A lot of bacteria, including those which cause tooth decay, will die if they absorb xylose, which they will happily do due to xylose’s resemblance of glucose, their favourite food.
Xylose is non toxic to humans and used as a calory-reduced sweetener (we’re only able to get ~half of the calories off it compared to glucose).
So, snacking on half a teaspoon of sweet xylose after brushing your teeth might feel strange at first (like snacking on pure sugar), but you’ll enjoy clean teeth far longer! Until your next encouter with “real” sugar.
That’s a very sad thing to read; I am sorry for you and your carpet bombed gut flora.
It happened to a lot of kids back then. They gave us antibiotics quite a lot more than doctors are willing to do today. I will admit that was an interesting turn of phrase though.