Periapical infection associated with root canaled tooth generally results from incomplete canal debridement or oburation, or root fracture.Elimination of the infection can be achieved through, redo root canal, periapical surgery with retrograde filling, root amputation(multirooted tooth), or extraction with thorough curettage of socket.Seeing an endodontist is advised.
you need to get rid of the infection first. infected teeth are very difficult to numb. usually a course of antibiotics before the extraction works well. have the tooth checked it might just be a case of needing the root canal redone and an extraction is not necessary.