Which dental structures appear white on an x-ray?

• A. Enamel and lamina dura absorb more x-rays.
• B. Dentin absorbs and transmits x-rays somewhere in between.
• C. Pulp and periodontal ligament (PDL) absorb more x-rays.
• D. Cortical bone appears white on radiographs.

Answer: (A)

Radiopaque structures on dental X-rays are the ones with high mineral content, which absorb more X-rays and show up white. Enamel is the most mineralized tissue in the tooth, forming the hard outer crown, so it appears very white on radiographs. Lamina dura is the dense bony lining surrounding the tooth socket, a thin but highly mineralized layer, so it also shows as a white line around the root.

Dentin is mineralized too, but not as much as enamel, so it appears whiter than pulp but not as bright as enamel. The pulp chamber and the periodontal ligament space are soft tissues, so they appear darker (radiolucent) on X-rays. Cortical bone is also radiopaque, but it’s not a dental structure in itself; the question focuses on structures within or immediately around the tooth, where enamel and lamina dura are the ones that appear white.