In addition to the above advice, another health group I am a part of has been discussing remineralization of teeth as of late, regarding children especially, and here is some advise I have copied and pasted. Just things to consider. I have not looked into these things, but these people tend to do their research, so perhaps these are things you can look up as well.
I can echo the comment about the clay. I got advice from Raymond Silkman (who presented at WAPF conference a couple of years ago on dental issues) that swishing with some clay right before bed and letting it sit on the teeth all night can help (and of course you're also swallowing those minerals). We've been doing this for about a month for my son who has weak teeth. It's surprisingly unyucky, too, doesn't taste like much of anything. Silkman recommended a brand called Terramin, available in California, but I'm sure there are lots of good clays out there. Of course, like everything else, it's not inexpensive.
Azomite powder was recommended as well, for this.
It's not that I can tell you what TO do, but maybe I can tell you some
things not to do.
Stop with the xylitol. It is NOT good for you, me or anybody else. Stop the baking soda. Taking calcium won't help. There is only one isolated calcium compound supplement that is any good for anybody and that is calcium orotate, and it won't help this, or at least not soon enough. You only assimilate calcium properly from plants, raw dairy or raw fermented dairy, or from plant food supplements (supplements that are actually green food/superfood). All other forms of supplmental calcium are just going to cause more calcification than anything else.
Don't overdo brushing. Don't use mouthwashes. Try Miracle II Neutralizer GEL for brushing your teeth; It is a MILD cleanser. I have never had such a
clean but non-astringent feeling in my mouth as I have with M2Neutralizer.
For flossing, get floss without anything else on it at all at least while
you are trying to remineralize. Try getting some hydroxyapatite powder and hold it in your mouth licking it around on your teeth after flossing &
brushing, but spit it out afterwards.
I would be very careful with any abrasive until I felt on the mend. Once in
a week or two, I brush my teeth with food grade diatomaceous earth for
cleaning of deposits, right after using a dental pick to get what I can see.
People have filled in caries with Hydroxyapatite and had it to solidify as
part of the tooth.