## 1 Introduction  
Computer-guided implant surgery has gained popularity because it helps surgeons to plan and place dental implants efficiently [1], for which two types of techniques have been advocated:static (template-based) and dynamic navigation [2]. Nowadays, the static approach is more popular because high-cost equipment is not needed. A virtual implant treatment plan can be performed using three-dimensional planning software and transferred to the patient by using computer-aided design and computer-aided manufacturing (CAD/CAM) surgical guides during implant surgery. The static guided implant surgery can help surgeons to achieve ideal implant position and avoid damaging surrounding anatomical structures [3]. Moreover, a proper implant position and angulation is essential for long-term success in terms of biomechanics and esthetics. To accomplish this treatment concept, a key determinant is the accuracy of the computer-guided implant placement [4].  
In the literature, the accuracy of computer-guided implant surgery had been widely examined and compared [1; 5; 6]. Conventionally, these studies used the method of overlapping the pre- and postoperative computed tomography (CT) images to measure the deviations of the placed implant [7; 8]. The problem of this CT matching method is that the outline of the postoperative implant could be ambiguous due to the artifacts produced from the titanium implant material. The overall implant contour could be enlarged, making the correct identification of the implant geometry difficult [9]. A different method for examining the accuracy using the optical scan has been described [9]. Although commonly applied to the accuracy studies, the CT matching method was reported to be less accurate than the CAD/CAM-based measurement method by scanning the abutment placed on the implant with an intraoral scanner [10].  
Many steps are involved in the static guided implant surgery, from the evaluation and collection of clinical data of the patient to the performance of the surgery. Errors in each step could affect the final accuracy of the implant placement. Among these factors, the surgeon's technical skills and experience are apparently influential [11]. Studies have shown that computer-guided implant placement is more accurate than nongguided or freehand implant placement [1; 3; 5; 12; 13]. Thus, the effect of operator experience in static guided implant surgery was of particular interest; if inexperienced doctors could perform static computer-guided implant placement as accurately as experienced doctors, this protocol should be highly recommended for clinicians with limited implant surgery experience. However, the effect of operator experience on the accuracy of static guided implant surgery remains an issue to be clarified. In the literature, the results are not consistent [14], and almost of all the studies have used the CT matching method to examine implant placement accuracy.  
To clarify the inconsistent results in the literature, another assessment method of the accuracy should be used considering the limitations of the CT matching method. The purpose of the present study, therefore, was to examine the influence of operator experience on the accuracy of static guided implant surgery, by using the optical scan to capture the postoperative implant position for the error measurement. In order to exclude the possible confounding factors associated with clinical trials, in vitro simulation implant surgeries performed on dental models were used for better control of the study variables.