# Evaluation of Tooth Movement Accuracy with the F22 Aligner System: A Retrospective Study
## 4 Discussion  
The aim of the study was to evaluate the accuracy of tooth movement via the F22 Aligner system, comparing clinical results with respect to those digitally planned, in a large sample affected with mild-moderate Class I malocclusion, without resorting to auxiliaries and adhering to literature recommendations during the virtual setup procedure [10; 22; 37]. The F22 alignment system was created after various research efforts and clinical testing in the University, before its distribution, and has some characteristics that distinguish it from other clear aligner systems present in the global market and described in the literature [19; 24; 26; 27; 28; 29; 30; 31; 38]. The treatment of the sample involved planned movements that were purely coronal, while movements considered unpredictable, such as radicular and translation movements, were avoided [12; 15]. The study was designed both to consider angular movements (inclination, angulation and rotation) and to investigate the expansive capacity of the F22 Aligner system, quantifying the change in intra-arch transverse measurements in both arches. The analyses were performed taking into account the different tooth types, whose responsiveness to orthodontic forces are conditioned by their different crown and root morphology [38], as well as their positions in different sections of the arch, with their different bone densities [39]. Despite this system not being the most widespread in the literature and on the market, findings could be generalized to other CAT systems, if attention is paid to what the literature has stated. The prescribed (T1) and achieved movements (T2) were measured via superimposing digital models using unmoved posterior teeth as reference landmarks. This explains why the number of molar measurements was very low, and the molar tooth type was therefore omitted from the subsequent comparative analyses. The principle used for superimposition was \"automatic best-fit registration\", which as [PERSON] et al. have reported yields excellent agreement for rotation movements (>0.90), is good for tip (0.890) and moderate for torque (0.740) [34]. This analysis showed that the F22 Aligner is most accurate for angulation (88.01% \(\pm\) 55.68%, n = 719), closely followed by inclination (86.76% \(\pm\) 44.89%, n = 975). This is in line with findings by [PERSON] et al. [37], [PERSON] et al. [8], [PERSON] et al. [38] and [PERSON] et al. [21], who all agree that crown tipping movements are the most readily achieved movements generally in CAT. Furthermore, a comparison between the various tooth types showed no differences in inclination accuracy, but in angulation there were significant differences in accuracy when comparing the maxillary incisors (91.16% \(\pm\) 58.31%, n = 229) with both the maxillary canines (72.73% \(\pm\) 41.45%, n = 97) and the mandibular premolars (79.51% \(\pm\) 69.65%, n = 174). This is likely due both to the coronal morphology (the premolars, especially mandibular, have a short clinical crown) and radicular morphology (canines have a very long root). Although our results are slightly different from those of [PERSON] et al. in this regard, the discrepancy could be due to the different recording method and the larger sample analyzed [38]. The lowest average accuracy was found for rotation (61.59% \(\pm\) 32.54%, n = 1224). This has also been found in other studies in the literature, which report an average accuracy ranging from 40% to 66.8% [7; 9; 10; 34]; [PERSON] et al. found greater accuracy, about 86%, also considering the finishing stage in the Invisalign system [21]. As reported in the literature, with the Invisalign system, the teeth whose rotation is least accurately corrected are the rounded teeth (canines and premolars) [10; 23; 37], as their coronal morphology prevents the transmission of adequate and effective force couples at the crown [36]. Moreover, the roots are relatively large, which makes the movement even more difficult to achieve.