## 4 Discussion
This study was designed to verify the accuracy and feasibility of this newly developed system. The mean values of the deviations in this study were intermediate values in all categories between the smallest and the largest deviations (Table 2). This finding implied that the newly developed system is clinically acceptable. However, a remarkable finding was that the implants placed in flapless surgeries were more accurate than the ones placed in open-flag surgeries, and the two surgical methods had medium strength. One proposed cause of this is that the surgeons tended to be more careful in an invisible situation, but this suggestion might be incorrect in this study. However, visual information during open-flag surgery might make the surgeon feel at ease. Actually, on-site modification of an implant position is known to be one of the specific features of dynamic navigation surgery [2; 3; 4; 6; 9; 12; 31]. Although all implants were intended to be placed according to preoperative planning in this study, \"real\" visual information in open-flag surgery might disturb accurate implant placement. The effect of the surgeons' experiences on the accurate positioning was also examined. Previous studies demonstrated that the contribution of the surgeons experiences to the accuracy remains controversial [4; 9; 21; 31; 32; 33]. A significant difference between the deviations of implants placed by more and less experienced surgeons was observed only in coronal lateral deviation and the calculation of effect size indicated that the strength was medium. It was suggested that the first drill tended to be unstable on crustal bone. However, the drill became stable in the implant bed, meaning that the modification of the preparation of the implant bed, according to preoperative planning could be possible and easier. Although this is nothing more than our speculation, a well-experienced surgeon (R.O.) might manage the first drilling. However, no significant differences between the two surgeons were observed in the other deviations, and it could be concluded that the effect of the surgeons' experiences on the accurate positioning was limited, although further evaluation with more surgeons might be favorable. A limitation of this study was that some variables, including bone quality, implant size (length and diameter) and implant sites, were not evaluated. Regardless of these variables, the surgeons generally need to confirm what they are doing using both a monitor and the implant site itself during the surgery. This implies that posterior sites are much more difficult than anterior sites. In this study, the implant beds were prepared according to dynamic navigation without a surgical guide. However, a previous study indicated that dynamic navigation with a surgical guide enabled more accurate implant placement [10]. As mentioned above, the position of the first drill prior to drilling might influence the implant position, especially the coronal lateral position. In other words, implant placement might be modified to be more accurate from the proper coronal position (the first step of drilling). In a future study, the comparison between anterior and posterior implant positioning, with or without a surgical stent, will be required. It will use a greater number of implants and subjects, in addition to other variables. If sufficiently many subjects can be enrolled, the randomization of the patients can be possible and the quality of the analyses will be higher. However, one of the main purposes of this study was to evaluate the accuracy of this system. Although this study had some limitations, it has suggested the clinical viability of this dynamic navigation system, as judged from the statistical variability (mean and 95% CI or median and IQR). To demonstrate the clinical viability clearly, a well-designed study must be conducted in the future.