Final answer:
In the Waters method with the CR directed through the open mouth, the maxillary sinus groups are demonstrated. This radiographic position offers a clear view of the maxillary sinuses while avoiding overlap with dental structures and the petrous ridge.
Step-by-step explanation:
The question pertains to radiographic imaging of the sinuses using the parietoacanthial projection, commonly known as the Waters method. When a patient is positioned for this method with the central ray (CR) directed through the patient's open mouth, the sinus groups that are demonstrated include the maxillary sinuses, which are the largest of the paranasal sinuses. This positioning allows for a clear view, minimizing the overlap of the sinuses with the teeth and the petrous ridge of the temporal bone. It provides a superior view of the maxillary sinuses with minimal distortion.
In the context of imaging, it is also critical to differentiate between the veins and sinuses of the head, as shown in various images like the veins of the head and neck. However, in the specific radiographic imaging technique referenced in the Waters method, the focus is on the paranasal sinuses, not the intracranial or head and neck veins.