How far does an E1 interproximal caries penetrate the enamel?

• A. Through to the dentin
• B. Precisely half the enamel thickness
• C. More than half the enamel thickness
• D. Less than half the enamel thickness

Answer: (D)

An E1 lesion is confined to the outer portion of enamel, involving less than half of the enamel thickness. On a radiograph, you’d see a small radiolucent area that stays within the enamel and does not cross the enamel–dentin boundary. This is an early enamel caries stage; it has not reached the inner enamel or dentin, so it’s typically managed with remineralization and good plaque control. If the radiolucency extended into the inner enamel or dentin, it would indicate a deeper, more advanced lesion.