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': 'Figure shows the clinician grasping a tooth between his thumb and foreﬁnger at the level of the middle third of the crown. This is: \nSelect and explain. \nA. Percussion, a method for testing pulp vitality, B. Percussion to check the Grade 1 mobility of teeth, C. Palpation to check for the buccolingual width of the tooth, D. Palpation to check crack tooth', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Percussion is one of the oldest pulp vitality tests used because it requires no armamentarium.\xa0Generally, patients who have a tooth sensitive to mastication have already percussed the tooth in\xa0question with their own ﬁnger tip(s) and informed the dentist which teeth are sensitive. Percussion is\xa0an indirect means of testing pulp vitality, because teeth that are sensitive to percussion often have\xa0existing periapical lesions associated with a necrotic pulp. However, this is not always the case, and false positives can result if the clinician is evaluating a cracked tooth or a ‘‘high’’ restoration. If a crack\xa0has developed in the crown of a tooth with a vital pulp, the tooth can still be exquisitely sensitive,\xa0because of the crown segments\xa0moving microscopically causes pain due to the movement of ﬂuid in\xa0the odontoblastic tubules. The tooth is sensitive to thermal stimuli as the pulp is vital. These mutually\xa0exclusive diagnostic ﬁndings, pain to percussion/mastication and thermal sensitivity, are\xa0pathognomonic for a cracked tooth.', 'role': 'assistant'}]