ObjectiveTo analyze caries activity of nasopharyngeal carcinoma（NPC） patients before and after radiation therapy. The study was also designed to analyze calcium and phosphorus concentrations in saliva of NPC patients before and after radiotherapy.Methods Twenty-eight NPC patients and 20 healthy controls were included in this study. Resazurin disc method was used to detect caries activity of NPC patients before and after 70 Gy radiotherapy. The atomic absorption spectrometry and molybdenum-stibium antispetrophotography method were used to analyze calcium and phosphorus concentrations in saliva of NPC patients before and after 70 Gy radiotherapy and the healthy controls.Results The results of resazurin disc method showed caries activity of NPC patients was increased after radiotherapy（Pphosphorus concentration was （132.96 ±5.13）mg·L -1. After 70 Gy radiotherapy, calcium concentration was （33.38 ± 0.32）mg·L-1, phosphorus concentration was （49.18±2.66）mg·L-1. The difference of calcium and phosphorus concentrations in saliva before and after radiotherapy was significan（t PConclusion Caries activities of NPC patients increase after radiotherapy. Calcium and phosphorus concentrations in saliva decrease after radiation therapy.
