Which feature appears radiopaque on radiographs?

• A. Mental ridge
• B. Lingual foramen
• C. Inferior border of the mandible
• D. Mental foramen

Answer: (C)

On radiographs, radiopacity comes from dense, mineralized structures that attenuate X-rays strongly, so they show up white. The inferior border of the mandible is a thick cortical bone margin, forming a continuous, dense line along the lower edge. That dense cortical bone attenuates X-rays more than the surrounding interior bone and soft tissues, so it appears radiopaque.

By contrast, openings in bone that contain vessels or nerves—the lingual foramen and the mental foramen—are radiolucent, appearing as dark areas because they are voids or contain less dense tissue. The mental ridge is also a bony feature, but the most clearly radiopaque margin on a radiograph is the inferior border due to its substantial cortical density.