but, let's take this at face value - it's claiming that you can catch the hydroxyapatite when it dissolves, and put it back in by replacing the hydroxyl group with fluoride.
i suppose it would then follow that that won't work anymore if you don't have any hydroxyapatite to catch. that is, the efficacy of fluoride would rely on the existence of degrading enamel to work.
but, that doesn't rule out uptake, it just presents a challenge - you need to introduce hydroxyapatite somehow, and i grasp that this has eluded engineers. but, that's why we have novamin, instead.
it also opens up a lot of questions about whether a partially decayed tooth can be restored using that mechanism. in theory, it should be possible for your saliva to take dissolved hydroxyapatite from a healthy part of your tooth and uptake it into a damaged part using fluoride. in theory, it should even be possible for your saliva to take dissolved hydroxyapatite from one tooth and redeposit it in another. how would it figure any of that out?
regardless, it seems like i want to find ways to get something like hydroxyapatite in there, and i knew that already. i get a lot of calcium, a lot of phosphorus, a lot of vitamin d, etc. the only thing i was missing was fluoride, and i've addressed that.
that clarifies a little, but it doesn't resolve the contradiction.