Irrigation is King
In endodontics as with many other things in life there are no shortcuts. Everything that leads to a successful outcome when doing root canal is dependent upon the preceding steps when initiating treatment. Obviously proper diagnosis is first. To avoid the dentolegal stuff; communication, alternatives, documentation and consent are paramount as well! Cutting to the nitty gritty, when doing root canal if you don't have proper irrigation, the treatment will probably not fall into the success rate of standard endodontics. Debridement is dependent on irrigation, thus If there is not enough irrigation solution in your canal contacting tissue and canal walls the you aren't debriding properly. Whether it's 5.25% sodium hypochlorite, 17% EDTA, or your final irrigation solution of 2% chlorhexidine, all must ultimately get close enough to the apex to do their job. Using 30 gauge needles bent to follow the canal with no wedging and light pressure is key. Delivering solution to the apex is also done with negative pressure irrigation systems where the irrigant is drawn from the pulp chamber to the apex under suction. Most importantly establishing a proper glide path and shape to a patent apex is the key to getting solution to the apical 1/3. Sonic activation with an instrument in a reciprocating hand piece going 3000 to 4000 repetitions per minute is also important. Once you start creating your shape and approach a .04 taper the irrigation needle can be placed in a more apical direction. You can't get a 30 gauge needle down a canal that's been instrumented to a 25 with no taper in the proper dimension. That's just math!
Here is a case where I hit a brick wall in the distal canal. No matter how I bent or twisted the end of the file I could not slip it out the apical opening ( X-ray 1). Thought it was calcified and was giving up hope. So to illustrate irrigation is key, I used plenty of it in the hopes that there was a distal path that would present. Between the hypochlorite digesting tissue and the EDTA removing the smear layer and opening the dentinal tubules, lo and behold the anatomical opening presented itself on the final fill film. (X-ray 2,3) The fistula has closed and so far a happy result.