Damn. All along, I'd been forgetting this, but DR Laura's comment about her crown made me remember:
Once when I had a temporary crown on a molar way back in my mouth, I had a lot of irritation in the gum or cheek for the next day or two, and it took me a while to get the idea to look in there with a flashlight to see if I could see anything. Indeed, there was a piece of something tooth-colored kind of sticking out of the gum around the wisdom tooth next to the crown, so I got my finger back there and found out it would move. I thought it wasn't really part of anything, but even if it was, I had to find out so I began pulling on it. Sure enough, it began coming out from under the gum and it turned out to be a long sort of spirally piece of -- I dunno -- some material obviously left in there by mistake. Maybe a glue thing, who knows. It seemed to have nothing to do with the crown, but it had been cutting into my cheek and feeling like a bad canker sore. Well, everything IMMEDIATELY felt better, felt right, and that little episode was all over.
Having now remembered that, I can't wait to hear what BK's issue turns out to be.
I rinsed it off and kept it for a couple of days, thinking I'd show the dentist, but I finally said why bother, who cares, it's resolved. But I wonder if I took a picture of it. Hmm...