The PA skull projection is the second most common skull radiograph used in dentistry. It involves positioning the patient so that the Frankfurt plane is perpendicular to the image receptor with the canthomeatal line forming a 9-degree angle to the horizontal plane. The central x-ray beam is directed perpendicular from the posterior to the anterior at the level of the bridge of the nose. This should result in a symmetric skull image divided by the midsagittal plane with the superior border of the petrous ridge in the lower third of the orbit, allowing for evaluation of facial asymmetries and assessment of orthognathic surgery outcomes.

1. POSTEROANTERIOR SKULL PROJECTION

2. PA cephalometric projection
 second most common skull radiograph used in dentistry
 evaluation of facial asymmetries
 assessment of orthognathic surgery
 outcomes involving the patient’s midline or mandibular-maxillary relationship

3. Image Receptor and Patient Placement
 image receptor is placed in front of the patient
 patient is placed so that the canthomeatal line forms a 9-degree angle with the horizontal plane
 Frankfurt plane is perpendicular to the image receptor
 For the standard PA skull projection, the canthomeatal line is perpendicular to the image receptor.

4. Position of Central X-Ray Beam
 perpendicular to the image receptor
 directed from the posterior to the anterior
 centered at the level of the bridge of the nose

6. Resultant Image
 The midsagittal plane should divide the skull image into two symmetric halves.
 The superior border of the petrous ridge should lie in the lower third of the orbit

8. Interpretation

9. The end