[Effect of anterior-lateral mandibular displacement occurring in lateral roentgenocephalometry at the open mouth position on the linea measurements].

The present study was undertaken to determine the effect of mandibular displacement occurring in lateral roentgenocephalometry at the open mouth position and of the resulting changes in the projected sites on linea measurements of the mandible. With use of a brachicephalic young (corresponding to age 7) and a dolichocephalic adult human dried mandible, lateral roentgenocephalograms taken under different conditions with angles and distances varied, simulating clinical lateral roentgenocephalometry at the open mouth position, were compared and studied. The results were as follows: 1. Displacement from 5 mm to 30 mm perpendicular to the central X-ray caused unfixed changes, presumed to be human errors in measuring, in the following ranges; brachicephaly: 0-1.4%, dolichocephaly: 0-0.9%. 2. As angles of rotation perpendicular to the central X-ray increase from 0 to 10 degrees clockwise, significant reduction in inverse proportion to the increase in angles of rotation were found; Cd-Gna: brachicephaly: 1.3%, dolichocephaly: 0.9-1.4%; Go-Gna: brachicephaly: 1.6-3.3%, dolicocephaly: 1.4-2.2%. However, unfixed changes in the following ranges were found for Cd-Go; brachicephaly: 0.5-2.3%, dolicocephaly: 0.6-1.2%. 3. Increase in angles of rotation counterclockwise also showed a similar tendency to that in clockwise rotation.