The long-term success of dental implant therapy is closely related to the correct achievement of various biological, functional, and esthetic parameters [1], [2], [3]. A correct three-dimensional (3D) implant position in the bone and the best possible emergence profile are two of the most important factors in obtaining successful, highly esthetic, and functional implant-supported restoration [4,5].

Several techniques have been proposed for precise and controlled implant placement; among them, the most important are static computer-assisted implant surgery (s-CAIS) [6,7] and dynamic navigation [8].

Under both protocols, powerful software can match anatomical information from 3D radiological devices (Cone Beam Computer Tomography, CBCT) with diagnostic waxing [9]. Then, the clinician can plan implant placement in the best position, inclination, depth in the available bone [6], [7], [8], and impact on the emergence profile according to the optimal prosthetic outcome [10]. The static approach (s-CAIS) is a technique in which surgery is performed using a special drilling set and surgical template manufactured directly from virtual planning [6,7]. The dynamic approach is instead a free-hand technique relying on a real-time tracking system to direct the drilling [8]. These solutions show no significantly different clinical outcomes [11,12] or different accuracies in expert hands [13,14], and currently, the use of the static approach is widespread [6,7]. The main advantage of s-CAIS is that it does not require the clinician to invest in dynamic navigation equipment; however, it has the drawback of not providing a free view of the surgical field. Moreover, no changes in implant positioning can be made during surgery, which is possible with the dynamic approach [6], [7], [8].

With s-CAIS, high accuracy can be obtained only by following a standardized workflow: each protocol step must be carefully respected to reduce extrinsic and intrinsic errors [15,16]. In fact, all errors collected during the workflow can lead to a final 3D position of the implant that differs from that planned [15,16].

The essential information for correct diagnosis and treatment planning can be collected in different ways. The “Double-Scan Technique” is the first possibility [17]. With this technique, the data retrieved from a CBCT of the patient wearing a radiological template are matched with the data from a second CBCT of the template itself [17]. The two files, imported into powerful software, provide a 3D visualization of the bone anatomy and the ideal prosthetic outcome. The clinician can prepare virtual planning for the correct insertion of the implants using this clear information. The final virtual design of the template can be sent to a manufacturing center to produce the surgical template.

The “Fusion Technique” is based on the match between patient data from a CBCT and those from an intraoral scan of the patient's dentition [18]. As an alternative, overlapping can be performed between the patient's CBCT and the scan of the patient's cast model together with a virtual or analogical wax-up [18,19]. From this point, the process follows the same steps as the Double Scan Technique.

Both methods allow the prosthodontist and technician to produce a working model directly from the template. The model can be used to manufacture a temporary prosthesis to be applied immediately after surgery when correct primary stability is achieved [20,21].

It has been demonstrated that the accuracy of guided implant placement is significantly higher than that of free-hand surgical procedures [22,23]. Regardless, due to the blind nature of the procedure, it is extremely important to be as accurate as possible to reduce the difference between the virtual and real positions of the implants. Some linear and angular deviations between the planned and placed implants can be expected even when performed by experienced clinicians [23].

Many studies have demonstrated different levels of discrepancy between the virtual and real positions of implants in guided surgery, which depend on many variables and not only on the clinician's experience [9,10,[12], [13], [14], [15], [16]]. The most important factors involved in errors are 3D radiological examination quality, correct virtual planning, template manufacturing procedures, and transfer and fixation of the guide into the surgical field [15,24]. The critical point of manufacturing has been investigated by Henprasert P. and coworkers, who did not find any significant difference between milling and 3D printing surgical template production [25]. Other critical parameters are the presence of sleeves [26], the distance between the sleeve shoulder and the bone level, and the length of the drills. Reducing these factors can significantly increase the accuracy of static computer-guided implant surgery [27].

Most published studies have focused on analyzing the deviation between the planned and placed implants, superimposing the virtual planning with a second CBCT taken after implant placement [28]. This solution, however, obliges the patient to undergo an unnecessary second CBCT exposure, an approach that has been criticized [29]. To avoid this problem, we conducted our present study using a different method: the matching of two standard tessellation language (STL) files obtained from the preoperative virtual plan and the postoperative intraoral scan (with the actual position of the fixtures after the surgery) using specific software [6].

This multicenter clinical study aimed to evaluate the accuracy of s-CAIS when performed in private practices using the same planning software and stent manufacturing process.