluorose. Of this, we can deduce that a topical application of a suitable quantity of fluorine on a daily basis in accordance with the precautions is not only the prevention of dental caries, but also to stabilize it if it already exists.