## 4 Discussion
The deviation parameters analyzed in this review were 3D angular deviations and global coronal and apical deviations since these were the ones reported in all the studies. Additionally, several authors [20; 21; 25; 27; 28; 32; 33; 35] measured other linear parameters in the mesiodistal (MD), buccolingual (BL), and apico-coronal (AC) directions, allowing them to obtain more conclusive evidence regarding the sources of deviation. [PERSON] et al. [33] report interesting findings regarding these linear measurements, whereby deviation in the BL direction has a significant impact on apical, coronal, and depth deviations, while deviations in the MD direction also have a significant impact on apical, coronal, and angular deviation. Comparing the accuracy of guided surgery in relation to the type of tissue support, a variety of results were reported. In the retrospective study by [PERSON] et al. [37], 10 adults were included, and 111 implants were available for a comparison of accuracy. With respect to surgical guide support, bone-supported guides (1.62 mm) provided better accuracy than mucosa-supported guides (2.10 mm) in apical deviation, while tooth-supported guides (1.36 mm apical, and 1.10 mm coronal) achieved greater accuracy than mucosa-supported guides (2.10 mm apical, and 1.63 mm coronal) in apical and coronal deviations. Overall, the present review found significantly better accuracy using tooth-supported guides. In the same way, in the multicenter clinical study by [PERSON] et al. [30], 25 patients were treated, placing a total of 117 implants using CAD/CAM surgical guides supported by mucosa, bone, and/or teeth. The results of this clinical study showed that implant placement using bone- and mucosa-supported guides was more accurate compared with tooth-supported guides or a combination of tooth and mucosa, although the differences were not statistically significant. When the three types of surgical guides (mucosa-, tooth- and bone-supported) were compared, findings were inconclusive due to the fact that only two studies made this comparison. However, the systematic review and meta-analysis by [PERSON] et al. [17] suggests that there is an association between guide support and the clinical accuracy of computer-guided implant surgery. Tooth-supported guides exhibited greater accuracy than bone and mucosa-supported guides. It would appear that the surgical guide does influence the deviation of the implant placement depending on whether the supporting tissue is soft or hard. The interpretation and measurement of soft tissue at the planning stage, together with the stability offered by hard tissues during the surgical procedure, may be the key determinants for greater precision in guided surgery. Finally, the capacity of a software program to accurately detect the bone-soft tissue interface and record linear measurements is a fundamental requirement if it is to perform the complex tasks involved in virtual implant placement and surgical guide design adequately. Increasing numbers of software programs are available for processing and analyzing CT images. So, a variety of different software programs were used in the studies included in this review for both planning and measuring linear and angular deviations. Nevertheless, it should be noted that the deviation ranges observed in this review did not vary widely despite the diversity of software used. In this regard, a study published by [PERSON] et al. [52], compared three types of software (Blue Sky Plan, coDiagnostiX, and RadiAnt) to assess the accuracy of linear measurements on CBCT images, concluding that, although all three software programs exhibited significant measurement errors of between 0.43 and 0.56 mm, no significant differences were identified between any of the programs. It would be intersting to study the accuracy of other widely used guided surgery system such as Avinent and ZimVie using this approach.