Chemistry of How Fluoride Prevents Tooth Decay and Other Advantages

Outer tooth enamel tends to decay before the inner, due to the fact that it is exposed. The outer enamel contains more fluorine than the inner so that it is fortified. Teeth need to be repaired with fluorine, that is where the fluoridation comes in. It protects the tooth from decay. Enamel is porous, so when bacteria enters and excretes acids, it breaks down the calcium and phosphorus.

Ca₅(PO₄)₃OH = calcium hydroxylapatite - the most main component of tooth enamel

H₂SiF₆ = hydrofluorosilic acid - most common compound used in fluoridation, when put through a series of reactions, it becomes SiF4 .

When SiF4 is added to water, it dissolves, isolating the fluoride ion:

SiF_{4 (aq)} → H₂O → Si ⁺⁴ _(aq) + 4F ^– _(aq)

When the fluoride ion reacts with tooth enamel, it replaces the hydroxide:

Ca₅(PO₄)₃OH _(s) + F ^– _(aq) → Ca₅(PO₄)₃F _(s) + OH ^– _(aq)

The bacteria that causes tooth decay release acids that break down the enamel. As the fluoride fortifies the enamel, the hydroxide neutralizes some of the acid. This neutralization, however, is short lived, seeing as the water is then swallowed.