In the event a retreatment has failed or would present too many risks, apical microsurgery is performed. Persistent infection is removed from a lateral approach, and a filling is placed inside the root end. If tissue is harvested, it will be sent to the University of Minnesota oral pathology lab for final diagnosis. A bone graft may be placed, depending on the location and extent of infection. Sutures are placed to assist healing, then removed at one week.