This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': 'Complication of irradiation of mouth may include all EXCEPT \nSelect and explain. \nA. Accelerated caries activity, B. Caries in unusual sites, C. Accelerated periodontal diseases, D. Xerostomia', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The extent of reduced flow is dose dependent and may reach essentially zero at 60 Gy. The mouth becomes dry (xerostomia) and tender, and\xa0swallowing\xa0is\xa0difficult\xa0and\xa0painful.\nRadiation caries is a rampant form of dental decay that may occur in individuals who receive a course of radiotherapy that includes exposure of the salivary glands.\nClinically,\xa0three\xa0types\xa0of\xa0radiation\xa0caries\xa0exist.\xa0\n\t\nThe\xa0most common is widespread superficial lesions attacking buccal, occlusal, incisal\xa0and palatal surfaces.\nAnother type involves primarily the cementum and dentin in the cervical region. These lesions may progress around the teeth circumferentially and result in loss of the crown.\nThe third type appears as a dark pigmentation of the entire crown. The incisal edges may be markedly worn.\n\n\nCombinations of all these lesions develop in some patients.The location, rapid course and widespread attack distinguish radiation\xa0caries.', 'role': 'assistant'}]