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 function of wetting agents used in casting procedures is \nSelect and explain. \nA. To facilitate wetting of ring liner, B. To facilitate mixing investment, C. To reduce contact angle of a liquid with the wax surface, D. For better wax elimination', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The surface of a wax pattern that is not completely wetted investment results in surface irregularities in the casting that destroy its accuracy.\nThese irregularities can be minimized by applying a surface-active wetting agent on the wax.\nThe function of the wetting agent is to reduce the contact angle of a liquid with the wax surface.\nWetting agents also remove any oily film that is left on the wax pattern from the separating medium.\nThe contact angles are 98 degrees for the plain wax surface and 61 degrees for the treated wax surface.\nThe lower contact angle indicates that the treated wax surface has an affinity for water, which results in the investment being able to spread more easily over the wax.\nBecause the surface-active agents are quite soluble, the wax pattern with water after the application defeats the purpose of their use.', 'role': 'assistant'}]