A

Radiation caries begins because head-and-neck radiotherapy damages the salivary glands, producing xerostomia with markedly reduced salivary flow; the resulting loss of saliva’s buffering and cleansing actions allows rapid enamel demineralization and decay, not a direct effect of the beam on enamel itself [Nilles & Stoll, 1992, PMID 1463563; Deng et al., 2015, PMID 26198979].