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': 'To contain gutta-percha within the canal, instrumentation should result in: \nSelect and explain. \nA. Cleaning beyond the anatomic apex, B. Cleaning beyond the radiographic apex, C. A cylindrical canal shape, D. The narrowest cross-sectional diameter at the terminus', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The instrumentation and obturation should not extend beyond the apical foramen.\nWhereas the guideline of 1 mm from the radiographic apex remains rational when using radiographs, the point of apical termination of the preparation and obturation remains empirical.\nThe need to compact the gutta-percha and sealer against the apical dentin matrix (constriction of the canal) is necessary to prevent extrusion of materials into the periapical tissues.\n\nTextbook of Endodontics 3rd Ed P:', 'role': 'assistant'}]