Effect of Fiducial Marker Design (Shape, Size, and Configuration) on the Trueness and Precision of CBCT Marker-Geometry Reproduction for CBCT–Intraoral Scan Registration: An In Vitro Study

Background/Objectives: Cone-beam computed tomography (CBCT)-to-intraoral-scan registration in edentulous implant planning relies on radiopaque fiducial markers, yet how marker design governs marker-geometry reproduction is unclear. We quantified the effects of shape, size and configuration and where the error arose. Methods: Eighteen edentulous mandibular denture designs (three shapes × three sizes, 2–4 mm × two configurations; five markers each) were printed and CBCT-imaged three times at 0.2 mm voxel. Distances, angles, a leave-one-marker-out (LOMO) error and a markerless control were analyzed at the design level (n = 18). Results: Acquisition reproducibility was voxel-limited (median 49 μm). Marker size governed trueness and precision (partial ω2p 0.25–0.65), with no shape effect detected. The LOMO error fell with size (541 to 359 μm; p = 0.004), whereas the markerless control did not (p = 0.653); the size effect differed between approaches. Twenty percent of 2 mm markers exceeded the 300 μm threshold—unstable localization, not failed detection. In the markerless control, 6 of 270 markers (2.2%) exceeded 1 mm despite acceptable global surface fits. Conclusions: A satisfactory global surface-fit residual may conceal substantial local misregistration, whereas fiducial landmarks permit independent verification of alignment. Marker size most directly governed reproduction fidelity; ≥3 mm diameters are recommended for the rotationally symmetric geometries tested.