3 missing for me, my dentist tell me that it could cause blood problem and can cause death, so I stopped brushing my teeth for around 11 years.
Stupid young idea, because after years of pain and long awake night (or sleeping sitting, it helped me to avoid pain sometimes), I decided to go at the dentist some years ago, no pain anymore, but it cost me around €3000, took around 6 month and most of my teeth are now repair with artificial teeth color things (I don't know the English word for that material).
I should put a tooth crown on 2 of my teeth but it's too expensive and I'm lazy to go to the dentist again (I'm resistant to dental anesthesia due to stress, high heart beat and drugs, that mean anesthesia take a long time and more product to take effect, and lasts less), so now I have just a half teeth on back and a teeth root remaining on another (without count the 3 missing)
if I can go back in past to advise the 11 years old me, brush my teeth will probably be the first advice I will tell him.
Now depression and lazy keep me forgetting this important thing, and certainly because I didn't get used to being younger, but I do it enough to not have pain from it anymore, and as a big smoker, it turn brown quickly.
That part of life when you are a living trash.