I feel as though teeth should be deprecated in favour of one of (or all of) these alternatives. As I mentioned in response to one of the linked forum posts, teeth seemed like it was intended to be used when they were distinctly drawn but I've seen it being used on anything ranging from a full white fill in the mouth to a 1px line across the top of the mouth.
I don't imagine people who have a fancy for teeth and want similar gratification that they'd get from araragi_karen toothbrush teeth (pretend this just leads to the infamous scene since a few of these posts don't have detailed teeth either) finding post #9619807 where yes they are definitely there but they're not the focus of the image and have no detail besides being an aligned rectangle.
I'd imagine teeth itself is hard to get rid of because of other tags like upper teeth only but then that becomes a whole new discussion of if some of the other teeth-related tags are also padding and should be taken out back. I've seen small tags like this excessively used by tag padders and Related Tags spammers who load their posts up with a bunch of tags, sometimes where they don't even fit, to make it seem like a post is well tagged, only for me to end up removing a boat load of them for being wrong.