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': 'Chamfer finish line is usually indicated in cases of: \nSelect and explain. \nA. All metal restorations, B. All ceramic restorations, C. Facial margin of PFM crown, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Chamfer\n\nIt is an obtuse-angled finish line.\nIt is distinct.\nExhibits least stress.\nMost conservative.\nIndicated where metal forms the margin of a restoration, e.g. complete metal crown. Should not be given for porcelain restorations as the obtuse angle produces shearing forces which is not well tolerated by porcelain.\nIt is prepared using a round-end tapering diamond. This is produced by sinking in half the diamond into the tooth. The tip produces the chamfer while the sides give the necessary taper to the axial surface.', 'role': 'assistant'}]