Accuracy evaluation of the implant via digital registration method
dentitions
The digital registration method was applied to identify the postsurgical position and assess the accuracy of each implant enrolled in this study.The independent implant used in the surgery (4.2 × 13 mm; Astra Tech Implant System® OsseoSpeed® EV, Dentsply Sirona) was connected to a compatible scan body(AE42-SB; TruAbutment, Irvine, CA, USA), and this integrated component defined as a registration unit was scanned by a lab scanner (3Shape E4, 3Shape). The virtual 3D model of the registration unit was reconstructed by reverse engineering and saved in STL format (STL-Registration unit) [Each enrolled implant inserted in the acrylic resin model was connected to the same scan body (AE42-SB; TruAbutment). Then the entire postsurgical model was optically scanned by the same lab scanner (3Shape E4; 3Shape), and scanning data of the model was also saved in STL format (STL-Actual model) [The files of STL-Registration unit and STL-Actual model were imported into reverse engineering software (Geomagic Studio 2014; Geomagic, 3D Systems) and superimposed by the “best-fit alignment” function, with reference to the scan body data, which was regarded as the common region within the two STL files. The postsurgical implant position was subsequently obtained by digital registration and was exported in STL format (STL-Actual model & implant) [The planned implant position data (STL-Planned model & implant) and the actual postsurgical implant position data (STL-Actual model& implant) were imported into Geomagic software (Geomagic Studio 2014), and aligned by the “best-fit alignment” function, according to the corresponding sites of the dentitions [To remain only the positional relationship between the planned and actual implant positions with a clear view, the redundant parts (such as dentition and gingiva) of the models were deleted by the “selecting bounded components” function, and the scan body part was also trimmed by the “trimming with a plane” function in Geomagic software [The implant coronal and apical points were labeled using the “rotation axis” function, which was automatically fitted by the software according to the contour of the implant. The intersections of the rotation axis and the implant cervix/bottom were regarded as the coronal/apical points of the implant. Points 1 and 2 were defined as the coronal and apical points of the planned implant, respectively. Points 3 and 4 were defined as the coronal and apical points of the actual implant, respectively [