In the open-mouth Waters projection, which pair is demonstrated?

• A. Frontal and Ethmoid
• B. Sphenoid and Maxillary
• C. Frontal and Maxillary
• D. Sphenoid and Ethmoid

Answer: (B)

Open-mouth Waters is a parietoacanthial projection that aims to visualize the sphenoid sinuses in addition to the maxillary sinuses. By having the mouth open, you reduce overlap from the oral cavity and allow the sphenoid region, which lies behind the nasal cavity, to be better seen along with the maxillary sinuses that sit beneath the orbits. This combination makes the maxillary and sphenoid sinuses the structures most clearly demonstrated on this view.

The frontal and ethmoid sinuses aren’t the focus of this projection because their outlines are less well revealed in this position due to their location and the way the skull’s bones overlap in this view. The open-mouth technique specifically enhances visibility of the sphenoid sinuses while preserving the maxillary sinuses.