Depends on the tooth, and depends on the dentist.  Some dentists here
(such as Newbie) will treat almost any teeth well.  I refer frequently
for second molars, and for curved canals, and for re-treatments
and...anything I think I might have trouble with.  Specialists obviously
will be more expensive, but this fee will be justified with a good
specialist, who of course tends to treat the more difficult teeth.
    I happen to be in Brooklyn, and work with plenty of good specialists
there (I unfortunately will be out of the office most of the coming
week).  Feel free to contact me if you wish off list (remove "mung" in
the e-mail addy) and if you tell me where you are I may be able to give
you names of good root canal specialists.

Steve