Failure of endodontic treatment due to a palatal gingival groove in a maxillary lateral incisor with talon cusp and two root canals.

A case is presented in which endodontic treatment of a maxillary lateral incisor with a talon cusp and two root canals failed following a mistaken diagnosis. What was first diagnosed as an endodontic lesion was, in all probability, a primary periodontal lesion caused by the advance of bacteria from the gingival crevice to the apex along the radicular groove between the main tooth and the talon cusp.