of the maxilla.'

Extension into the maxillary alveolar process may cause the roots of the molars and even premolars to lie just beneath the floor of the sinus or even project through the floor and into the sinus; in such cases, the roots of the teeth are typically surrounded by a thin layer of bone, but may sometimes lie directly underneath the mucous membrane of the sinus. Projection of the roots into the maxillary sinus is more common in advanced age due to bone resorption. In such