How far does a D2 interproximal caries penetrate the dentin?

• 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 caries depth is categorized helps you know what D2 means. Dentin is divided from the enamel junction toward the pulp into three roughly equal parts: outer, middle, and inner. When a lesion has penetrated into the middle portion, it’s classified as D2. That corresponds to more than one-third of the dentin thickness being affected. If the lesion stayed in the outer third, it would be D1 (less than the middle third). If it reached the inner third near the pulp, it would be D3. If the lesion were still in enamel, it wouldn’t be a dentin depth category at all. So D2 specifically means penetration into the middle third, i.e., more than one-third of dentin thickness.