Fluoride can be found in the Earth's crust, water, food and in our bodies as one of the building blocks of many tissue systems, primarily of bones and teeth. Fluoride plays an important role in the prevention and reduction of dental caries. Reduces the demineralisation process and promotes remineralisation of dental hard tissue. Reduces the number of microorganisms, affects their metabolism, increases salivation and thus prevents the formation of acidic media and the decline in pH value in the oral cavity. Systematically fluorine is entered through food, drinking water, milk, salt or tablets containing fluoride. After absorption it is secreted via saliva and incorporated into tooth enamel. The world's most widely used method of fluoride consumption is the fluoridation of water although recent research has questioned the effectiveness of such procedure. In Republic of Croatia water, milk and salt are not fluoridated. The most important method in caries prevention is the topical fluoridation by which a constant, low concentration of fluoride is achieved. It is carried out daily in homes or professionally in dental medicine practices, mostly in the form of toothpastes, solutions, gels, varnishes, and lately in chewing gums, restorative materials and devices, which release fluorine. Excessive intake of fluoride can have toxic effects on the human body. During the period of growth and development of teeth small quantities can lead to the development of dental fluorosis, while larger amounts cause general body reaction and even death. Preventive measures and education of people are the most important factors in reducing tooth decay and preservation of oral health.