Dens invaginatus is a developmental malformation of teeth that most commonly affects permanent maxillary lateral incisors. Presence of dens invaginatus in mandibular permanent teeth is relatively rare. The purpose of this report is to describe the combined nonsurgical and surgical management of a mandibular lateral incisor associated with a rare type of dens invaginatus. Pulp involvement of the malformed tooth, periapical abscess, and severe periodontal destruction were observed. The signs (sinus tracts) and symptoms ceased after completion of the treatment. Satisfactory healing of the periradicular lesion was observed at the 6-month and 2-year follow-up examinations.