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': 'Permanent loss of root structure related to orthodontic treatment occurs primarily at the: \nSelect and explain. \nA. Coronal third, B. Middle third, C. At apex, D. All of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: It is estimated that root resorption occurs in at least 12% of all orthodontic patients presently being treated by competent orthodontists.\xa0\nThe apex of the root is more susceptible than the other parts.\xa0\nDeviating root form is more susceptible to post orthodontic root resorption. Convergent apical root canal is considered to be an indication of high root resorption potential.\xa0\nThe degree of root resorption in teeth with blunt or pipette-shaped roots was significantly higher than in teeth with normal root form.\xa0\nThe pipette-shaped root was shown to be the most susceptible root form to root resorption.\n\n\u200bTextbook of ORTHODONTICS Sridhar Premkumar', 'role': 'assistant'}]