## 1 Introduction  
Critical anatomic structures such as the maxillary sinus, infra-alveolar nerve, and adjacent teeth must be considered while planning the positioning of dental implants before surgery [1]. The accurate placement of implants is essential to minimize periodontal, prosthetic, and esthetic complications [2; 3; 4]. Incorrect placement can decrease the longevity of implants due to serious complications [5; 6]. Surgical guide templates have been traditionally used to transfer the planned position of implants into the oral cavity [7]. Conventional surgical guide systems are designed based on two-dimensional radiographic images and stone casts [8]; however, their fabrication is labor-intensiveand incorporates only limited details of the gingiva and underlying bone structures [9]. With the development of medical imaging technologies, cone-beam computed tomography (CBCT) has been introduced for the diagnosis and planning of implant placement, enabling clinicians to evaluate the site of surgery by three-dimensional (3D) visualization [10]. Computer-aided design/computer-aided manufacturing (CAD/CAM) has also revolutionized the process of implant treatment and the fabrication of guide templates [11]; in this context, the guide template is designed using a dedicated computer software program, incorporating the sleeve parts for directing the osteotomy drills, where the design can be directly converted to a polymethyl methacrylate guide template with the aid of a subtractive or additive machining process [12]. Image-merging between CBCT and optical scan data not only facilitates the guide template fabrication process but also helps to enhance the accuracy and predictability of implant placement [13; 14; 15]. The effect of using a guide template on the accuracy of implant placement has been of interest [16]. In general, previous studies have concluded that the CAD/CAM guide system is accurate and clinically acceptable [15; 17; 18], yet the degree of error is inconsistent. This variability of error of guided implant surgery seems to originate from intrinsic and extrinsic error sources appearing during each step of the treatment process [19]. Possible individual errors from intrinsic sources include radiograph quality, file reformatting, computer software, and the restriction of drilling motion. Extrinsic sources encompass the adaptation of the guide template, the underlying condition of the supporting structures at the surgical site, and the operator's degree of experience. The summation of individual errors leads to the total discrepancy between the planned and postoperative results. The methodology for locating the actual implant position is an important factor in determining whether the drawn accuracy results of an implant guide system are reliable. Several methods have been used to analyze the position of implants placed in the oral cavity [10; 20; 21]. The first approach directly adopts postoperative CBCT images, wherein a virtual implant image is overlaid on the radiographic image of the actual corresponding implant [17; 22]. The second method involves using a 3D surface mesh image that is constructed by converting the postoperative CBCT scans [18]. Here, a virtual implant can be overlaid over the surface mesh image of the actual implant. Finally, a third method involves using a scan abutment as a medium to investigate the actual position of the implant [7]. With this approach, the scan abutment is connected to the implant placed in the oral cavity and scanned using an intraoral scanner. The actual implant position is tracked in the computer software by matching the image of the scan abutment [20]. Although these different methods have been used for detecting the actual positioning of implants, their accuracy profiles have not been clarified. The purpose of this study was therefore to evaluate the accuracy of postoperative detection methods for locating actual implants by comparing the outcomes of the different methods according to multiple raters.