## 1 Introduction  
Digital workflow has been recently improved in dentistry, with the development of low-dose high-resolution cone beam computed tomography (CBCT), intraoral scanners (IOS), CAD/CAM software programs, 3D printers, and computer-assisted implant surgery (s-CAIS) systems [1, 2]. Computer-assisted implant procedures are supposed to result in more precise implant positioning [3], and surgical templates might be fabricated in different ways with the same level of accuracy [4]. With the constant development of s-CAIS, several concerns have been raised about the reliability, accuracy, and precision of templates to replicate the planned implant position [5]. This is especially important in edentulous patients, where angulated implants should be placed in the exact planned position to allow the corresponding screw-retained abutments (SRA) axis to correspond to the prosthetically-oriented planning [6]. Although dental implants have proven to be reliable devices to replace missing teeth, they are, however, not free from mechanical or biological complications [7, 8, 9]. According to [PERSON] et al. [10] and [PERSON] et al. [11], mucosa-, tooth-, and mini-implant-supported templates demonstrate superior accuracy in implant placement to bone-supported guides. [PERSON] et al. state that computer-assisted flapless implant placement, using mucosa-supported templates in complete-arch restorations, can be considered a reliable and predictable treatment choice, despite the potential effects that a flapless approach could bring to the overall treatment [12]. Flapless and fully guided implant placement has the potential to maximize efficacy outcomes, and at the same time, minimize surgical invasiveness [13]. But in daily clinical practice, clinicians often face the necessity of bone reduction to place implants. Bone reduction may be required to level the alveolar crest to create the desired bone architecture, allowing for sufficient bone width for implant placement and ensuring adequate inter-arch restorative space [14]. Patients can rehabilitate full arches, even when bone reduction is mandatory because of a gummy simile or because of an irregular, or thin, bone crest [15]. The use of computer-guided surgery to rehabilitate edentulous arches by using four dental implants supporting a fixed screw-retained prosthesis could be a valid treatment option in the short and medium term [16]. When rehabilitating the edentulous jaw with four implants, the technique involves alveoolplasty before implant placement to provide space for the prosthetic components and to provide a platform on which dental implants can be placed in clinical situations where a knife-edge alveolar ridge is present [17]. As the aim of the present study was to evaluate the in vivo and in vitro accuracy of s-CAIS in an edentulous patient, the clinical situation was to be duplicated, and so the bone-supported template design was chosen. [PERSON] et al., in the systematic review, state that several studies have provided information on the accuracy of s-CAIS, but a lack of homogeneity was found for accuracy assessment techniques and protocols: many different surgical factors and techniques were not standardized between the studies, which served to confound the true accuracy of guided surgery; there were many steps within the digital workflow itself, where there was a possibility of accumulating error, which also served to mask the real accuracy of the technique [5]. Most studies compare CBCT data before and after implant placement. However, the lack of precision of CBCT machines represents a major issue. To date, around 279 CBCT devices exist in the market with different technical parameters, which makes it difficult to standardize scanning protocols [18]. According to [PERSON] et al. [19], the visualization of implant dimensional alterations varied between different CBCT devices and scanning protocols with an increase in diameter ranging from 0.27 to 1.04 mm.