Are lemons good or bad for your teeth? I’ve heard that they’ll stain your teeth, that they’ll clean your teeth, and that the citric acid will eat away at your teeth’s enamel. When the waiter drops a slice of lemon in my water, should I squeeze it with vigor and leave the remains floating inside or remove it with disgust?
Closing in on the half-century mark, my teeth have been exposed to lemonade, raw lemons, and their cousins-oranges and limes on a regular basis. Other than wisdom teeth, all of my teeth, even those teeth that were temporarily removed via a motor vehicle accident are happy teeth still gummily ensconced in my mouth. 
OK this a WAFG…
Puke is bad for your teeth and it’s acidic.
Baking soda is good for your teeth and it’s basic.
While chewing a lime or lemon once in a while, usually after hours of smoking and drinking, does seem to relieve that plaquey film, I’d hazard to guess that acid in general is bad for them.
It’s a tossup, and neither side amounts to much. Lemon juice has a slight bleaching effect, but it’s really slow, and won’t help whiten your teeth much. Lemon juice is also acidic, but not much more than most foods are. If you fell asleep with a lemon slice in your mouth, your teeth might be a little whiter, and the enamel a little thinner, maybe, by morning. Squeeze a slice into your drink? No help or harm in that.
I’ve spent a lifetime slicing lemons and limes in half, salting them vigorously, and then squeezing the juice straight into my mouth, 2-3 fruit per sitting.
The undiluted lemon and lime juice is a bit hard on the tooth enamel but probably nothing compared to the wear and tear of fingernail removal activities.
I eat lemons and limes as fruit, so I’ve worried about this on occasion (but as with most things, never really stopped doing it!).
I’ve got one dodgy patch of enamel on one tooth (I made a thread about it earlier this month if you want to search) but the rest are alright, so I’m inclined to blame something else for that.