Head-and-neck radiation therapy contributes to dental caries ('radiation caries') primarily by:

Correct answer: A. Causing xerostomia through salivary gland damage

• A. Correct. Radiation damages the salivary glands, causing xerostomia (loss of the saliva's cleansing, buffering, and remineralizing effects), which drives rampant cervical/radiation caries.
• B. Radiation does not directly demineralize enamel with the X-ray beam itself; the caries is mediated by xerostomia (and dietary/flora changes).
• C. Radiation reduces, not increases, salivary buffering.
• D. Radiation weakens, not strengthens, tooth structure.

Note: Source stem was garbled; reconstructed to test the xerostomia → radiation-caries mechanism.