Class 1. Primary endodontic lesion draining through the periodontal ligament
Class l lesions present as an isolated periodontal pocket or swelling beside the tooth. The patient rarely complains of pain, although there will often be a history of an acute episode. The cause of the pocket is a necrotic pulp draining through the periodontal ligament. The furcation area of both premolar and molar teeth may be involved. Diagnostically, one should suspect a pulpally induced lesion when the crestal bone levels on both the mesial and distal aspects appear normal and only the furcation shows a radiolucent area.