Radiographically detectable caries corresponds most closely to which histological zone of an enamel carious lesion?

Correct answer: B. The body of the lesion

• A. The TRANSLUCENT ZONE is the advancing front, with only 1–2% mineral loss — far too little to register radiographically.
• B. CORRECT. The BODY OF THE LESION is the zone of greatest demineralisation, losing in the order of 25% or more of its mineral content. Since radiographic radiolucency depends on mineral loss, this is the zone that produces the visible change. It is also why radiographs UNDERESTIMATE lesion depth — the leading edge of demineralisation has advanced beyond the point at which enough mineral has been lost to register on film.
• C. The SURFACE ZONE is relatively well mineralised, losing only about 1%, because it is continually remineralised by ions from saliva and plaque fluid. It is the intact layer that makes non-cavitated lesions reversible.
• D. The DARK ZONE (about 5–8% mineral loss) represents areas of remineralisation and is a sign that the lesion has been arresting and reactivating.

Note: Zones from the advancing front outward: translucent → dark → body → surface. Only the body has lost enough mineral to appear radiographically, which is why a lesion is always deeper than the film suggests.