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: ENT
[{'content': 'Which sinus is involved in a patient with a toothache and sinusitis \nSelect and explain. \nA. Maxillary, B. Ethmoid, C. Frontal, D. Sphenoid', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Dental infections are an important source of maxillary sinusitis. \nRoots of premolar and molar teeth are related to the floor of sinuses and may be separated only by a thin layer of mucosal covering. \nA peripheral dental abscess may burst into the sinus or the root of a tooth during extraction may be pushed into the sinus.\nIn the case of oroantral fistula following tooth extraction bacteria from the oral cavity enter the maxillary sinus.', 'role': 'assistant'}]