While meth can be extremely hard on your teeth, you acknowledge another serious concern and cause of tooth decay in your question: smoking. Tobacco, whether smoked or chewed, is (in addition to being carcinogenic--meaning it causes cancer) extremely bad on your teeth and gums. The inflammation and irritation it causes can have numerous effects on the health of your gingiva. This inflammation can add
to the detrimental effects that smoking has on your heart, as new research is showing that oral cavity inflammation can have long term detrimental effects on your heart health.
Smoking cessation would be the absolute first place to start to preserve the health of your teeth. Your oral cavity hygiene could also be improved, as it is recommended to brush your teeth at least twice a day. As long as the toothpaste contains fluoride, the specific brand should not matter too much (although checking that it is approved by the ADA-American Dental Association- is valuable). Daily flossing will also improve the health of your teeth.
Finally, it is important to have an honest relationship with your health care providers--in both directions. If you feel that your dentist
is not being frank about his concerns with you, then you should discuss this with him or her so that you can both work together to help take care of your mouth.