How is a second root canal possible, if there is no root and no pain?

technically your tooth its death, has no nerve or blood support, so the normal way of the bone and body to react its to make a microscopical rejection, there is no root canal that seals 100 %, and all the root canals if you see them with a microscopic microscope,there is a halo, around the tooth, of the body rejecting that tooth, that has or either infection, or its a death tooth ,so no matter if any doctor makes or perform a root canal,there is always a chance of rejection always, this is more determined by the body acceptance,and tolarance,and just a few years ago root canals are performed, time before they used to extract teeth, now there is a an option,materials are organic,and 100 %compatible,but if the body reacts by making an infection,anaerobic microorganism are present, and once there is a communication with air, they will die,and antibiotics will help, and you will still be able to save that tooth,so re do that root cannal, and problem solved,try a dental vacation in sunny cancun,and for half you will pay ,you will find a solution,

Root canals work 90% of the time, and root canals done today with better techniques even exceed that success rate! It is possible that all the bacteria weren't removed before the root canal filling done. Also possible is that the root canal filling, although removing the entire nerve, did not go down all the way to the root tip, leaving a very small area that could harbor bacteria and continue to infect the bone. And sometimes there are extra canals in the root that weren't detected and filled.Antibiotics don't work because it takes a good blood supply to an area to work, and there is none inside the root canaled tooth. Best thing is to go to a root canal specialist, he will remove the old root canal filling, redo it and give you a better chance of saving the tooth. Sometimes it is necessary to do a small gum surgery to clean out the infection. All that the endodontist (root canal specialist) can explain to you at your consultation.

If the tooth is worth saving, then a re-treatment could be indicated.I would seek the opinion of an Endodontist (specialist in root canals) and
find out the prognosis.