Validity of digital manual and automated 2D structural superimposition on the anterior cranial base

To evaluate the validity of digital manual and automated structural superimposition on the anterior cranial base using Björk's two-dimensional (2D) cephalometric method. Secondary aims included assessing repeatability and reproducibility, comparing manual and automated methods, and testing a color blending superimposition mode.

Fourteen dry human skulls were radiographed twice. A gold standard superimposition was established using metallic markers. Three observers performed digital manual superimpositions twice on each skull; once using grayscale images and once using a color blending mode. Superimpositions were repeated one week later. An automated mutual information-based superimposition was also performed. Validity was assessed using root mean square error (RMSE) at 14 standardized cephalometric landmarks from a reference template. The RMSE of the automated method was compared with the average RMSE of each examiner across both trials using General Linear Models. Alignment time was recorded for the manual methods.

The automated method demonstrated high validity (RMSE 0.48 mm, SD 0.35), closely matching the performance of the most accurate observer (RMSE 0.38 mm, SD 0.22), and showed no statistically significant difference when compared with the digital manual methods. A statistically significant difference in accuracy was observed between the observers (F = 4.76, P = 0.017). Color blending did not improve accuracy, but significantly reduced alignment time for two observers. No significant differences were found between repeats (P > 0.5).

The digital manual and automated methods showed comparable validity. While color blending did not improve accuracy, it may reduce alignment time for some clinicians. Both approaches appear reliable and efficient.