I would trust your dentist - after all, if it's a black spot, what would it be? If it's not a hole, what would cause a black spot stain that can't be removed?
To the best of my knowledge, a cavity cannot heal on its own. This isn't like a broken bone, but rather, bone that's simply gone (eroded by acid from bacteria). One can have a cavity for a while without any major issues. This is why there doesn't appear to be change. And you probably aren't feeling pain as the cavity is not large enough to expose your nerves - or even your dentin - to air. But if the cavity does grow, and you don't do anything, you may ultimately need a root canal or extraction.
If your wisdom teeth came in nicely and you want to keep all your teeth, I recommend a filling. These days, it can be done in one appointment. Get the white filling material (as opposed to an amalgam) and you probably won't even notice that it's there. Plus, insurance - if you have it - covers 80-90% (depending on your coverage) of the filling.
Last edited by WhoU80; 01-15-2013 at 06:32 PM.
Reason: Corrected typo