I had a little 'blister' on my gum for about 5 months. It would fill and I would pop it. I visited my dentist yesterday for another problem , showed him the blister and he said I had an absessed tooth. I have never had a bit of pain, none. This tooth was crowned in 1990. he suggested a root canal. Two days later and the 'blister' is drying up, not filling anymore. If the nerve is dead and the infection is over, do I still need a root canal?

You still need a root canal. The reason it didn't hurt was because it was draining (the blister) which keeps it from hurting most of the time. However, you still have an active infection that will flare up and drain again. Additionally, an infected tooth can pose more serious health conditions, so I would go ahead and treat the tooth while you are not in pain. You may very well develop a very painful infection (in fact, I put money on the fact that you will!) and then the root canal won't be quite as simple and uneventful.

I agree with KIKKI- You have what they call a fistula, into which infection from the tooth drains and appears as a little bubble on the gum.

A xray would usually show infection around the root tips.

I had a fistula caused by infection in a lower back molar and lived with it for several years, with my dentist warning me that unless we acted now, "someday this is going to blow, kid".

Xrays don't always show a fracture but mine DID show infection.
I was so comfortable, I ignored him. Said I wanted to live with it a little longer. DUMB.
Then sure enough, on a vacation in Europe, wham. Serious pain, no drainage anymore, all infection building up under the tooth. Dentist opened it all up. Tooth was cracked with plenty infection. No option but extraction.

Best to deal with it now, as KIKKI suggested. If you need root canal, go for it.
If the tooth is cracked, it may be too late for root canal, but you won't know until you get in there.

zuzu xx

Wow, yeah that stinks that you still need the rc, but I agree, get it over with NOW. I was lucky, I got mine done early--my dentist told me I had a "ticking time bomb" in my mouth and I was in enough pain to just do it--turns out I have other teeth that could do this, but thankfully no abcess!

I do have a question though--you say you had a sore on the gum--was it a perfect cirrcle in shape? How high did it sit? I just wonder because my very back bottom tooth that was recently filled and was a very deep cavity: ie close to the never and you all know what that means.... it has this swelled area around the gum--but the dentist has X rayed it and looked in there and I 'd think if it were infection it would have been noted by now, although I was on antibiotic well before the root canal was scheduled...I wsa just in a lot of pain suddenly so I went in for the root canal sooner than they had me scheduled for!

Good luck w/ that!

what if you have that little blister right next to the tooth that has already been root-canaled? what could be causing the infection?

If the blister or little bubble is indeed a fistula, it means infection is draining into it from somewhere. Sometimes this happens if a fracture occurs at the root of a tooth. One would not necessarily experience pain because the pus is draining into the fistula and not building up under the tooth in question. *

Hi, I'm having the same problem. Did you ever find out what was causing it? Had the fistula (pimple) come up almost 3 weeks ago, had the root canal and now the first part of the crown process and the fistula is still there and ruptured last night with blood coming out. It's on the last upper tooth. Called the dentist and I'm going back on antibiotics. Any suggestions? Thanks!