Question for a dentist or a chemist?

Since fluorine is added to a lot of public water sources, including the one nearest me, how come my brother has filing yet drinks tap water there fluorine in that right, but my teeth are like super strong cause my mum gave me load's of Fluorine, before they were told they shouldn't give baby's fluorine and so didn't risk my brother health, lame. So if we have both been ingesting fluorine for years, why didn't the fluorine he ingested from the water supply was far less effective then the fluorine I was given, although I don't know she got fluorine in me, I must of drank it right so, yeah what? Help if you can, oh and the last thing I need is people moaning about giving kids fluorine, it was early nineties and I was the first aka trial and error kid, I also didn't have some injection that all the others had, so my school gave it to me for some reason and then sent me home, weird.