For D3 interproximal caries, which dentin third is the lesion located in?

• A. Outer third
• B. Middle third
• C. Pulp chamber
• D. Inner third

Answer: (D)

Dentin is divided into thirds from the enamel-dentin junction toward the pulp, and D3 designates the inner third closest to the pulp. So a D3 interproximal caries lesion has penetrated into the inner dentin, the layer just before the pulp, rather than the outer or middle dentin. It’s near the pulp but not yet inside the pulp chamber, which is why this depth is clinically significant for treatment planning.