He took one look, and immediately took some x-rays. Which is a much faster process nowadays - pop a metal thing in my mouth, point the camera at me, pop out of the room while the shot happens, and it was up on a monitor within three minutes (which he spent checking everywhere else).
And it seems I have an abcess forming beneath one of my troublesome teeth. A tooth that's only 2/3 there anyway, because of my previous trouble with my wisdom teeth*. And when he showed me the x-ray I could see the previous attempt at a root canal (from about 15 years ago) which only went halfway down the sodding tooth. A complete botch job (I said so out loud, the dentist said he couldn't possibly comment).
So now I need to have a proper root canal in two weeks time. I've booked the day off work, but it's going to cost me about £80, and it really isn't a lot of fun.
*They came through at right angles. Literally. Which pushed the teeth in front of them together, causing a pile-up in my mouth. All of my teeth are in good condition, apart from the four in the pile-up.