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: Dental
[{'content': 'For a tooth with open apex, treated with calcium hydroxide for apexiﬁcation, the most reliable sign before obturation is: \nSelect and explain. \nA. Electric pulp testing, B. Thermal pulp testing, C. Tooth mobility, D. Tenderness on percussion', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Weine recommends that the apexiﬁcation procedure be completed in two appointments. After\xa0instrumentation, irrigation and drying of the canal during the ﬁrst appointment, he advises sealing a\xa0sterile, dry, cotton pellet in the pulp chamber for 1 to 2 weeks. Placing a calcium hydroxide dressing in\xa0the canal is optional at the ﬁrst appointment.\xa0\nDuring the second appointment, the debridement\xa0procedures are repeated before the canal is ﬁlled with a thick paste of calcium hydroxide and\xa0CMCP or calcium hydroxide in a methylcellulose paste. Whether the\xa0tooth is ﬁlled in one or two appointments (or more) should be determined to a large extent by the clinical signs and symptoms present and to a lesser extent by operator convenience.\nAll signs and\xa0symptoms of active infection should be eliminated before the canal is ﬁlled with the treatment paste.\xa0\nAbsence of tenderness to percussion is an especially good sign before the canal is obturated.\nBecause of\xa0the wide-open access to periapical tissues, it is not always possible to maintain complete dryness in\xa0the root canal.\xa0\nIf the canal continues to weep but other signs of infection seem to be controlled after\xa0two or three appointments, the dentist may elect to proceed with the calcium hydroxide paste\xa0treatment.', 'role': 'assistant'}]