Which sinus is involved in a patient with a toothache and sinusitis?

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)