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': 'Center of rotation for tipping is present at: \nSelect and explain. \nA. Long axis of tooth, B. Between B-L axis of tooth, C. Between M-D axis of tooth, D. Infinity', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Uncontrolled tipping:\nA single force is applied at the crown, whereby the tooth rotates around a point just apical to the CRes. The crown moves in the direction of the force and the apex of the root moves in the opposite direction. The CRes of the tooth also moves in the direction of the force.\nControlled tipping:\nExample of a healthy maxillary\nThe force but the root apex does not move forward in the opposite direction. The CRes also moves in the direction of the force. This kind of movement may be indicated when retracting excessively proclined maxillary incisors.\nKey concept:\nCenter of rotation of single rooted teeth for tipping is present along the long axis of tooth.', 'role': 'assistant'}]