Why is the periodontal ligament space so widened around this abutment?

Correct answer: C. Torquing of the abutment by the distal extension base

• A. Hypercementosis is excessive cementum deposition making the root bulbous — and the discriminator is that the periodontal ligament space FOLLOWS the enlarged root outline and remains of NORMAL width. Here the space itself is widened.
• B. Internal resorption expands the CANAL outline from within the pulp space, producing a balloon-like enlargement centred on the canal. It does not widen the ligament space around the outside of the root, and this tooth is vital and asymptomatic to cold.
• C. CORRECT. This is OCCLUSAL TRAUMA generated by the prosthesis. A distal extension base is supported partly by MUCOSA, which displaces under load, and partly by a TOOTH, which does not. When the base settles it rotates about the rest — and with the rest placed DISTALLY, the fulcrum lies distal to the abutment, so the retentive arm is driven further into the undercut and the tooth is TORQUED. Sustained lateral and torquing forces widen the periodontal ligament space, characteristically funnel-shaped and widest at the crest, and combined with plaque-induced inflammation this produces the mobility and angular bone loss seen here.
• D. Condensing osteitis is INCREASED bone density around the apex of a tooth with low-grade pulpal inflammation — a radiopacity, the opposite radiographic change to a widened lucent ligament space.

Note: The design answer is the RPI or RPA concept: a MESIAL rest with a distal proximal plate and an I-bar, so that loading DISENGAGES the retentive components rather than torquing the abutment. Add broad tissue coverage of the base, a functional (altered cast) impression, narrowed occlusal tables, periodic relining as the ridge resorbs, and instruction to leave the denture out at night. Note separately that SYMMETRICALLY widened periodontal ligament spaces around MULTIPLE teeth have a quite different differential — scleroderma and osteosarcoma.