How Does Fluoride Toothpaste Protect Teeth?

Tooth enamel is made mostly of a mineral called hydroxyapatite. Bacteria in plaque feed on sugars and produce acids that dissolve minerals from enamel, a process called demineralisation. Saliva helps redeposit minerals, and fluoride speeds this up while forming fluorapatite, which is more resistant to acid. Fluoride also interferes with the bacteria's ability to produce acid. Dentists often advise spitting out after brushing rather than rinsing, so more fluoride stays on the teeth.