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': 'Principles of condensation for direct filling gold include all of the following except: \nSelect and explain. \nA. Forces of condensation should be 90◦ to the cavity walls and floors, B. Forces of condensation should be 90◦ to previously condensed gold, C. Condensation is done by a process called ‘stepping’, D. The gold pellet used must be of minimal thickness', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Principles of condensation\nThe unique thing about direct gold materials and restorations is that certain principles must be strictly followed to arrive at a successful restoration. Any deviation from such principles leads to immediate failure. These essential condensation principles are as follows:\n\nThe forces of condensation must be at 45o to cavity walls and floors. In other words, they should bisect line angles and trisect point angles. This leads to the maximum adaptation of gold against walls, floors, line, and point angles, with minimal irritation to the vital pulp-dentin organ.\nForces of condensation must be directed\xa0 at 90o to previously condensed gold. This avoids shear components that can displace or loosen the already condensed pieces of gold.\nWhenever condensing a piece of direct gold, always start at a point on one side and proceed in a straight line to another point on the opposite side, then back to the original side on a different straight line, also starting at and arriving to a specific point. This ensures that the condenser has covered the entire surface of that\xa0 piece of gold. During these disciplined movements, the condenser should overlap at least ¼ of the previously condensed area. This further assures that each portion of the gold increment has been welded and cold worked and cold worked and that there are no voids present. This process, called “stepping” ensures the maximal adaptation of the gold to the cavity walls.\nUse the minimal thickness of pellet possible, provided that the condensers will not penetrate it. The thinner that the cross-section of each increment is, the easier will be the fulfillment of the objectives of condensation.\nEnergy of condensation - Energy used in condensing direct gold restorations should only be dissipated in fulfilling the objectives of condensation.', 'role': 'assistant'}]