What does a D1 interproximal caries do and where is it located?

• A. Penetrates into inner third
• B. Causes widening of pulp chamber
• C. Extends into middle third of dentin
• D. Undermines enamel, extends into outer third of dentin

Answer: (D)

D1 interproximal caries are lesions that have reached the outer third of dentin, just beneath the enamel, and as they progress they undermine the enamel from below. In other words, the decay has moved from the enamel into the outer portion of dentin, not yet into the middle or inner thirds. This depth (outer third of dentin) distinguishes D1 from D2 (middle third) and D3 (inner third) caries.