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': 'All are true about lingual ledges except: \nSelect and explain. \nA. Part of tooth preparation for a resin bonded retainer, B. Increases the retention and resistance form, C. Decreases the casting rigidity, D. Aids in orientation of the casting during cementation', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Lingual ledges are small horizontal grooves placed on the lingual aspect while preparing a tooth for resin bonded retainers. These increase the retention and resistance forms, increase casting rigidity and aid in orienting the casting while cementation of the prosthesis.', 'role': 'assistant'}]