## 2 Materials and Methods  
The experimental workflow of the current study is presented in Figure 1. A dendiform model with missing mandibular left posterior teeth was prepared and scanned using a desktop scanner (IDC S1; [PERSON], Koblach, Germany). Three implants (10 mm in length and 4 mm in diameter; AnyOne, MegaGen, Daegu, Korea) were placed in the edentulous area using freehand drilling with flap elevation (Figure 2). To locate the position of the placed implant for the first molar, the following three different methods were chosen: manual matching on a CBCT image (MC group), manual matching on a mesh model of a CBCT image (MM group), and automatic matching on a scan abutment of the scan image (AS group). To condition the MC group (Figure 3a), radiographic images of the anatomic structures and implants were obtained using a CBCT system (PaXFlex3D, Vatech, Hwasung, Korea) with a field of view of 120 x 85 mm, a voxel size of 0.2 mm, and exposure conditions of 80 kVp and 8 mA, with resulting images saved in the digital imaging and communications in medicine (DICOM) format. The DICOM data and surface scans were exported to an implant planning software program (R2 GATE 2.0, MegaGen, Daegu, Korea), where the two 3D images were then merged. A virtual implant was then created and manually overlaid onto the position of the actual implant on the radiographic image. The determined position of the virtual implant was combined with the surface scan image and saved as a single standard tessellation language (STL) file. To condition the MM group (Figure 3b), the CBCT data of the study model were converted into a 3D reconstruction mesh image using an image-control software program (Mimics, Materialise, Leuven, Belgium). The 3D mesh image and surface scan data were merged in the implant-planning software. Subsequently, a virtual implant was manually overlaid on the  
Figure 1: Workflow for this study. MC: Manual matching on a CBCT image; MM: Manual matching on a mesh model of a CBCT image; AS: Automatic matching on a scan abutment of the scan image. Figure 2: Study model. reconstructed image of the actual implant; these were then saved together as a single STL file. Lastly, to condition the AS group (Figure 3c), a scan abutment (4.0 mm in diameter and 9.0 mm in height; AnyOne scan abutment, MegaGen, Daegu, Korea) was connected to the implant in the dendiform and digitized using the desktop scanner. This scan image was transferred as an STL file to a dental design software program (IDC D1, Amann Girrbach, Koblach, Austria), where the position of the actual implant was calculated by matching the image of the scan abutment. The image of the virtual scan abutment was provided by the manufacturer of the implant and was automatically matched onto the scanned image of the scan abutment using the embedded best-fit registration module of the CAD software program. A virtual implant image was then created based on the position of the virtual scan abutment. Finally, the virtual implant was combined with the surface model scan and saved as a single STL file. Thirty dental clinicians participated in this study to validate the three detection methods for locating the actual implants. All attendees were blinded to the purpose of this study and performed each method in a random order (n = 30 per group; total n = 90). The study design was approved by the institutional review board of Kyungpook National University Dental Hospital (2019-03-03-00). The accuracy of the geometric position of the virtual implant with respect to the position of the actual implant was evaluated by comparison with a reference image in an image analysis software program (Geomagic Design X; 3D Systems, Morrisville, NC, USA). The reference image was created by directly scanning the surface of the implant in the dendiform model (Figure 4). First, the buccal side of the dendiform model around the implant was removed to expose the threads on half of the implant surface.