Good news: The upper-left-side teeth that have been intermittently hurting for actually a couple years now but nobody can find anything wrong with them? There's nothing wrong with them.
Bad news: Because that pain, along with the brand-new cold sensitivity, is actually coming from a tooth in my lower jaw, which is already about half-filling. That giant filling is pretty much touching the nerve; this appears to be the source of the problem. It is unclear why all the sensation gets transferred to the upper teeth, but all those nerves go through just about the same place so the transference is apparently fairly common.
Worse news: The only thing that can be done about it is to dig a great big hole in the tooth, dig out all the nerve tissue so everything in there is dead, dead, dead, and slap a crown on it. They call this a "root canal." The other option is, pretty much, "learn to enjoy pain."
I really, really don't want a root canal. ::whine::
I am also frustrated at the length of time it has taken to figure this out. I was warned when I got this filling that it might just be too deep, and a root canal would be the only thing to do at that point, but I wasn't expecting pain in entirely different parts of my mouth to be the signal for that, you know?
Rip 'em all out and replace them with titanium, that's what I say.
The other thing I did today was take Niobe to the vet to get her teeth looked at; the neck abscess and resulting fuss seems to have caused her to move her jaw oddly, and her incisors had become misaligned and therefore sort of pointy. Once that was all cleared up, she managed to get nearly everything ground more-or-less straight again, but we noticed recently that she had (1) a rather long spike sticking out past the rest of the tooth on one side and (2) quite a bit of decay on the upper front surfaces. The vet's opinion is that there is basically nothing to be done about the decay, and that while she [Dr. Griscom, whom I haven't seen before] could grind the spike down, the chances of this being stressful enough to cause, um, instant death were pretty high. (Her first words: "This is a rat? And she's really over three years old? Wow.") So we'll just be keeping an eye on that, and encouraging her to chew on hard things, and hope it doesn't get enough longer that she starts cutting up her mouth.
 This is in fact almost exactly what happened to Ariadne, except for the part where Andres and I did it all by ourselves and therefore the vet (different vet, in Pittsburgh) didn't have to feel guilty about it. And also she had a tumor, and a number of other things wrong with her, and was in fact supposed to have been euthanized earlier that day, but the vet and Andres between them were a whole lot more optimistic than I was. So dying very suddenly in my lap was probably not the worst of all possible things that could have happened to her, but it was still fairly traumatic for everyone involved.
 Since that first line sounds kind of dumb if one is looking at Niobe, I will point out that at that point Niobe was hiding in a box, having realized that she was at the vet's office! where terrible things happen! and you feel woozy for days afterwards! and Dr. Griscom was just looking at her chart.