Have you tried Stevia?

It grows really well in my backyard. Smells badly(but tastes sweet) but is a great sugar replacement for making lemonade or ice cream or sweets without the high glycemic index.

You also probably have to learn to brush your teeth better. When I was a kid I had lots of cavities, then I learned that I was doing it badly(I had plaque and tartar in my teeth and I got used to it). No one really told me, dentist don't feel the teeth the way your tongue does, they use a piece of metal.

So I brushed better so the surfaces of the teeth became smooth(it took some time but then maintaining that is really easy).

Since then, decades had passed and no new cavities.