Which statement best differentiates D2 from D1 interproximal caries in terms of depth?

• A. D2 is located in the middle third of dentin, while D1 is in the outer third
• B. D2 is in outer third, D1 in middle third
• C. D2 is enamel-only
• D. D2 reaches the pulp

Answer: (A)

The depth of interproximal caries is described by which dentin layer the lesion has reached, using thirds of dentin: outer, middle, and inner (near the pulp). In this system, D1 corresponds to dentin at the outer third, and D2 corresponds to the middle third. So D2 is deeper than D1. If the lesion extended to the inner third near the pulp, that would be categorized as a deeper stage (often D3). The option stating that D2 is in the middle third and D1 is in the outer third captures this depth progression, making it the best differentiator.