This review consolidates the major ideas that lead to the current concept of the initiation of the carious process. The most effective way of cariesprevention is water fluoridation; tablet fluoridation represents an alternative. Their effects is dependent on the dose and the regular use in infancy. The co-operation between dentists, paediatrists, parents and children is indispensable for tablet fluoridation. The combination of intern with extern fluoridation results in additive effect. The review describes the mechanism of action for fluoride in dental enamel and in dental plaque. Intoxicationes due to ingestion of fluorides tablets, such as used in caries prophylaxis, are pratically impossible.