What would happen if you brush all of your teeth properly and regularly except one that you never brush at all?

would that neglected tooth turn black and fall off?What would happen if you brush all of your teeth properly and regularly except one that you never brush at all?
I do not think that it would turn black and fall off, even though you are not brushing it, the chemicals are still in your mouth and help that tooth. Even though that would probably not happen, I would suggest you brush it anyway.Good Luck!