Something new! The American Chemical Society recently published the results of a study showing that fluoride in the environment, like in your saliva because you drink fluoridated water, reduces the stickiness of streptococcus mutans. Strep mutans is one of the major cavity causing bacteria in our mouths. It's stickiness allows it to stick to teeth and allow other cavity causing bugs to stick to it. This conglomeration of bacteria, a bio-film, creates and concentrates the acids that dissolve holes in our teeth, cavities. This stickiness reduction becomes one more way fluoride resists cavity formation.
Other ways include reducing the bacteria's ability to create the acids that dissolve teeth. Also as a salt (sodium-fluoride or calcium-fluoride) in solution in your saliva, the fluoride will exchange with the hydroxide in the tooth enamel crystal (hydroxyapatite to fluorapatite) making it about 100x more difficult to dissolve with acid.
Fluoride is ubiquitous in nature, 2 parts per million in sea water and naturally occurring in fresh water in widely varying levels. At 1 part per million in drinking water it is an excellent
preventer of cavities. If you live in a non-fluoridated area, the simplest way to maximize your fluoride benefit, without risking too much fluoride is to simply 'spit your toothpaste after brushing and don't rinse afterward.' The lingering bit on your teeth will have a longer time to interact with the enamel of your teeth as well as the germs themselves.
Photo Credit: wikipedia commons