## 4 Discussion
The literature indicates that these deviations are the result of errors that accumulate from the acquisition of CBCT and STL images for virtual planning to the execution of the surgical procedure. Various guided surgery protocols have been designed in order to reduce errors in implant placement and control the variables involved. Several studies have compared pilot drill-guided, partially guided, and fully guided implant surgery [25; 26; 27]. Others compare the different types of surgical guide support (bone, mucosa, and tooth support) [23; 34; 41]. It is evident that there are a variety of possible factors that influence the accuracy of guided surgery, ranging from the most evident, such as the surgeon's experience when performing the surgical procedure, to the less evident, such as the physical properties of the materials used to manufacture surgical guides. In recent years, special interest has been placed on evaluating the influence of the surgeon's experience. In this context, [PERSON] et al. [9] evaluated the accuracy of implants placed with tooth-supported surgical guides and concluded that the group of expert surgeons performed a more accurate implant placement compared with novice surgeons. Regarding the manufacture of surgical guides, most are currently manufactured using CAD/CAM technology [48], either by additive methods (stereolithography laser, digital light processing, selective laser sintering) or subtractive methods such as milling. Stereolithographic 3D printed surgical guides are the most frequently used, although milling seems to achieve greater accuracy and better outcomes according to [PERSON] et al. [10]. Two methods for assessing the accuracy of guided surgery were described in this review. The first and most widely used was the \"radiographic-matching method\", in which STL files of the planned implant positions were superimposed over DICOM files obtained from a postoperative CBTC scan. However, exposing patients to a second CBCT to determine the final implant position is controversial since the use of CBCT images after implant insertion should be restricted to a small number of indications: for evaluating graft healing, assessing complications related to neuromuscular trauma, or monitoring complex surgical procedures [49]. CBCT scans are not considered appropriate for routine monitoring. Likewise, exposing patients to a second dose of radiation does not fulfill radiological safety standards [50] according to the ALARA (As Low As Reasonably Achievable) principle. Previous studies have also indicated that voxel size, metal implant artifacts, patient movement, and scanning parameters directly influence CBCT image quality and so affect the accuracy of these images' superimposition, limiting their usefulness [49; 51]. The \"digital registration method\" has been proposed as an alternative method that avoids a second postoperative CBCT scan and overcomes the disadvantages described above [34; 41]. In this method, the postsurgical implant positions are determined with a digital impression of scan bodies/transfers connected to the placed implants. The STL files resulting from preoperative virtual planning are superimposed on the STL files generated from the postoperative digital scan. This digital method can avoid the effects of CBCT quality on data registration accuracy [41]. Although both methods offer alternatives intended to reduce the accumulation of error, a recent in vitro study by [PERSON] et al. [47] compared these two methods in terms of their capacity to assess the accuracy of guided surgery implant placement, concluding that both digital registration and conventional radiographic methods achieve good agreement using tooth-supported surgical templates. Likewise, analyzing the deviation data obtained in the studies included in the present review, the deviation ranges obtained with the two methods were comparable (Table 2). Nevertheless, it should be noted that the quality of postoperative images constitutes a factor that could prejudice the quantification of deviation parameters.