Inferior border of the mandible is?

• A. A cancellous bone area
• B. Dense cortical bone; appears radiopaque.
• C. A thin radiolucent line
• D. A suture line in mandible

Answer: (B)

The lower edge of the mandible is formed by dense cortical bone, which shows up as a bright, radiopaque line on radiographs. Cortical bone is highly mineralized and attenuates X-rays more than the interior cancellous bone, so the inferior border appears as a solid, white border along the jaw. Inside the mandible, the cancellous (trabecular) bone is less dense and appears comparatively darker. So the best description is a dense cortical bone line that is radiopaque. The other ideas don’t fit because cancellous bone would not create that bright border, a thin radiolucent line would suggest something like a canal or a fracture, and a suture line would not describe the continuous radiopaque border along the mandible’s bottom edge.