first of all, I would absolutely see a naturopath or holistic dentist before ubdergo any conventional medicine treatment.
I went fruitarian for 6 months and my teeth became see-through. Many teeth decayed and I got 5 root canals! I was able to reverse it 100% during the following year. I still have the yucky RC there and I wish I didn't try fruitarianism.
I believe that many things can be done. I have read about remineralization of teeth by applying a paste of raw cheese that has been previously coated and made into paste with raw honey. Raw honey with its enzymes breaks down the cheese freeing the minerals and making them bioavailable. I hope it's not hogwash.
From my personal experience I can tell you that eating fruit can worsen the situation. I would avoid most fruit and stick to vegetables.
I would try metabolic type test tosee whether your son is properly fed. He might be missing some nutrient very bad.