okay, this is not going to be terribly well researched due to the hour, but I do seem to recall an article (or more than one) in New Scientist in the past few years saying that there is little evidence to back up the hypothesis that fluoride in water contributes to declining rates of tooth decay. They compared the US (which is, overall, pretty keen on fluoride, although I think deliberate fluoridation of water varies from state to state) to other developed countries with little to no fluoride in the water and found the same decrease in rates of tooth decay. I can't remember whether they talked about fluoride in toothpastes or not ,but the implication of the article was that dentists and others have absorbed the correlation as 'fact' just because they have heard it so many times, but that it hasn't really been tested properly.
okay, ds2 has just woken up so I can't finish this message properly. Those who don't mind reading scientific abstracts could check this link, which shows a positive correlation between fluoride levels in water and dental caries (i.e. higher fluoride levels lead to a higher incidence of tooth decay)
www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids==11572269
I also seem to recall reading something about how fluoride strengthens your teeth - it does so by changing the mineral composition and it's an irreversible process, which worries me somewhat because it rather interferes with the way our teeth have evolved, and enamel was probably quite a good way of protecting our teeth before we started eating loads of sugary food and drinking highly acidic drinks.
Interesting that this BBC article (which I would expect to be fairly well researched and quite trustworthy) only says that it's 'probably' a good idea to use fluoride toothpaste
212.58.240.36/1/hi/health/medical_notes/3776459.stm
I also found this page which looks interesting but I haven't had a chance to check out how reliable the sources are
www.slweb.org/bibliography.html
sorry for not formatting the links properly but I now have a wriggly boy on my lap and I really should put him back to bed.
but i hope that gives you more to chew on