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': 'Who has given root canal isthmus classification? \nSelect and explain. \nA. Kim, B. Schielder, C. Krasner and Rankow, D. Vertucci', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Kim et al\xa0Classification\nRoot apex cross-section\nNarrow ribbon-shaped connection that contains pulp or pulpally derived tissue -\xa0ISTHMUS\nAccording to Kim et al classification; there are 5 types:\n\nType I :\xa0Incomplete isthmus between 2 canals.\nType II : Well defined, complete isthmus between 2 canals.\nType III : Very short, but complete isthmus between 2 canals.\nType IV :\xa03 or more\xa0canals with the complete or incomplete isthmus.\nType V :\xa03 or more\xa0canals without any visible connection.', 'role': 'assistant'}]