Which of the following statements is (are) correct regarding the parietoacanthial projection (waters' method) of the skull? 1. the head is rested on the extended chin. 2. the orbitomeatal line (oml) is perpendicular to the (ir). 3. the maxillary antra should be projected above the petrosa. a 1 onlyb 1 and 2 onlyc 1 and 3 onlyd 1, 2, and 3

The correct option is A. 1 Only. In a parietoacanthial projection (Waters' method) of the skull, the head must rest on the extended chin.

Explanation:

The parietoacanthial projection (Waters' method) is a widely used radiography method that demonstrates if there are any facial bone fractures, inflammation, or foreign body in the patient skull.  

The patient must be in an erect position or prone. They must rest their head on the tip of the extended chin against the table surface. The neck must be hyperextended so that the orbitomeatal line (OML) forms a 37-degrees angle with the plane of the image receptor (IR) -Notice that this is not a perpendicular angle-. The mentomeatal line (MML) must be perpendicular to the image receptor plane. Finally, the midsagittal plane must be perpendicular to the plane of the image  receptor.

There is an alternative to parietoacanthial projection (Waters' method) called “Shallow waters”, by which the patients use less neck extension, increasing the angulation of the OML by placing it more perpendicular to the image receptor plane. The OML form and approximately 55-degrees angle with the plane of the IR.