Which dental structures appear black on an x-ray?

• A. Pulp and PDL transmit more x-rays.
• B. Enamel and lamina dura absorb more x-rays.
• C. Dentin transmits all X-rays.
• D. Cortical bone transmits fewer X-rays.

Answer: (C)

Dark areas on a dental X-ray are radiolucent—structures that allow X-rays to pass through with little attenuation. The pulp and the periodontal ligament space are soft tissues with little mineral content, so they transmit X-rays more readily and show up as black on the film. Enamel and lamina dura are highly mineralized and block X-rays more, so they appear light or white. Dentin is denser than pulp but less dense than enamel, so it isn’t completely transparent; it appears as a gray shade rather than black. Cortical bone is dense and also appears white. So, the correct idea is that the structures appearing black are the pulp and the PDL spaces.