HypersomniacLive: Mine were also impacted with no prospect of emerging, and I did get all four removed at once, but I still got only localised anaesthesia. I'm surprised because I don't recall having been offered the choice, not that I'd have gone with the general one. :-)
And now general notifications are borked. *sigh*
Anyway, they brought up the choice because my two impacted teeth were emerging - you could see what should have been the upper left edge of the bottom left tooth as it pushed out, right against the tooth next to it. Both bottom teeth were essentially parallel to my jawbone, but the left one was a few degrees up. I already have issues with my bottom jaw, so it was joyful. And very, very painful. Between that and the number of teeth they had to take surgically (out of the seven, at least five, if not six, had to be surgically extracted rather than pulled), they offered up general anaesthesia as a (greatly more expensive) option. I took it, because dentists don't bother me and I have a very high pain tolerance level, but that was more than I wanted to be awake for. ;)