## 4 Discussion  
We attempted to examine the accuracy of postoperative methods for detecting the actual position of an implant and to compare the accuracy profiles of several methods using multiple raters. The deviations and variations in measurement values derived from each method were significantly different among groups in this study. Specifically, the method relying on automatic image-matching of the scan abutment had more accurate outcomes than the radiographic and mesh data-based methods. Thus, the null hypothesis stating that the accuracy of detection methods for locating the implant position does not differ according to the method was rejected. [PERSON] et al. [23] previously evaluated the positioning of implants using both the CBCT and scan abutment methods and also observed a level of disagreement between the outputs of the two methods that corresponds well with the findings of the present study. Notably, we detailed the methodologies for evaluating the agreement of the planned and actual positions of implants. When the implant position is planned before the surgery, it is assumed that the actual implants will be positioned in the planned places in the oral cavity. The importance of agreement between the planned and actual positions of implants has been emphasized as a method to reduce biological, esthetic, and prosthodonic complications [2; 3; 5]. It is necessary for clinicians to know what they can expect in terms of the error profile of guided surgery systems that they are using in the clinic. To investigate the error, an accurate postoperative method for locating the placed implants is required. Good methodological accuracy is also important for evaluating the reliability of reports that measure the accuracy of implant placement in the literature. Based on the findings of the present study, we recommend using scan abutments for locating the actual implant position to minimize possible errors derived from the evaluation method. Special care should also be taken in interpreting the results of the accuracy of implant placement reported in other studies if these investigations adopted CBCT-based manual matching methods for their evaluations. The scan abutment method has commonly been used in the field of prosthodonics [24; 25]. To design a customized abutment, the position of the implant placed in the oral cavity should be visualized in a CAD software program together with the adjacent oral structures. Scan abutments constitute a method for transferring the 3D position of the implant inside the oral cavity into the software program [26]. The scan abutment is connected to the actual implant and digitized using optical scanners [27]; the scan data are then delivered to a dedicated design software program, where a virtual implant is created at the identical position of the actual implant by using an automatic image-matching process for the scan abutment. After this registration process, a customized abutment is designed based on the position of the virtual implant. The tracking function of the scan abutment can be applied for evaluation of the accuracy of implant placement. This analysis method is more applicable in cases of computer-guided implant surgery because the information on the planned implant's position is already saved within the planning software program. The digitally obtained position of actual implants can be conveniently compared with the planned position in 3D. Consequently, the use of scan abutments for investigating the position of actual implants has been explored in recent studies [7; 20]. [PERSON] et al. [7] performed a multicenter clinical study where scan abutments were tightened onto implants placed within the oral cavity and intraoral scans were taken to locate the position of the implants. [PERSON] et al. [20] used scan abutments to evaluate the postoperative positions of implants placed in an effort to investigate the effects of the sleeve structure of the guide template on the accuracy of a static computer-assisted implant surgery system.