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': 'Back pressure porosity can be reduced by: \nSelect and explain. \nA. Vacuum investing, B. Proper or increased burnout temperature and proper casting pressure, C. Reduced firing temperature, D. All', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Back pressure porosity\nThis is caused by inadequate venting\xa0 of the mold. Air is trapped in the mold and is unable\xa0to escape. The sprue pattern length should be adjusted so that there is not more than 1/4”\xa0thickness of the investment between the bottom of the casting ring and the wax pattern. When the molten metal enters the mold, the air inside is pushed out through the porous\xa0investment at the bottom. If the bulk of the investment is too great, the escape of air becomes\xa0difficult causing increased pressure in the mold. The gold will then solidify before the mold is\xa0completely filled resulting in a porous casting with rounded short margins.\nAvoided by\n\nUsing adequate casting force.\nUse investment of adequate porosity.\nPlace pattern not more than 6 to 8 mm away from the end of the ring.\nProviding vents in large castings.\nProper burnout temperature.\n\nBasic Dental Materials by John Manappallil ed 4 pg370', 'role': 'assistant'}]