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': 'Quad Helix is: \nSelect and explain. \nA. Widens the upper arch, B. Is used in cleft lip, C. Retracts the upper canine, D. Is a bite opening device', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Indications of quad helix appliance: \n\nNarrow upper arch that needs expansion, e.g., in cross-bites.\nCrowded mixed or permanent dentition in which long-range growth can be predicted and requires mild expansion as there is lack of space for the upper laterals.\nClass II malocclusions where upper arch needs effective widening and upper molars need distal rotation.\nClass III malocclusions where upper arch needs effective widening and advances with class III elastics.\nThumb sucking and tongue thrusting cases with its modifications.\nUnilateral or bilateral cleft palate.\xa0\n\nTextbook of ORTHODONTICS Sridhar Premkumar', 'role': 'assistant'}]