Ever since Dr. Strangelove I’ve found the fluoride controversy interesting and scary (for many reasons). I can’t verify any of this, but from a Digg article entitled Fluoride’s glory may be cresting, here was a comment that seemed to have enough info to worthwhilely put it here:

Fluoride replaces the hydroxyl ion in the naturally occurring calcium hydroxyapatite causing a stronger nuclear bond. In that respect it strengthens the tooth. The problems associated with flouride come from poor understanding of the inherent dangers of ingestion.

When it comes to toothpaste, I alternate a flouride containing paste with a paste containing sodium-calcium phosphosilicate which adheres to the surface of the tooth enamel creating new calcium hydroxyapatite. It does this by a simple mechanism. The sodium raises the ph of the saliva which causes the calcium and phosphorous to plate out of solution onto the tooth and re nourishing any damaged areas.