Effect of Scan Body Design on Dental Implant Transfer Accuracy

Objectives: To evaluate the effect of size and geometry of implant scan body on the accuracy of optical 3D scanning.
Methods: Three calibration blocks were milled from polyether ether ketone (PEEK). The first block comprised 3 different geometries, including a sphere, a cylinder, and a cuboid. The second and third blocks comprised 9 cylinders and 5 cuboids with different cross-sectional areas and heights. The spatial position and angulation of each scan body were measured by a coordinate measuring machine 3 times (CMM, reference group) and a structured light laboratory scanner 10 times (test groups). Centroids and centre axes of each scan body in the virtual models were determined. Linear and angular trueness and precision of the scan bodies were calculated with reference to the CMM.
Results: The sphere showed significantly higher linear trueness (12.5 µm) and precision (2.5 µm) than the cylinder (trueness 16.3 µm, precision 5.5 µm) and cuboid (trueness 19.5 µm, precision 2.8 µm), but the angular measurements cannot be obtained from the sphere. The 5.5 mm diameter cylinder showed significantly higher trueness and precision than those of 4.8 mm and 6.5 mm. The 12 mm height cylinder showed significantly higher linear but lower angular trueness than those of the 8 mm and 4 mm. The 6 mm height and 24 mm² cross-sectional area cuboids showed the worst linear and angular trueness than those of the 8 mm / 12 mm and 18 mm² / 30 mm², respectively.
Conclusions: The geometry and size of the implant scan body significantly affect the scanning accuracy. Although spheres can achieve good linear accuracy, it is not suitable to be used as implant scan body. 5.5 mm diameter × 8 mm height would be an optimal size for cylindrical scan bodies. The cuboidal scan body should not be shorter than 6 mm.