Dental infections are an important 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.