Pain is never normal, but it is to be expected after certain events.  Most
RCT is performed with no pain during or after.  Some, however, do result in
some pain during the procedure.  Often the tooth will be sore to biting
pressure for a week or two.  Every once in a great while, one will hurt for
the first 2-3 days, then just be sore to biting pressure for a few days
more.  There are occasional cases where the tooth needs RCT because there is
a crack in the tooth.  Sometimes, this crack is not easily found during RCT.
It often requires high magnification and stripping all filling out of the
tooth to find these fractures.  If there is a fracture which is open enough
to allow bacteria to "wick" along it, the tooth will never get better and
will need to be removed.

I feel bad for patients when this happens, but it happens.  Nothing we
do is 100% guaranteed, unfortunately.

In cleaning out the root canals of the tooth, often, the instruments we
use go beyond the tooth, and therefore will cause lingering
inflammation afterwards.  Sometimes, these canal system are very tricky
and sometimes we dentists miss the smallest of canals that don't get
instrumented.

Typically, what I do after performing a root canal, I don't immediately
restore the tooth with a crown, but leave a temporary filling in and
wait and see if any symptoms develop.  If so, we go back in.  If not,
we restore.

"Pain is never normal..."
the pain it shows you that you are alive :)

Most of the time, if no periapical pathology is detected...the pain
after
root treatement is because of
the bone lesion made by the needles

What about after treatment?
In most cases after the procedure is completed, you can expect mild
discomfort. In other less frequent occasions there might be some more
discomfort. But the truth is that in the majority of cases you will not
feel
anything at all. If you feel anything this can be very easily treated
for a
few days with an over the counter analgesic.

Sure, there are no nerve fibers INSIDE the root itself but there are
plenty inside the alveolus (jawbone).

If the bacteria are pushed a little past the apical formen (hole in de
end of de root ~ apex = apical), then you get pain!

Joel