## 3 Results  
Four mini-implants were excluded from the evaluation for the following reasons: one implant fracture occurred during the insertion process; two implants collided; and one implant was found not to be placed into bone at the CBCT evaluation. Moreover, one sample was excluded due to not reliable measurements. Thus, a total of 46 mini-implants were analyzed.  
Out of these 46 included in the final evaluation, due to hard bone, 10 were inserted using pre-drilling despite being planned to be inserted without. Therefore, 32 implants (\(n=15\) full-arch; \(n=17\) skeletonized) were inserted with a pre-drilling procedure and 14 implants (\(n=7\) full-arch; \(n=7\) skeletonized) without.  
Mini-implants with planned pre-drilling and unplanned pre-drilling presented no significant differences for all the investigated variables, i.e., neck (\(p=0.795\)), apex (\(p=0.610\)), and angle (\(p=0.388\)).  
The distance between the planned and the real position of the mini-implant neck is reported in Figure 4. The highest mean deviation at the implant neck was \(2.09\pm 0.92\) mm, recorded in the skeletonized/pre-drilling group. The Kruskal-Wallis test revealed a statistically significant difference between the four groups (\(p=0.012\)). Therefore, a post hoc test was conducted, and corrected \(p\) values are reported in Table 2. Deviations at the neck were statistically higher in the skeletonized guides with pre-drilling as compared to full-arch guides with pre-drilling. No other significant differences were observed among the groups.  
Figure 4: Boxplot reporting the deviations (in mm) from the planned and the real mini-implant neck position in the four groups.  
The deviation between the planned and the real position of the mini-implants was analyzed also at their apex, with median values above 1 mm in all groups (Figure 5). At the apex, the highest deviation was of 3.04 \(\pm\) 1.44 mm and was registered in the full-arch/no pre-drilling group, while the lower mean deviation of 1.72 \(\pm\) 1.22 mm was observed in the skeletonized/no pre-drilling one. No statistically significant difference was found between the four groups, as revealed by the Kruskal-Wallis test (\(p\) = 0.131).  
Finally, the angle between the planned and the real position of each mini-implant was measured (Figure 6). The lower mean angular deviation was of 8.23 \(\pm\) 4.24\({}^{\circ}\) and was registered in mini-implants inserted using a skeletonized guide without a pre-drilling procedure, while in all the other groups, the mean angular deviation was higher than 11\({}^{\circ}\). Even for this variable, it was not possible to find a statistically significant difference between the four groups (\(p\) = 0.511). Further details on descriptive statistical analysis are provided in Table 3.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **Full-Arch/** & **Full-Arch/** & **Skeletonized/** \\  & **No Pre-Drilling** & **Pre-Drilling** & **No Pre-Drilling** \\ \hline
**Full-arch/pre-drilling** & 0.910 & – & – \\
**Skeletonized/no** & 0.626 & 0.492 & – \\
**pre-drilling** & 0.141 & 0.014 * & 0.910 \\ \hline \end{tabular}  
* Corrected \(p\) values are reported in the above table. Significant values are labeled as follows:
* \(p\) \(<\) 0.05, **\(p\) \(<\) 0.01, ***\(p\) \(<\) 0.001.  
\end{table}
Table 2: The Wilcoxon post hoc test with \(p\)-value correction using the Holm method was performed to compare deviations in implant neck position in the four groups.  
Figure 5: Boxplot reporting the deviations (in mm) from the planned and the real mini-implant apex position in the four groups.