Effect of facial asymmetry on 2-dimensional and 3-dimensional cephalometric measurements.

Abstract

To test the hypothesis that facial symmetry affects both 2-dimensional (2D) and 3-dimensional (3D) cephalometric measurements. A baseline model of a preferred symmetrical face was first constructed. It consisted of a set of commonly used cephalometric landmarks. Seven cephalometric measurements were selected for testing. Each of them represented a different set of geometrical conditions related to the geometric parameters being measured, the elements involved, and the type of measurements. They served as a control group. The baseline model was then modified to simulate 10 different asymmetric models, 6 with maxillary asymmetries and 4 with mandibular asymmetries. The same 7 cephalometric analysis were utilized again on each of the 10 asymmetric models. They served as an experimental group. The resulted measurements were tabulated and compared. For the measurements of shape, the 2D cephalometric measurement was distorted by roll and yaw asymmetries, while the same measurement in 3D was not. For the measurements of size, the 2D measurement was also distorted by yaw, but not by roll, while again this measurement in 3D was not distorted. For measurements of position, the results were reversed. The 2D cephalometric measurements of position were not distorted, while all measurements in 3D were distorted. Of note, the magnitude of the distortion was much larger for the linear measurement than angular measurement. Finally, measurements of orientation, both 2D and 3D measurements were distorted by asymmetry, although the magnitude of the distortion was larger for the 3D measurements. This study confirmed the hypothesis that facial asymmetry affects both 2D and 3D cephalometric measurements. It also demonstrated that the effects of asymmetry on cephalometric measurements depend on the geometric parameter being measured (ie, shape, size, position, or orientation).