If you're lucky, it's a bone fragment. If you're not lucky, maybe you went to the same oral surgeon I did. He cut me four times, and I had four sets of stitches, but when I went back for my next routine checkup, my regular dentist said "How many extractions did you have?" "Four." "Are you sure? The source of your discomfort appears to be a partially-erupted tooth."
So I got a panoramic X-ray, and lo, guess what? Right. I guess while I was sitting there under general anesthesia with my gums sliced open, the phone rang, or his hot secretary came in and distracted him or something, and he closed me up without removing the blarfin' tooth. Unbelievable!
When I woke up from the general the second time, he handed me the tooth in a bag, and said "If you grow any more teeth, we need to do some tests to see if you're an alien."
ARRRRRRRRRRRRGH!
There was only one tooth. I saw the before and after, and it was in exactly the same place on the second X-ray. That jerk just didn't do the job I paid him almost a thousand bucks to do!
Oh well. They fixed it in the end, for free, and I decided not to try to sue anybody. Maybe I should have.
Anyway, I guess by now you know what it was. Here's hoping it was just a bone fragment.