I have had a pustule reappear in the same spot for 6 years. I have had root canals and a redo root canal done on either side of the pustule. X-rays show a dark mass surrounding the two teeth. Friday I had an acipoectomy done on two of the root canal molars and my endodontist found a large lesion or mass under my gums just below my nose, which he removed. What is this and how did it get there?