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
All are true about lingual ledges except: 
Select and explain. 
A. 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
C: Decreases the casting rigidity
Answer: C: Decreases the casting rigidity 
Explanation: 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.