Correction of positional change of frontal cephalometric landmarks caused by vertical head rotation

Kim, Mi Young; Lee, Kyung Min; Cho, Jin Hyoung; Hwang, Hyeon Shik

Abstract

OBJECTIVE
Superimposition of frontal cephalograms cannot be performed when the cephalograms are taken with different vertical head rotations. The purpose of the present study was to evaluate the validity of correcting the positional change of frontal cephalometric landmarks caused by vertical head rotation.
METHODS
In 30 adult individuals, frontal and lateral cephalograms were taken at a 90degrees angle. Geometric principles of radiography were used to calculate the possible vertical and horizontal landmark changes if the head should be rotated down 5degrees about an ear rod axis. The calculated changes were then compared with cephalometric changes measured on frontal cephalogram actually taken with the head rotated down 5degrees.
RESULTS
When the frontal cephalograms were taken with the head rotated down 5degrees about an ear rod axis, significant changes in the vertical position of the landmarks occurred, particularly in the landmarks located farther anteriorly from the ear rod axis. The comparison of calculated changes and real cephalometric changes showed that the differences were less than 0.4 mm in the vertical direction and less than 0.2 mm in the horizontal direction. The differences between calculated and real changes were smaller in the landmarks less affected by vertical head rotation.
CONCLUSIONS
Even when frontal cephalograms are taken at different vertical head rotations, the concomitant changes in the position of the landmarks can be corrected through calculation using the geometric principle of radiography as long as frontal and lateral cephalograms are taken perpendicular to each other.