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': 'Class III amalgam restoration is not indicated in which of the following cases? \nSelect and explain. \nA. Extensive preparation with only minimal facial involvement, B. Mesial surface of canines, C. The gingival margin involves primarily cementum, D. Moisture control is difficult', 'role': 'user'}, {'content': 'Answer: B \nExplanation: There are few indications for a Class III amalgam restoration. It is generally reserved for the distal surface of maxillary and mandibular canines if:\n\nThe preparation is extensive with only minimal facial involvement.\nThe gingival margin involves primarily cementum.\nMoisture control is difficult.\xa0\xa0\n\nFor esthetic reasons, amalgam is rarely indicated for the proximal surfaces of incisors and the mesial surface of canines.\nHowever, amalgam may be used for any Class III restoration that does not involve the facial surface or undermine the incisal corner.\xa0\nReference: Sturdevant operative dentistry. 4th edition: page no.744,743', 'role': 'assistant'}]