Hi.. Can understand your concern.. As per your complain recurring pain in a root canal treated tooth can be due to a number of reasons.. It can be due to a missed canal present in roots of tooth.. At times there is an extra root canal present in the root of the tooth and if it is left undetected the nerves and blood vessels in it can be remained un-cleaned leading to infection in it sometimes later and it can lead to pain. Other reason can be that any canal was left unfilled or partially filled during the filling procedure.. In this case it can lead to an open area where the bacteria can flourish leading to infection and pain.. Other reason can be the filling material placed in the canals for filling up of the canal has crossed the tips of root of the tooth and reaching below the root tips and outside the tooth it acts as a foreign body leading to inflammatory reaction causing pus formation and pain. One reason can be that when the root canal filling is done the infection has not completely subsided and just reduced due to antibiotics and pain subsided due to painkillers.. Now the bacterial growth has exaggerated in that area causing infection and pain. I would suggest you to consult your dentist for a clinical evaluation so that he can take an x-ray and find out the cause of pain. If there is infection a course of antibiotics and painkiller can help.. But if there is pus formation below the root tips of the tooth leading to abscess formation then the root canal treatment needs to be repeated.. Hope your query is solved.. Thanks and regards.. Dr.Honey Nandwani Arora.