That is a good point, but according to http://www.ada.org/~/media/ADA/Member%20Center/FIles/fluoridation_facts.ashx http://www.ada.org/~/media/ADA/Member%20Cent

That is a good point, but according to http://www.ada.org/~/media/ADA/Member%20Center/FIles/fluoridation_facts.ashx http://www.ada.org/~/media/ADA/Member%20Center/FIles/fluorid... (p.10) "Systemic fluorides can also give topical protection because ingested fluoride is present in saliva, which continually bathes the teeth providing a reservoir of fluoride that can be incorporated into the tooth surface to prevent decay." It also says fluoride ingested during teeth-formation is incorporated into the teeth.