Many things are not only bad for your general health, but very bad for your teeth. Please be aware of the following:
Soda (Soft Drinks): Any soda is bad for your teeth, and your health also. Soda truly dissolves your enamel and leaves your teeth wide open for decay in multiple areas (wherever the soda touches). Even if you see a dentist 12 times a year, they cannot protect your teeth from the ravages of soda. Soda is also bad for your health in general, and I personally do not believe diet sodas are any better.
Tobacco: Smoking will kill you one way or the other, and when you die, you probably will not have your natural teeth. Smoking has innumerable toxins. It can cause mouth, throat, and lung cancer. It causes hardening of the arteries, high blood pressure, and heart attacks. Smoking dries your mouth, making you more prone to decay. Smoking is a significant risk factor for periodontal disease, which causes loss of bone (the supportive structure) around teeth and can lead to tooth mobility, infection, pain, and loss. Smokeless tobacco is in my experience one of the most addictive, and hard to quit, forms of tobacco. It can cause cancer, loss of gums around the base of the teeth, and severe decay causing tooth loss.
Sugar: My dear mother would always tell me, "Everything in moderation, Eric!" I cannot tell you that I don't have a soda every now and then. I eat cake and pie. But, I do so in moderation, and always find a toothbrush as soon after as I can. Excesses of anything can be bad. We have to have water to survive, but people have died by ingesting too much water. Sugar also should not be used in excess!
Bottom line: the more natural the things you ingest, the healthier you will remain. Processed foods, sugary treats, and habits such as tobacco use will not only shorten the life of your teeth, but your life as a whole!