A patient has received head and neck radiation for treatment of oral cancer. All of the following are causes of radiation-related dental caries EXCEPT one. Which is the EXCEPTION?

Correct answer: B. Radiation directly demineralizes enamel and dentin

• A. Reduced saliva allows cariogenic bacteria (especially S. mutans and Lactobacillus) to colonize tooth surfaces more effectively.
• B. CORRECT. Radiation does NOT directly demineralize enamel or dentin. Radiation caries is INDIRECT — it is caused by: (1) radiation damage to salivary glands → xerostomia, (2) reduced saliva → loss of buffering, cleansing, remineralizing, and antibacterial properties → bacterial proliferation → acid production → demineralization. The radiation beam does not strip calcium from teeth; it damages the glands that protect them.
• C. Radiation-induced salivary gland hypofunction (xerostomia) is the primary mechanism of radiation caries — damage to acinar cells reduces saliva flow.
• D. Xerostomia reduces salivary buffering capacity, allowing plaque acid to lower pH below 5.5 and initiate enamel demineralization.