Assessment of Image Distortion from Head Rotation in Lateral Cephalometry

The patient's head can be slightly rotated sagitally vertically or transversely within the head holding device. Because of such improper positions due to the head rotation, an error can occur in cephalometric measurements. The purpose of this study was to identify the potential projection errors of lateral cephalometric radiograph due to head rotation toward X-ray film in the vertical Z-axis.

Totally, 10 human dry skulls with permanent dentition were collected from the Department of Anatomy, J.J.M.C. Medical College, Davanagere. Each dry skull was rotated from 0° to -20° at 5° intervals. A vertical axis, the Z-axis, was used as a rotational axis to have 100 lateral cephalometric radiographs exposed. Four linear (S-N, Go-Me, N-Me, S-Go) and six angular measurements (SNA, SNB, N-S-Ar, S-Ar-Go, Ar-Go-Me, AB-Mandibular plane angle) were calculated manually.

The findings were that: (1) Angular measurements have fewer projection errors than linear measurements; (2) the greater the number of landmarks on the midsagittal plane that are included in angular measurements, the fewer the projection errors occurring; (3) the horizontal linear measurements have more projection errors than vertical linear measurements according to head rotation.

In summary the angular measurements of lateral cephalometric radiographs are more useful than linear measurements in minimizing the projection errors associated with head rotation on a vertical axis.