Which of the following are examples of radiolucent structures?

Radiolucent structures are those that allow X-rays to pass through with relatively little attenuation, appearing darker on radiographs. This characteristic is typically observed in soft tissues, air-filled spaces, and some fluid-filled cavities.

Incisal foramen and maxillary sinus are appropriate examples of radiolucent structures. The incisal foramen represents a small opening in the maxilla for vascular and nervous supply, and it appears dark on radiographs due to the soft tissue and potential air within. The maxillary sinus, also filled with air, shows up radiolucently as well, providing clear evidence of a space that does not absorb X-rays significantly.

In contrast, bone and enamel are examples of radiopaque structures, which appear lighter on films due to their density and ability to absorb more X-rays. Similarly, cementum and dentin, though less dense than enamel, still have some radiopacity. Amalgam and composite materials used in dental restorations are also radiopaque so they appear distinctly on radiographs against the surrounding tooth structure.