## 4 Discussion
### Splinting ISBs to Improve the Accuracy of IOSs
The overall deviations between the reference STL file and the investigated test (\(n\) = 30) and control (\(n\) = 30) scans were measured for each analogue position (\(n\) = 240) on the Y-, X-, Z-axes and angulation. Considering the deviations on the three axes, a positive effect of the ISS was observed regarding the X-axis (longitudinal) (\(-\)1.6 \(\pm\) 44.4 vs \(-\)12.5 \(\pm\) 52.5 \(\upmu\)m) and Z-axis (vertical) (\(-\)4.4 \(\pm\) 18.6 vs \(-\)10.8 \(\pm\) 41.5 \(\upmu\)m), while similar results were reported for the Y-axis (lateral) (\(-\)21.1 \(\pm\) 87.2 vs \(-\)23.2 \(\pm\) 74.7 \(\upmu\)m). Extreme negative values (deviation towards left) up to \(-\)398.5 \(\upmu\)m were reported on the Y-axis (lateral), mainly found on position 3.6 (Y-axis deviation \(-\)131.2 \(\pm\) 85.6 \(\upmu\)m). Position 3.6 was also the most critical considering angular deviation (0.5489 \(\pm\) 0.1866\(\circ\)). Position 4.7 showed the highest linear deviations (X-axis: 63.7 \(\pm\) 27.7 \(\upmu\)m). This technique positively influenced the accuracy of the complete-arch digital impression, reducing the linear and angular deviations at the most critical posterior implant positions [34]. In 2023, [PERSON] et al. investigated the trueness of seven different IOSs to take a complete-arch digital implant scan using a splinting technique and to compare the trueness of the splinted and non-splinted intraoral scanning procedures [14]. A model with four dental implant replicas (MIS Implant Technologies/Dentsply Sirona) was used for the measurements, and the reference model was scanned with ISBs that were not splinted in the control groups and which were splinted in the study groups. The IOSs investigated were Cerec Primescan (Dentsply Sirona), Cerec Omnicam (Dentsply Sirona), 3 Shape Trios 4 (3 Shape), 3 Shape Trios 3 (3 Shape), Planmeca Emerald (Planmeca), Medit 500 (Medit), and Carestream 3600 (Carestream Health). The splinting technique was performed using CAD-CAM 3D-printed splinting bars with a square cross-section of 5 \(\times\) 5 mm, secured to the ISBs with clear polyvinyl siloxane material (Memosil 2; Kulzer). A significant association was found between the trueness values and all three tested variables, including the splinting of the scan bodies, type of IOS, and inter-implant distance (\(p<0.001\)). The highest trueness value was found in Primescan, followed by Omnicam, Carestream, Planmeca, Trios 4, Trios 3, and Medit, respectively. The overall trueness value of the Primescan scanner was significantly higher than that of the other scanners, except for Omnicam. No significant differences were found between Omnicam and Carestream, Carestream and Trios 4, Carestream and Planmeca, Trios 3 and Trios 4, and Planmeca and Trios 4 (\(p>0.05\)). [39] Their results show that the type of scanner had a significant effect on the accuracy of the digital model, which is in agreement with the literature [36] and could be explained by the different hardware and software characteristics and different stitching algorithm adopted by the different scanners. The splinting of the scan bodies resulted in a significant improvement in the trueness of the digital scan, and the authors found that adding splinting bars improved the accuracy of the digital scans in most of the tested scanners. The splinting technique of the investigated ISBs improved the stitching process, providing a scanning track and avoiding the possibility that a scanner may mistakenly recognize one scan body as another, leading to inaccuracies and distortions in the final impression [40]. The main limitations of this review are related to the study design of the included studies, which were all in vitro, and the low number of high-quality studies that investigated this topic. Several in vivo randomized studies should be conducted to better understand the limits and potential of IOSs.