>>The key ingredient to look for would be fluoride.

There are two kinds, depending on what it's bound with, sodium or tin (marketed as 'stannous'). The tin version does a far better job at remineralizing teeth, but it's toxic (joint issues mostly) if you swallow it.

There's something that works better than tin/stannous fluoride: nano-hydroxyapatite (a nano-ceramic) originally developed to help wounded soldiers regrow shattered bones. First developed in the US, available through Rx only. Company that developed it was bought by the co that makes Sensodyne, and they incorporated it into some of their varieties - but you can't buy those here. I buy my Sensodyne from overseas (and other brands that also use hydroxyapatyte. BioMin(UK) has a version of the ceramic that includes sodium fluoride. There's one from Italy with no fluoride at all that I rather like.

I care about this stuff as I'm a clencher who didn't know until into my 50s, so my teeth are very much in need of remineralization. Dentists all figured I knew I was a clencher and said nothing. Grumble, grumble.

Hope this helps someone.