## 4 Discussion
The results of the present study demonstrated that operator experience is not a crucial factor for achieving the implant placement accuracy via tooth-supported SLA surgical guides. Further in vivo studies, preferably under the supervision of experienced doctors, are needed to validate this finding. From another standpoint, [PERSON] et al. [24] investigated the clinical accuracy of implant positioning using a partially guided protocol instead of a fully guided implant placement. They concluded the level of surgeon experience affected the accuracy of the implant positioning via a tooth-supported surgical guide. In a similar in vivo study, [PERSON] et al. [25] also suggested that experience and training may play an important role in guided surgery. Indeed, using a partially guided surgical protocol, the surgeon must understand the treatment plan thoroughly and place the implant freehand. Therefore, the surgical training and experience of the surgeon are crucial for appropriately executing the implant surgery, which may not be so significant for fully guided implant placement in terms of accuracy, such as in the present study. In this study, we had tried to adjust the covariance between individual performances of the dentists and their level of experience, and the levels of significance were almost the same after the statistical adjustment. Personal skill or performance was not easy to quantify. Nevertheless, in our study, a sample size of 15 with 80% power was enough to detect the association between individual performance and experience. Large positional and angular deviations were found in both experienced and inexperienced groups; hence, based on considerable variation in the deviation values among the operators in both experienced and inexperienced groups, human error in executing the simulation surgery, rather than experience, was reasonably inferred to be a significant factor contributing to the more substantial errors of some operators. Furthermore, although not statistically significant, the mean values of the deviations of the inexperienced group were generally smaller than the experienced group in this study. This trend has also been noticed in a clinical report [21]. The large apical and angular deviations appeared more in the experienced groups, possibly meaning that the inexperienced operator could be paying more attention to following the instructed procedures than the experienced operators, because of their lack of experience. We also found that the operator's age had a significant influence on accuracy. Younger dentists had better performance than senior doctors, regardless of their experiences on the static guided implant surgery. To date, all the studies examining the impact of operator experience on static guided implant surgery focused only on the experience level of the dentist, but not the age, probably because senior doctors were naturally regarded as experienced. In the present study, however, dentists with varying ages and specialties were recruited in both experienced and inexperienced groups. Therefore, we could examine the effect of the demographics of the dentist on the accuracy of static guided implant surgery. For dynamic computer-guided navigation systems, junior dentists or dental students were reported to have better performance in terms of the accuracy of implant placement [26; 27]; However, we did not find similar studies for the static guided implant surgery in the literature. The effect of age on the accuracy of static guided implant surgery remains an issue to be clarified. Another finding of this study was that, even under well-controlled laboratory conditions, significant errors could still occur when placing implants via the SLA surgical guide. For static guided implant surgery, multiple steps were involved, and errors could take place in any of the steps from the acquisition of patient data to the execution of surgery [1]. In the literature, relatively high maximum deviations were also revealed [3; 4; 13; 28], which coincided with the results of this study.