For all tooth surfaces, there is a continuous cycle of demineralization and remineralization of tooth enamel. Tooth decay (dental caries) is an infectious, transmissible disease caused by bacteria colonizing on the teeth and producing acid that dissolves enamel, resulting in greater demineralization. All fluorides act to slow demineralization and boost remineralization. Fluorides work in at least four different ways to protect teeth from tooth decay. Fluoride is incorporated in tooth structure when small amounts are swallowed daily while teeth are forming. Fluoride becomes concentrated in the outer enamel surfaces when applied topically after the teeth erupt. Dental plaque and saliva act as fluoride reservoirs to enhance the remineralization process. In addition, fluorides interfere with the decay-causing bacteria colonizing on teeth and reduce their acid production, thus slowing demineralization.