How do landmark deviations affect angular measurements? The concept of individual cephalometric calibration

Abstract

Background. Cephalometr is an ancillary test that is widely used in orthodontics and maxillofacial surgery. Any cephalometric analysis is based on measurements performed between manually selected specific landmarks. Any inaccuracies in landmarks selection may bias the results of diagnosis, treatment planning or evaluation of craniofacial growth. Objectives. The aim of this study was to identify the possible influence of linear landmark deviations on the X and Y axes on angular measurements, and to propose an individual cephalometric calibration concept to increase the landmark selection accuracy. Material and Methods. A reference cephalometric template was created in GeoGebra software (International GeoGebra Institute, Linz, Austria). Based on the template, the values of the “S”, “N”, “ANS”, “A”, “B”, “Go”, “tgo”, “Pm”, and “Gn” cephalometric landmark locations were modified for 0.5 mm, 1 mm, 2 mm, 3 mm and 4 mm in each direction on the X and Y axis and angular changes were noted. Results. For all angular measurements, a landmark selection error equal to or greater than 2 mm resulted in a change of more than 1 degree. Finally a four-step process of individual calibration was presented. Conclusions. Depending on the landmark dislocation direction (horizontal or vertical), the angular measurements can be affected in either a minor or major way. Individual calibration allows for the detection of inaccuracies in the X and Y axis. Detailed analysis of the calibration results makes possible the correction of the selected errors, which could lead to more accurate measurements during cephalometric analysis and the detection of more subtle changes.