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 minimum force required to retard and redirect the maxillary growth \nSelect and explain. \nA. 300 - 400 gm/side, B. 500 - 550 gm/side, C. 500 - 600 gm/side, D. 450 -550 gm/side', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Biomechanical Considerations\nThe maxilla can be advanced 2-4 mm forward over a period of 8-12 months. The amount of maxillary movement is influenced by a number of factors like:\n\nAmount of force:\xa0 Successful maxillary protraction can be brought about by 300-500 gm of force per side in the primary or mixed dentition.\nDirection of force: According to most authors, a 15- 20° downward pull to the occlusal plane is required to produce forward maxillary movement.\xa0\n\tIn most cases of maxillary deficiency, maxilla is deficient in the vertical plane as well, therefore, a slight downward, direction of force is usually desirable. The line of force passes below the center of resistance of the maxilla producing a counter-clockwise moment on the maxilla and dentition. This results in a possible extrusion of maxillary posterior teeth leading to a downward and backward rotation of the mandible.\n\tHowever, in patients with increased anterior facial height, downward pull is contradicted.\nDuration of force:\xa0A review of literature shows duration to vary between 3 and 16 months. On an average at least 8-12 months of wear is required to produce the desired effect.\nFrequency of use:\xa012-14 hrs/day\n\nKey Concept:\nSuccessful maxillary protraction can be brought about by\xa0300-500 gm of force per side\xa0in the primary or mixed dentition.\nReference: Textbook of orthodontics 2nd\xa0ed Gurkeerat Singh page no 502', 'role': 'assistant'}]