A grown tooth has a fixed structure. On the outside you find a hard glossy surface layer. This is the enamel. Underneath this enamel you find the tooth bone or dentine. And further inside you find a space containing blood vessels and nerves forming the so called the pulp. Take note that the blood vessels and nerves do not reach into the enamel. So, any ingested fluoride cannot get via the blood stream to the enamel and to force feed an entire population fluoride to improve their teeth is rather futile. http://mizar5.com/demin.htm Once a tooth is in place, you cannot change it anymore through dietary means.
Mottled teeth or dental fluorosis occurs when before tooth eruption an infant or child gets so much daily fluoride that the tooth forming cells are poisoned and form a botched enamel. Once you have it, you have it for life. It results in a porous, brittle enamel with reduced mineral content. Dental fluorosis is the clinical symptom of chronic fluoride poisoning during tooth formation.
Graphic from: http://upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Tooth_Section.svg/496px-
