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': 'Given instrument is called as: \nSelect and explain. \nA. Apexum, B. Apex locator, C. Vitalometer, D. Electronic canal cleaner', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Electronic Method of Determining Working Length (Electronic Apex Locators)\nIn recent years, electronic devices have been developed for determining the working length of a root canal without resorting to radiography.\xa0\nConcept:\xa0\n\nThe working length is determined by comparing the electrical impedance of the periodontal membrane with that of the oral mucosa both of which should be similar at 6.5 KΩ.\xa0\nThis is done with the help of an electronic apex locator cord that has two ends.\xa0\nOne end is termed as a “lip hook” that is kept in contact with the oral mucosa of the patient, while the other end is termed as “file holder” that is a probe which is attached to an endodontic instrument (K file or rotary file).\xa0\nThe attached file is slowly inserted into the root canal up to the estimated working length.\xa0\nWhen the endodontic file touches the soft tissues of the periodontal membrane, the electrical-resistance gauges for both oral mucosa and periodontal ligament would have similar readings.\xa0\nBy measuring the depth of insertion of the endodontic file, one may determine the exact working length of the root canal.', 'role': 'assistant'}]