Comparison of the Repeatability and Reproducibility Levels of ANB, Tau and Yen Angle Measurements Used in Cephalometric Diagnostics in the Assessment of Sagittal Discrepancy: A Comparative Study

<b>Introduction</b>: Cephalometric analysis is an essential tool used in orthodontic diagnosis and treatment planning. <b>Aim</b>: The aim of this study was to compare the measurement reliabilities (repeatability and reproducibility) of the Tau and Yen angles and compare them to the results obtained for the ANB angle. <b>Methods</b>: Repeatability and reliability assessments for the seven points (N, A, B, S, W, M, G) used in the analysis of ANB, Yen and Tau angles were performed twice with an interval of 7 days by 22 orthodontists. The measurement results for ANB, Yen and Tau angles were assessed using the Bland-Altman formula, Dahlberg formula, intraclass correlation coefficients (ICCs), R² coefficients and R&R. In order to assess the number of individual skeletal classes of sagittal discrepancy, the Pearson chi-squared test was used. With common parameters of df = 4, <i>p</i> < 0001, for the ANB angle, the result was χ² = 9104; for the Tau angle, χ² = 4556; and for the Yen angle, χ² = 4207. In order to determine the inter-rater reliability based on two-way ANOVA analysis without repetitions, the ICC (2,2) was used. The ICC (2,2) index at the 95% confidence level was 0.998 for the ANB angle, 0.997 for Tau and 0.998 for Yen. High values of the ICC index close to 1 indicate the agreement of the measurements and their high reliability. <b>Results</b>: The orthodontists in the study measured sagittal discrepancy significantly more accurately using the ANB angle compared to the Yen and Tau angles. Using a Bland-Altman plot, the bias and range of agreement within which 95% of the differences between measurements were accounted for were determined. For the ANB angle, the mean difference between measurements was 0.07 with a confidence interval of -1.55 to +1.69; for the Tau angle, the mean difference between measurements was 0.19 with a confidence interval of -2.92 to 3.30; and for the Yen angle, the mean difference was 0.09 with a confidence interval of -2.71 to +2.89. Using regression analysis, the measurements were assessed using the R2 index, which for the ANB angle was 0.952 (<i>p</i> < 0.001); for the Tau angle, R2 = 0.928 (<i>p</i> < 0.001), and for the Yen angle, R2 = 0.942 (<i>p</i> < 0.001). <b>Conclusions:</b> The obtained results of the assessment of the ANB, Tau and Yen angles confirm the thesis of the highest reliability, including repeatability and reproducibility, in the assessment of sagittal discrepancy in orthodontic diagnostics using the ANB angle, previously considered the gold standard. One of the basic factors attributed to the poorer repeatability and reproducibility of Tau and Yen measurements is human error related to the precision of determining new anthropometric points. Further studies to assess the usefulness of using the new Tau and Yen angle measurements in orthodontic diagnostics for sagittal discrepancy should be correlated with other measurements used so far, depending on the type of defects in the vertical dimension. It is necessary to consider enlarging the study group and performing longitudinal studies.