Often times, patients hear that brushing, flossing, and the elimination of sweets is the solution to preventing decay. I have found that there is a large percentage of people that like you brush and floss regularly and conscientiously try and take care of their teeth. When I examine their teeth there is no plaque or tartar and they do not have bleeding gums, yet they still have decay. On the other hand, I know people that do not seem to take care of their teeth, they have tons of buildup on their teeth and they have no cavities.
We also found that a certain percentage of the patients that had normal saliva that tested about pH 7.4 still had decayed, but it was usually on the posterior teeth. These people had a history of heartburn and took a lot of Tums or medications for ulcers and heartburn. It seems that as the stomach acid surges from the stomach to the back of the mouth it causes heartburn, but it also decays the back teeth that are bathed in the acid.
In your situation, you may get a swimming pool tester and see if you have acid saliva. If you do not, but do have heartburn, this could be the cause of your problem. Your doctor could put you on Prilosec or Pepcid A/C. You may already be using Tums or Rolaids. If you do get the acid reflux into your mouth rinse it out immediately and do not brush. You can get a prescription for a fluoride gel toothpaste from your dentist that can help reverse some of the damage.
Unfortunately, if you have acid saliva the teeth are bathed in the acid 24 hours a day. The best solution is to find ways to make your saliva turn more basic. A urologist may have a medication that can do this, or you may try altering your diet to see if you can find a way to make the saliva more basic. Some purport that green leafy vegetables help make the saliva more basic. This is a very individual thing and you have to try to make the changes by trial and error. Thank goodness the cost of a pool test kit is really low.
One other cause of decay is acid reflux. If you get heartburn, the acid from your stomach may eat your teeth. If you do get reflux, medications like Prevacid can help. If you get the acid in your mouth, rinse quickly. Some even suggest rinsing with baking soda water.
The good news is that candy and sugar are not the big culprits we were taught, so while you are looking for ways to reduce the acidity have a candy bar. It may help and if it doesn't, at least it will taste good.