Previous root canal treatment. It appears that there are spaces in the root canal system that have not been negotiated or cleaned, especially the distal root.
Note: 3 files in distal root
|Photo: 5 canal orifices|
All canals were cleaned and filled to the radiographic apex.
Though teeth may have multiple canal systems and some of the canals may meet apically, a dirty canal will inevitably cause periapical symptoms as contamination may occur from the unclean canal. A canal obturated with gutta percha will not stop contamination from a neighboring canal that joins it.