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

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

doi:10.4041/kjod.2011.41.2.98

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Kim, Lee, Cho, and Hwang: Correction of positional change of frontal cephalometric landmarks caused by vertical head rotation

Original Article

Korean Journal of Orthodontics

Korean Journal of Orthodontics 2011; 41(2): 98-111.

Published online: 30 April 2011

DOI: https://doi.org/10.4041/kjod.2011.41.2.98

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

Mi-Young Kim, DDS, MSD^a, Kyung-Min Lee, DDS, MSD^a, Jin-Hyoung Cho, DDS, MSD, PhD^b, Hyeon-Shik Hwang, DDS, MSD, PhD^c

^aGraduate Student, Department of Orthodontics, 2nd Stage of Brain Korea 21, Dental Science Research Institute, School of Dentistry, Chonnam National University, Korea.

^bAssistant Professor, Department of Orthodontics, 2nd Stage of Brain Korea 21, Dental Science Research Institute, School of Dentistry, Chonnam National University, Korea.

^cProfessor, Department of Orthodontics, 2nd Stage of Brain Korea 21, Dental Science Research Institute, School of Dentistry, Chonnam National University, Korea.

Corresponding author: Hyeon-Shik Hwang. Department of Orthodontics, School of Dentistry, Chonnam National University, 300 Yongbong-dong, Buk-gu, Gwangju 500-757, Korea. +82 62 530 5656; hhwang@chonnam.ac.kr

Received 22 December 2010 Revised 28 February 2011 Accepted 4 March 2011

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 90° angle. Geometric principles of radiography were used to calculate the possible vertical and horizontal landmark changes if the head should be rotated down 5° 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 5°.

Results

When the frontal cephalograms were taken with the head rotated down 5° 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.

Keywords: Frontal cephalogram, Vertical head rotation, Correction

Figures and Tables

Fig. 1

The modified Head Posture Aligner used in this study.

Fig. 2

A, Frontal and lateral cephalograms were taken without head rotation using biplanar radiography; B, an additional frontal cephalogram was taken with the head rotated 5° down from the ear rod axis.

Fig. 3

The horizontal reference line on frontal cephalogram was defined as a line passing through the two ear rod ball markers, and the vertical reference line as a perpendicular line passing mid-point of the length of the horizontal reference line. The horizontal reference line on lateral cephalogram was established by drawing a line parallel to the horizontal wire incorporated in the Head Posture Aligner and passing through the ear rod ball marker, and the vertical reference line as a perpendicular line passing through the ear rod ball marker.

Fig. 4

Simulation of positional change of a landmark before and after a 5° downward head rotation and represented using an x, y coordinate system. Antegonion is used as an example. A, Frontal cephalometric tracings before and after head rotation; B, lateral cephalometric tracings before and after head rotation.

Fig. 5

Method of calculating z₀' from lateral cephalogram. z₀' is the actual horizontal distance from the ear rod axis to midpoint between right and left antegonions. z_0-Rt is the horizontal position of right antegonion and z_0-Lt is the horizontal position of left antegonion on lateral cephalogram.

Fig. 6

Schematic representation of radiographic magnification. Magnification of frontal cephalogram can be calculated using the lateral cephalogram, and magnification of lateral cephalogram can be calculated using the frontal cephalogram.

Fig. 7

Bland-Altman plots for variables ANS, U1, L1, Ag_Rt, and Me in the vertical direction. The x-axis shows the average of the calculated and cephalometric changes, whereas the y-axis represents the difference between the two measurements. The limits of agreement are indicated by horizontal lines.

Table 1

Description of cephalometric landmarks used in this study

Table 2

Comparison of calculated change with real cephalometric change in the vertical direction (unit: mm)

SD, Standard deviation. ^*p < 0.05.

Table 3

Comparison of calculated change with real cephalometric change in the horizontal direction (unit: mm)

SD, Standard deviation.

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