This study was performed to find out how much projection errors in the cephalometric measurements were made by vertical head rotation in taking posteroanterior cephalograms. 25 adults without any apparent facial asymmetry or severe sagittal skeletal discrepancy were selected and the posteroanterior cephalograms were taken with the head rotated 5° , 10 superior and inferior each to the reference position(0´ ). The 7 height. 5 width and 6 angular measurements were taken at each 5 positions. Through the statistical analysis of all measurements taken at each rotated position, following results were obtained.
1. The projection errors of height measurements were remarkably larger than those of width or angular measurements.
2. Among the height measurements, the farther to the rotation axis the measurements were, the larger the projection errors were.
3. Among the width measurements, mandibular width and intermolar width of mandibular first molars showed significant differences between the values taken at each rotated position, while nasal width, maxillary width and intermolar width of maxillary first molars did not.
4. Among the angular measurements, the angle between horizontal reference line and the line that is connected to crista galli and antegonion or maxillare showed significant differences between the values taken at each rotated position.
The above results suggest that it is needed to the effort to keep constant head position for taking the useful posteroanterior cephalogram, because projection errors are caused by vertical head rotation.
|