Radioprotection-based cephalometric analysis: validation of AB-ratio for sagittal assessment of malocclusion

This study aimed to validate the AB-ratio metric, a novel 3D cephalometric tool for assessing skeletal malocclusions, and to evaluate its reliability in comparison to the traditional ANB angle and Wits appraisal, with a focus on minimizing radiation exposure in orthodontic diagnostics.

A retrospective CBCT analysis was conducted on 352 full-cranium scans. Twelve anatomical landmarks were manually annotated. ANB (°), Wits (mm) and AB-ratio were calculated. Following the assessment of data non-normality using the Shapiro-Wilk test and the removal of outliers via Tukey's fences, statistical analyses were conducted using Spearman's rank correlation coefficient (ρ) and Kendall's tau (τ) to evaluate associations. Additionally, the Siegel non- parametric linear regression estimator was applied to assess the relationships between AB-ratio and ANB, as well as between AB-ratio and Wits. Cohen's kappa coefficient (κ) and percentage of agreement also evaluated the contingency between methods. Significance (p) was set at 0.05.

A strong and significant correlation (ρ=0.787; τ=0.569; p < 0.001) was found between the AB-ratio and ANB angle while a moderate correlation was reported between AB-ratio and Wits (ρ=0.733; τ=0.551; p < 0.001). Linear regressions provided the following equations: AB-ratio=0.04*ANB+0.76 and AB-ratio=0.03*Wits+0.99. The κ scores of diagnostic concordances between AB-ratio and ANB and Wits were 0.562 and 0.089, respectively, showing different agreements (75.44% vs 31.67%). All tests comparing ANB and Wits showed lower correlations (ρ=0.659; τ=0.484) and agreement (κ =0.042; 29.89%).

The AB-ratio metric might significantly enhance 3D cephalometric analysis by providing reliable assessments of skeletal malocclusions while adhering to radioprotection principles. The AB-ratio classified sagittal discrepancies with norms of 0.84±0.08 for Class I, <0.76 for Class III, and >0.92 for Class II malocclusions.

The AB-ratio offers a reliable 3D alternative to the ANB angle and Wits appraisal for diagnosing skeletal malocclusions, with strong and moderate correlation and moderate and poor classification agreement, respectively.