I don't usually check my teeth after smoking, but I don't ever remember seeing stuff on my teeth after a night of smokin....but one time I did notice a bunch of brown gunk on my lips after taking a hit from a bong...I don't know what it came from....maybe somebody was licking ass a few hours earlier lol. I thought bongs helped eliminate most of the ash/gunk from smoking, I usually smoke from pipes and have never had that problem....I would think if anything causes that it would come from a pipe, not a bong or a bubbler