Hi I am a smooker too with a partial and a bridge. Have you ever soaked it in peroxide --mix it half and half with water? If that doesn't help try Clorox--no I am not nuts--I have done this and it works with tough Blueberry stains. One teaspoon clorox and enough water to cover the teeth. Follow this with a good scrubbing of bakeing soda--which by the way will also bring those choppers back to their original color and shine. Hope this helps!
I just read your post again and you didn't say if the top ones come out--If they don't then scrub daily with the soda on your toothbrush. They will be back to normal in no time at all. Your gumbs will be healthier also! Smile !