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': 'Tooth movement is primarily a phenomenon involving: \nSelect and explain. \nA. Pulp, B. Periodontal ligament, C. Dentin, D. Cementum', 'role': 'user'}, {'content': 'Answer: B \nExplanation: PDL ligament is primarily associated with orthodontic tooth movement.', 'role': 'assistant'}]