A patient with a history of head and neck radiation develops rampant ROOT caries. What is the underlying cause?

Correct answer: D. Radiation-induced salivary hypofunction (xerostomia)

• A. Mucositis is an acute, self-limiting mucosal reaction during radiotherapy and is unrelated to the chronic caries pattern.
• B. Osteoradionecrosis is a bone complication of radiation and extraction; it does not cause caries.
• C. Enamel does become slightly more soluble, but this is a minor contributor compared with the loss of salivary protection. The distribution of the lesions — cervical and root, not occlusal — points squarely at saliva.
• D. CORRECT. 'Radiation caries' is not a direct radiation effect on tooth structure — it is the downstream consequence of XEROSTOMIA. Irradiated salivary glands (especially serous acini) lose flow, buffering capacity, and antimicrobial proteins, and the flora shifts toward S. mutans and Lactobacillus. The result is a rapidly progressing pattern of cervical and ROOT-surface caries, often circumferential, that can amputate crowns within months.

Note: Prevention: daily high-fluoride (5000 ppm) toothpaste or custom trays, salivary substitutes, pilocarpine where appropriate, aggressive recall, and diet counselling — starting BEFORE radiation begins.