A bitewing shows a lesion on a premolar extending through the enamel and into the OUTER THIRD of dentin. How is this classified?

Correct answer: B. D1

• A. E2 denotes a lesion in the INNER half of enamel but not through the dentino-enamel junction.
• B. CORRECT. The radiographic depth classification designates dentin lesions D1 through D3. D1 is the outer third of dentin, which is exactly what the stem describes.
• C. E1 denotes a lesion confined to the OUTER half of enamel, not yet reaching dentin.
• D. D3 denotes a lesion in the inner third of dentin, approaching the pulp.

Note: Full scale: E1 outer half of enamel, E2 inner half of enamel, D1 outer third of dentin, D2 middle third, D3 inner third. Treatment implication: E1 and E2 lesions are candidates for remineralization and monitoring; D1 and beyond generally require restoration since cavitation is likely. Remember that radiographic lesions are consistently DEEPER histologically than they appear on film.