He told me why he does it a while ago. As I recall, he read that there is "bad" stuff in most toothpaste. I think it is the stuff that makes it taste good. He claims plain old cheap bar soap does a much better job cleaning and of course doesn't contain any of that bad stuff to make it taste good.
I think he said it took him about a week to get used to it and then it was fine.
“You can discover more about a person in an hour of play than in a year of conversation” – Plato