A radiograph of tooth #29 shows bone loss, with caries at and below the cementoenamel junction. What is the most likely cause of the bone loss?

Correct answer: B. The carious lesion acting as a plaque-retentive factor

• A. Occlusal trauma alone does not cause attachment loss. It can widen the periodontal ligament space and increase mobility, but bone loss requires bacterial plaque — and the stem gives you the plaque-retentive factor directly.
• B. CORRECT. A subgingival carious lesion is a powerful local plaque-retentive factor. The rough, cavitated surface is impossible to clean, harbours biofilm continuously against the attachment apparatus, and produces localized attachment and bone loss around that tooth alone.
• C. A vertical root fracture typically produces a narrow, J-shaped or halo radiolucency tracking along the root, with a deep isolated probing defect. The stem describes caries, not a fracture pattern.
• D. Aggressive periodontitis produces a characteristic pattern affecting incisors and first molars bilaterally, not isolated bone loss around a single premolar with obvious local caries.

Note: The general principle: LOCALIZED bone loss around a single tooth almost always has a LOCAL cause. Work through the list — subgingival caries, an overhanging restoration margin, an open contact causing food impaction, a root fracture, a furcation involvement, a palatogingival groove, or endodontic-periodontal communication.