Reproducibility of Three-Dimensional Facial Surface Models Generated from Repeated CT and CBCT Scans: An Ex Vivo...

Background/Objectives: This study aimed to evaluate the reproducibility of 3D facial skeletal surface models generated from repeated computed tomography (CT) and cone bean CT (CBCT) scans. Methods: Four hydrated-dry skull specimens, with soft-tissue simulation using water, were scanned twice within seconds using a single CT scanner. Eight skulls were scanned twice using two CBCT scanners with different settings. An experienced operator segmented all facial skeletal surfaces using a visually estimated optimal threshold. 3D models from repeated scans were superimposed on the forehead, zygomatic area, and maxilla using a best-fit algorithm. Deviations between superimposed models were assessed through distances in predefined areas and color-coded maps, attributed to segmentation errors or tomographic volume generation inaccuracies. Two facial surfaces from each acquisition setting with the largest deviations were resegmented using the original threshold value. Results: Repeated threshold determinations showed no significant differences (p = 0.266; median difference: -6.0, IQR: 39.5). Significant differences were noted between CT and CBCT scanners, but not among CBCT scanners. The median Mean Absolute Distance (MAD) for CBCT was 0.059 mm (IQR: 0.032) versus 0.016 mm (IQR: 0.007) for CT. Color-coded maps confirmed higher consistency in CT and Newtom models, with the low-radiation Planmeca protocol achieving comparable reproducibility. Differences primarily arose from image generation parameters, not threshold estimation. Conclusions: CT provides slightly more consistent 3D facial skeletal surface models. However, CBCT scanners, including those using low-radiation protocols, also demonstrate high reproducibility, reinforcing their reliability in diagnosing and planning treatment for facial morphology variations.