Reliability and the smallest detectable difference of measurements on 3-dimensional cone-beam computed tomography images

INTRODUCTION: The aim of this study was to determine the reliability and the measurement error (by means of the smallest detectable error) of 17 commonly used cephalometric measurements made on 3-dimensional (3D) cone-beam computed tomography images.METHODS: Twenty-five cone-beam computed tomography scans were randomly selected, and 3D images were rendered, segmented, and traced with the SimPlant Ortho Pro software (version 2.1, Materialise Dental, Leuven, Belgium). This was repeated twice by 2 observers during 2 sessions at least 1 week apart. Measurement error was determined by means of the smallest detectable difference. Differences were analyzed with Wilcoxon signed rank tests. Intraobserver and interobserver reliability values were calculated by means of intraclass correlation coefficients (ICC) based on absolute agreement.RESULTS: There were great variations of measurement errors between the angular (range, 0.88°-6.29°) and linear (range, 1.33-3.56 mm) variables. The greatest measuring error was associated with the dental measurements U1-FHPL, L1-MdPL. and L1-FHPL (range, 3.80°-6.29°). ANB angle was the only variable with a measuring error of 1° or less for both observers. The intraobserver agreement of all measurements was very good (ICC, 0.86-0.99). Except for SN-FHPL (ICC, 0.76), interobserver agreement was very good (ICC, >0.88).CONCLUSIONS: The measurement errors of 3D cephalometric measurements (except for the ANB angle) can be considered clinically relevant. This questions the use of linear and angular 3D measurements to detect true treatment effects when a high level of accuracy is required.