This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nose and paranasal sinuses, 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 impoant source of maxillary sinusitis. Roots of premolar and molar teeth are related to the floor of sinuses and may be separated only by a thin layer of mucosal covering. A peripheral dental abscess may burst into the sinus or the root of a tooth during extraction may be pushed into the sinus. In the case of oroantral fistula following tooth extraction bacteria from the oral cavity enter the maxillary sinus. (Ref: Textbook of diseases of ENT, PL Dhingra, 7th edition, pg no. 214)', 'role': 'assistant'}]