I'd suggest you look into Weston A Price's information on nutrition for good teeth. Using cod liver oil and grassfed butter oil for the combination effect to feed teeth what they need to stay healthy.
There is a procedure that some dentist's do call Healozone, where essentially they use ozone insufflation on a tooth to kill the S. Mutans bacteria in it and then use remineralation at home to harden the dentin.
I think you might get the same effect by swishing with ozonated oil. Then finding some oral remineralization products. There are some you can get without fluoride online.
Xylitol is a product that is excellent for keeping down the S. Mutans bacteria in the mouth and promoting remineralization. There are toothpastes made with it. There are also xylitol candies and gum that you can order online.
Also, supplementing with Lactobacillus Reuteri can help the whole system. It also has a good effect on controlling S. Mutans.