What shape may an E2 interproximal caries have?

• A. Equilateral triangle with base at proximal surface
• B. Isosceles triangle with base at proximal surface
• C. Right triangle with leg along the enamel surface
• D. Circular patch within enamel

Answer: (B)

When you look at how interproximal enamel caries develop on a bitewing radiograph, the lesion tends to grow as a wedge between the teeth. It starts at the proximal contact and extends apically into the enamel toward the dentin, slicing more or less evenly from the sides around the contact. That symmetric inward progression makes the radiolucent area look like a triangle with the base along the proximal surface (the side facing the neighboring tooth) and the apex pointing deeper into the tooth toward the enamel–dentin junction. Because the two sides are usually of similar length, the triangle is isosceles. So an E2 interproximal caries on radiographs is best described as an isosceles triangle with its base at the proximal surface.