miig wrote:And if I'm correct, the older the leaves, the more fluoride... so Green tea shouldn't be too high in flouride since its usually made out of young leaves, but the brick teas (Fu Cha) and similar stuff should be quite high in fluoride.
Now, I have no idea if this is right or not so don't take what I'm saying as I do know the answer! But, I am in chemistry and fluoride isn't the sort of thing that would just develop with time... C-F bonds are very strong and wouldn't break down with simple ageing of green tea so, I'd imagine it's more to do with mineral content in the soil/water where the tea was grown.
If it's an organic molecule of some sort, then yes ageing may contribute to it's development because the original molecules are prone to oxidation and hydrolysis by the air (or some sort of reduction perhaps).
Anyways, that's an answer drawing on my chemistry knowledge, not specific knowledge so don't take it to heart XD
EDIT: To mention the fluoride for your friends teeth, fluoride ingested in the diet is incorporated into the crystal of your developing teeth to form a stronger fluorine based crystal. Topical fluoride, that is just passing through the mouth, this repairs cavities by remineralisation, but whether that is quantitatively negligible is a matter of debate. I'd suggest seeing a dentist and brushing their teeth twice a day