Trust me, you don't want to need root canals. I had one tooth that went completely abscessed, and it was the most pain I ever felt in my life (Put it this way, I partially tore my achilles tendon, and needed surgery on it). I just kept shrugging it off, the initial sensitivity, then the pressure, etc...
Once it got to the point I couldn't sleep I went to a dentist, who sent me to an endodontist, etc... By the end of the whole ordeal, I was in so much pain it wasn't even funny. I had to have an emergency root canal, but since I was home from school for the weekend, and it was a Monday off that this happened, he couldnt do me there. So what he did was drill the tooth, and push all of the pus out through it. I had instant relief, and I wanted to hug and kiss the guy. I had the root canal started the next day.
I have since had two others. I didnt want to wait on them, once I started noticing the same symptoms, I called the endodontist up. I don't have dental, so as you can guess, my moth has cost me a very pretty penny. The root canals themselves run around 950-1000 dollars, and the crowns ran around 900 or so (I dont know for sure, they coulda been less).
All my problems came from bad dental work done by a dentist I will never, ever go to again. He improperly put in acrylic fillings, which were leaking, and causing my nerve cavity's to get infected.
Trust me, if you need a cavity filled, or a root canal done, go now, don't wait. The procedure itself isn't very painfull, just a little uncomfortable when they get to the part of the nerve that is still alive. The uncomfortableness of the procedure pales in comparison to the pain of the abscessed tooth tho.