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: Radiology
[{'content': 'The following radiograph shows; the total number of teeth present in oral cavity are one less than normal: \nSelect and explain. \nA. Fusion, B. Gemination, C. Concrescence, D. Dilaceration', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Fusion\nFused\xa0teeth\xa0arise\xa0through\xa0union\xa0of\xa0two\xa0normally\xa0separated tooth germs. Depending upon the stage of development of the teeth at the time of the union, fusion may be either complete or incomplete. It has been thought that some physical force or\xa0pressure\xa0produces\xa0contact\xa0of\xa0the\xa0developing\xa0 teeth\xa0 and their subsequent fusion. If this contact occurs early, at least before calcification begins, the two teeth may be completely united to form a single large tooth.\xa0If the contact of teeth occurs later, when a portion of the tooth crown has completed\xa0its\xa0formation,\xa0there\xa0may\xa0be\xa0union\xa0of\xa0the\xa0roots only.\xa0The\xa0 dentin;\xa0however,\xa0is\xa0always\xa0confluent\xa0in\xa0cases\xa0of true fusion. The tooth may have separate or fused root canals, and the condition is common in the deciduous as well as in permanent dentition.\nRadiological signs\nThe tooth has a notched incisal margin and there is evidence of conjoined dentine between the involved teeth. The fused tooth may present with two distinct pulp chambers/pulp canal systems or a joined system.', 'role': 'assistant'}]