## 4 Discussion
The present cadaver study aimed to assess the accuracy of digitally planned mini-implants inserted using four different procedures. When assessing the distance between the planned and the real positions of the mini-implants, the lowest discrepancies were found at the neck, where the full-arch guides exhibited better results compared to the skeletonized ones; while for full-arch guides, the deviation from the planning was comparable between pre-drilling and no pre-drilling procedures; the mini-implants inserted with the skeletonized guides without pre-drilling tended to perform better than self-drilling ones. When the distance between the real and the planned positions was measured at the apex of the mini-implants, like values were obtained with pre-drilling, independently of the insertion guide. By trend, despite their insignificance, more pronounced differences were observed between the two self-drilling groups, with the biggest deviation from the plan in the full-arch group. As regards the angular deviation between the planned and the real positions, comparable values were observed between the four investigated groups. In some of the analyzed samples, high angular deviation was observed, with maximum values above 30\({}^{\circ}\) in the pre-drilling groups. A recent in vitro study in resin models analyzed the accuracy of mini-implants inserted with two traditionally manufactured and three different 3D-printed rigid tooth-borne templates [31]. Despite an acceptable accuracy being achieved with all templates, better outcomes were obtained with the conventional ones. In this study, the median deviation between the planned and the true position of the mini-implants at the neck ranged between +0.73 mm and \(-\)0.76 mm, between +0.57 mm and \(-\)0.66 mm at the apex, while the angular deviation ranged between 0.70\({}^{\circ}\) and 6.03\({}^{\circ}\)[31]. In our study, higher median deviation values were found for all the considered measurements. However, the lower accuracy observed in our study might be related to the use of a cadaveric model. Contrary to resin models, which present a homogeneous structure, the density and thickness of human bone differed between the included samples and the different palatal insertion regions. In another cadaveric study, comparing the accuracy between the real and the planned position of mini-implants inserted using gingival-borne or tooth-born guides, a statistically higher accuracy was found using the latter [25]. The authors reported a mean sagittal angular deviation of 3.67\({}^{\circ}\) and 6.46\({}^{\circ}\) (\(p\) = 0.043) and a mean transverse angular deviation of 3.60\({}^{\circ}\) and 4.06\({}^{\circ}\) (\(p\) = 0.62) in the tooth-borne and gingival-borne guide group, respectively [25]. Another factor that might have affected our results was the absence of a stop during the insertion, which could be responsible for an incorrect vertical placement. This problem could partially be solved with the use of skeletonized guides which do not cover the whole palate, thus allowing for a visual check of the insertion depth. Pre-drilling is deemed to be a useful procedure by which to reduce the insertion torque and, consequently, the risk of mini-implant fracture during the insertion or removal [15; 32]. Interestingly, in this study, the median distance between the real and planned position, when measured at the mini-implant neck, was lower with the full-arch guides than with the skeletonized ones. By contrast, at the apex, the highest median values were observed in the full-arch groups, particularly without pre-drilling (2.64 mm). This finding might be the result of a slight deviation of the pre-drilling path, leading to an incorrect angulation of the mini-implant, and this would be in line with angular measurements.