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': 'Cusp reduction can be considered in all of the following situations except: \nSelect and explain. \nA. When the outline form has extended one third the distance from a primary groove to a cusp tip, B. When the outline form has extended two third the distance from an adjacent primary groove to the cusp tip, C. When the operator judges that adequate cuspal strength (adequate dentin support) remains, D. If the reduction of cusp improves the accessibility and visibility for operator', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The most important aspect in the evaluation of a suspicious cusp is the judgment of the amount of remaining dentin\xa0support. Cusp reduction should be considered when the outline\xa0form has extended half the distance from a primary groove to a\xa0cusp tip. Cusp reduction is strongly recommended when the outline\xa0form has extended two third\xa0the distance from an adjacent primary\xa0groove to the cusp tip.\nThe exception to reducing a cusp, where an extension has been two third\xa0from a primary groove toward the\xa0cusp tip, is when the operator judges that adequate cuspal strength\xa0(adequate dentin support) remains. Reduction of cusps occurs as\xa0early as possible in the preparation process so as to improve access\xa0and visibility for the operator.', 'role': 'assistant'}]