Sodium fluoride is used in toothpastes and dental rinses
to protect tooth enamel from attack by bacteria (cavities,
also known as caries).
The active part of the molecule is the fluoride ion, which
is why two other fluorine containing compounds,
stannous fluoride (tin fluoride),
are also used.
Fluorides work in two ways. They reduce the ability of
bacteria to make acids, and they remineralize the areas of
the tooth that have been attacked by acids from bacteria.