Are the results of the Wits appraisal clinically interchangeable when evaluating 2D and 3D images? : A CBCT-dataset...

To assess whether the results of the Wits appraisal derived from two- (2D) and three-dimensional (3D) images of the same cone-beam computed tomography (CBCT) acquisition are numerically interchangeable and to quantify diagnostic reclassification when conventional 2D thresholds are applied to 3D values.

This retrospective method-comparison study analyzed 233 CBCT datasets with a field-of-view adequate for evaluating the Wits appraisal. A CBCT-derived lateral cephalogram was generated for each scan as a digitally reconstructed radiograph (DRR), and 2D Wits (AO-BO) was computed by projecting Points A and B onto an occlusal line (interincisal-MVC6). The 3D Wits was computed on the volume by orthogonally projecting Points A and B onto an occlusal plane (interincisal, 1.6CF, 2.6CF) and measuring the signed in-plane anteroposterior distance (AO_3D-BO_3D). The linear association between 2D and 3D measurements was assessed using Pearson's correlation coefficient (r). Agreement was evaluated using Bland-Altman bias and limits of agreement (LoA), Lin's concordance correlation coefficient (CCC), κ statistics, and equivalence testing (two one-sided tests [TOST]; δ = ±1 and ±2 mm). Diagnostic categories were defined using clinically used ±2 mm thresholds (class II > 2; class I -2 to +2; class III < -2 mm). Exploratory subgroup analyses assessed whether Δ = 3D - 2D Wits differed across 3D skeletal classes and vertical skeletal patterns.

The 3D method yielded systematically lower values than the 2D (Δ = 3D - 2D: -1.97 ± 1.39 mm; p < 0.001) with LoA from -4.69 to +0.76 mm. Statistical correlation was strong (r = 0.935), but concordance was incomplete (CCC = 0.814). Using ±2 mm class cut-offs, three-class agreement was 60.1% (κ = 0.380), and 39.5% of the cases shifted toward class III on the 3D analysis. TOST did not demonstrate equivalence for δ = ±1 mm or δ = ±2 mm. In the available-case exploratory vertical-pattern analysis (n = 225), the difference between 3D skeletal classes differed modestly across hypodivergent, normodivergent, and hyperdivergent groups, but the continuous SN^MP angle was not significantly associated with 3D - 2D Δ.

Wits values computed in 2D on CBCT-derived DRRs and in 3D on the corresponding CBCT volume were strongly associated but not numerically interchangeable in this dataset; therefore, conventional 2D thresholds should not be transferred directly to 3D values without 3D-specific validation.