How is a pit-and-fissure carious lesion shaped as it progresses through enamel?

Correct answer: A. A cone with its apex at the enamel surface and its base toward the enamel-dentine junction

• A. CORRECT. In a pit or fissure the lesion begins on the WALLS of the narrow defect, so the small entrance forms the APEX and the lesion spreads laterally as it deepens, giving a base at the enamel-dentine junction. This is why occlusal caries is so treacherous: a tiny surface opening conceals a broad zone of undermined dentine, and the lesion is often far larger than it appears.
• B. This describes the SMOOTH SURFACE lesion, which has its broad base at the surface and its apex pointing inward.
• C. A spherical lesion within enamel with no surface connection does not occur.
• D. Caries does not progress as a uniform cylinder; the shape is determined by the direction of the enamel rods and the geometry of the surface.

Note: Then in DENTINE both types invert: the lesion follows the tubules and spreads laterally along the enamel-dentine junction, forming a cone with its base at the junction and its APEX toward the PULP.