It’s well known that fluoride is good for teeth, that it stops or slows down tooth decay. How does it do that? This video explains the process by which fluorapatite is formed and remineralises the teeth. For a more detailed look, there’s also this technical article I found that’s worth getting your teeth into digesting. 🙂
The hydroxyapatite of tooth enamel is primarily composed of phosphate ions (PO43–) and calcium ions (Ca2+). Under normal conditions, there is a stable equilibrium between the calcium and phosphate ions in saliva and the crystalline hydroxyapatite that comprises 96% of tooth enamel. When the pH drops below a critical level (5.5 for enamel, and 6.2 for dentin), it causes the dissolution of tooth mineral (hydroxyapatite) in a process called demineralization. When the pH is elevated by the natural buffer capacity of saliva, mineral gets reincorporated into the tooth through the process of remineralization.
When fluoride is present in oral fluids (i.e., saliva), fluorapatite, rather than hydroxyapatite, forms during the remineralization process. Fluoride ions (F–) replace hydroxyl groups (OH–) in the formation of the apatite crystal lattice (Figure 3). In fact, the presence of fluoride increases the rate of remineralization.
Fluorapatite is inherently less soluble than hydroxyapatite, even under acidic conditions. When hydroxyapatite dissolves under cariogenic (acidic) conditions, if fluoride is present, then fluorapatite will form. Because fluorapatite is less soluble than hydroxyapatite, it is also more resistant to subsequent demineralization when acid challenged.