<prompt> All are true about lingual ledges except:Part of tooth preparation for a resin bonded retainerIncreases the retention and resistance formDecreases the casting rigidityAids in orientation of the casting during cementation  <response>: 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. 