Maxillary Sinuses

The maxillary sinuses can vary in size from patient to patient.  A small maxillary sinus may not be evident on periapical radiographs as it does not encroach on the posterior teeth roots.  A large maxillary sinus sometimes will share the same border as the crest of the alveolar ridge and may extend into the midline of the maxillary appearing superior to the maxillary incisors.

TIP: On a periapical radiographs it is important to be aware when the floor of the maxillary sinus is superimposed over the roots of the posterior teeth this does not mean the teeth are actually in the maxillary sinus.  A periapical radiograph is a 2D image and flattens everything out.  There is a thin bony covering around the entire root separating it from the maxillary sinus.

Large maxillary sinus

(arrows pointing to extension over the lateral incisor roots)

Large maxillary sinus without arrows

Large maxillary sinus

Small maxillary sinuses

Occasionally, thin bony septa or septum are evident in the sinus.  A septa or septum does not divide the maxillary sinus but is merely a projection of bone off the border of the maxillary sinus.  Septa or septum appear as thin radiopaque line or lines coming off the border of the maxillary sinus.

Maxillary sinus septum

(arrows pointing to thin radiopaque line extending from the floor of the maxillary sinus)

Maxillary sinus septum without arrows

Maxillary sinus septum

For more information and radiographs on the following entities.