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': 'Problems encountered during instrumentation : \nSelect and explain. \nA. Ledging., B. Stripping / lateral wall Perforation ., C. Zipping., D. All of the above.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Problems Encountered during\xa0Instrumentation\n\nLoss of working length due to a blockage of the canal system\nLedging (shelf formation)\nBreakage of instrument\nDeviation from the normal canal anatomy\nZipping (elliptication)\nStripping/lateral wall perforation\nInadequate canal preparation\nOverinstrumentation (beyond apical constriction)\nOver preparation (excessive removal of tooth structure)\nUnder preparation (insufficient canal preparation)', 'role': 'assistant'}]