## 4 Discussion
### Use of Auxiliary Geometry Part to Improve the Accuracy of IOSs  
In 2019, [PERSON] et al. investigated the effects of the use of an auxiliary geometry part (AGP), simulating a jaw with teeth and different intraoral scanners on the accuracy (trueness and precision) of the intraoral scans of edentulous patients [33]. A stainless-steel model of a completely edentulous patient who had a restoration with four implants was scanned using three intraoral scanners: Trios 3 (3 Shape A/S), 3M\({}^{\text{TM}}\) True Definition (3M ESPE), and Itero Element 1 (Align Technology Inc., Tempe, AZ, USA) with and without the AGP. The AGP was positioned by matching its circular holes with the ISBs screwed onto the implant analogs and fixed with light-polymerizing resin (CONLIGHT, Kuss Dental). According to this protocol, it was necessary to create four points, one in each model protrusion (parts resembling scan bodies), for the measurements. Each point was created at the intersection of a cylinder axis and a plane. By measuring three distances between these four points, three reference distances, D12, D13, and D14, were defined. Additional steps were required to use this protocol with AGP, such as the design and fabrication of the framework, placement in the mouth, and securing it to the soft tissues of the mandible or maxilla; however, accuracy results improved both in precision and trueness. At the D12 and D13 reference distances, the intraoral scanner had no statistically significant effect (\(p>0.05\)) on trueness values, while the use of the AGP had statistically significant effects (\(p<0.05\)). However, in D14, both the intraoral scanner used and the use of the AGP had a statistically significant effect (\(p<0.05\)) on the deviation measurement and consequently on trueness. The lowest measured mean deviation value was 8 \(\pm\) 6 \(\upmu\)m. This was achieved from digital impressions obtained using the True Definition Scanner, using the AGP and D12 reference distance. The highest mean deviation value of 189 \(\pm\) 70 \(\upmu\)m was achieved with the Itero scanner without using the AGP and at a D14 reference distance. At both the reference distances (D12 and D13), neither the scanner nor the interaction between it and the AGP had statistically significant effects on the results (\(p>0.05\)). However, at the reference distance D14, the intraoral scanner used did have statistically significant effects on the results (\(p<0.05\)), while the use or not of the AGP and the interaction with the scanner used did not have statistically significant effects (\(p>0.05\)). After analyzing the descriptive statistics, all mean precision values and corresponding standard deviations were obtained. The highest mean precision values were 8 \(\pm\) 6 \(\upmu\)m and 7 \(\pm\) 7 \(\upmu\)m. They were measured in digital impressions achieved using True Definition and Trios3, respectively, using the AGP and a D12 reference distance. The lowest mean precision values, 118 \(\pm\) 97 \(\upmu\)m, were achieved with the Itero IOS without using the AGP at the D14 reference distance. The improvement occurred with all IOSs analyzed and in all distances analyzed. The conclusion of this study was that, by covering the dedentulous ridges with an AGP, the authors achieved a significant improvement in both the trueness and precision of the complete-arch digital impression of the dedentulous maxilla, which also facilitated the scanning procedure [33]. In 2021, [PERSON] et al. evaluated the accuracy of complete-arch implant scanning with the aid of an auxiliary device [34], which consisted of well-defined landmarks and a solid opaque surface. A master model (group 0) and three types of auxiliary devices were designed: group 1 included a base with a thickness of 1.5 mm that covered the master model with access openings at the implant sites; in group 2, a cuboid reference block (8.0 \(\times\) 4.0 \(\times\) 7.0 mm) and four fiducary spheres (\(\diameter\) 5.0 mm) were added onto the base. For group 3, the four spheres were replaced by standard premidars.