## 4 Discussion
It has been emphasized that implant placement using a guide will depend on the feasibility of prosthetic rehabilitation, bone availability, and the condition of the surrounding target tissues. However, the characteristics of the implants and their compatibility with the guidedprocedure also influence the predictability of prosthetic rehabilitation for implants placed using a guide [24]. When evaluating the accuracy of implant placement, the various types of support for the different types of guides in different clinical situations should be observed. As shown in Table 2, most of the studies were performed with tooth-supported guides because, according to the literature, these guides are the most accurate during surgery for implant placement. In a study by [PERSON] et al. in 2018, it was also demonstrated that guides supported by teeth were more accurate than those supported on bone and mucosa [25]. Most of the studies chosen demonstrate that there is less angular deviation with tooth-supported guides. The highest degree of angular deviation (2.42\({}^{\circ}\)) (Table 3) occurred in one case involving mucosa-supported guidewires. _Method for the elaboration of digital prosthetically-derived surgical guides for dental implants._  
Undoubtedly, several factors influence the accuracy of digital prosthetically-derived surgical guides for implant placement. One of these factors is the manufacturing technique. Digital prosthetically-derived surgical guides for implants can be manufactured in two ways: additive (3D printing) or subtractive (milling or grinding). The additive technique is based on a union of sequential printed layers, while subtractive production is based on a polymeric structure produced by a milling machine [26; 27]. The technology behind the development of digital prosthetically-derived surgical guides is still being studied to determine which is the best option for successful results in terms of the least discrepancy between planning and placement of the implant. Deformation of the guides has been observed more in printed guides than in milled guides because the latter are manufactured from machined blocks whose structure is not altered dimensionally. However, studies such as those of [PERSON] et al. concluded, based on the results of an in vitro study, that there were no differences in the overlap of printed and milled guides [28]. A study by [PERSON] et al. also indicated that there were no significant differences in terms of the type of guide fabrication since 3D-printed guides have the same degree of accuracy as milled guides. This study highlights the advantages of printed guides: easier fabrication, less material waste, reduced laboratory time, and increased cost-effectiveness [29]. According to a study by [PERSON] et al., printing technology, whether it was stereolithography (SLA), polyjet, or multijet technology, had no significant effect on the accuracy of the guide. As shown in Table 2, all publications included in this review used 3D manufacturing from 2014 to 2022. It is currently the most commonly chosen manufacturing method by professionals, taking into account the disadvantages of milled guides, such as the high cost of materials and equipment and the difficulty in producing highly complex models [30; 31]. In addition, the four articles included in this review described fully constrained guides using 3D printing, where their high accuracy can be related to this type of manufacturing. Currently, postproduction processes on printed guides have substantially improved due to the use of specific, automatic, and integrated machines for washing, drying, and polymerization of the material. _Number of fixation screws._  
The digital prosthetically-derived surgical guides must transport the planned implant position to the correct clinical location for successful treatment [32]. The number of fixation screws in surgical guides is another factor that may influence the discrepancy in the results obtained for the placed implants. [PERSON] et al.