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': 'A male 25 years old presents to the dental clinic with black spot .He also gives the history of previous dental treatments of other teeth as well . Intraoral examination reveals pit and fissure caries with 17. The alignment of the rotary instrument shank axis in this patient should be: \nSelect and explain. \nA. Parallel with the long axis of the tooth crown, B. Perpendicular to the long axis of the tooth crown, C. Parallel to the transverse axis of the tooth crown, D. Perpendicular to the transverse axis of the tooth crown', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The anatomic orientation of caries lesion formation in the pit and fissure areas of posterior teeth requires alignment of the rotary instrument shank axis (through proper positioning of the handpiece) so that it is parallel with the long axis of the tooth crown prior to initiation of the preparation. Correct alignment of the long axis of the shank limits the likelihood of iatrogenic removal, and thereby weakening, of adjacent healthy (occasionally referred to as “sound”) coronal tooth structure.\nMost\xa0proximal caries lesions associated with posterior teeth also require that the shank axis be aligned parallel with the long axis of the tooth crown. Caries lesion formation associated with the facial or lingual surfaces of the dentition require that the shank axis be aligned perpendicular to the external surface of the tooth where the lesion is located.\nSturdevant operative dentistry\xa0 7th E D I T I O N, Page No:125', 'role': 'assistant'}]