In dental radiographs, the term lamina dura refers specifically to the dense cortical bone lining the tooth socket. This structure appears as a thin radiopaque (white) line surrounding the roots of the teeth. The lamina dura corresponds anatomically to the alveolar bone proper, which is the part of the alveolar bone directly adjacent to the periodontal ligament space.

Key points to note:

- The lamina dura represents the alveolar bone proper, which provides support and attachment sites for the periodontal ligament fibers.
- It appears as a continuous, radiopaque border on radiographs, indicating healthy bone surrounding the tooth root.
- The periodontal ligament space is seen as a thin radiolucent (dark) line between the root surface and the lamina dura.
- The cortical bone of the mandible is a thicker bone layer found on the outer surface of the mandible and does not correspond specifically to the lamina dura.
- The alveolar mucosa is soft tissue and is not visible on radiographs.

Therefore, the lamina dura's radiographic appearance is due to the alveolar bone proper, making Option 1 the correct answer.

Reference: Orban's Oral Histology, 14th Edition, Chapter 9: Alveolar Bone, Page 195