The Superimposition of Lateral Skull Radiographs by Subtraction: A New Method

A method of direct superimposition of an individual's lateral skull radiographs using a radiographic subtraction technique is outlined. The errors introduced by superimposition on two different occasions by the same operator are quantified, 30 pairs of radiographs being superimposed on the anterior cranial base. The average landmark displacement is less than 1·16 mm and very little rotational displacement occurs in relation to the plane of superimposition, this being an average 0·38°. In cephalometric superimposition the errors occurring add to those in landmark identification and should be considered in individual case analysis.