Mary Lou
I went to a special dental clinic at the University of Buffalo (NY) where they diagnosed that the foul breath was caused by bacteria lodged at the back of my tongue. In addition to all the good oral hygiene you are obviously doing, they prescribed a special rinse "chlorhexidine gluconate" which kills the bacteria causing the problem. The rinse can eventually leave some stains on the teeth but they can be cleaned away by a dental hygienist. It worked for me. Once I got rid of the bacteria I have been able to use Listerine and tongue scraping and other usual good dental care techniques and I seem able to maintain a fresher mouth odor. You might check around for a university dental clinic near you or ask your dentist about the rinse. I had to push my dentist into suggesting the clinic. Too many dentists don't get involved beyond the health of your teeth. Good luck!