How far does a D1 interproximal caries penetrate the dentin?

• A. More than one-third of dentin thickness
• B. Enamel only
• C. Less than one-third of dentin thickness
• D. The whole dentin thickness

Answer: (C)

Dentin caries are described by how deep they go. When a lesion has reached dentin but is still only in the outer part, that is described as the outer third of the dentin thickness. In other words, the caries has penetrated enamel and entered dentin, but it hasn’t extended into the middle or inner dentin. That corresponds to less than about one-third of the dentin thickness. If the decay were deeper, reaching the middle or inner dentin, it would be classified as a deeper stage, which carries different implications for pulp proximity and treatment.