What is the minimum thickness of remaining dentine that should be preserved over the pulp during caries excavation or cavity preparation?

Correct answer: D. 2 mm

• A. 1 mm leaves the pulp inadequately protected — bacterial toxins, restorative monomers and thermal stimuli reach it readily.
• B. 3 mm would be desirable but is rarely achievable in a deep lesion, and demanding it would mean leaving substantial caries or preparing far too conservatively.
• C. 5 mm exceeds the total dentine thickness available in most teeth and is not a clinical target.
• D. CORRECT. Approximately 2 mm of REMAINING DENTINE THICKNESS is the accepted threshold for protecting the pulp. Dentine acts as a diffusion barrier, and its protective capacity falls off sharply as it thins: at 2 mm the pulpal response to restorative and bacterial insult is minimal, whereas below roughly 0.5 mm the odontoblastic response becomes marked and permeability rises steeply because the tubules are wider and more numerous near the pulp.

Note: This threshold underpins the modern shift to SELECTIVE caries removal: in a deep lesion, remove peripheral caries to firm dentine at the margins to permit a durable seal, but leave soft affected dentine over the pulpal floor rather than risk exposure. A sealed restoration arrests the residual lesion.