Which projection uses a parietoacanthial angle with a mouth open?

• A. Lateral projection
• B. Caldwell method
• C. Open-mouth Waters method
• D. Towne method

Answer: (C)

The key idea is the parietoacanthial projection used for viewing facial sinuses, typically the Waters view. In this setup, the CR is directed through the parietoacanthial point, and the head is positioned so the orbitomeatal line creates the required angle with the IR. When the mouth is opened in this projection, the palate moves away from the sphenoid region, reducing overlap and allowing better visualization of the sphenoid sinuses. That specific combination—parietoacanthial angling with the mouth open—is unique to the open‑mouth Waters method. The other views shown—lateral (side view), Caldwell (frontal sinus/AP axial), and Towne (skull/occipital region with a different tilt)—do not involve an open mouth with a parietoacanthial orientation.