In a Posterior PA radiograph, which arches are visible?

In a Posterior PA radiograph, which arches are visible?

• A. One Arch
• B. Two Arches
• C. All Arches
• D. No Arches

Answer: (A)

The way x‑ray beams and receptors are positioned in a posterior PA view limits the image to the posterior portion of a single dental arch. Directing the beam from the posterior toward the front and placing the film to capture that arch means the opposite arch either lies outside the field or is highly overlapped and not clearly visible. So you end up seeing one arch clearly rather than both arches in the same image. If you need both arches, other views or a full mouth series would be used, but this projection is designed to isolate and image one arch at a time.

The way x‑ray beams and receptors are positioned in a posterior PA view limits the image to the posterior portion of a single dental arch. Directing the beam from the posterior toward the front and placing the film to capture that arch means the opposite arch either lies outside the field or is highly overlapped and not clearly visible. So you end up seeing one arch clearly rather than both arches in the same image. If you need both arches, other views or a full mouth series would be used, but this projection is designed to isolate and image one arch at a time.