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': 'The six keys to normal occlusion were given by: \nSelect and explain. \nA. Lawrence F. A., B. Angle, C. Lischer, D. Moyer', 'role': 'user'}, {'content': 'Answer: A \nExplanation: ANDREWS SIX KEYS TO NORMAL OCCLUSION\nLawrence F Andrews studied 120 casts of non-orthodontic patients with normal occlusion for four years (1960-1964). He identified 6 key characteristics.\nHe was of the opinion, that for normal occlusion to exist these six characteristics had to be present. According to Andrews, the 6 keys to normal occlusion contributed individually and collectively to the total scheme of occlusion and, were therefore essential for an orthodontic treatment to be considered successful.\nRef: Textbook of orthodontics Gurkeerat Singh 2nd ed page no 59', 'role': 'assistant'}]