Link below is to a web-based article, "Mouth Odor in Yorkshire Terriers."
https://pets.thenest.com/mouth-odor-...ers-12530.html
You wrote, "I've tried the stuff you put in the water not much help." There are several dental health products that are added to water. I've been led to believe these are most effective is you start the regiment after a good vet dental cleaning. Ala, the products help prevent build up, but are less effective (or not at all effective) in reducing the existing buildup. (I read an article about this recently ... will try to find the link.)