CIGARETTES are definitely bad for dental health ... they cause bone loss in upper & lower jaws, not to mention all the 3000+ carcinogens that get in your mouth (not to mention lungs) with each puff. Nicotine would be the only harmful ingredient in vaping as it does have a vasoconstriction effect ... but that is still only one "bad" vs. 3000+ "bads".
Amusingly enough, there is a significant debate going on over the effects of nicotine. Some studies have apparently shown that there may be benefits to nicotine (not advocating) The problems seem to arise more when intake is too high. Pop "nicotine health benefits" into the google machine, rather interesting reads. I am def not a Dr. though
From personal xp, Ever since (a few years now) I have been using a pre-brush (peroxide) rinse as well as the post brush anti-septic. This on top of quitting smoking, drinking soda/sugary + acidic beverages has made a world of difference. Unfortunately though my teeth are far from perfect