The worst experience of my life. Root canal work, upper jaw. I have never experienced pain like it. It must be worse than child birth.
I think it depends on whether the nerve is dead or not doesn't it? I know when i had mine the dentist bloke said it'll only hurt if the nerve is still alive, but invariably with an abscess it's the nerve being killed off or something.
So i got lucky. It was also the lower jaw, so don't know whether that made any difference, but it was completely pain free... Apart from the massive bill... And the knowledge that it only happened because my dentist cracked my tooth.