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
Decay of enamel following radiotherapy is initiated due to: 
Select and explain. 
A. Decrease in salivary flow, B. Direct radiations contacting the enamel, C. Dessication of tooth structure, D. Hypocalcification and pitting of enamel
A: Decrease in salivary flow
Answer: A: Decrease in salivary flow 
Explanation: Radiation 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. Patients receiving radiation therapy to oral structures have increase in Streptococcus mutans, Lactobacillus, and Candida. Caries results from changes in the salivary glands and saliva, including reduced flow, decreased pH, reduced buffering capacity, increased viscosity, and altered flora. 
White and Pharoah, pg-22