Which description correctly matches the penetration depth for a D3 interproximal caries?

• A. More than one-third of dentin thickness
• B. Less than one-third of dentin thickness
• C. Entire dentin thickness
• D. Through enamel only

Answer: (A)

Understanding how interproximal caries depth is categorized helps you gauge how far decay has progressed. The system uses dentin thickness to describe depth: caries limited to enamel is the earliest stage, then into dentin but not very deep, and finally a deeper stage. The D3 designation specifically means the decay has penetrated into dentin more than one-third of its thickness. That deeper involvement signals a more advanced lesion that often influences treatment decisions, since it’s closer to the pulp and carries a higher risk of progression.

If the decay were less than one-third of dentin, that would be the D2 category, indicating shallower dentin involvement. If the lesion were still confined to enamel, that would be D1. Describing a depth as going through the entire dentin or beyond would imply a different, even more advanced scenario not captured by D3, which is why "more than one-third of dentin thickness" is the correct match for D3.